U.S. patent application number 11/208724 was filed with the patent office on 2006-03-02 for ultrasonic sensor.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Makiko Sugiura, Yasutoshi Suzuki, Masatoshi Tokunaga, Takahiko Yoshida.
Application Number | 20060043843 11/208724 |
Document ID | / |
Family ID | 35853755 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060043843 |
Kind Code |
A1 |
Sugiura; Makiko ; et
al. |
March 2, 2006 |
Ultrasonic sensor
Abstract
An ultrasonic sensor includes a plurality of converters and a
protection component. The plurality of converters convert one of a
received ultrasonic wave into an electric signal and an electric
signal into an ultrasonic wave for transmission. The plurality of
converters are juxtaposed. The protection component protects each
of the converters.
Inventors: |
Sugiura; Makiko;
(Hekinan-city, JP) ; Yoshida; Takahiko;
(Okazaki-city, JP) ; Tokunaga; Masatoshi;
(Chiryu-city, JP) ; Suzuki; Yasutoshi;
(Okazaki-city, JP) |
Correspondence
Address: |
POSZ LAW GROUP, PLC
12040 SOUTH LAKES DRIVE
SUITE 101
RESTON
VA
20191
US
|
Assignee: |
DENSO CORPORATION
NIPPON SOKEN, INC.
|
Family ID: |
35853755 |
Appl. No.: |
11/208724 |
Filed: |
August 23, 2005 |
Current U.S.
Class: |
310/348 |
Current CPC
Class: |
B06B 1/0629 20130101;
G01S 7/521 20130101; H04R 1/02 20130101 |
Class at
Publication: |
310/348 |
International
Class: |
H01L 41/053 20060101
H01L041/053 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2004 |
JP |
2004-245541 |
Feb 18, 2005 |
JP |
2005-42449 |
Claims
1. An ultrasonic sensor comprising: a plurality of conversion means
for converting one of a received ultrasonic wave into an electric
signal and an electric signal into an ultrasonic wave for
transmission, the plurality of conversion means being juxtaposed;
and protection means for protecting each of the conversion
means.
2. The ultrasonic sensor according to claim 1, wherein the
protection means includes: a protective film provided above each of
the conversion means; and a first gap provided between the
protective film and the conversion means.
3. The ultrasonic sensor according to claim 2, wherein the first
gap is filled with a filler selected from a liquid, a sol, and a
gel.
4. The ultrasonic sensor according to claim 3, further comprising a
vent hole for bringing the first gap and exterior into
communication with each other.
5. The ultrasonic sensor according to claim 2, further comprising
separation means for separating the conversion means and the first
gap located above the conversion means and the protective film for
each of the conversion means.
6. The ultrasonic sensor according to claim 2, further comprising:
a housing member for housing each of the plurality of the
conversion means therein; a second gap surrounded by the housing
member and the conversion means; and a vent hole for bringing the
second gap and exterior into communication with each other.
7. The ultrasonic sensor according to claim 6, wherein at least one
of the conversion means is a transmission element for converting an
electric signal into an ultrasonic wave for transmission.
8. The ultrasonic sensor according to claim 2, further comprising:
a housing member for housing each of the plurality of conversion
means therein; and a second gap corresponding to a sealed space
surrounded by the housing member and the conversion means.
9. The ultrasonic sensor according to claim 8, wherein the second
gap is filled with a filler selected from a liquid, a sol, and a
gel.
10. The ultrasonic sensor according to claim 8 or 9, wherein each
of the conversion means is a receiving element for converting a
received ultrasonic wave into an electric signal.
11. The ultrasonic sensor according to claim 2, further comprising
a transfer member for independently connecting each of the
conversion means and the protective film with each other for each
of the conversion means.
12. The ultrasonic sensor according to claim 1, wherein: the
protection means comprises a protective member attached to and
fixed in front of each of the plurality of conversion means; the
protective member is provided for each of the conversion means; a
clearance is provided between the protective members; and the
clearance serves to separate the protective members from each other
for each of the conversion means.
13. The ultrasonic sensor according to claim 1, further comprising
an acoustic horn provided in front of each of the plurality of
conversion means, wherein the acoustic horn is provided for each of
the conversion means so as to have a gradually increasing sectional
area from a throat provided in front of each of the conversion
means toward an opening.
14. The ultrasonic sensor according to claim 1, wherein: each of
the conversion means is formed on a surface of a semiconductor
substrate; the surface side of the semiconductor substrate is
regarded as the top side of each of the conversion means so as to
serve as any one of a receiving surface and a transmission surface
of an ultrasonic wave; a bonding wire is connected to the surface
side of the semiconductor substrate; and each of the conversion
means is surface-mounted on a sensor substrate by a wire bonding
method through the bonding wire.
15. The ultrasonic sensor according to claim 1, wherein each of the
conversion means is formed on a surface of a semiconductor
substrate; a bottom side of the semiconductor substrate is regarded
as the top side of each the conversion means so as to serve as any
one of a receiving surface and a transmission surface of an
ultrasonic wave; a bump is connected to the surface side of the
semiconductor substrate; and each of the conversion means is
surface-mounted on a sensor substrate by flip-chip connection
through the bump.
16. The ultrasonic sensor according to claim 1, wherein each of the
conversion means is any one of a piezoelectric conversion type and
a capacitive conversion type.
17. An ultrasonic sensor comprising: a plurality of converters for
converting one of a received ultrasonic wave into an electric
signal and an electric signal into an ultrasonic wave for
transmission, the plurality of converters being juxtaposed; and a
protection component for protecting each of the converters.
18. The ultrasonic sensor according to claim 17, wherein the
protection component includes: a protective film provided above
each of the converters; and a first gap provided between the
protective film and the converters.
19. The ultrasonic sensor according to claim 18, wherein the first
gap is filled with a filler selected from a liquid, a sol, and a
gel.
20. The ultrasonic sensor according to claim 19, further comprising
a vent hole for bringing the first gap and exterior into
communication with each other.
21. The ultrasonic sensor according to claim 18, further comprising
a separating member for separating the converters and the first gap
located above the converters and the protective film for each of
the converters.
22. The ultrasonic sensor according to claim 18, further
comprising: a housing member for housing each of the plurality of
the converters therein; a second gap surrounded by the housing
member and the converters; and a vent hole for bringing the second
gap and exterior into communication with each other.
23. The ultrasonic sensor according to claim 22, wherein at least
one of the converters is a transmission element for converting an
electric signal into an ultrasonic wave for transmission.
24. The ultrasonic sensor according to claim 18, further
comprising: a housing member for housing each of the plurality of
converters therein; and a second gap corresponding to a sealed
space surrounded by the housing member and the converters.
25. The ultrasonic sensor according to claim 24, wherein the second
gap is filled with a filler selected from a liquid, a sol, and a
gel.
26. The ultrasonic sensor according to claim 24, wherein each of
the converters is a receiving element for converting a received
ultrasonic wave into an electric signal.
27. The ultrasonic sensor according to claim 18, further comprising
a transfer member for independently connecting each of the
converters and the protective film with each other for each of the
converters.
28. The ultrasonic sensor according to claim 17, wherein: the
protection component includes a protective member attached to and
fixed in front of each of the plurality of converters; the
protective member is provided for each of the converters; a
clearance is provided between the protective members; and the
clearance serves to separate the protective members from each other
for each of the converters.
29. The ultrasonic sensor according to claim 17, further comprising
an acoustic horn provided in front of each of the plurality of
converters, wherein the acoustic horn is provided for each of the
converters so as to have a gradually increasing sectional area from
a throat provided in front of each of the converters toward an
opening.
30. The ultrasonic sensor according to claim 17, wherein: each of
the converters is formed on a surface of a semiconductor substrate;
the surface side of the semiconductor substrate is regarded as the
top side of each of the converters so as to serve as any one of a
receiving surface and a transmission surface of an ultrasonic wave;
a bonding wire is connected to the surface side of the
semiconductor substrate; and each of the converters is
surface-mounted on a sensor substrate by a wire bonding method
through the bonding wire.
31. The ultrasonic sensor according to claim 17, wherein each of
the converters is formed on a surface of a semiconductor substrate;
a bottom side of the semiconductor substrate is regarded as the top
side of each the converters so as to serve as any one of a
receiving surface and a transmission surface of an ultrasonic wave;
a bump is connected to the surface side of the semiconductor
substrate; and each of the converters is surface-mounted on a
sensor substrate by flip-chip connection through the bump.
32. The ultrasonic sensor according to claim 17, wherein each of
the converters is any one of a piezoelectric conversion type and a
capacitive conversion type.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority of Japanese Patent Application No. 2004-245541, filed on
Aug. 25, 2004 and Japanese Patent Application No. 2005-42449, filed
on Feb. 18, 2005, the contents of which are incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an ultrasonic sensor and,
more particularly, to an ultrasonic sensor for converting a
received ultrasonic wave into an electric signal or an electric
signal into an ultrasonic wave so as to transmit it.
BACKGROUND
[0003] Recently, a technique of monitoring the vicinity of a
vehicle for the purpose of driving safety has been developed.
According to this technique, an ultrasonic sensor is mounted in the
vehicle, which may include an automobile. The ultrasonic sensor
receives a reflected wave of an ultrasonic wave harmless to a human
body, which is transmitted from the ultrasonic sensor, so as to
measure the position of or a distance from an object present in the
vicinity of the automobile, a two-dimensional shape, or a
three-dimensional shape of the object and the like.
[0004] For example, the following automatic parking system has been
put into practical use. An ultrasonic sensor is mounted in a rear
part of an automobile. A device, generally called "a back sonar,"
is used while reversing the automobile into a parking space to
avoid the collision with an object. The "back sonar" is for
detecting the object, which may include a human or another
obstacle, present behind the automobile.
[0005] As an ultrasonic sensor used for the above-described usage,
a piezoelectric or a capacitive (condenser) ultrasonic sensor
fabricated by employing a Micro Electro Mechanical Systems (MEMS)
technique is known.
[0006] For example, a technique of juxtaposing a plurality of
ultrasonic sensor elements has been disclosed as a piezoelectric
ultrasonic sensor employing the MEMS technique. Each of the
ultrasonic sensor elements is composed of a piezoelectric sensor,
which includes a ferroelectric member interposed between a pair of
electrodes. The piezoelectric sensor has a predetermined resonance
frequency to detect an ultrasonic wave. Such a device is disclosed
in Japanese Patent Laid-Open Publication No. 2003-284182.
[0007] The ultrasonic sensor disclosed in the above publication
includes a piezoelectric element, which serves as a piezoelectric
sensor, formed on a semiconductor chip having a "Silicon On
Insulator" (SOI) structure. The piezoelectric element includes a
thin film made of a PZT (lead zirconate titanate) ceramic
corresponding to a ferroelectric material interposed between two
thin electrode layers including an upper electrode layer and a
lower electrode layer.
[0008] Therefore, each of the electrode layers and the PZT ceramic
thin film have a low mechanical strength. As a result, there arises
a problem that each of the electrode layers or the PZT ceramic thin
film is vulnerable to damage upon application of an external force
to the upper electrode layer so that the piezoelectric element is
likely to be broken.
[0009] On the other hand, the capacitive ultrasonic sensor using
the MEMS technique includes: a fixed electrode layer formed on a
semiconductor chip; and a thin movable electrode layer provided on
the fixed electrode layer through a gap. The fixed electrode layer
and the movable electrode layer form a capacitive element.
[0010] With the above structure, the movable electrode layer has a
low mechanical strength. Therefore, there arises a problem that the
movable electrode layer is vulnerable to damage upon application of
an external force to the movable electrode layer so that the
capacitive electrode is likely to be broken.
[0011] As described above, the conventional piezoelectric or
capacitive ultrasonic sensors fabricated by employing the MEMS
technique are likely to be damaged under the application of an
external force. Therefore, it is difficult to mount the
conventional ultrasonic sensor in an automobile as external
equipment.
SUMMARY
[0012] The present invention was devised to solve the
above-described and other problems and to provide a robust
ultrasonic sensor that that can withstand the application of an
external force.
[0013] An ultrasonic sensor according to a first aspect of the
present invention includes a plurality of conversion means and a
protection means. The plurality of conversion means are for
converting one of a received ultrasonic wave and an electric signal
to the other of the electric signal and the ultrasonic wave for
transmission. The plurality of conversion means are juxtaposed. The
protection means is for protecting each of the conversion
means.
[0014] An ultrasonic sensor according to a second aspect of the
present invention is characterized in that the protection means
includes a protective film provided in front of each of the
plurality of conversion means and a first gap is provided between
the protective film and the conversion means.
[0015] An ultrasonic sensor according to a third aspect of the
present invention is characterized in that the first gap is filled
with a filler selected from a liquid, a sol, and a gel.
[0016] An ultrasonic sensor according to a fourth aspect of the
present invention is characterized in that the ultrasonic sensor
includes a vent hole for bringing the first gap and exterior into
communication with each other.
[0017] An ultrasonic sensor according to a fifth aspect of the
present invention includes separation means for separating the
conversion means and the first gap located in front of the
conversion means and the protective film for each of the conversion
means.
[0018] An ultrasonic sensor according to a sixth aspect of the
present invention includes a housing member for housing each of the
plurality of the conversion means therein; a second gap surrounded
by the housing member and the conversion means; and a vent hole for
bringing the second gap and exterior into communication with each
other.
[0019] An ultrasonic sensor according to a seventh aspect of the
present invention is characterized in that the conversion means is
a transmission element for converting an electric signal into an
ultrasonic wave for transmission.
[0020] An ultrasonic sensor according to an eighth aspect of the
present invention includes a housing member for housing each of the
plurality of conversion means therein; and a second gap
corresponding to a sealed space surrounded by the housing member
and the conversion means.
[0021] An ultrasonic sensor according to a ninth aspect of the
present invention is characterized in that the second gap is filled
with a filler selected from a liquid, a sol, and a gel.
[0022] An ultrasonic sensor according to a tenth aspect of the
present invention is characterized in that each of the conversion
means is a receiving element for converting a received ultrasonic
wave into an electric signal.
[0023] An ultrasonic sensor according to an eleventh aspect of the
present invention includes a transfer member for independently
connecting each of the conversion means and the protective film
with each other for each of the conversion means.
[0024] An ultrasonic sensor according to a twelfth aspect of the
present invention includes a protective member attached to and
fixed in front of each of the plurality of conversion means, the
protective member being provided for each of the conversion means,
a clearance being provided between the protective members, and the
clearance serving to separate the protective members from each
other for each of the conversion means.
[0025] An ultrasonic sensor according to a thirteenth aspect of the
present invention includes an acoustic horn provided in front of
each of the plurality of conversion means, wherein the acoustic
horn is provided for each of the conversion means so as to have a
gradually increasing sectional area from a throat provided in front
of each of the conversion means toward an opening.
[0026] An ultrasonic sensor according to a fourteenth aspect of the
present invention is characterized in that each of the conversion
means is formed on a surface of a semiconductor substrate, the
surface side of the semiconductor substrate being regarded as the
front side of each of the conversion means so as to serve as any
one of a receiving surface and a transmission surface of an
ultrasonic wave, a bonding wire is connected to the surface side of
the semiconductor substrate, and each of the conversion means is
surface-mounted on a sensor substrate by a wire bonding method
through the bonding wire.
[0027] An ultrasonic sensor according to a fifteenth aspect of the
present invention is characterized in that each of the conversion
means is formed on a surface of a semiconductor substrate, a bottom
side of the semiconductor substrate being regarded as the front
side of each the conversion means so as to serve as any one of a
receiving surface and a transmission surface of an ultrasonic wave,
a bump is connected to the surface side of the semiconductor
substrate, and each of the conversion means is surface-mounted on a
sensor substrate by flip-chip connection through the bump.
[0028] An ultrasonic sensor according to a sixteenth aspect of the
present invention is characterized in that each of the conversion
means is any one of a piezoelectric conversion type and a
capacitive conversion type.
[0029] According to the first aspect of the present invention, the
conversion means is composed of the receiving element for
converting the received ultrasonic wave into the electric signal or
the electric signal into the ultrasonic wave so as to transmit it.
The plurality of conversion means are juxtaposed.
[0030] Moreover, according to the first aspect of the present
invention, the protection means for protecting each of the
conversion means is provided. Therefore, even if each of the
conversion means has a low mechanical strength, it becomes possible
to prevent the conversion means from being damaged so as to be
hardly broken. As a result, a robust ultrasonic sensor can be
obtained.
[0031] According to the second aspect of the present invention, the
protective film is provided in front of the plurality of the
conversion means, and the first gap is provided between the
protective film and the conversion means. Therefore, even if an
external force is applied to the ultrasonic sensor, the external
force is applied only to the protective film but not directly to
each of the conversion means.
[0032] Thus, according to the second aspect of the present
invention, even if each of the conversion means has a low
mechanical strength, it is possible to prevent the conversion means
from being damaged so that the conversion means is hardly broken,
thereby obtaining a robust ultrasonic sensor.
[0033] Therefore, the ultrasonic sensor according to the second
aspect of the present invention can be mounted in an automobile as
external equipment without any modification. If the ultrasonic
sensor is to be mounted in an automobile as external equipment of
an automobile, it is necessary to use a highly weather-resistant
material for the protective film. Examples of such a material
include various metals (such as an aluminum alloy), various
synthetic resins, glasses, rubbers, and the like.
[0034] According to the third aspect of the present invention, an
acoustic impedance of the filler selected from a liquid, a sol, and
a gel filling the first gap is brought close to that of the
protective film. As a result, the propagation of oscillation of the
protective film to each of the conversion means through the filler
can be ensured so as to enhance receiving sensitivity in the case
where each of the conversion means is used as a receiving
element.
[0035] The acoustic impedance of a material corresponds to a
product of a density of the material and a propagation acoustic
speed. Then, as a difference in acoustic impedance between
materials becomes larger, the propagation characteristic of an
acoustic wave is degraded. Specifically, as a difference in
acoustic impedance between the filler in the first gap and the
protective film becomes greater, an ultrasonic wave is reflected by
the protective film so as to be less likely to propagate to the
filler.
[0036] Therefore, if a synthetic resin film is used as the
protective film, a sol obtained by dispersing fine particles of the
synthetic resin in a liquid or a polymer gel made of the synthetic
resin is used as the filler. Moreover, the filler is required not
to affect the conversion means. Examples of the filler meeting such
a requirement include a silicon gel, a fluorine gel, and the
like.
[0037] As an example, if the first gap is filled with one of
various gases (air, an inert gas, and the like), the oscillation of
the protective film does not satisfactorily propagate to each of
the conversion means because the gas has an acoustic impedance
extremely smaller than that of the protective film. Accordingly,
there is a possibility that receiving sensitivity is lowered when
each of the conversion means is used as a receiving element.
[0038] If air remains in the first gap, the oscillation of the
protective film is less likely to propagate to each of the
conversion means. Therefore, it is desirable to completely remove
air from the first gap so as to fill the first gap with the
filler.
[0039] If each of the conversion means is used as a transmission
element, the acoustic impedance of the filler selected from a
liquid, a sol, and a gel filling the first gap is brought close to
that of the protective film. As a result, the propagation of
oscillation of the transmission element through the filler to the
protective film can be ensured, thereby enhancing a transmission
output of the transmission element.
[0040] Moreover, if the first gap is filled with one of various
gases, the oscillation of the transmission element does not
satisfactorily propagate to the protective film because the
acoustic impedance of the gas is extremely smaller than that of the
protective film. As a result, there is a possibility that a
transmission output of the transmission element becomes low.
[0041] Moreover, if the first gap is filled with the filler such as
a liquid, a sol, or a gel, it is desirable to completely remove air
from the first gap so as to fill the first gap with the filler
because the oscillation of the transmission element is less likely
to propagate to the protective film if air remains in the first
gap.
[0042] According to the fourth aspect of the present invention,
when the filler in the first gap contains air bubbles, it is
possible to remove the air bubbles from the first gap through the
vent hole to the exterior.
[0043] Specifically, if the filler in the first gap contains air
bubbles, the air bubbles make it hard to propagate the oscillation
of the protective film to each of the conversion means.
[0044] On the other hand, according to the fourth aspect of the
present invention, since the air bubbles are removed through the
vent hole, it becomes possible to completely fill the first gap
with the filler. Therefore, if each of the conversion means is used
as a receiving element, the receiving sensitivity can be prevented
from being lowered by the presence of air bubbles contained in the
filler in the first gap.
[0045] If each of the conversion means is used as a transmission
element, it becomes possible to completely fill the first gap with
the filler because the air bubbles contained in the filler in the
first gap are removed through the vent hole. In this manner, the
propagation of oscillation of the transmission element through the
filler to the protective film can be ensured to prevent the
transmission output of the transmission element from being
lowered.
[0046] According to the fifth aspect of the present invention, the
oscillation of a single protective film separated by the separation
means propagates only to the conversion means through the first gap
situated below the protective film but not to the other conversion
means.
[0047] Therefore, according to the fifth aspect of the present
invention, the propagation of an ultrasonic wave to each of the
conversion means can be performed in a completely separate manner.
Therefore, a crosstalk characteristic of each of the conversion
means can be prevented from being degraded. Alternatively, a
plurality of adjacent conversion means can be grouped into one.
Separation means may be provided for each group of the conversion
means so as to separate the corresponding group from the other
groups.
[0048] The separation means has to surely block the oscillation of
the protective film, the first gap, and the conversion means, which
are vertically provided so as to be grouped into one, so that the
oscillation does not propagate to members of the other adjacent
groups.
[0049] For this reason, a material having a high oscillation
blocking property is required to be used for the separation means.
Examples of the material include rubbers.
[0050] According to the sixth aspect of the present invention,
since the oscillation of each of the conversion means is not
inhibited, receiving sensitivity when each of the conversion means
is used as a receiving element can be prevented from being
lowered.
[0051] Specifically, if a vent hole is not provided for the second
gap, the second gap forms a sealed space. Air filling the sealed
space acts as a spring so as to apply a damping force due to air
onto the back face side of each of the conversion means. As a
result, the free oscillation of each of the conversion means is
inhibited.
[0052] On the other hand, according to the sixth aspect of the
present invention, air passes through the vent hole. Accordingly,
no damping force due to air is applied onto the back face side of
each of the conversion means. As a result, each of the conversion
means is capable of freely oscillating.
[0053] If each of the conversion means is used as a transmission
element, air passes through the vent hole of the second gap.
Therefore, no damping force due to air is applied to the back face
side of a transmission surface of the transmission element for
transmitting an ultrasonic wave. As a result, the transmission
surface can freely oscillate without inhibiting the oscillation.
Therefore, the transmission output of the transmission element can
be increased.
[0054] To obtain satisfactory functions and effects described
above, the number, the position, the shape, and the size of the
vent hole may be set by experimentally finding their optimal values
in a cut-and-try method.
[0055] When air passes through the vent hole of the second gap, no
damping force due to air is applied onto the back face side of the
transmission element so as not to inhibit the free oscillation of
the transmission surface. Accordingly, a resonance value Q of the
transmission element (a diaphragm of the conversion means) is
increased.
[0056] The resonance value Q of the transmission element and the
transmission output are positively correlated with each other.
Thus, as the resonance value Q increases, the transmission output
becomes greater.
[0057] The transmission element including a piezoelectric element
or a capacitive element fabricated by employing the MEMS technique
is not suitable for the transmission element because of its small
transmission output of an ultrasonic wave. Therefore, such a
transmission element is required to increase the transmission
output as much as possible.
[0058] Thus, the seventh aspect of the present invention can
demonstrate the functions and effects of the sixth aspect
particularly when the aspect is embodied as the transmission
element fabricated by employing the MEMS technique.
[0059] According to the eighth aspect of the present invention, air
filling the second gap corresponding to the sealed space acts as a
spring so as to apply a damping force due to air onto the back face
side of each of the conversion means. As a result, since the free
oscillation of each of the conversion means is inhibited, the
resonance value Q of the diaphragm of the conversion mean is
reduced.
[0060] Moreover, according to the sixth aspect of the present
invention, if each of the conversion means is used as a receiving
element, the receiving sensitivity is lowered because the
oscillation of each of the conversion means is inhibited.
[0061] According to the ninth aspect of the present invention, by
filling the second gap with a material for suppressing the
oscillation of the diaphragm of the conversion means (for example,
a liquid, a sol, a gel, or the like), the diaphragm of the
conversion means can be prevented from excessively oscillating to
be broken.
[0062] The resonance value Q of the receiving element and the
receiving sensitivity are positively correlated with each other.
Thus, as the resonance value Q increases, the receiving sensitivity
becomes greater.
[0063] Herein, a plurality of receiving elements have a fluctuation
in primary resonance frequency due to a fabrication process.
[0064] If the resonance value Q of the receiving element is
increased, the receiving sensitivity is increased. However, since
the receiving sensitivity exhibits a steep characteristic with
respect to a change in frequency, the receiving sensitivity
suddenly drops at a frequency offset from the primary resonance
frequency even if the offset is slight.
[0065] On the contrary, if the resonance value Q of the receiving
element is set small, the receiving sensitivity become
correspondingly low. However, since the receiving sensitivity
exhibits a gentle characteristic with respect to a change in
frequency, the receiving sensitivity does not greatly drop even at
a frequency far from the primary resonance frequency.
[0066] The receiving element comprising a piezoelectric element or
a capacitive element fabricated by employing the MEMS technique is
suitable for a receiving element because of its high receiving
sensitivity of an ultrasonic wave. Therefore, it is necessary to
increase the receiving sensitivity over a broad frequency range as
much as possible rather than to increase the receiving sensitivity
at the primary resonance frequency.
[0067] Therefore, the tenth aspect of the present invention can
demonstrate the functions and effects of the eighth aspect
particularly when the aspect is embodied as a receiving element
fabricated by employing the MEMS technique.
[0068] According to the tenth aspect of the present invention, by
filling the second gap with a material for suppressing the
oscillation of the diaphragm of the conversion means, the resonance
value Q of the diaphragm of the conversion means can be reduced as
compared with the case where the second gap is filled with air.
[0069] Accordingly, if the filler in the second gap is
appropriately selected, a desired resonance characteristic can be
obtained without changing the structure of the receiving
element.
[0070] According to the eleventh aspect of the present invention,
when an ultrasonic wave oscillates the protective film, the
oscillation of the protective film propagates to each of the
conversion means through each of the transfer members.
[0071] Herein, since the transfer member is provided for each of
the conversion means, the oscillation of an arbitrary transfer
member never propagates to the other transfer members. As a result,
since the reception or transmission of an ultrasonic wave can be
performed in a separated manner for each of the conversion means, a
crosstalk characteristic of each of the conversion means can be
prevented from being degraded.
[0072] Moreover, the acoustic impedance of each of the transfer
members is brought close to that of the protective film. As a
result, the propagation of oscillation of the protective film to
each of the conversion means can be ensured, thereby enhancing the
receiving sensitivity in the case where each of the conversion
means is used as a receiving element.
[0073] Furthermore, the acoustic impedance of each of the transfer
members is brought close to that of the conversion means. As a
result, the propagation of oscillation of each of the transfer
members to each of the conversion means can be ensured, thereby
enhancing the receiving sensitivity in the case where each of the
conversion means is used as a receiving element.
[0074] Therefore, it is desirable that the transfer member be made
of the same material as that of the protective film or the
conversion means.
[0075] If each of the conversion means is used as a transmission
element, the propagation of oscillation of the transfer member to
the protective film can be ensured by bringing the acoustic
impedance of the transfer member close to that of the protective
film. As a result, the transmission output of the transmission
element can be increased.
[0076] Moreover, if each of the conversion means is used as a
transmission element, the propagation of oscillation of the
transmission element to the transfer member can be ensured by
bringing the acoustic impedance of the transfer member close to
that of the transmission element. As a result, the transmission
output of the transmission element can be increased.
[0077] According to the twelfth aspect of the present invention, if
each of the conversion means is used as a receiving element, the
oscillation of the protective member propagates to the receiving
element when an ultrasonic wave oscillates the protective member
because the protective film is attached and fixed in front of the
receiving element.
[0078] On the other hand, according to the twelfth aspect of the
present invention, if each of the conversion means is used as a
transmission element, the oscillation of the transmission element
propagates to the protective member when the transmission element
oscillates because the protective member is attached and fixed in
front of the transmission element. As a result, the protective
member oscillates to transmit an ultrasonic wave.
[0079] Herein, since each of the conversion means is reinforced by
the protective member, each of the conversion means can be
prevented from being damaged so as to be hardly broken even if an
external force is applied to the ultrasonic sensor. As a result, a
robust ultrasonic sensor can be obtained.
[0080] Therefore, the ultrasonic sensor according to the twelfth
aspect of the present invention can be mounted as external
equipment of an automobile without any modification. If the
ultrasonic sensor is mounted as external equipment of an
automobile, it is necessary to use a highly weather-resistant
material for the protective member. Examples of the material
include various metals (such as an aluminum alloy), various
synthetic resins, glasses, rubbers, and the like.
[0081] As a method of attaching and fixing the protective member to
each of the conversion means, any method (for example, thermal
welding, ultrasonic welding, bonding with an adhesive, and the
like) may be used.
[0082] According to the thirteenth aspect of the present invention,
an acoustic horn is provided for each of the conversion means. As a
result, each of the conversion means can be imparted with
directivity of a receiving direction or a transmitting direction of
an ultrasonic wave.
[0083] Specifically, each of the acoustic horns has acute
directivity on its horn axis. Therefore, by forming the acoustic
horns to have the same size and shape, the directivity of each of
the conversion means can be the same if the horn axes of the
acoustic horns are set in the same direction. Moreover, in the case
where the horn axes of the acoustic hones are set to be in
arbitrary different directions by changing the size and shape of
each of the acoustic horns, the directivity of each of the
conversion means can also be set in an arbitrary direction.
[0084] A horn wall member of each of the acoustic horns is required
to be formed of a material having enough strength to hardly cause
oscillation by an ultrasonic wave. Examples of the material include
various metals, various synthetic resins, and the like.
[0085] According to the fourteenth aspect of the present invention,
the ultrasonic sensor formed by surface-mounting each of the
conversion means on a sensor substrate by using wire bonding can be
obtained.
[0086] According to the fifteenth aspect of the present invention,
each of the conversion means and the sensor substrate are connected
and fixed to each other through a bump. Therefore, since it can be
ensured to keep the electric connection between each of the
conversion means and the sensor substrate, the reliability of the
ultrasonic sensor can be enhanced while extending a lifetime of the
ultrasonic sensor.
[0087] Moreover, by employing flip-chip connection, the fabrication
cost for surface-mounting each of the conversion means onto the
sensor substrate can be reduced as compared with the case where the
wire bonding is employed.
[0088] In the case where each of the conversion means is used as a
receiving element, a bonding wire is not provided above the
receiving surface of an ultrasonic wave and therefore no obstacle
is present in front of the receiving surface. Therefore, the
ultrasonic wave is not inhibited from getting to the receiving
surface, thereby enhancing the receiving sensitivity of the
receiving element. Moreover, since a bonding wire is not provided
above the receiving surface of the receiving element, the bonding
wire is not cut by an ultrasonic wave received by the receiving
element.
[0089] Moreover, in the case where each of the conversion means is
used as a transmission element, a bonding wire is not provided
above the transmission surface of the transmission element and
therefore no obstacle is present in front of the transmission
surface. Therefore, the ultrasonic wave is not inhibited from being
transmitted from the transmission surface, thereby enhancing the
transmission output of the transmission element. Moreover, since a
bonding wire is not provided above the transmission surface of the
receiving element, the bonding wire is not cut by an ultrasonic
wave transmitted from the transmission element.
[0090] Furthermore, since an inductance of the bump is reduced as
compared with that of the bonding wire, a transfer rate of an
electric signal in each of the conversion means can be
increased.
[0091] Moreover, it is no longer necessary to provide an electrode
pad to which the bonding wire is connected. Since the sensor
substrate is reduced by an area occupied by the electrode pad, the
ultrasonic sensor can be reduced in size as well as in weight.
[0092] In addition, according to the fifteenth aspect of the
present invention, if a thickness of the diaphragm of each of the
conversion means is reduced by forming a concave portion on the
bottom face side of a semiconductor substrate so as to facilitate
the oscillation of each of the conversion means, the functions and
effects of the thirteenth aspect of the invention can be easily
obtained without providing the acoustic horn as an independent
member.
[0093] Moreover, since the acoustic horn is not required to be
provided as an independent member, the fabrication cost can be
reduced. At the same time, the ultrasonic sensor can be reduced in
size as well as in weight.
[0094] According to the sixteenth aspect of the present invention,
a piezoelectric or capacitive ultrasonic sensor can be
obtained.
[0095] Other features and advantages of the present invention will
be appreciated, as well as methods of operation and the function of
the related parts from a study of the following detailed
description, appended claims, and drawings, all of which form a
part of this application. In the drawings:
BRIEF DESCRIPTION OF THE DRAWINGS
[0096] FIG. 1 is a cross-sectional side view of a receiving section
of an ultrasonic sensor according to a first embodiment of the
present invention;
[0097] FIG. 2 is an enlarged cross-sectional side view of a
piezoelectric receiving element of the receiving section of FIG.
1;
[0098] FIG. 3 is a perspective view of a first ultrasonic sensor
according to the principles of the present invention;
[0099] FIG. 4 is a cross-sectional side view of a receiving section
of an ultrasonic sensor according to a second embodiment of the
present invention;
[0100] FIG. 5 is a cross-sectional side view of a receiving section
of an ultrasonic sensor according to a third embodiment of the
present invention;
[0101] FIG. 6 is a cross-sectional side view of a receiving section
of an ultrasonic sensor according to a fourth embodiment of the
present invention;
[0102] FIG. 7 is a cross-sectional side view of a receiving section
of an ultrasonic sensor according to a fifth embodiment of the
present invention;
[0103] FIG. 8 is a cross-sectional side view of a receiving section
of an ultrasonic sensor according to a sixth embodiment of the
present invention;
[0104] FIGS. 9A and 9B are cross-sectional side views of a
receiving section of an ultrasonic sensor according to a seventh
embodiment of the present invention;
[0105] FIG. 10 is a cross-sectional side view of a receiving
section of an ultrasonic sensor according to an eighth embodiment
of the present invention;
[0106] FIG. 11 is an enlarged cross-sectional side view of a
capacitive receiving element adapted for use in any one of the
receiving sections in the first through eighth embodiments of the
present invention;
[0107] FIG. 12 is a perspective view of a second ultrasonic sensor
according to the principles of the present invention;
[0108] FIG. 13 is a cross-sectional side view of the receiving
section of FIG. 4 and a transmission section of the ultrasonic
sensor of FIG. 12;
[0109] FIG. 14 is a cross-sectional side view of the receiving
section of FIG. 5 and a transmission section of the ultrasonic
sensor of FIG. 12;
[0110] FIG. 15 is a cross-sectional side view of the receiving
section of FIG. 8 and a transmission section of the ultrasonic
sensor of FIG. 12;
[0111] FIGS. 16A and 16B are cross-sectional side views of the
receiving section of FIGS. 9A and 9B and a transmission section of
the ultrasonic sensor of FIG. 12;
[0112] FIG. 17 is a cross-sectional side view of the receiving
section of FIG. 10 and a transmission section of the ultrasonic
sensor of FIG. 12;
[0113] FIG. 18 is a cross-sectional side view of a receiving
section of an ultrasonic sensor according to a ninth embodiment of
the present invention;
[0114] FIG. 19 is an enlarged cross-sectional side view of a
piezoelectric receiving element of the receiving section of FIG.
18;
[0115] FIG. 20 is a perspective view of a third ultrasonic sensor
according to the principles of the present invention;
[0116] FIG. 21 is a cross-sectional side view of a receiving
section according to a tenth embodiment of the present invention
adapted for use in the ultrasonic sensor of FIG. 20;
[0117] FIG. 22 is a cross-sectional side view of a receiving
section according to an eleventh embodiment of the present
invention adapted for use in the ultrasonic sensor of FIG. 20;
[0118] FIG. 23 is a perspective view of a fourth ultrasonic sensor
according to the principles of the present invention;
[0119] FIGS. 24A and 24B are graphs showing a resonance
characteristic corresponding to the relation between a resonance
value of a diaphragm and a frequency according to the principles of
the present invention;
[0120] FIG. 25 is a cross-sectional side view of a receiving
section according to an twelfth embodiment of the present invention
adapted for use in the ultrasonic sensor of FIG. 20;
[0121] FIG. 26 is a cross-sectional side view of a first
alternative receiving section of the twelfth embodiment of the
present invention;
[0122] FIG. 27 is a cross-sectional side view of a second
alternative receiving section and a transmission section of the
twelfth embodiment of the present invention;
[0123] FIG. 28 is a cross-sectional side view of a receiving
section according to a thirteenth embodiment of the present
invention adapted for use in the ultrasonic sensor of FIG. 20;
[0124] FIG. 29 is a cross-sectional side view of a first
alternative receiving section of the thirteenth embodiment;
[0125] FIG. 30 is a cross-sectional side view of a second
alternative receiving section according to the thirteenth
embodiment and the transmission section adapted for use in the
ultrasonic sensor of FIG. 23;
[0126] FIG. 31 is a cross-sectional side view of a receiving
section according to a fourteenth embodiment of the present
invention adapted for use in the ultrasonic sensor of FIG. 20;
[0127] FIG. 32 is a cross-sectional side view of a first
alternative receiving section of the fourteenth embodiment of the
present invention adapted for use in the ultrasonic sensor of FIG.
20;
[0128] FIG. 33 is a cross-sectional side view of a second
alternative receiving section of the fourteenth embodiment and a
transmission section adapted for use in the ultrasonic sensor of
FIG. 23;
[0129] FIG. 34 is an enlarged cross-sectional side view of a
capacitive receiving element adapted for use in any one of the
receiving sections of the ninth to the fourteenth embodiments
including the alternatives to these embodiments;
[0130] FIG. 35 is a cross-sectional side view of the receiving
section and the transmission section of the ninth embodiment
adapted to the ultrasonic sensor of FIG. 23;
[0131] FIG. 36 is a cross-sectional side view of the receiving
section and the transmission section of the twelfth embodiment
adapted to the ultrasonic sensor of FIG. 23;
[0132] FIG. 37 is a cross-sectional side view of the receiving
section and the transmission section of the thirteenth embodiment
adapted to the ultrasonic sensor of FIG. 23; and
[0133] FIG. 38 is a cross-sectional side view of the receiving
section and the transmission section of the fourteenth embodiment
adapted to the ultrasonic sensor of FIG. 23.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0134] Hereinafter, embodiments where the present invention is
embodied will be described with reference to the accompanying
drawings. In the embodiments, the same components are denoted by
the same reference numerals, and the description of the same
contents is herein omitted.
Embodiment 1
[0135] FIG. 1 is a cross-sectional side view showing a receiving
section 10 in an ultrasonic sensor M according to Embodiment 1.
[0136] The receiving section 10 includes a plurality of
piezoelectric receiving elements 11 arranged in an array. In an
example shown in FIG. 1, a cross-sectional side view of three
receiving elements 11 is shown.
[0137] Each of the receiving elements 11 is formed on a
single-crystalline silicon substrate (a single-crystalline silicon
chip) 12 having an SOI structure.
[0138] The substrate 12 is housed within a housing member 13 having
a rectangular parallelepiped box shape with an upper open end.
Moreover, an outer circumferential end of the substrate 12 is
attached and fixed to an inner wall of the housing member 13 by an
appropriate method (for example, thermal welding, ultrasonic
welding, bonding with an adhesive or the like) so as to air-seal a
connection part between the outer circumferential end of the
substrate 12 and the housing member 13.
[0139] Each of the receiving elements 11 is located so that a
receiving surface 11a for receiving an ultrasonic wave is oriented
toward an opening 13a of the housing member 13.
[0140] A protective film 14 for closing the opening 13a is attached
over the opening 13a of the housing 13. Specifically, the
protective film 14 is provided in front of the receiving elements
11.
[0141] An outer circumferential end of the protective film 14 is
attached and fixed to an inner circumferential end of the opening
13a of the housing member 13 by the above-described appropriate
method so as to air-seal a connection part between the outer
circumferential end of the protective film 14 and the housing
member 13.
[0142] The protective film 14 is a thin film made of a material
that is likely to be oscillated by an ultrasonic wave. Although the
material of the protective film 14 transmits an ultrasonic wave
without refraction, it does not transmit air, dust, water and the
like.
[0143] A gap S is provided between the protective film 14 and the
substrate 12. The gap S is filled with a gas, a liquid, a sol, a
gel or the like.
[0144] A gap R surrounded by the back face side (the bottom face
side) of the substrate 12 and the housing member 13 is filled with
air.
[0145] FIG. 2 is an enlarged cross-section side view showing one
piezoelectric receiving element 11.
[0146] A through hole 12a passing through the substrate 12 is
formed in the substrate 12.
[0147] On a surface of the substrate 12, an insulating layer 21, a
silicon active layer 22, and an insulating layer 23 are formed in
this order. Each of the layers 22 and 23 is formed to close the
upper opening of the through hole 12a.
[0148] On a surface of the insulating layer 23 situated above (in
front of) the through hole 12a, a lower electrode layer 24, a thin
film layer 25 made of a ferroelectric (for example, PZT or the
like), and an upper electrode layer 26 are formed in this
order.
[0149] An insulating layer 27 is formed around the layers 24 to 26.
Surfaces of the insulating layer 27 and the upper electrode layer
26 (a device surface) are evened.
[0150] A bonding wire (a lead wire) 28 is connected to the lower
electrode layer 24, whereas a bonding layer 29 is connected to the
upper electrode layer 26.
[0151] In the above-described manner, a piezoelectric element (a
piezoelectric sensor) E having a structure in which the
ferroelectric thin film layer 25 is sandwiched between the two thin
electrode layers 24 and 26 is formed. The receiving element 11
includes the piezoelectric element E fabricated by employing the
MEMS technique.
[0152] Moreover, a receiving surface 11a of the receiving element
11 is formed by the surface of the upper electrode layer 26.
[0153] When the thin film layer 25 is oscillated by an ultrasonic
wave, an electric signal is generated by a piezoelectric effect.
The thus generated electric signal is output from each of the
electrodes 24 and 26 through the bonding wires 28 and 29.
[0154] The through hole 12a is provided so as to facilitate the
oscillation of a diaphragm composed of the layers 22 to 26.
[0155] FIG. 3 is a perspective view showing the ultrasonic sensor
M.
[0156] The ultrasonic sensor M is composed of a hybrid IC
(Integrated Circuit) including: a receiving section 10; a
transmission section 31; a sensor substrate 32; and electrode pads
33.
[0157] The sensor substrate 32 is a printed wiring board. A
plurality of electrode pads 33 are formed on a surface of the
sensor substrate 32 formed of an insulating plate material while
the receiving section 10 and the transmission section 31
corresponding to chip parts are attached and fixed thereto.
[0158] A tip of each of the bonding wires 28 and 29 led from each
of the receiving elements 11 in the receiving section 10 is
connected to each of the electrode pads 33.
[0159] In the example shown in FIG. 3, the receiving section 10 is
constituted by nine receiving elements 11 arranged 3 by 3.
[0160] The transmission section 31 has the same structure as that
of the receiving section 10. The transmission section 31 includes a
single piezoelectric transmission element having the same structure
as that of the receiving element 11. The thin film layer 25
oscillates due to the piezoelectric effect to produce an ultrasonic
wave in accordance with input signals applied from the electrode
layers 24 and 26 to the thin film layer 25 made of a ferroelectric.
In this case, the receiving surface 11a of the receiving element 11
acts as a transmission surface for transmitting the ultrasonic wave
from the transmission element.
[0161] Specifically, the transmission element of the transmission
section 31 converts an electric signal into an ultrasonic wave so
as to transmit it.
[0162] Then, the transmission section 31 transmits an ultrasonic
wave in accordance with an input signal from the exterior. A
reflection sound generated by the ultrasonic wave reflected by an
object to be detected is received by each of the receiving elements
11 in the receiving section 10.
[0163] Specifically, each of the receiving elements 11 in the
receiving section 10 converts the received ultrasonic wave into an
electric signal.
[0164] The ultrasonic wave transmitted from the transmission
section 31 and the ultrasonic wave received by each of the
receiving elements 11 in the receiving section 10 are compared with
each other so as to obtain an acoustic pressure difference, a time
difference, and a phase difference between them. As a result, the
position of the object to be detected, a distance between the
ultrasonic sensor M and the object to be detected, a
two-dimensional or three-dimensional shape of the object to be
detected and the like can be measured based on the obtained
differences.
Functions and Effects of Embodiment 1
[0165] According to Embodiment 1, the following functions and
effects can be obtained.
[1-1]
[0166] The protective film 14 is provided in front of the substrate
12 on which the receiving elements 11 are formed. The gap S is
provided between the protective film 14 and the substrate 12.
[0167] Therefore, even if an external force is applied to the
receiving section 10 of the ultrasonic sensor M, the external force
is applied merely to the protective film 14 but not directly to
each of the thin layers 22 to 26 formed on the substrate 12.
[0168] Therefore, according to Embodiment 1, even if each of the
thin layers 22 to 26 has a low mechanical strength, each of the
layers 22 to 26 can be prevented from being damaged so as to be
unlikely to break the receiving section 10. As a result, the robust
receiving section 10 can be obtained.
[0169] Moreover, since the transmission element of the transmission
section 31 has the same structure as that of the receiving element
11, each of the layers 22 to 26 can be prevented from being damaged
so that the transmission section 31 is hardly broken. As a result,
the robust transmission section 31 can be obtained.
[0170] Therefore, the ultrasonic sensor M including the receiving
section 10 and the transmission section 31 can be mounted as
external equipment of an automobile without any modification. If
the ultrasonic sensor M is to be mounted as external equipment of
an automobile, it is necessary to use a highly weather-resistant
material for the protective film 14. Examples of the material
include various metals (such as an aluminum alloy), various
synthetic resins, glasses, rubbers, and the like.
[1-2]
[0171] In the case where the gap S between the protective film 14
and the substrate 12 is filled with a filler selected from a
liquid, a sol and a gel, an acoustic impedance of the filler is
brought close to that of the protective film 14, so that it becomes
possible to propagate the oscillation of the protective film 14
through the filler to each of the receiving elements 11. As a
result, the receiving sensitivity of each of the receiving elements
11 can be enhanced.
[0172] The acoustic impedance of a material is a product of a
density of the material and a propagation acoustic speed. Then, as
a difference in acoustic impedance between materials becomes
larger, the propagation characteristic of an acoustic wave is
degraded. Specifically, as a difference in acoustic impedance
between the filler in the gap S and the protective film 14 becomes
greater, an ultrasonic wave is reflected by the protective film 14
so as be less likely to propagate to the filler.
[0173] Therefore, if a synthetic resin film is used as the
protective film 14, a sol obtained by dispersing fine particles of
the synthetic resin in a liquid or a polymer gel made of the
synthetic resin is used as the filler. Moreover, the filler is
required not to affect the receiving elements 11. Examples of the
filler meeting such a requirement include a silicon gel, a fluorine
gel, and the like.
[0174] In order to fill the gap S with the filler, after the
attachment of the protective film 13 onto the housing member 13,
the filler is injected into the gap S while removing air from the
gap S.
[0175] Alternatively, after the substrate 12 is housed within the
housing member 13 and the filler is then poured on the substrate 12
through the upper opening of the housing member 13, the protective
film 14 may be attached onto the housing member 13.
[0176] Further alternatively, after the filler is dropped onto the
substrate 12, the substrate 12 is rotated so as to form a thin film
made of the filler on the surface of the substrate 12 by spin
coating. Subsequently, the substrate 12 may be housed within the
housing member 13.
[0177] As an example, if the gap S is filled with one of various
gases (air, an inert gas and the like), the oscillation of the
protective film 14 does not satisfactorily propagate to the
receiving elements 11 because the gas has an acoustic impedance
extremely smaller than that of the protective film 14. Accordingly,
there is a possibility that the receiving sensitivity of each of
the receiving elements 11 is lowered.
[0178] In the case where the gap S is filled with the filler such
as a liquid, a sol, and a gel, the oscillation of the protective
film 14 is less likely to propagate to the receiving elements 11 if
air remains in the gap S. Therefore, it is desirable to completely
remove air from the gap S so as to fill the gap S with the
filler.
[0179] If the gap S between the protective film 14 and the
substrate 12 is filled with the filler selected from a liquid, a
sol and a gel, the propagation of oscillation of the transmission
element through the filler to the protective film 14 can be ensured
by bringing the acoustic impedance of the filler close to that of
the protective film 14 because the transmission element in the
transmission section 31 has the same structure as that of the
receiving element 11. As a result, a transmission output of the
transmission element can be enhanced.
[0180] Moreover, if the gap S is filled with one of various gases,
the oscillation of the transmission element does not satisfactorily
propagate to the protective film 14 because the acoustic impedance
of the gas is extremely smaller than that of the protective film
14. Therefore, there is a possibility that a transmission output of
the transmission element becomes low.
[0181] Moreover, in the case where the gap S is filled with the
filler such as a liquid, a sol and a gel, it is desirable to
completely remove air from the gap S so as to fill the gap S with
the filler because the oscillation of the transmission element is
less likely to propagate to the protective film 14 if air remains
in the gap S.
[1-3]
[0182] In the example shown in FIG. 3, the ultrasonic sensor
includes the receiving section 10 including nine receiving elements
11 (piezoelectric elements E). However, the number of the receiving
elements 11 constituting the receiving section 10 affects the
accuracy of the measurement (the measurement of position, a
distance and a shape) of the object to be detected; as the number
of the receiving elements 11 is increased, the accuracy can be
enhanced.
[0183] An interval between the receiving elements 11 is required to
be set shorter than a wavelength of the ultrasonic wave transmitted
from the transmission section 31. The interval between the
receiving elements 11 also affects the measurement accuracy.
[0184] Therefore, the number of and the interval between the
receiving elements 11 can be set by experimentally finding their
optimal values in a cut-and-try method in accordance with the
required measurement accuracy.
[0185] For example, if only the directional position of the object
to be detected with respect to the ultrasonic sensor M is to be
measured, several receiving elements 11 are satisfactory. However,
if a precise two-dimensional shape of the object to be detected is
measured, it is necessary to provide several tens to several
hundreds of the receiving elements 11. Furthermore, if a precise
three-dimensional shape of the object to be detected is measured, a
larger number of the receiving elements 11 than the number needed
for two-dimensional shape measurement are required.
[1-4]
[0186] In the example shown in FIG. 3, the arrangement of the
transmission elements constituting the transmission section 31 is
appropriately determined so as to adjust the directivity of a
transmission direction of an ultrasonic wave.
[0187] Therefore, the number and the arrangement of the
transmission elements constituting the transmission section 31 can
be set by experimentally fining their optimal values in a
cut-and-try method in accordance with the required transmission
output and directivity.
Embodiment 2
[0188] FIG. 4 is a cross-sectional side view showing a receiving
section 40 in the ultrasonic sensor M according to Embodiment
2.
[0189] The receiving section 40 according to Embodiment 2 differs
from the receiving section 10 in Embodiment 1 only in that the
protective film 14 is replaced by a thin-plate like protective
member 41 attached and fixed onto the receiving surface 11a of each
of the receiving elements 11.
[0190] Specifically, in the receiving section 40, the protective
member 41 is attached to the front side of each of the receiving
elements 11. A clearance K is provided between the protective
members 41 of the respective receiving elements 11. The clearance K
separates the protective members 41 for each of the receiving
elements 11.
[0191] The structure of the ultrasonic sensor M according to
Embodiment 2 is obtained by replacing the receiving section 10 in
the ultrasonic sensor M shown in FIG. 3 according to Embodiment 1
with the receiving section 40.
Functions and Effects of Embodiment 2
[0192] According to Embodiment 2, the following functions and
effects can be obtained in addition to the same functions and
effects described in [1-3] and [1-4] of Embodiment 1 above.
[2-1]
[0193] The thin plate-like protective member 41 is attached and
fixed to the receiving surface 11a of each of the receiving
elements 11. Therefore, when the protective member 41 is oscillated
by an ultrasonic wave, the oscillation of the protective member 41
propagates to each of the layers 22 to 26 (not shown in FIG. 4; see
FIG. 2) on the receiving surface 11a. As a result, the thin film
layer 25 made of a ferroelectric oscillates to generate an electric
signal due to a piezoelectric effect.
[0194] Herein, since the layers 22 to 26 on the receiving surface
11a are reinforced with the protective member 41, each of the thin
layers 22 to 26 can be prevented from being damaged so as to be
unlikely to break the receiving section 40 even if an external
force is applied to the receiving section 40 of the ultrasonic
sensor M. As a result, the robust receiving section 40 can be
obtained.
[0195] Moreover, in the case where the transmission section 31 is
made to have the same structure as that of the receiving section 40
so that the thin plate-like protective member 41 is attached and
fixed to the transmission surface of the transmission element, the
oscillation of the thin film layer 25 propagates to the protective
member 41 when the thin film layer 25 is oscillated by the
piezoelectric effect. Then, the protective member 41 is oscillated
in turn to transmit the ultrasonic wave.
[0196] In this case, since the layers 22 to 26 on the transmission
surface of the transmission element are reinforced by the
protective member 41, each of the thin layers 22 to 26 can be
prevented from being damaged so as to be unlikely to break the
transmission section 31 even if an external force is applied to the
transmission section 31 of the ultrasonic sensor M. As a result,
the robust transmission section 31 can be obtained.
[2-2]
[0197] Since the receiving section 40 and the transmission section
31 are robust, the ultrasonic sensor M including the receiving
section 40 and the transmission section 31 can be mounted as
external equipment of an automobile without any modification. If
the ultrasonic sensor M is to be mounted as external equipment of
an automobile, it is necessary to use a highly weather-resistant
material as a material of the protective member 41. Examples of
such a material include various metals (such as an aluminum alloy),
various synthetic resins, glasses, rubbers, and the like.
[0198] As a method of attaching and fixing the protective member 41
onto the receiving surface 11a of each of the receiving elements 11
(the transmission surface of the transmission element), any method
(for example, thermal welding, ultrasonic welding, bonding with an
adhesive and the like) may be used.
[2-3]
[0199] The clearance K is provided between the protective members
41 of the respective receiving elements 11. The clearance K serves
to separate the protective members 41 for each of the receiving
elements 11. Therefore, the oscillation of one protective member 41
propagates only to the receiving element 11 to which the protective
member 41 is attached and fixed but not to the other receiving
elements 11 through the adjacent protective member 41.
[0200] Thus, according to Embodiment 2, since an ultrasonic wave
can be received by each of the receiving elements 11 in a
completely separate manner, a crosstalk characteristic of each of
the receiving elements 11 can be prevented from being degraded.
Embodiment 3
[0201] FIG. 5 is a cross-sectional side view showing a receiving
section 50 in the ultrasonic sensor M according to Embodiment
3.
[0202] The receiving section 50 according to Embodiment 3 differs
from the receiving section 10 according to Embodiment 1 merely in
that separation members 51 and separation grooves 52 are
provided.
[0203] A lower end of each of the separation members 51 is embedded
in each of the separation grooves 52 formed in the substrate 12
between the receiving elements 11. On the other hand, an upper end
of each of the separation members 51 separates the gaps S and the
protective films 14 for each of the receiving elements.
[0204] Specifically, in the example shown in FIG. 5, the lower end
of each of the separation members 51 is embedded into each of the
separation grooves 52 formed in the substrate 12 between three
receiving elements 11A to 11C. As a result, the receiving elements
11A to 11C are separated from each other by the separation members
51 and the separation grooves 52.
[0205] The gaps SA to SC and the protective films 14A to 14C
situated above (in front of) the respective receiving elements 11A
to 11C are also separated from each other by the separation members
51 for each of the receiving elements 11A to 11C.
[0206] The structure of the ultrasonic sensor M according to
Embodiment 3 is obtained by replacing the receiving section 10 of
the ultrasonic sensor M shown in FIG. 3 according to Embodiment 1
with the receiving section 50.
Functions and Effects of Embodiment 3
[0207] According to Embodiment 3, the following functions and
effects can be obtained in addition to the above-described
functions and effects according to Embodiment 1.
[3-1]
[0208] The receiving elements 11, and the gaps S and the protective
films 14 situated above (in front of) the respective receiving
elements 11 are separated by the separation members 51 and the
separation grooves 52 for each of the receiving elements 11.
Therefore, the oscillation of one protective film 14A obtained by
the separation propagates only to the receiving element 11A through
the gap SA situated below the protective film 14A but not to the
other receiving elements 11B and 11C.
[0209] Therefore, according to Embodiment 3, an ultrasonic wave can
be received by each of the receiving elements 11A to 11C in a
completely separate manner. Accordingly, a crosstalk characteristic
of each of the receiving elements 11A to 11C can be prevented from
being degraded.
[0210] Alternatively, a plurality of the receiving elements 11
adjacent to each other may be grouped into one. The separation
member 51 and the separation groove 52 may be provided for each
group so as to separate the group from the other groups.
[3-2]
[0211] Each of the separation members 51 is required to surely
block the oscillation of the protective film 14A, the gap SA and
the receiving element 11A, which are vertically arranged to be
grouped into one, so that the oscillation does not propagate to the
members of the other adjacent groups (the protective films 14B and
14C, the gaps SB and SC, and the receiving elements 11B and
11C).
[0212] For this reason, a material having a high oscillation
blocking property is required to be used for each of the separation
members 51. Examples of the material include rubbers.
Embodiment 4
[0213] FIG. 6 is a cross-sectional side view showing a receiving
section 60 in the ultrasonic sensor M according to Embodiment
4.
[0214] The receiving section 60 according to Embodiment 4 differs
from the receiving section 50 according to Embodiment 3 only in
that a vent hole 61 for bringing the gap R and the exterior of the
housing member 13 into communication with each other is formed in
the bottom face of the housing member 13 below each of the
receiving elements 11.
[0215] The structure of the ultrasonic sensor M according to
Embodiment 4 is obtained by replacing the receiving section 10 of
the ultrasonic sensor M shown in FIG. 3 according to Embodiment 1
with the receiving section 60.
[0216] However, it is necessary to provide a clearance between the
receiving section 60 and the sensor substrate 32 so that each of
the vent holes 61 is not closed when the receiving section 60 is
attached and fixed onto the sensor substrate 32. Specifically, a
spacer may be provided between the receiving section 60 and the
sensor substrate 32, or a groove or a vent hole may be provided in
the sensor substrate 32 at a position corresponding to each of the
vent holes 61.
Functions and Effects of Embodiment 4
[0217] According to Embodiment 4, the receiving sensitivity of each
of the receiving elements 11 can be prevented from being lowered in
addition to the above-described functions and effects according to
Embodiment 3 because the oscillation of each of the layers 22 to 26
(not shown in FIG. 6; see FIG. 2) on the receiving surface 11a of
each of the receiving elements 11 is not inhibited.
[0218] Specifically, in the case where the vent holes 61 are not
provided for the housing member 13, the gap R surrounded by the
substrate 12 and the housing member 13 becomes a sealed space. In
this manner, air filling the sealed space acts as a spring so as to
apply a damping force due to air to the back face side of the
receiving surface 11a of each of the receiving elements 11.
Therefore, there is a possibility that free oscillation of each of
the layers 22 to 26 on the receiving surface 11a is inhibited so as
to lower the receiving sensitivity of each of the receiving
elements 11.
[0219] On the other hand, in Embodiment 4, air passes through the
vent holes 61. Therefore, a damping force due to air is not applied
to the back face side of the receiving surface 11a of each of the
receiving elements 11. As a result, each of the layers 22 to 26 on
the receiving surface 11a is capable of freely oscillating.
[0220] The number, the arrangement, and the size and shape of the
vent holes 61 can be determined by experimentally finding their
optimal values in a cut-and-try method so as to obtain satisfactory
functions and effects described above.
[0221] In the case where the transmission section 31 is made to
have the same structure as that of the receiving section 60 and the
vent holes 61 are provided for the housing member 13 of the
transmission section 31, air passes through the vent holes 61.
Therefore, a damping force due to air is not applied onto the back
face side of the transmission surface of the transmission element.
As a result, since the oscillation is not inhibited so that each of
the layers 22 to 26 on the transmission surface can freely
oscillate, the transmission output of the transmission element can
be enhanced.
Embodiment 5
[0222] FIG. 7 is a cross-sectional side view showing a receiving
section 70 in the ultrasonic sensor M according to Embodiment
5.
[0223] The receiving section 70 according to Embodiment 5 differs
from the receiving section 10 according to Embodiment 1 only in
that a vent hole 71 for bringing the gap S and the exterior of the
housing member 13 into communication with each other is provided
through a side wall of the housing member 13.
[0224] The structure of the ultrasonic sensor M according to
Embodiment 5 is obtained by replacing the receiving section 10 of
the ultrasonic sensor M shown in FIG. 3 according to Embodiment 1
with the receiving section 70.
[0225] However, it is necessary to attach and fix a side wall of
the housing member 13, which faces the side wall carrying the vent
hole 71, onto the sensor substrate 32 so that an opening of the
vent hole 71 is oriented upward when the receiving section 70 is
attached and fixed onto the sensor substrate 32.
Functions and Effects of Embodiment 5
[0226] According to Embodiment 5, in addition to the
above-described functions and effects of Embodiment 1, if a filler
such as a liquid, a sol or a gel contains air bubbles when the gap
S is filled with the filler, the air bubbles can be removed through
the vent hole 71 to the exterior of the gap S.
[0227] Specifically, if the filler filling the gap S contains air
bubbles, the air bubbles make it difficult to propagate the
oscillation of the protective film 14 to the receiving elements
11.
[0228] On the other hand, according to Embodiment 5, the air
bubbles are removed through the vent hole 71. Therefore, the gap S
can be completely filled with the filler so as to prevent the
receiving sensitivity of each of the receiving elements 11 from
being lowered by the air bubbles contained in the filler filling
the gap S.
[0229] In the case where the transmission section 31 is made to
have the same structure as that of the receiving section 70 and the
vent hole 71 is provided for the housing member 13 of the
transmission section 31, the air bubbles contained in the filler of
the gap S are removed through the vent hole 71. As a result, the
gap S can be completely filled with the filler. In this manner, the
oscillation of the transmission element is allowed to surely
propagate through the filler to the protective film 13 so as to
prevent the transmission output of the transmission element from
being lowered.
Embodiment 6
[0230] FIG. 8 is a cross-sectional side view showing a receiving
section 80 in the ultrasonic sensor M according to Embodiment
6.
[0231] The receiving section 80 according to Embodiment 6 differs
from the receiving section 10 in Embodiment 1 only in that
column-like transfer members 81 for independently connecting the
receiving surfaces 11a of the respective receiving elements 11 and
the protective film 14 with each other for each of the receiving
elements 11 are provided in the gap S.
[0232] The structure of the ultrasonic sensor M according to
Embodiment 6 is obtained by replacing the receiving section 10 of
the ultrasonic sensor M shown in FIG. 3 according to Embodiment 1
with the receiving section 80.
Functions and Effects of Embodiment 6
[0233] According to Embodiment 6, the following functions and
effects can be obtained in addition to the above-described
functions and effects [1-1], [1-3], and [1-4] according to
Embodiment 1.
[6-1]
[0234] When the protective film 14 is oscillated by an ultrasonic
wave, the oscillation of the protective film 14 propagates through
each of the transfer members 81 to each of the receiving elements
11.
[0235] In this case, since the transfer member 81 is provided for
each of the receiving elements 11, the oscillation of an arbitrary
one of the transfer members 81 does not propagate to the other
transfer members 81. Therefore, an ultrasonic wave can be received
by each of the receiving elements 11 in a separate manner. As a
result, a crosstalk characteristic of each of the receiving
elements 11 can be prevented from being degraded.
[0236] Moreover, an acoustic impedance of each of the transfer
member 81 is brought close to that of the protective film 14 so as
to surely propagate the oscillation of the protective film 14 to
each of the transfer members 81. As a result, the receiving
sensitivity of each of the receiving elements 11 can be
enhanced.
[0237] Furthermore, by bringing the acoustic impedance of each of
the transfer members 81 close to that of the upper electrode layer
26 (not shown in FIG. 8; see FIG. 2), it becomes possible to surely
propagate the oscillation of each of the transfer members 81 to the
upper electrode layer 26 so as to increase the receiving
sensitivity of each of the receiving elements 11.
[0238] Therefore, it is desirable to form the transfer member 81 of
the same material as that of the protective film 14 or the upper
electrode layer 26.
[0239] In the case where the transmission section 31 is made to
have the same structure as that of the receiving section 80 and the
transfer member 81 for connecting the transmission surface of the
transmission element and the protective film 14 with each other is
provided, it becomes possible to surely propagate the oscillation
of the transfer member 81 to the protective film 14 by bringing the
acoustic impedance of the transfer member 81 close to that of the
protective film 14. As a result, the transmission output of the
transmission element can be increased.
[0240] Moreover, by bringing the acoustic impedance of the transfer
member 81 close to that of the upper electrode layer 26 of the
transmission element, it becomes possible to surely propagate the
oscillation of the upper electrode layer 26 of the transmission
element to the transfer member 81. As a result, the transmission
output of the transmission element can be increased.
[6-2]
[0241] In order to prevent the crosstalk characteristic of each of
the receiving elements 11 from being degraded, it is necessary to
prevent the oscillation of an arbitrary one of the transfer members
81 from propagating to the other transfer members 81 through the
filler in the gap S.
[0242] Therefore, it is the most desirable in Embodiment 6 to put
the gap S in a vacuum state.
[0243] In the case where the gap S is filled with the filler in
Embodiment 6, a gas having a small acoustic impedance or a highly
vibration absorbent material (for example, a gel having a high
viscosity or the like) is used as the filler.
Embodiment 7
[0244] FIGS. 9A and 9B are cross-sectional side views, each showing
a receiving section 90 in the ultrasonic sensor M according to
Embodiment 7.
[0245] The receiving section 90 according to Embodiment 7 differs
from the receiving section 50 in Embodiment 3 only in that acoustic
horns 91 are provided on the outer side of the protective film
14.
[0246] Each of the acoustic horns 91 is formed so as to have a
gradually increasing sectional area from a throat 91a toward an
opening 91b.
[0247] The acoustic horn 91 is provided for each of the receiving
elements 11.
[0248] The throat 91a of each of the acoustic horns 91 is located
on the protective film 14 situated above (in front of) each of the
receiving elements 11. Specifically, the throat 91a of each of the
acoustic horns 91 is provided in front of each of the receiving
elements 11.
[0249] In each of the acoustic horns 91, a horn wall member 91c on
an outer circumference of the throat 91a is attached and fixed to
an upper end of each of the separation members 51.
[0250] Specifically, in the example shown in FIGS. 9A and 9B, the
acoustic horns 91A to 91C are provided for three receiving elements
11A to 11C, respectively. The throats 91a of the respective
acoustic horns 91A to 91C are provided on the protective films 14A
to 14C situated above (in front of) the receiving elements 11A to
11C, respectively.
[0251] The structure of the ultrasonic sensor M in Embodiment 7 is
obtained by replacing the receiving section 10 of the ultrasonic
sensor M shown in FIG. 3 according to Embodiment 1 with the
receiving section 90.
Functions and Effects of Embodiment 7
[0252] According to Embodiment 7, the following functions and
effects can be obtained in addition to the above-described
functions and effects of Embodiment 3.
[7-1]
[0253] By providing the acoustic horn 91 for each of the receiving
elements 11, the directivity of a receiving direction of an
ultrasonic wave can be provided for each of the receiving elements
11.
[0254] Specifically, the acoustic horns 91A to 91C have acute
directivity on their horn axes a to .gamma., respectively.
[0255] Therefore, the acoustic horns 91A to 91C are formed to have
the same size and shape as shown in FIG. 9A, so that the
directivity of the receiving elements 11A to 11C can be set in the
same direction if the horn axes a to y of the respective acoustic
horns 91A to 91C are set in the same direction.
[0256] Moreover, as shown in FIG. 9B, if the horn axes a to y of
the respective acoustic horns 91A to 91C are set in arbitrary
different directions by changing the size and shape of each of the
acoustic horns 91A to 91C, the directivity of each of the receiving
elements 11A to 11C can be set in an arbitrary direction.
[0257] If the transmission section 31 is made to have the same
structure as that of the receiving section 90 and the acoustic
horns 91 are provided on the outer side of the protective film 14,
the directivity of a transmission direction of an ultrasonic wave
can be imparted to the transmission element.
[7-2]
[0258] In each of the acoustic horns 91, the horn wall member 91c
on the outer circumference of the throat 91a is attached and fixed
to the upper end of each of the separation members 51.
[0259] Therefore, the oscillation of each of the protective films
14A to 14C is not inhibited even if the acoustic horns 91 are
provided, the receiving sensitivity of each of the receiving
elements 11 can be prevented from being degraded.
[0260] The horn wall member 91c of the acoustic horn 91 is required
to be formed of a material having enough strength to be hardly
oscillated by an ultrasonic wave. Examples of the material include
various metals, various synthetic resins, and the like.
[0261] If the transmission section 31 is made to have the same
structure as that of the receiving section 90 and the acoustic
horns 91 are provided on the outer side of the protective film 14,
the oscillation of the protective film 14 is not inhibited even if
the acoustic horns 91 are provided because the horn wall member 91c
on the outer circumference of the throat 91a is attached and fixed
to the upper end of each of the separation members 51. Accordingly,
the transmission output of the transmission element can be
prevented from being lowered.
Embodiment 8
[0262] FIG. 10 is a cross-sectional side view showing a receiving
section 100 in the ultrasonic sensor M according to Embodiment
8.
[0263] The receiving section 100 according to Embodiment 8 differs
from the receiving section 80 according to Embodiment 6 only in
that the acoustic horns 91 are provided on the outer side of the
protective film 14 as in the receiving section 90 according to
Embodiment 7.
[0264] In Embodiment 8, however, the horn wall member 91c on the
outer circumference of the throat 91a in each of the acoustic horns
91 is attached and fixed to the protective film 14.
[0265] The structure of the ultrasonic sensor M according to
Embodiment 8 is obtained by replacing the receiving section 10 of
the ultrasonic sensor M shown in FIG. 3 according to Embodiment 1
with the receiving section 100.
[0266] Therefore, according to Embodiment 8, the functions and
effects described in [7-1] above in Embodiment 7 can be obtained in
addition to the above-described functions and effects of Embodiment
6.
Exemplary Variations of Embodiments 1 to 8
[0267] Embodiments 1 to 8 may be changed as follows. Even in such a
case, the functions and effects equivalent to or superior to those
of each of the embodiments described above can be obtained.
[1]
[0268] Each of the receiving sections 10 to 100 in Embodiments 1 to
8 includes the plurality of piezoelectric receiving elements
11.
[0269] However, the piezoelectric receiving elements 11 may be
replaced by capacitive receiving elements 111 so that the plurality
of capacitive receiving elements 111 constitute each of the
receiving sections 10 to 100.
[0270] FIG. 11 is an enlarged cross-sectional side view showing one
capacitive receiving element 111.
[0271] An insulating layer 112 is formed on the surface of the
substrate 12. A fixed electrode layer 113 is formed on a surface of
the insulating layer 112. A movable electrode layer 114 is formed
on a surface of the fixed electrode layer 113 through a clearance
P.
[0272] An insulating layer 115 is formed around the electrode
layers 113 and 114. Surfaces of the insulating layer 115 and the
movable electrode layer 114 (a device surface) are evened.
[0273] The bonding wires 28 and 29 are connected to the electrode
layers 113 and 114, respectively.
[0274] In this manner, a capacitive element F is formed to have a
structure in which the two electrodes 113 and 114 are provided so
as to be opposed to each other through the clearance P. The
receiving element 111 includes the capacitive element F fabricated
by employing the MEMS technique.
[0275] The surface of the movable electrode layer 114 forms the
receiving surface 111a of the receiving element 111.
[0276] When the movable electrode layer 114 is oscillated by an
ultrasonic wave, a distance between the electrode layers 113 and
114 changes so as to change a capacitance. Therefore, a conversion
circuit (not shown) connected to the bonding wires 28 and 29 is
used so as to convert a change in capacitance between the electrode
layers 113 and 114 into an electric signal.
[0277] As described above, even in each of the receiving elements
10 to 100 is formed to include the plurality of capacitive
receiving elements 111, the movable electrode layer 114 can be
prevented from being damaged so as to hardly break the receiving
sections 10 to 100 even if the thin movable electrode layer 114 has
a low mechanical strength as in the case where each of the
receiving sections 10 to 100 is formed with the piezoelectric
receiving elements 11. As a result, the robust receiving sections
10 to 100 can be obtained.
[2]
[0278] The transmission section 31 in Embodiments 1 to 8 is formed
with the piezoelectric transmission element having the same
structure as that of the piezoelectric receiving element 11.
[0279] However, the transmission section 31 may also be formed with
a capacitive transmission element having the same structure as that
of the capacitive receiving element 111 shown in FIG. 10. In such a
case, electrostatic attraction is generated between the electrode
layers 113 and 114 in accordance with input signals applied to the
electrode layers 113 and 114. The electrostatic attraction
oscillates the movable electrode layer 114 to generate an
ultrasonic wave.
[0280] In this case, the receiving face 11a of the receiving
element 111 acts as the transmission face of the transmission
element for transmitting an ultrasonic wave.
[3]
[0281] In Embodiments 1 to 8, the gap R surrounded by the substrate
12 and the housing member 13 is filled with air.
[0282] However, if the gap R is filled with a material (for
example, a liquid, a sol, a gel or the like) for suppressing
excessive oscillation of the layers 22 to 26, each of the layers 22
to 26 can be prevented from being excessively oscillated to be
damaged.
[4]
[0283] The ultrasonic sensor M according to Embodiments 1 to 8 is
composed of a hybrid IC in which any one of the receiving sections
10 to 100 and the transmission section 31 corresponding to chip
parts are attached and fixed onto the sensor substrate 32 made of
an insulating plate material.
[0284] Alternatively, the ultrasonic sensor M may also be composed
of a monolithic IC in which any one of the receiving sections 10 to
100 and the transmission section 31 are formed on the single
substrate 12. In this manner, the ultrasonic sensor M can be
further reduced in size as well as in weight.
[0285] In this case, any one of or a plurality of the receiving
elements 11 arranged on the substrate 12 may be made to act as a
transmission element(s) of the transmission section 31.
[0286] FIG. 12 is a schematic perspective view showing an
ultrasonic sensor T.
[0287] The ultrasonic sensor T includes: a monolithic IC in which
receiving section 10, 40, 50, 80, 90 or 100 and a transmission
section U are formed on the single substrate 12 (not shown in FIG.
12; see FIGS. 13 to 17); the bonding wires 28 and 29; the sensor
substrate 32; and electrode pads 33.
[0288] With this structure, the ultrasonic sensor T is further
reduced in size as well as in weight as compared with the
ultrasonic sensor M.
[0289] The transmission section U is composed of a single
transmission element W. The transmission element W has the same
structure as that of each of the receiving elements 11 constituting
the receiving section 10, 40, 50, 80, 90, or 100.
[0290] A tip of each of the bonding wires 28 and 29 led from the
transmission element W is connected to each of the electrode pads
33 as in the case of the receiving element 11.
[0291] Moreover, the transmission element W having the same
structure as that of the receiving element 11 transmits an
ultrasonic wave from a transmission surface Wa (not shown)
corresponding to the receiving surface 11a of the receiving element
11 (not shown in FIG. 12; see FIGS. 13 to 17).
[0292] In the example shown in FIG. 12, among nine elements having
the same structure arranged 3 by 3 on the single substrate 12 (not
shown), one element arranged at the corner is made to act as the
transmission element W, whereas the other eight elements are made
to act as the receiving elements 11.
[0293] However, a plurality of arbitrary elements may be made to
act as the transmission elements W among a plurality of elements
having the same structure arranged on the substrate 12.
[0294] FIG. 13 is a cross-sectional side view showing an example in
which Embodiment 2 is applied to the ultrasonic sensor T,
illustrating the receiving section 40 and the transmission section
U of the ultrasonic sensor T.
[0295] FIG. 14 is a cross-sectional side view showing an example in
which Embodiment 3 is applied to the ultrasonic sensor T,
illustrating the receiving section 50 and the transmission section
U of the ultrasonic sensor T.
[0296] FIG. 15 is a cross-sectional side view showing an example in
which Embodiment 6 is applied to the ultrasonic sensor T,
illustrating the receiving section 80 and the transmission section
U of the ultrasonic sensor T.
[0297] FIGS. 16A and B are cross-sectional side views showing an
example in which Embodiment 7 is applied to the ultrasonic sensor
T, illustrating the receiving section 90 and the transmission
section U of the ultrasonic sensor T.
[0298] FIG. 17 is a cross-sectional side view showing an example in
which Embodiment 8 is applied to the ultrasonic sensor T,
illustrating the receiving section 100 and the transmission section
U of the ultrasonic sensor T.
Embodiment 9
[0299] FIG. 18 is a cross-sectional side view showing a receiving
section 200 in an ultrasonic sensor N according to Embodiment
9.
[0300] The receiving section 200 includes a plurality of
piezoelectric receiving elements 201 arranged in an array. The
example shown in FIG. 18 illustrates a cross-sectional side view of
three receiving elements 201.
[0301] The receiving elements 201 are formed on a
single-crystalline silicon substrate (a single-crystalline silicon
chip) 202 having an SOI structure.
[0302] The substrate 202 is provided on the sensor substrate 32.
The substrate 202 is surrounded by a rectangular frame member 203.
An outer circumference of the substrate 202 is attached and fixed
to an inner wall of the frame member 203 by an appropriate method
(for example, thermal welding, ultrasonic welding, bonding with an
adhesive and the like) so as to air-seal a connection part between
the outer circumference of the substrate 202 and the frame member
203.
[0303] A lower end of the frame member 203 is attached and fixed to
the sensor substrate 32 by the above-mentioned appropriate method
so as to air-seal a connection part between the lower end of the
frame member 203 and the sensor substrate 32.
[0304] The frame member 203 and the sensor substrate 32 form a
housing member 204 having a rectangular parallelepiped box shape
with an upper open end.
[0305] Specifically, the substrate 202 is housed within the housing
member 204 having a rectangular parallelepiped box shape with an
upper open end.
[0306] Each of the receiving elements 201 is arranged so that a
receiving surface 201a for receiving an ultrasonic wave is oriented
toward an opening 204a of the housing member 204. Moreover, the
receiving surfaces 201a of the respective receiving elements 201
are arranged so as to be flush with each other.
[0307] The protective film 14 for closing the opening 204a is
attached over the opening 204a of the housing member 204.
Specifically, the protective film 14 is provided in front of the
receiving elements 201.
[0308] An outer circumference of the protective film 14 is attached
and fixed to an inner circumference of the frame member 203 (an
inner circumference of the opening 204a of the housing member 204)
so as to air-seal a connection part between the outer circumference
of the protective film 14 and the frame member 203.
[0309] The gap S, which is provided between the protective film 14
and the substrate 202, is filled with a gas, a liquid, a sol, a gel
or the like.
[0310] The gap R surrounded by the back face side (the bottom face
side) of the substrate 202 and the housing member 204 (the frame
member 203 and the sensor substrate 32) is filled with air.
[0311] FIG. 19 is an enlarged cross-sectional side view showing one
piezoelectric receiving element 201.
[0312] A through hole 202a penetrating through the substrate 202 is
formed in the substrate 202.
[0313] On the back face side of the substrate 202, the insulating
layer 21, the silicon active layer 22, and the insulating layer 23
are formed on the surface of the substrate 202 in this order. The
layers 22 and 23 are formed to close a lower end of the through
hole 202a.
[0314] On the back face side, the lower electrode layer 24, the
thin film layer 25 made of a ferroelectric (for example, PZT or the
like), and the upper electrode layer 26 are formed in this order on
the surface of the insulating layer 23 situated below (behind) the
through hole 202a.
[0315] The sensor substrate 32 is a printed wiring board. Wiring
layers 205 and 206 are formed on a surface of the sensor substrate
32.
[0316] The lower electrode layer 24 and the wiring layer 205 are
connected to each other through a bump 207, whereas the upper
electrode layer 26 and the wiring layer 206 are connected to each
other through a bump 208.
[0317] The bumps 207 and 208 may be formed by an appropriate method
(plating, a stud method or the like) using various conductive
materials (metals such as a solder, gold, copper and nickel, a
conductive adhesive or the like).
[0318] In this manner, a piezoelectric element (the piezoelectric
sensor) E is formed to have a structure in which the thin film
layer 25 made of a ferroelectric is sandwiched between the two thin
electrode layers 24 and 26. The piezoelectric element E fabricated
by employing the MEMS technique constitutes the receiving element
201.
[0319] A surface of the silicon active layer 22 exposed through the
through hole 202a forms the receiving surface 201a of the receiving
element 201.
[0320] When the thin film layer 25 is oscillated by an ultrasonic
wave, an electric signal is generated by a piezoelectric effect.
The thus generated electric signal is output from the electrode
layers 24 and 26 through the bumps 207 and 208 and the wiring
layers 205 and 206, respectively.
[0321] The through hole 202a is provided so that a diaphragm
composed of the layers 22 and 26 is more likely to be
oscillated.
[0322] FIG. 20 is a schematic perspective view showing the
ultrasonic sensor N.
[0323] The ultrasonic sensor N is composed of a hybrid IC including
the receiving section 200, a transmission section 209, and the
sensor substrate 32.
[0324] The receiving section 200 and the transmission section 209
corresponding to chip parts are attached and fixed to the surface
of the sensor substrate 32.
[0325] In the example shown in FIG. 20, the receiving section 200
includes nine receiving elements 201 arranged 3 by 3.
[0326] The transmission section 209 has the same structure as that
of any one of the receiving sections 10 to 100 and 200. The
transmission section 209 includes one piezoelectric transmission
element having the same structure as that of the receiving element
11 or 201. The thin film layer 25 is oscillated by a piezoelectric
effect in accordance with an input signal applied to the thin film
25 made of a ferroelectric from the electrode layers 24 and 26,
thereby generating an ultrasonic wave.
[0327] In the case where the transmission element of the
transmission section 209 is made to have the same structure as that
of the receiving element 201, the receiving surface 201a of the
receiving element 201 serves as a transmission surface for
transmitting an ultrasonic wave.
[0328] Specifically, the transmission element of the transmission
section 209 converts an electric signal into an ultrasonic wave so
as to transmit it.
[0329] Then, the transmission section 209 transmits an ultrasonic
wave in accordance with an input signal from the exterior. A
reflection sound generated by the ultrasonic wave reflected by an
object to be detected is received by each of the receiving elements
201 of the receiving section 200.
[0330] Specifically, each of the receiving elements 201 of the
receiving section 200 converts the received ultrasonic wave into an
electric signal.
[0331] Then, the ultrasonic wave transmitted from the transmission
section 209 and the ultrasonic wave received by each of the
receiving elements 201 of the receiving section 200 are compared
with each other so as to obtain a sound pressure difference, a time
difference, and a phase difference between them. As a result, the
position of an object to be detected, a distance between the
ultrasonic sensor N and the object to be detected, a
two-dimensional shape or a three-dimensional shape of the object to
be detected and the like can be measured based on the thus obtained
differences.
Functions and Effects of Embodiment 9
[0332] According to Embodiment 9, the following functions and
effects can be obtained in addition to the same functions and
effects as [1-1] to [1-4] described above in Embodiment 1.
[9-1]
[0333] In each of the receiving elements 11 shown in FIGS. 1 to 3
in Embodiment 1, the surface of the upper electrode layer 26 serves
as the receiving surface 11a.
[0334] On the other hand, in each of the receiving elements 201 in
Embodiment 9, the surface of the silicon active layer 22 exposed
through the bottom face of the through hole 202a serves as the
receiving surface 202a.
[0335] Specifically, the receiving element 201 according to
Embodiment 201 corresponds to a reversed version of the receiving
element 11 according to Embodiment 1 for use.
[0336] Moreover, in Embodiment 1, the packaged receiving section 10
including the substrate 12 housed within the housing member 13 is
attached and fixed onto the sensor substrate 32. Then, the
electrode layers 24 and 26 of each of the receiving elements 11
constituting the receiving section 10 and each of the electrode
pads 33 are connected to each other through the bonding wires 28
and 29, respectively.
[0337] Specifically, since the receiving section 10 (each of the
receiving elements 11) is surface-mounted on the sensor substrate
32 by using a wire bonding technique in Embodiment 1, the
ultrasonic sensor according to Embodiment 1 has the following
problems [A] to [E].
[0338] [A] There is a possibility that each of the bonding wires 28
and 29 is cut by the oscillation. In the case where the ultrasonic
sensor M is to be mounted on an automobile, in particular, each of
the bonding wires 28 and 29 is more likely to be cut because the
oscillation of an engine or the oscillation propagating from a road
surface is applied to the ultrasonic sensor M.
[0339] [B] The fabrication cost for surface-mounting the receiving
section 10 on the sensor substrate 32 is high.
[0340] If the transmission element of the transmission section 209
is made to have the same structure as that of the receiving element
11, the fabrication cost for surface-mounting the transmission
section 209 on the sensor substrate 32 is high.
[0341] [C] Since the bonding wires 28 and 29 are provided above the
receiving surface 11a of each of the receiving elements 11, there
is a possibility that the bonding wires 28 and 29 become obstacles
to inhibit an ultrasonic wave from getting to the receiving surface
11a, resulting in a lowered receiving sensitivity of each of the
receiving elements 11.
[0342] Since the bonding wires 28 and 29 are provided above the
receiving surface 11a of each of the receiving elements 11, the
bonding wires 28 and 29 are likely to be cut by an ultrasonic wave
received by each of the receiving elements 11.
[0343] Moreover, if the transmission element of the transmission
section 209 is made to have the same structure as that of the
receiving element 11, the bonding wires 28 and 29 become obstacles
to inhibit an ultrasonic wave from being transmitted from the
transmission surface of the transmission element. As a result,
there is a possibility that the transmission output is lowered.
[0344] Moreover, since the bonding wires 28 and 29 are provided
above the transmission surface of the transmission element, the
bonding wires 28 and 29 are likely to be cut by an ultrasonic wave
transmitted from the transmission element.
[0345] [D] Since an inductance of a signal wiring in the receiving
section 10 is increased by a length of each of the bonding wires 28
and 29, a transfer rate of an electric signal generated from the
receiving section 10 is lowered.
[0346] Moreover, if the transmission element of the transmission
section 209 is made to have the same structure as that of the
receiving element 11, an inductance of a signal wiring in the
transmission section 209 is increased by a length of each of the
bonding wires 28 and 29. Therefore, a transfer rate of an input
signal to the transmission section 209 is lowered to lower an
operation speed of the transmission section 209.
[0347] [E] Since the sensor substrate 32 is increased in size by an
area occupied by the electrode pads 33 (a layout area) formed on
the sensor substrate 32, the ultrasonic sensor M is
disadvantageously increased in size.
[0348] On the other hand, in each of the receiving elements 201
according to Embodiment 9, the unpackaged substrate 202
corresponding to a bare chip (die) is directly mounted facedown on
the sensor substrate 32. The electrode layers 24 and 26 of each of
the receiving elements 201 formed on the substrate 202 and the
wiring layers 205 and 206 on the sensor substrate 32 are connected
through the bumps 207 and 208, respectively.
[0349] Specifically, since the receiving elements 201 are
surface-mounted on the sensor substrate 32 by flip-chip connection
in Embodiment 9, the above-described problems [A] to [E] can be
solved to obtain the following effects [F] to [J].
[0350] [F] Since the receiving section 200 (the receiving elements
201) and the sensor substrate 32 are connected and fixed to each
other through the bumps 207 and 208, it can be ensured that the
electrical connection between each of the receiving elements 201
and the substrate 32 is kept. As a result, the reliability of the
ultrasonic sensor N can be enhanced with an extended lifetime.
[0351] Moreover, if the transmission element of the transmission
section 209 is made to have the same structure as that of the
receiving element 201, it can be ensured that the electrical
connection between the transmission element and the sensor
substrate 32 is kept.
[0352] [G] The fabrication cost for surface-mounting the receiving
section 200 on the sensor substrate 32 can be lowered.
[0353] Moreover, if the transmission element of the transmission
section 209 is made to have the same structure as that of the
receiving element 201, the fabrication cost for surface-mounting
the transmission section 209 on the sensor substrate 32 can be
lowered.
[0354] [H] Since the bonding wire is not provided above the
receiving surface 201a of each of the receiving elements 201 and
therefore no obstacle is present in front of the receiving surface
201a, an ultrasonic wave is not inhibited from getting to the
receiving surface 201a. Therefore, the receiving sensitivity of
each of the receiving surface 11 can be increased.
[0355] Moreover, since the bonding wire is no longer provided above
the receiving surface 11a of each of the receiving elements 11, the
bonding wire is never cut by the ultrasonic wave received by each
of the receiving elements 11.
[0356] Moreover, if the transmission element of the transmission
section 209 is made to have the same structure as that of the
receiving element 201, the transmission of an ultrasonic wave from
the transmission surface is not inhibited because the bonding wire
is not provided above the transmission surface of the transmission
element and therefore no obstacle is present in front of the
transmission surface. As a result, the transmission output of the
transmission element can be enhanced.
[0357] Moreover, since the bonding wire is not provided above the
transmission surface of the transmission element, the bonding wire
is never cut by the ultrasonic wave transmitted from the
transmission element.
[0358] [I] Since an inductance of each of the bumps 207 and 208 is
smaller than that of each of the bonding wires 28 and 29, an
inductance of the signal wiring of the receiving section 200 is
reduced to allow a transfer rate of the electric signal generated
from the receiving section 200 to be increased.
[0359] Moreover, if the transmission element of the transmission
section 209 is made to have the same structure as that of the
receiving element 201, the inductance of the signal wiring of the
transmission section 209 becomes smaller. Accordingly, the transfer
rate of an input signal to the transmission section 209 becomes
higher to increase the operation speed of the transmission section
209.
[0360] [J] It is no longer necessary to provide the electrode pads
33 on the sensor substrate 32. As a result, since the sensor
substrate 32 can be reduced in size by the area which was otherwise
occupied by the electrode pads 33, the ultrasonic sensor N can be
reduced in size as well as in weight.
[9-2]
[0361] If the through hole 202a is formed in the substrate 202 so
that its sectional area gradually increases from the bottom of the
through hole 202a closed by the silicon active layer 22 toward the
opening, the through hole 202a can be made to act as the same
acoustic horn as the acoustic horn 91 in Embodiment 7. In this
case, the bottom of the through hole 202a corresponds to the throat
91a of the acoustic horn 91.
[0362] In this manner, the acoustic horn formed by the through hole
202a can be provided for each of the receiving elements 201. As a
result, each of the receiving elements 201 can be provided with the
directivity of a receiving direction of an ultrasonic wave as in
the above-described [7-1] in Embodiment 7.
[0363] Moreover, if the transmission element of the transmission
section 209 is made to have the same structure as that of the
receiving element 201, the transmission element can be provided
with the directivity of a transmission direction of an ultrasonic
wave.
[0364] Moreover, according to Embodiment 9, the through hole 202a
can be made to act as an acoustic horn simply by appropriately
shaping the through hole 202a. Since it is no longer necessary to
provide the acoustic horn 91 as an independent member as in
Embodiment 7, the fabrication cost of the receiving section 200 and
the transmission section 209 can be lowered as compared with the
receiving section 90 and the transmission section 31 in Embodiment
7. At the same time, the receiving section 200 and the transmission
section 209 can be reduced in size as well as in weight.
Embodiment 10
[0365] FIG. 21 is a cross-sectional side view showing a receiving
section 220 in the ultrasonic sensor N according to Embodiment
10.
[0366] The receiving section 220 according to Embodiment 10 differs
from the receiving section 200 according to Embodiment 9 only in
that at least one (three in the illustrated example) vent hole 221
for bringing the gap R and the exterior of the housing member 204
into communication with each other is formed at a position of the
sensor substrate 32 below each of the receiving elements 201.
[0367] The structure of the ultrasonic sensor N according to
Embodiment 10 is obtained by replacing the receiving section 200 in
the ultrasonic sensor N shown in FIG. 20 according to Embodiment 20
with the receiving section 220.
Functions and Effects of Embodiment 10
[0368] According to Embodiment 10, in addition to the
above-described functions and effects of Embodiment 9, the
receiving sensitivity of each of the receiving elements 201 can be
prevented from being lowered because the oscillation of the layers
22 to 26 on the receiving surface 201a of each of the receiving
elements 201 is not inhibited.
[0369] Specifically, in the case where the vent holes 221 are not
provided in the sensor substrate 32, the gap R surrounded by the
substrate 202 and the housing member 204 the frame member 203 and
the sensor substrate 32) forms a sealed space. Air filling the
sealed space acts as a spring so as to apply a damping force due to
air on the back face side of the receiving surface 201a of each of
the receiving elements 201. As a result, there is a possibility
that the free oscillation of the layers 22 to 26 on the receiving
surface 201a is inhibited to lower the receiving sensitivity of
each of the receiving elements 201.
[0370] On the other hand, in Embodiment 10, since air passes
through the vent holes 221, a damping force due to air is not
applied to the back face side of the receiving surface 201a of each
of the receiving elements 201. As a result, each of the layers 22
to 26 on the receiving surface 201a is capable of freely
oscillating.
[0371] The number, the position of arrangement, and the size and
shape of the vent hole 221 can be determined by experimentally
finding their optimal values by a cut-and-try method so as to
obtain satisfactory functions and effects described above.
[0372] Moreover, a filter material (for example, a mesh filter or
the like), which does not suppress the air permeability of the vent
hole 221, may be attached and fixed.
[0373] If the transmission section 209 is made to have the same
structure as that of the receiving section 220 and the vent hole
221 is provided at a position of the sensor substrate 32 below each
of the transmission elements in the transmission section 209, a
damping force due to air is not applied to the back face side of
the transmission surface of the transmission element because air
passes through the vent holes 221. Accordingly, the layers 22 to 26
on the transmission surface can freely oscillate so as not to
suppress the oscillation, thereby increasing the transmission
output of the transmission element.
Embodiment 11
[0374] FIG. 22 is a cross-sectional side view showing a receiving
section 230 and a transmission section 231 in an ultrasonic sensor
L according to Embodiment 11.
[0375] FIG. 23 is a schematic perspective view showing the
ultrasonic sensor L.
[0376] The ultrasonic sensor L according to Embodiment 11 differs
from the ultrasonic sensor N according to Embodiment 9 only in the
following points.
[0377] [a]
[0378] The ultrasonic sensor L is composed of the monolithic IC
including the receiving section 200 and the transmission section
231 formed on the single substrate 202 so as to be further reduced
in size and weight as compared with the ultrasonic sensor N.
[0379] The transmission section 231 is composed of one transmission
element 232. The transmission element 232 has the same structure as
that of each of the receiving elements 201 constituting the
receiving section 200.
[0380] The transmission element 232 having the same structure as
that of the receiving element 201 transmits an ultrasonic wave from
a transmission surface 232a corresponding to the receiving surface
201a of the receiving element 201.
[0381] In the example shown in FIG. 23, among nine elements having
the same structure arranged 3 by 3, one element arranged at the
corner is made to act as the transmission element 232, whereas the
other eight elements are made to act as the receiving elements
201.
[0382] However, among a plurality of elements having the same
structure arranged on the substrate 12, an arbitrary number of
elements can be made to act as the transmission elements 232.
[0383] [b]
[0384] Partition members 233 are provided in the gap R surrounded
by the substrate 202 and the housing member 204 (the frame member
203 and the sensor substrate 32).
[0385] A lower end of each of the partition members 233 is attached
and fixed to an upper surface of the sensor substrate 32 by an
appropriate method (for example, thermal welding, ultrasonic
welding, bonding with an adhesive or the like) so as to air-seal a
connection part between the lower end of each of the partition
members 233 and the sensor substrate 32. An upper end of each of
the partition members 233 is attached and fixed to a lower face of
the insulating layer 23 on the substrate 202 by the above-mentioned
appropriate method so as to air-seal a connection part between the
upper end of each of the partition members 233 and the substrate
202.
[0386] The partition members 233 partition the gap R for each of
the elements 201 and 232 in an air-tight manner.
[0387] [c]
[0388] At least one (three in the illustrated example) vent hole
221 for bringing the gap R and the exterior of the housing member
204 into communication with each other is formed at a position of
the sensor substrate 32 below each of the transmission elements
232.
[0389] The vent hole 221 is not formed at a position of the sensor
substrate 32 below each of the receiving elements 201.
Functions and Effects of Embodiment 11
[0390] According to Embodiment 11, the following functions and
effects can be obtained in addition to the above-described
functions and effects of Embodiment 9.
[0391] [11-1]
[0392] When the gap R surrounded by the substrate 202 and the
housing member 204 (the frame member 203 and the sensor substrate
32) is formed as a sealed space, air filling the sealed space acts
as a spring so as to apply a damping force due to air on the back
face side of each of the faces (the receiving surface and the
transmission surface) 201a and 232a of the respective elements 201
and 232. Since the free oscillation of the layers 22 to 26 on each
of the faces 201a and 232a is inhibited, a resonance value Q of the
diaphragm composed of the layers 22 to 26 is reduced.
[0393] On the other hand, in the case where the vent holes 221 are
provided in the sensor substrate 32, air passes through the vent
holes 221. Therefore, a damping force due to air is not applied on
the back face side of each of the faces 201a and 232a of the
respective elements 201 and 232, the free oscillation of the layers
22 to 26 on each of the faces 201a and 232a is not inhibited.
Accordingly, the resonance value Q of the diaphragm composed of the
layers 22 to 26 becomes large.
[0394] FIGS. 24A and 24B are characteristic views, each showing a
resonance characteristic corresponding to the relation between the
resonance value Q of the diaphragm and a frequency f.
[0395] As shown in FIG. 24A, if a peak value Qa of the resonance
value Q of the diaphragm is large, the resonance value Q
demonstrates a steep change with respect to a change in frequency f
corresponding to the peak value Qa mainly at primary resonance
frequencies fa and fb.
[0396] As shown in FIG. 24B, if a peak value Qb of the resonance
value Q of the diaphragm is small, the resonance value Q
demonstrates a gentle change with respect to a change in frequency
f corresponding to the peak value Qb mainly at the primary
resonance frequencies fa and fb.
[0397] The resonance value Q of the diaphragm and the transmission
output of the transmission element 232 are positively correlated
with each other; as the resonance value Q becomes larger, the
transmission output becomes greater.
[0398] The piezoelectric element or the capacitive element
fabricated by employing the MEMS technique is not suitable as a
transmission element because it has a small transmission output of
an ultrasonic wave.
[0399] Thus, the piezoelectric transmission element 232 fabricated
by employing the MEMS technique is required to increase its
transmission output as much as possible so as to have the resonance
characteristic shown in FIG. 24A.
[0400] Therefore, according to Embodiment 11, since air passes
through the vent holes 221 formed in the sensor substrate 32, a
damping force due to air is not applied to the back face side of
the transmission surface 232a of each of the transmission elements
232. As a result, since the layers 24 to 26 on the transmission
surface 232a can freely oscillate so as not to be inhibited from
oscillating, each of the transmission elements 232 can be provided
with the resonance characteristic shown in FIG. 24A so as to
increase the transmission output.
[0401] [11-2]
[0402] The resonance value Q of the diaphragm and the receiving
sensitivity of the receiving element 201 are positively correlated
with each other; as the resonance value Q becomes larger, the
receiving sensitivity becomes greater.
[0403] Herein, each of the receiving elements 201 has a fluctuation
in primary resonance frequency due to a fabrication process.
[0404] For example, if two receiving elements 201 have the
resonance characteristic shown in FIG. 24A so that one of the
receiving elements 201 has the primary resonance frequency fa
whereas the other receiving element 201 has the primary resonance
frequency fb, the receiving sensitivity at the frequencies fa and
fb becomes extremely high. However, the receiving sensitivity at a
frequency fc between the frequencies fa and fb becomes extremely
low.
[0405] On the other hand, if two receiving elements 201 have the
resonance characteristic shown in FIG. 24B so that one of the
receiving elements 201 has the primary resonance frequency fa
whereas the other receiving element 201 has the primary resonance
frequency fb, the receiving sensitivity at the frequencies fa and
fb is lower than that in FIG. 24A. However, the receiving
sensitivity at the frequency fc becomes higher than that in FIG.
24A.
[0406] Specifically, if the resonance value Q of the receiving
element 201 is increased, the receiving sensitivity demonstrates a
steep characteristic with respect to a change in frequency although
the receiving sensitivity becomes high. Therefore, the receiving
sensitivity at a frequency offset from the primary resonance
frequency is suddenly lowered even if the offset is slight.
[0407] On the contrary, if the resonance value Q of the receiving
element 201 is reduced, the receiving sensitivity demonstrates a
gentle characteristic with respect to a change in frequency
although the receiving sensitivity is lowered. Therefore, the
receiving sensitivity at a frequency offset from the primary
resonance frequency is not greatly lowered.
[0408] Since the piezoelectric element or the capacitive element
fabricated by employing the MEMS technique has a high receiving
sensitivity of an ultrasonic wave, it is suitable as the receiving
element.
[0409] Therefore, the piezoelectric receiving element 201
fabricated by employing the MEMS technique is required to have a
high receiving sensitivity over a broad frequency range as much as
possible rather than to have a high receiving sensitivity at the
primary resonance frequency. Therefore, the piezoelectric receiving
element 201 is required to have the resonance characteristic shown
in FIG. 24B.
[0410] Thus, according to Embodiment 11, since the vent hole 221 is
not formed at a position of the sensor substrate 32 below each of
the receiving elements 201, a damping force due to air is applied
to the back face side of the receiving surface 201a of each of the
receiving elements 201. As a result, the oscillation of the layers
24 to 26 on the receiving surface 201a is inhibited. Accordingly,
each of the receiving elements 201 is provided with the resonance
characteristic shown in FIG. 24B to increase receiving sensitivity
over a broad frequency range as much as possible.
[0411] [11-3]
[0412] If the gap R situated below each of the receiving elements
201 is filled with a material for suppressing the oscillation of
the layers 22 to 26 (for example, a liquid, a sol, a gel or the
like), the resonance value Q of the diaphragm composed of the
layers 22 to 26 can be reduced as compared with the case where the
gap R is filled with air.
[0413] Therefore, if the material for filling the gap R situated
below each of the receiving elements 201 is appropriately selected,
a desired resonance characteristic can be obtained without altering
the structure of each of the receiving elements 201.
[0414] Moreover, if the gap R is filled with a material for
preventing the layers 22 to 26 from being excessively oscillated,
the layers 22 and 26 can be prevented from being excessively
oscillated to be broken.
[0415] As the filler in the gap R situated blow each of the
receiving elements 201, an optimal material can be experimentally
found by a cut-and-try method so as to obtain satisfactory
functions and effects described above in [11-2].
[0416] Even in Embodiments 1, 3 and 5 to 8, a desired resonance
characteristic can be obtained without altering the structure of
each of the receiving elements 11.
Embodiment 12
[0417] FIG. 25 is a cross-sectional side view showing a receiving
section 240 in the ultrasonic sensor N according to Embodiment
12.
[0418] The receiving section 240 according to Embodiment 12 differs
from the receiving section 200 according to Embodiment 9 only in
that separation members 241 are provided.
[0419] A lower end of each of the separation members 241 is
attached and fixed to the substrate 202 between the receiving
elements 201 by an appropriate method (for example, thermal
welding, ultrasonic welding, bonding with an adhesive or the like)
so as to air-seal a connection part of the lower end of each of the
separation members 241 and the substrate 202.
[0420] The upper end of each of the separation members 241
separates the gap S and the protective film 14 for each receiving
element.
[0421] Specifically, in the example shown in FIG. 25, the lower
ends of the separation members 241 are attached and fixed to the
substrate 202 between the receiving elements 201A and 202B, and
202B and 202C, respectively.
[0422] Then, the gaps SA to SC and the protective films 14A to 14C
situated above (in front of) the receiving elements 201A to 201C
are separated by the separation members 241 for the receiving
elements 201A to 201C, respectively.
[0423] The structure of the ultrasonic sensor N according to
Embodiment 12 is obtained by replacing the receiving section 200 of
the ultrasonic sensor N shown in FIG. 20 according to Embodiment 9
with the receiving section 240.
Functions and Effects of Embodiment 12
[0424] According to Embodiment 12, the following functions and
effects can be obtained in addition to the above-described
functions and effects of Embodiment 9.
[12-1]
[0425] The gaps SA to SC and the protective films 14A to 14C
situated above (in front of) the receiving elements 201A to 201C
are separated by the separation members 241 for each of the
receiving elements 201A to 201C, respectively. Therefore, the
oscillation of the single protective film 14A obtained by the
separation propagates only to the receiving element 201A through
the gap SA situated below the protective film 14A but not to the
other receiving elements 201B and 201C.
[0426] Therefore, according to Embodiment 12, an ultrasonic wave
can be received by each of the receiving elements 201A to 201C in a
separate manner. Accordingly, a crosstalk characteristic of each of
the receiving elements 201A to 201C can be prevented from being
degraded.
[0427] Alternatively, a plurality of the adjacent receiving
elements 201 may be grouped into one. The separation member 241 may
be provided for each group so as to separate the group from the
other groups.
[12-2]
[0428] The separation members 241 have to surely block the
oscillation of the protective film 14A and the gap SA vertically
arranged to be grouped into one so that the oscillation does not
propagate to the members of the other adjacent groups (the
protective films 14B and 14C and the gaps SB and SC).
[0429] For this reason, a material having a high oscillation
blocking property is required to be used for the separation members
241. Examples of the material include rubbers.
[12-3]
[0430] FIG. 26 is a cross-sectional side view showing the receiving
section 240 in the ultrasonic sensor N according to a first
variation of Embodiment 12.
[0431] The first variation shown in FIG. 26 differs from Embodiment
12 shown in FIG. 25 only in that the vent holes 221 for bringing
the gap R and the exterior of the housing member 204 into
communication with each other are formed at a position of the
sensor substrate 32 below each of the receiving elements 201.
[0432] Specifically, the first variation of Embodiment 12
corresponds to the combination of Embodiments 12 and 10.
Accordingly, the functions and effects of Embodiment 10 can be
obtained in addition to the functions and effects of Embodiment
12.
[12-4]
[0433] FIG. 27 is a cross-sectional side view showing the receiving
section 240 and the transmission section 231 in the ultrasonic
sensor L according to a second variation of Embodiment 12.
[0434] The second variation shown in FIG. 27 differs from
Embodiment 12 shown in FIG. 25 only in that the same points as
described in [a] to [c] of Embodiment 12.
[0435] Specifically, the second variation of Embodiment 12
corresponds to the combination of Embodiments 12 and 11. Therefore,
the above-described functions and effects of Embodiment 11 can be
obtained in addition to the functions and effects of Embodiment
12.
Embodiment 13
[0436] FIG. 28 is a cross-sectional side view showing a receiving
section 250 in the ultrasonic sensor N according to Embodiment
13.
[0437] The receiving section 250 of Embodiment 13 differs from the
receiving section 200 of Embodiment 9 only in that separation
members 251 are provided.
[0438] A lower end of each of the separation members 251 is
attached and fixed to an upper surface of the sensor substrate 32
by an appropriate method (for example, thermal welding, ultrasonic
welding, bonding with an adhesive and the like) so as to air-seal a
connection part between the lower end of each of the separation
members 251 and the sensor substrate 32.
[0439] The upper end of each of the separation members 251
separates the space S and the protective film 14 for each of the
receiving elements 201.
[0440] Specifically, in the example illustrated in FIG. 28, the
lower ends of the separation members 251 are attached and fixed to
the upper surface of the sensor substrate 32 between the receiving
elements 201A and 201B, and 201B and 201C, respectively, whereby
the separation members 251 separate the receiving elements 201A to
201C from each other.
[0441] The gaps SA to SC and the protective films 14A to 14C
respectively situated above (in front of) the receiving elements
201A to 201C are separated by the separation members 251 for each
of the receiving elements 201A to 201C, respectively.
[0442] Specifically, the receiving section 200 according to
Embodiment 9 is composed of a monolithic IC including the receiving
elements 201 of the receiving section 230 formed on the single
substrate 202.
[0443] On the other hand, the receiving section 250 of Embodiment
13 is composed of a hybrid IC including the receiving elements 201
corresponding to chip parts attached and fixed on the sensor
substrate 32.
[0444] The structure of the ultrasonic sensor N according to
Embodiment 13 is obtained by replacing the receiving section 200 of
the ultrasonic sensor N shown in FIG. 20 according to Embodiment 9
with the receiving section 250.
Functions and Effects of Embodiment 13
[0445] According to Embodiment 13, the following functions and
effects can be obtained in addition to the functions and effects of
Embodiment 9.
[13-1]
[0446] The receiving elements 201A to 201C, and the gaps SA to SC
and the protective films 14A to 14C situated above (in front of)
the receiving elements 201A to 201C are separated by the separation
members 251 for each of the receiving elements 201. Therefore, the
oscillation of one protective film 14A obtained by the separation
propagates only to the receiving element 201A through the gap SA
situated below the protective film 14A but not to the other
receiving elements 201B and 201C at all.
[0447] Thus, according to Embodiment 13, an ultrasonic wave can be
received by each of the receiving elements 201A to 201C in a
completely separate manner, so that a crosstalk characteristic of
each of the receiving elements 201A to 201C can be prevented from
being degraded.
[0448] A plurality of adjacent receiving elements 201 may be
grouped into one. The separation member 251 may be provided for
each of the groups so as to separate the group from the other
groups.
[13-2]
[0449] The separation members 251 have to surely block the
oscillation of the protective film 14A, the gap SA and the
receiving element 201A, which are vertically arranged so as to be
grouped into one, so that the oscillation does not propagate to the
members of the other adjacent groups (the protective films 14B and
14C, the gaps SB and SC, and the receiving elements 201B and
201C).
[0450] For this reason, a material having a high oscillation
blocking property is required to be used for the separation member
251. Examples of the material include rubbers.
[13-3]
[0451] FIG. 29 is a cross-sectional side view showing the receiving
section 250 in the ultrasonic sensor N according to a first
variation of Embodiment 13.
[0452] The first variation shown in FIG. 29 differs from Embodiment
13 shown in FIG. 28 only in that the vent holes 221 for bringing
the gap R and the exterior of the housing member 204 into
communication with each other are formed at a position of the
sensor substrate 32 below each of the receiving elements 201.
[0453] Specifically, the first variation of Embodiment 13
corresponds to the combination of Embodiments 13 and 10. Therefore,
in addition to the functions and effects of Embodiment 13, the
functions and effects of Embodiment 10 can be obtained.
[13-4]
[0454] FIG. 30 is a cross-sectional side view showing the receiving
section 250 and the transmission section 231 in the ultrasonic
sensor L according to a second variation of Embodiment 13.
[0455] The second variation shown in FIG. 30 differs from
Embodiment 13 shown in FIG. 28 only in that one of the receiving
elements 201 (the receiving element 201A) constituting the
receiving section 250 is made to act as the transmission element
232 constituting the transmission section 231 as in the ultrasonic
sensor L and the same points as the above-described [b] and [c] in
Embodiment 11. The separation members 251 function as the partition
members 233 of Embodiment 11.
[0456] Specifically, the second variation of Embodiment 13
corresponds to the combination of Embodiments 13 and 11. Therefore,
in addition to the functions and effects of Embodiment 13, the
functions and effects of Embodiment 11 can be obtained.
Embodiment 14
[0457] FIG. 31 is a cross-sectional side view showing a receiving
section 260 in the ultrasonic sensor N in Embodiment 14.
[0458] The receiving section 260 of Embodiment 14 differs from the
receiving section 200 of Embodiment 9 only in that a column-like
transfer member 261 for connecting the receiving surface 201a of
each of the receiving elements 201 and the protective film 14 with
each other independently for each of the receiving elements 201 is
provided in the gap S.
[0459] The structure of the ultrasonic sensor N according to
Embodiment 14 is obtained by replacing the receiving section 200 of
the ultrasonic sensor N shown in FIG. 20 according to Embodiment 9
with the receiving section 260.
Functions and Effects of Embodiment 14
[0460] According to Embodiment 14, the following functions and
effects can be obtained in addition to the functions and effects
described above in [9-1] of Embodiment 9.
[14-1]
[0461] When the protective film 14 is oscillated by an ultrasonic
wave, the oscillation of the protective film 14 propagates to each
of the receiving elements 201 through each of the transfer members
261.
[0462] Herein, since the transfer member 261 is provided for each
of the receiving elements 201, the oscillation of arbitrary one of
the transfer members 261 does not propagate to the other transfer
members 261. Therefore, an ultrasonic wave can be received by each
of the receiving elements 201 in a separate manner, thereby
preventing a crosstalk characteristic of each of the receiving
elements 201 from being degraded.
[0463] The propagation of oscillation of the protective film 14 to
each of the transfer members 261 can be ensured by bringing an
acoustic impedance of each of the transfer members 261 close to
that of the protective film 14. As a result, the receiving
sensitivity of each of the receiving elements 201 can be
enhanced.
[0464] Moreover, the propagation of oscillation of each of the
transfer members 261 to the silicon active layer 22 can be ensured
by bringing an acoustic impedance of each of the transfer members
261 close to that of the silicon active layer 22 of each of the
receiving elements 201. As a result, the receiving sensitivity of
each of the receiving elements 201 can be enhanced.
[0465] Therefore, it is desirable to form the transfer members 261
of the same material as that of the protective film 14 or the
silicon active layer 22.
[0466] If the transmission section 209 is made to have the same
structure as that of the receiving section 260 and the transfer
member 261 for bringing the transmission surface of the
transmission element and the protective film 14 into communication
with each other is provided, the propagation of oscillation of the
transfer member 261 to the protective film 14 can be ensured by
bringing the acoustic impedance of the transfer member 261 close to
that of the protective film 14. As a result, the transmission
output of the transmission element can be enhanced.
[0467] Moreover, the propagation of oscillation of the silicon
active layer 22 of the transmission element to the transfer member
261 can be ensured by bringing the acoustic impedance of the
transfer member 261 close to that of the silicon active film 22. As
a result, the transmission output of the transmission element can
be enhanced.
[0468] More specifically, according to Embodiment 14, the same
functions and effects as those in [6-1] of Embodiment 6 described
above can be obtained.
[14-2]
[0469] In order to prevent the crosstalk characteristic of each of
the receiving elements 201 from being degraded, it is necessary to
prevent the oscillation of arbitrary one of the transfer members
261 from propagating to the other transfer members 261 through the
filler in the gap S.
[0470] Therefore, in Embodiment 14, it is the most desirable that
the gap S be in a vacuum state.
[0471] If the gap S is filled with a filler in Embodiment 14, a gas
with a small acoustic impedance or a material having a high
oscillation absorbance (for example, a highly viscous gel or the
like) is used as the filler.
[0472] Specifically, according to Embodiment 14, the same functions
and effects as those in [6-2] in Embodiment 6 above can be
obtained.
[14-3]
[0473] FIG. 32 is a cross-sectional side view showing a receiving
section 260 in the ultrasonic sensor N according to a first
variation of Embodiment 14.
[0474] The first variation shown in FIG. 32 differs from Embodiment
14 shown in FIG. 31 only in that the vent holes 221 for bringing
the gap R and the exterior of the housing member 204 into
communication with each other are formed at a position of the
sensor substrate 32 below each of the receiving elements 201.
[0475] Specifically, the first variation of Embodiment 14
corresponds to the combination of Embodiments 14 and 10. Therefore,
the functions and effects of Embodiment 10 described above can be
obtained in addition to the above-described functions and effects
of Embodiment 14.
[14-4]
[0476] FIG. 33 is a cross-sectional side view showing the receiving
section 260 and the transmission section 231 in the ultrasonic
sensor N according to a second variation of Embodiment 14.
[0477] The second variation shown in FIG. 33 differs from
Embodiment 14 shown in FIG. 31 only in the same points as [a] to
[c] of Embodiment 11 described above.
[0478] Specifically, the second variation of Embodiment 14
corresponds to the combination of Embodiments 14 and 11. Therefore,
the functions and effects of Embodiment 11 described above can be
obtained in addition to the above-described functions and effects
of Embodiment 14.
Exemplary Variations of Embodiments 9 to 14
[0479] Each of the receiving sections 200 to 260 according to
Embodiments 9 to 14 is constituted by the plurality of
piezoelectric receiving elements 201.
[0480] However, each of the piezoelectric receiving elements 201
may be replaced by a capacitive receiving element 271 so that each
of the receiving sections 200 to 260 is constituted by the
plurality of capacitive receiving elements 271.
[0481] FIG. 34 is an enlarged cross-sectional side view showing one
capacitive receiving element 271.
[0482] The through hole 202a penetrating through the substrate 202
is formed in the substrate 202.
[0483] On the back face side of the substrate 202, an insulating
layer 272 is formed on the surface of the substrate 202 so as to
close the lower end of the through hole 202a.
[0484] On the back face side of the substrate 202, a fixed
electrode layer 273 is formed on a surface of the insulating layer
272 situated below (behind) the through hole 202a. On a surface of
the fixed electrode layer 273, a movable electrode layer 274 is
formed on a surface of the fixed electrode layer 273 through a
clearance P. Spacers 275 are provided between the electrode layers
273 and 274 in their circumferential area. The electrode layers 273
and 274 are connected and fixed to each other through the spacers
275.
[0485] The wiring layers 205 and 206 are formed on the surface of
the sensor substrate 32.
[0486] The fixed electrode layer 273 and the wiring layer 205 are
connected with each other through the bump 207, whereas the movable
electrode layer 204 and the wiring layer 206 are connected with
each other through the bump 208.
[0487] In this manner, a capacitive element F having a structure in
which the electrodes 273 and 274 are opposed to each other through
the clearance P is formed. The receiving element 271 includes the
capacitive element F fabricated by employing the MEMS
technique.
[0488] The surface of the insulating layer 272 exposed through the
bottom of the through hole 202a forms a receiving surface 271a of
the receiving element 271.
[0489] When the movable electrode layer 274 is oscillated by an
ultrasonic wave, a distance between the electrode layers 273 and
274 changes so as to change a capacitance. Then, a converting
circuit (not shown) connected to the wiring layers 205 and 206 is
used to convert a change in capacitance between the electrode
layers 273 and 274 into an electric signal.
[0490] As described above, even if a plurality of the capacitive
receiving elements 271 constitute each of the receiving sections
200 to 260, the movable electrode layer 274 is prevented from being
damaged so as to be unlikely to break each of the receiving
sections 200 to 260 even if the thin movable electrode layer 274
has a low mechanical strength as in the case where each of the
receiving sections 200 to 260 includes the piezoelectric receiving
elements 201. As a result, the robust receiving sections 200 to 260
can be obtained.
[0491] [2]
[0492] Each of the transmission sections 209 and 231 according to
Embodiments 9 to 14 includes the piezoelectric transmission
elements having the same structure as that of the piezoelectric
receiving element 201.
[0493] However, each of the transmission sections 209 and 231 may
be composed of a capacitive transmission element having the same
structure as that of the capacitive receiving element 271 shown in
FIG. 34. In such a case, electrostatic attraction is generated
between the electrode layers 273 and 274 in accordance with an
input signal applied to each of the electrode layers 273 and 274.
The electrostatic attraction causes the oscillation of the movable
electrode layer 274 to generate an ultrasonic wave.
[0494] In this case, the receiving surface 271a of the receiving
element 271 acts as a transmission surface of the transmission
element for transmitting an ultrasonic wave.
[0495] [3]
[0496] In Embodiment 14, the protective film 14 may be omitted
while the transfer member 261 may be replaced by the same
protective member as the protective member 41 in Embodiment 2.
[0497] In this manner, the same functions and effects as those of
Embodiment 2 can be obtained.
[0498] [4]
[0499] The ultrasonic sensor N according to Embodiments 9, 10, 12
and 14 and the first variations of Embodiments 12 and 14 is
composed of a hybrid IC in which the receiving section 200, 220,
240 or 260 and the transmission section 209 corresponding to chip
parts are attached and fixed onto the sensor substrate 32 made of
an insulating plate material.
[0500] However, the ultrasonic sensor N according to Embodiments 9,
10, 12 and 14 and the first variations of Embodiments 12 and 14 may
be composed of a monolithic IC in which the receiving section 200,
220, 240 or 260 and the transmission section 231 are formed on the
single substrate 202 as in the case of the ultrasonic sensor L
shown in FIG. 23.
[0501] As in the case of the ultrasonic sensor L according to the
second variation of Embodiment 13, at least arbitrary one of the
receiving elements 201 constituting the receiving section 250 may
be made to act as the transmission element 232 constituting the
transmission section 231 in the ultrasonic sensor N according to
Embodiment 13 and the first variation of Embodiment 13.
[0502] FIG. 35 is a cross-sectional side view showing an example in
which Embodiment 9 is applied to the ultrasonic sensor L,
illustrating the receiving section 200 and the transmission section
231 of the ultrasonic sensor L.
[0503] This example differs from Embodiment 9 only in the
above-described point [a] in Embodiment 11.
[0504] FIG. 36 is a cross-sectional side view showing an example in
which Embodiment 12 is applied to the ultrasonic sensor L,
illustrating the receiving section 240 and the transmission section
231 of the ultrasonic sensor L.
[0505] This example differs from Embodiment 12 only in the
above-described point [a] in Embodiment 11.
[0506] FIG. 37 is a cross-sectional side view showing an example in
which Embodiment 13 is applied to the ultrasonic sensor L,
illustrating the receiving section 250 and the transmission section
231 of the ultrasonic sensor L.
[0507] This example differs from Embodiment 13 only in that one
(the receiving element 201A) of the receiving elements 201
constituting the receiving section 250 is made to act as the
transmission element 232 constituting the transmission section
231.
[0508] FIG. 38 is a cross-sectional side view showing an example in
which Embodiment 14 is applied to the ultrasonic sensor L,
illustrating the receiving section 260 and the transmission section
231 of the ultrasonic sensor L.
[0509] This example differs from Embodiment 14 only in the
above-described point [a] in Embodiment 11.
The Other Embodiments
[0510] The present invention is not limited to the above-described
embodiments, but can also be embodied as follows. In such a case,
the functions and effects equivalent to or higher than those of
each of the embodiments described above can be obtained.
[0511] [1]
[0512] For each of the transmission sections 31, 209, 231, an
existing small ultrasonic sensor may be used.
[0513] Although a piezoelectric element or a capacitive element
fabricated by employing the MEMS technique is suitable for a
receiving element for its high receiving sensitivity of an
ultrasonic wave, it is not suitable for a transmission element for
its small transmission output of an ultrasonic wave.
[0514] Therefore, optimal one of the transmission sections 31 and
209 and 231 may be selected for use in accordance with the field of
use of the ultrasonic sensor M.
[0515] [2]
[0516] The above-described embodiments may be carried out in
appropriate combination. In such a case, the effects of each of the
above embodiments can be further enhanced by the synergistic effect
of the combination.
* * * * *