U.S. patent application number 14/050630 was filed with the patent office on 2014-02-06 for thermal detector, thermal detection device, electronic instrument, and thermal detector manufacturing method.
This patent application is currently assigned to SEIKO EPSON CORPORATION. The applicant listed for this patent is SEIKO EPSON CORPORATION. Invention is credited to Yasushi TSUCHIYA.
Application Number | 20140038336 14/050630 |
Document ID | / |
Family ID | 46315491 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140038336 |
Kind Code |
A1 |
TSUCHIYA; Yasushi |
February 6, 2014 |
THERMAL DETECTOR, THERMAL DETECTION DEVICE, ELECTRONIC INSTRUMENT,
AND THERMAL DETECTOR MANUFACTURING METHOD
Abstract
A thermal detector manufacturing method includes: forming a
sacrificial layer on a structure including an insulating layer;
forming a support member on the sacrificial layer; forming on the
support member a heat-detecting element; forming a first
light-absorbing layer so as to cover the heat-detecting element,
and planarizing the first light-absorbing layer; forming a contact
hole in a portion of the first light-absorbing layer, subsequently
forming a thermal transfer member having a connecting portion that
connects to the heat-detecting element and a thermal collecting
portion having a surface area greater than that of the connecting
portion as seen in plan view; forming a second light-absorbing
layer on the first light-absorbing layer; and removing the
sacrificial layer to form a cavity between the support member and
the structure including the insulating layer formed on the surface
of the substrate.
Inventors: |
TSUCHIYA; Yasushi;
(Fujimi-machi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
46315491 |
Appl. No.: |
14/050630 |
Filed: |
October 10, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13329485 |
Dec 19, 2011 |
|
|
|
14050630 |
|
|
|
|
Current U.S.
Class: |
438/54 |
Current CPC
Class: |
G01J 5/024 20130101;
H01L 35/34 20130101; G01J 5/025 20130101; Y10T 29/4981 20150115;
G01J 5/0853 20130101; H01L 37/02 20130101; G08B 13/19697 20130101;
G01J 5/34 20130101; G01J 5/0225 20130101 |
Class at
Publication: |
438/54 |
International
Class: |
G01J 5/34 20060101
G01J005/34; G01J 5/02 20060101 G01J005/02; H01L 35/34 20060101
H01L035/34 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2010 |
JP |
2010-286334 |
Dec 27, 2010 |
JP |
2010-289491 |
Dec 27, 2010 |
JP |
2010-289492 |
Jan 24, 2011 |
JP |
2011-012060 |
Feb 23, 2011 |
JP |
2011-036886 |
Claims
1. A thermal detector manufacturing method comprising: forming a
structure including an insulating layer on a surface of a
substrate; forming a sacrificial layer on the structure including
the insulating layer; forming a support member on the sacrificial
layer; forming on the support member a heat-detecting element
having a structure in which a pyroelectric material layer is
disposed between a lower electrode and an upper electrode, the
lower electrode having an extending portion extending around the
pyroelectric material layer as seen in plan view, and the extending
portion having light-reflecting properties by which arriving light
is reflected; forming a first light-absorbing layer so as to cover
the heat-detecting element, and planarizing the first
light-absorbing layer; forming a contact hole in a portion of the
first light-absorbing layer, subsequently forming a material layer
which is thermally conductive and optically transmissive at least
with respect to light of a prescribed wavelength, and patterning
the material layer to form a thermal transfer member having a
connecting portion that connects to the heat-detecting element and
a thermal collecting portion having a surface area greater than
that of the connecting portion as seen in plan view; forming a
second light-absorbing layer on the first light-absorbing layer;
patterning the first light-absorbing layer and the second
light-absorbing layer; patterning the support member; and removing
the sacrificial layer to form a cavity between the support member
and the structure including the insulating layer formed on the
surface of the substrate.
2. The thermal detector manufacturing method according to claim 1,
wherein the forming of the first light absorbing layer includes
forming the first light-absorbing layer on the support member
around the heat-detecting element.
3. The thermal detector manufacturing method according to claim 2,
wherein the forming of the first light absorbing layer includes
forming the first light-absorbing layer so as to be contacting the
thermal transfer member and disposed between the thermal transfer
member and the extending portion of the lower electrode of the
heat-detecting element, and the forming of the second
light-absorbing layer includes forming the second light-absorbing
layer so as to be contacting the thermal transfer member and
disposed on the thermal transfer member.
4. The thermal detector manufacturing method according to claim 3,
further comprising forming a first optical resonator for a first
wavelength between a surface of the extending portion of the lower
electrode and an upper surface of the second light-absorbing layer,
and forming a second optical resonator for a second wavelength that
is different from the first wavelength between a lower surface of
the second light-absorbing layer and the upper surface of the
second light-absorbing layer.
5. The thermal detector manufacturing method according to claim 1,
wherein the thermal transfer member also serves as wiring that
electrically connects the heat-detecting element to another
element.
6. The thermal detector manufacturing method according to claim 1,
wherein the thermal detector is configured and arranged to detect
infrared light.
7. The thermal detector manufacturing method according to claim 1,
wherein the thermal detector is configured and arranged to detect
terahertz light.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 13/329,485 filed on Dec. 19, 2011, now
pending. This application claims priority to Japanese Patent
Application No. 2010-286334 filed on Dec. 22, 2010, Japanese Patent
Application No. 2010-289491 filed on Dec. 27, 2010, Japanese Patent
Application No. 2010-289492 filed on Dec. 27, 2010, Japanese Patent
Application No. 2011-012060 filed on Jan. 24, 2011 and Japanese
Patent Application No. 2011-036886 filed on Feb. 23, 2011. The
entire disclosures of U.S. application Ser. No. 13/329,485 and
Japanese Patent Application Nos. 2010-286334, 2010-289491,
2010-289492, 2011-012060 and 2011-036886 are hereby incorporated
herein by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to a thermal detector, a
thermal detection device, an electronic instrument, and a thermal
detector manufacturing method.
[0004] 2. Related Art
[0005] Thermal detection devices are known as light sensors.
Thermo-optical detectors absorb light that has been emitted from an
object in a light-absorbing layer, convert the light to heat, and
measure the change in temperature with a heat-detecting element.
Thermo-optical detectors include thermopiles that directly detect
the increase in temperature accompanying light absorption,
pyroelectric-type elements that detect a change in electrical
polarity, and bolometers that detect the increase in temperature as
a change in resistance. Thermo-optical detectors have a
characteristically wide wavelength range over which measurements
can be made. In recent years, semiconductor fabrication
technologies (e.g., MEMS technologies) have been used, and the
production of smaller-scale thermal detectors has been
attempted.
[0006] In order to increase detection sensitivity and improve
response in thermal detectors, it is critical to efficiently
transfer the heat that is generated in the light-absorbing layer to
the heat-detecting element.
[0007] The structure of a heat-detecting element for improving
thermal transfer efficiency is described, for example, in Japanese
Patent No. 3339276. The infrared detecting element described in
Japanese Patent No. 3339276 (herein referred to as a
thermopile-type infrared detecting element) has a highly thermally
conducting layer that is provided between an infrared light sensing
part and an infrared light absorbing layer. Specifically, a
membrane is formed over a cavity, and the membrane is supported on
the surrounding substrate by protruding beams that are provided at
the four corners. The center membrane portion has a highly
thermally conducting layer and an infrared light absorbing layer,
and the edge portions have thermopile elements. In addition, the
highly thermally conducting layer is made from a material having
excellent infrared light reflectance, such as aluminum or gold.
SUMMARY
[0008] In addition, with the infrared light detecting element
described in Japanese Patent No. 3339276, a high thermal transfer
member is provided under the light-absorbing layer, but the
heat-detecting element is not provided below the light-absorbing
layer and the high thermal conduction member. The infrared light
absorbing layer is at a position that is separated from the
infrared sensing part heat-detecting element, and so the heat that
is generated in the infrared light absorbing layer cannot be
supplied, in some cases, directly to the heat-detecting element
infrared light sensing part.
[0009] With the infrared light solid-state image capture element
described in Japanese Patent Application Republication No.
99/31471, an insulating layer that constitutes an infrared
light-absorbing part is in a position that is separated from the
temperature detector, and so the heat that is generated in the
insulating layer of the infrared light absorbing part, in some
cases, cannot be supplied directly to the temperature detector.
[0010] In accordance with at least one aspect of the present
invention, it is possible to increase the detection sensitivity of
a thermal detector.
[0011] A thermal detector according to one aspect of the present
invention includes a substrate, a support member, a heat-detecting
element, a light-absorbing layer and a thermal transfer member. The
support member is supported on the substrate so that a cavity is
formed between the substrate and the support member. The
heat-detecting element is formed on the support member and having a
structure in which a pyroelectric material layer is disposed
between a lower electrode and an upper electrode. The
light-absorbing layer is formed on the heat-detecting element. The
thermal transfer member includes a connecting portion connected to
the heat-detecting element and a thermal collecting portion
disposed inside the light-absorbing layer and having a surface area
larger than a surface area of the connecting portion as seen in
plan view, the thermal collecting portion being optically
transmissive at least with respect to light of a prescribed
wavelength. The lower electrode has an extending portion extending
around the pyroelectric material layer as seen in plan view. The
extending portion has light-reflecting properties by which at least
a part of the light transmitted through the thermal collecting
portion of the thermal transfer member is reflected.
[0012] In the thermal detector of the aspect described above, for
example, a part of the light that is incident on the thermal
detector (for example, infrared light) is first absorbed by a
second light-absorbing layer, and the remainder thereof arrives at
the thermal transfer member without being absorbed. The thermal
transfer member, being optically transmissive to light of at least
part of a wavelength region, can be translucent in, for example, an
infrared region (for example, a far infrared region). In the
thermal transfer member, for example, a part of the light that has
arrived is reflected, and the remainder thereof is transmitted
through the thermal transfer member. A part of the light that is
transmitted through the thermal transfer member is absorbed by a
first light-absorbing layer, and the remaining light thereof
arrives at the heat-detecting element.
[0013] The heat-detecting element is formed on the support member.
Herein, the expression "on . . . " may refer to "directly above,"
or may alternatively refer to the upper part (in cases in which
another layer is interposed). A similarly broad interpretation is
possible in other places as well.
[0014] The lower electrode of the heat-detecting element comprises
the extending portion that extends on the support member; this
extending portion has light-reflecting properties. Namely, the
lower electrode comprises a material with excellent conductivity
(for example, a metallic material); the light reflectance of
metallic materials and the like is generally high. Accordingly,
much of the light that is incident on the surface of the extending
portion of the lower electrode, which is a constituent element of
the heat-detecting element, is reflected, this reflected light
being absorbed in either the first light-absorbing layer or the
second light-absorbing layer. The reflected light can accordingly
be used without waste, and can be converted to heat. A part of the
light that arrives at the surface of the support member may also
possibly be reflected and absorbed in either the first
light-absorbing layer or the second light-absorbing layer. In this
regard as well, the incident light can be used efficiently.
[0015] The lower electrode (which comprises a metallic material or
the like), having high thermal conductivity as well, therefore also
exerts the effect of transferring to the pyroelectric material
layer heat that, for example, has been generated at places distant
from the pyroelectric material layer in a light-absorbing layer.
That is, the lower electrode, for example, extends broadly on the
support member, and is therefore capable of efficiently
transferring heat generated in a broad range in the light-absorbing
layers to the pyroelectric material layer. In this regard, it can
be said that the lower electrode also serves as a thermal transfer
member (that is, as a thermal transfer member which can be said to
be, for example, a second thermal transfer member, distinct from
the thermal transfer member formed on the upper part of the
heat-detecting element, which can then be said to be the first
thermal transfer member).
[0016] The thermal transfer member comprises a material that is
optically transmissive (for example, semi-transmissive), and
comprises a connecting portion and a thermal collecting portion
that has a greater surface area than that of the connecting portion
in plan view, the thermal collecting portion being formed on the
heat-detecting element. The thermal collecting portion of the
thermal transfer member is tasked with collecting heat that, for
example, has been generated in a region having a broad range, and
transferring the same to the heat-detecting element. Any metallic
compound that, for example, has favourable thermal conductivity and
is optically translucent (for example, AlN or AlO.sub.x) can be
used for the thermal transfer member.
[0017] The following is an example of how, in a case in which the
incident light exhibits such behaviour as described above, heat is
generated in the first light-absorbing layer and the second
light-absorbing layer, and of how the generated heat is transferred
to the heat-detecting element. Namely, a part of the light that is
incident on the thermal detector is first absorbed in the second
light-absorbing layer, heat then being generated in the second
light-absorbing layer. Light that is reflected by the thermal
transfer member is also absorbed in the second light-absorbing
layer, heat thereby being generated in the second light-absorbing
layer.
[0018] A part of the light that is transmitted through (passes
through) the thermal transfer member is also absorbed in the first
light-absorbing layer, thus generating heat. Much of (for example,
the majority of) the light that arrives at the extending portion of
the lower electrode is also reflected on the surface thereof and is
absorbed in at least one of either the first light-absorbing layer
or the second light-absorbing layer, heat being thereby generated
in the first light-absorbing layer or second light absorbing layer.
The light that is reflected by the surface of the support member is
also absorbed in at least one of either the first light-absorbing
layer or the second light-absorbing layer, heat being thereby
generated in the first light-absorbing layer or second
light-absorbing layer.
[0019] The heat that has been generated by the second
light-absorbing layer is then transferred efficiently through the
thermal transfer member to the heat-detecting element, and the heat
that has been generated by the first light-absorbing layer is
efficiently transferred, either directly or via the thermal
transfer member, to the heat-detecting element. Specifically, the
thermal collecting portion of the thermal transfer member is formed
so that it covers a large region of the heat-detecting element, and
thus most of the heat that has been generated by the first
light-absorbing layer and the second light-absorbing layer can be
transferred efficiently to the heat-detecting element, regardless
of the site at which it was generated. For example, even heat that
has been generated at locations that are distant from the
heat-detecting element can be efficiently transferred to the
heat-detecting element via the thermal transfer member having high
thermal conductivity.
[0020] Because the collecting portion of the thermal transfer
member and the heat-detecting element are connected by the
connecting portion of the thermal transfer member, the heat that is
transferred via the thermal collecting portion or the thermal
transfer member can be directly transferred to the heat-detecting
element via the connecting portion. Moreover, because the
heat-detecting element is positioned below the thermal transfer
member (provided in an overlapping position as seen in plan view),
for example, it is possible to connect the middle part of the
thermal transfer member and the heat-detecting element by the
shortest possible length, as seen in plan view. Thus, the loss
occurring with heat transfer can be decreased, and an increase in
footprint can be minimized.
[0021] In addition, in this aspect, absorption efficiency is
increased because heat is generated by a two-layer light-absorbing
film. Moreover, the heat can be directly transferred to the
heat-detecting element via the first light-absorbing layer. Thus,
in comparison to the infrared light solid-state image capture
element described in Japanese Patent Application Republication No.
99/31471 and the infrared light detection element described in
Japanese Patent No. 3339276, the detection sensitivity of the
thermal detector can be increased. Moreover, in this aspect, the
heat-detecting element is connected to the thermal transfer member,
and the response rate is thus high, as with the infrared
light-detecting element described in Japanese Patent No. 3339276.
In this aspect, because the thermal transfer member is directly
connected to the heat detecting element, a higher response rate can
be obtained in comparison to the infrared light solid state image
capture element described in Japanese Patent Application
Republication No. 99/31471.
[0022] In another aspect of the thermal detector of the present
invention, the light-absorbing layer is preferably disposed on the
support member around the heat-detecting element.
[0023] According to the aspect described above, the light-absorbing
layers are formed around the heat-detecting element in plan view.
Heat that has been generated in a broad range on the
light-absorbing layers is thereby effectively transferred to the
heat-detecting element, either directly, or indirectly through the
thermal transfer member. The thermal detector can accordingly
detect light at an even higher degree of sensitivity. The thermal
detector also has a further improved response speed.
[0024] In another aspect of the thermal detector of the present
invention, the light-absorbing layer preferably has a first
light-absorbing layer contacting the thermal transfer member and
disposed between the thermal transfer member and the extending
portion of the lower electrode of the heat-detecting element, and a
second light-absorbing layer contacting the thermal transfer member
and disposed on the thermal transfer member.
[0025] The aspect described above, being provided with the first
light-absorbing layer and the second light-absorbing layer as the
light-absorbing layers, utilizes a configuration in which the
thermal collecting portion of the thermal transfer member is
sandwiched by the two light-absorbing layers. Heat that is
generated in a broad range on the first light-absorbing layer and
the second light-absorbing layer is efficiently transferred to the
heat-detecting element, either directly, or indirectly through the
thermal transfer member. Moreover, the light of the incident light
that is reflected by the thermal transfer member can be absorbed by
the second light-absorbing layer, which is the upper layer, and the
light that is transmitted through the thermal transfer member can
be absorbed by the first light-absorbing layer, which is the lower
layer.
[0026] According to the thermal detector of this aspect, the heat
that has been generated in a broad range in the (plurality of) two
light-absorbing layers can be efficiently transferred to the
heat-detecting element, and, accordingly, a small thermal detector
can detect light with significantly improved sensitivity. Further,
because the time required to transfer heat is curtailed, the
thermal detector can have a faster response speed.
[0027] In another aspect of the thermal detector of the present
invention, a first optical resonator for a first wavelength is
preferably formed between a surface of the extending portion of the
lower electrode and an upper surface of the second light-absorbing
layer, and a second optical resonator for a second wavelength that
is different from the first wavelength is preferably formed between
a lower surface of the second light-absorbing layer and the upper
surface of the second light-absorbing layer.
[0028] This aspect is configured such that the film thickness of
each light-absorbing layer is adjusted to provide two optical
resonators having different resonance wavelengths. The first
optical resonator for the first wavelength is formed between the
upper surface of the second light-absorbing layer and the surface
of the extending portion of the lower electrode, which is formed on
the support member and is a constituent element of the thermal
detector. The light that is reflected by the surface of the
extending portion of the lower electrode is absorbed in at least
one of either the first light-absorbing layer or the second
light-absorbing layer, but the first optical resonator is
constituted such that, at this time, each light-absorbing layer has
a high effective absorptivity. The lower electrode comprises a
material that has excellent conductivity (for example, a metallic
material); the light reflectance of metallic materials and the like
is generally high. Accordingly, much of the light that is incident
on the surface of the extending member can be reflected upwards. It
is accordingly easy to create optical resonances.
[0029] Herein, the first optical resonator can be, for example, a
so-called .lamda./4 optical resonator. That is, the film thickness
of the first light-absorbing layer and the second light-absorbing
layer may be adjusted such that the distance between the surface of
an extending portion RX of a lower electrode (first electrode) 234
of a pyroelectric capacitor 230 and the upper surface of the second
light-absorbing layer satisfies the relationship n(.lamda.1/4) (n
is an integer equal to or greater than 1), where .lamda.1 is the
first wavelength. The film thickness of the lower electrode can be
made so thin that the film thickness can be ignored; in this case,
the total film thickness of the first light-absorbing layer and the
second light-absorbing layer may satisfy the relationship
n(.lamda.1/4) (n is an integer equal to or greater than 1). The
light of the wavelength .lamda.1 that is incident and the light of
the wavelength .lamda.1 that is reflected by the surface of the
support member are thereby cancelled out by mutual interference,
thus increasing the effective absorptivity in the first
light-absorbing layer and the second light-absorbing layer.
[0030] Moreover, as described above, the light that has been
reflected by the thermal transfer member is absorbed by the second
light-absorbing layer, and the effective absorption in the second
light-absorbing layer can be increased, in this case, by providing
a second optical resonator. For example, a so-called .lamda./4
optical resonator may be used as the second optical resonator.
[0031] Specifically, taking the second wavelength as .lamda.2, the
second optical resonator can be constituted by setting the distance
between the bottom surface of the second light-absorbing layer and
the top surface of the second light-absorbing layer (specifically,
the film thickness of the second light-absorbing layer) at
n(.lamda.2/4). As a result, incident light of wavelength .lamda.2
and light of wavelength .lamda.2 that has been reflected by the
bottom surface of the second light-absorbing layer (interface
between the first light-absorbing layer and second light-absorbing
layer) are canceled out due to mutual interference, thereby
increasing the effective absorption at the second light-absorbing
layer.
[0032] According to this aspect, because resonance peaks are
created in two different wavelengths, the band of wavelengths
(wavelength width) in which the thermal detector is able to detect
light can be widened. Also, the light-reflecting layer and the
thermal collecting portion of the thermal transfer member are
disposed in parallel with each other. A parallel between the upper
surface of the light-reflecting layer and the upper surface of the
second light-absorbing layer is accordingly maintained.
[0033] In another aspect of the thermal detector of the present
invention, the thermal transfer member preferably also serves as
wiring that electrically connects the heat-detecting element to
another element.
[0034] The thermal transfer member, as described above, can be
constituted by a metal compound such as AlN or AlO.sub.x, but a
material having metal as a primary component is preferred, due to
its favorable electrical conductivity, and the thermal transfer
member may also be used as wiring (or a portion of the wiring) that
connects the heat-detecting element with other elements. By using
the thermal transfer member as wiring, the production steps can be
simplified, because it is not necessary to provide the wiring
separately.
[0035] A thermal detection device according to another aspect of
the present invention includes a plurality of the thermal detectors
described in any of the aspects above disposed
two-dimensionally.
[0036] As a result, a thermal detection device (thermal-type
optical array sensor) is realized in which a plurality of the
thermal detectors (thermo-optical detection elements) have been
disposed two-dimensionally (e.g., disposed in an array formed along
two perpendicular axes).
[0037] An electronic instrument according to another aspect of the
present invention comprises the thermal detector described in any
of the aspects above and a control part configured to process an
output of the thermal detector.
[0038] All of the thermal detectors described above have high
detection sensitivity, and thus the performance of the electronic
instruments that contain these thermal detectors is improved.
Examples of electronic instruments include infrared sensor devices,
thermographic devices, on-board automotive night-vision cameras,
and surveillance cameras. The control part may be constituted, for
example, by an image processing part or a CPU.
[0039] A thermal detector manufacturing method according to another
aspect of the present invention includes: forming a structure
including an insulating layer on a surface of a substrate; forming
a sacrificial layer on the structure including the insulating
layer; forming a support member on the sacrificial layer; forming
on the support member a heat-detecting element having a structure
in which a pyroelectric material layer is disposed between a lower
electrode and an upper electrode, the lower electrode having an
extending portion extending around the pyroelectric material layer
as seen in plan view, and the extending portion having
light-reflecting properties by which arriving light is reflected;
forming a first light-absorbing layer so as to cover the
heat-detecting element, and planarizing the first light-absorbing
layer; forming a contact hole in a portion of the first
light-absorbing layer, subsequently forming a material layer which
is thermally conductive and optically transmissive at least with
respect to light of a prescribed wavelength, and patterning the
material layer to form a thermal transfer member having a
connecting portion that connects to the heat-detecting element and
a thermal collecting portion having a surface area greater than
that of the connecting portion as seen in plan view; forming a
second light-absorbing layer on the first light-absorbing layer;
patterning the first light-absorbing layer and the second
light-absorbing layer; patterning the support member; and removing
the sacrificial layer to form a cavity between the support member
and the structure including the insulating layer formed on the
surface of the substrate.
[0040] According to the aspect described above, the main surface of
the substrate is laminated with a multilayer structure including
inter-layer insulating layers, the sacrificial layer, and the
support member, and the support member is also laminated with the
heat-detecting element including the lower electrode having the
light-reflecting properties (that is, the lower electrode serving
as a light-reflecting member), the first light-absorbing layer, the
thermal transfer member, and the second light-absorbing layer. A
planarization treatment is used to planarize the upper surface of
the first light-absorbing layer. The first light-absorbing layer is
also provided with a contact hole, the connecting portion of the
thermal transfer member being embedded in this contact hole. The
thermal collecting portion of the thermal transfer member, provided
on the first light-absorbing layer, is connected to the
heat-detecting element (for example, to an electrode on a
pyroelectric capacitor) via the connecting portion. According to
this aspect, a semiconductor manufacturing technology (for example,
MEMS technology) can be used to achieve a thermal detector that is
both small and detects with a high degree of sensitivity. Also, it
is preferable that the light-reflecting layer and the thermal
collecting portion of the thermal transfer member be disposed in
parallel with each other. A parallel between the upper surface of
the light-reflecting layer and the upper surface of the second
light-absorbing layer is thereby maintained.
[0041] In accordance with at last one of the aspects of the present
invention, for example, it is possible to additionally increase the
detection sensitivity of the thermal detector.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] Referring now to the attached drawings which form a part of
this original disclosure:
[0043] FIG. 1A is a schematic top plan view of an example of a
thermal detector according one embodiment.
[0044] FIG. 1B is a sectional view of the thermal detector as taken
along a section line A-A' in FIG. 1A.
[0045] FIG. 2A is a diagram showing an example of the spectral
characteristics (light-reflecting characteristics and
light-transmission characteristics) of an alumina plate in the
far-infrared wavelength range.
[0046] FIG. 2B is a diagram showing an example of the detection
sensitivity of the thermal detector having a double optical
resonator configuration.
[0047] FIGS. 3A to 3E are diagrams showing the steps for forming
the first light-absorbing layer in the thermal detector
manufacturing method.
[0048] FIGS. 4A to 4C are diagrams showing the steps for patterning
the first light-absorbing layer and the second light-absorbing
layer in the thermal detector manufacturing method.
[0049] FIGS. 5A and 5B are diagrams showing the steps for
completion of the thermal detector in the thermal detector
manufacturing method.
[0050] FIG. 6 is a diagram showing another example of the thermal
detector.
[0051] FIG. 7 is a circuit diagram showing an example of the
circuit configuration of a thermal detection device (thermal
detector array).
[0052] FIG. 8 is a diagram showing an example of the configuration
of an electronic instrument.
[0053] FIG. 9 is a diagram showing another example of the
configuration of an electronic instrument.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0054] Preferred embodiments of the present invention are described
below. The matter of the present invention described in the claims
is not unduly limited by the embodiments described below, and it is
not essential for all of the configurations described in the
embodiments to be used as means for solving the problems.
Embodiment 1
[0055] FIGS. 1A and 1B are plan view and a sectional view of an
example of the thermal detector. FIG. 1B is a sectional view of the
thermal detector, taken along line A-A' in FIG. 1A. In FIGS. 1A and
1B, an individual thermal detector is shown, but a plurality of
thermal detectors may be disposed in the form of a matrix in order
to produce the configuration of a thermal detector array (e.g., a
thermal-type detection device).
[0056] The thermal detector shown in FIGS. 1A and 1B is a
pyroelectric infrared detector (a type of light sensor) 200
(however, this is only an example and does not limit the
invention). This pyroelectric-type infrared photodetector 200 can
efficiently transfer the heat that is generated by light absorption
in the two-layer light-absorbing films 270 and 272 to the
heat-detecting element (here, a pyroelectric capacitor 230) via a
thermal transfer member 260 having favorable thermal transfer
properties.
[0057] The thermal transfer member 260 can comprise a material (for
example, AlN, AlO.sub.x, or other metallic compounds) that, for
example, has high thermal conductivity, and is optically
transmissive (for example, semi-transmissive) to the light of at
least some wavelength regions (the light of a wavelength region, in
which the thermal detector has detection sensitivity for at least a
part of a band of wavelength (width of wavelength)) of the light.
The optical transparency of the thermal transfer member 260 will be
described later with reference to FIG. 2.
[0058] The pyroelectric capacitor 230 serving as a heat-detecting
element converts heat to electrical signals. A detection signal
(for example, an electric current signal) that corresponds to the
intensity of the received light is thereby obtained. The
pyroelectric capacitor 230 serving as the heat-detecting element is
formed on the support member 215. Herein, the expression "on . . .
" may refer to "directly above," or may alternatively refer to the
upper part (in cases in which another layer is interposed). A
similarly broad interpretation is possible in other places as well.
The following is a detailed description.
Example of Thermal Detector (Pyroelectric Infrared Detector)
[0059] The sectional structure will first be described with
reference to FIG. 1B.
Sectional Structure of Pyroelectric Infrared Detector
[0060] The pyroelectric-type infrared detector 200 that is used as
the thermal detector is constituted by a multilayer structure that
is formed on a substrate (silicon substrate) 10. Specifically, the
pyroelectric type infrared light detector that is used as the
thermal detector 200 comprises a substrate (in this case, a silicon
substrate) 10, a structure 100 including an insulating layer that
is formed on the primary surface (in this case, the top surface) of
the substrate 10 (e.g., a multilayer structure including an
interlayer insulating film; refer to FIG. 6 for details concerning
the multilayer structure), an etching stopper film 130a formed on
the surface of the structure 100 including the insulating layer, a
cavity for thermal isolation (thermal isolation cavity) 102, a
support member (membrane) 215 that is constituted by a mounting
part 210 and arm parts 212a and 212b, a pyroelectric capacitor 230
as a heat detection element that is formed on the support member
(membrane) 215, an insulating layer 250 that covers the surface of
the pyroelectric capacitor 230, a first light-absorbing layer
(e.g., an SiO.sub.2 layer) 270, a thermal transfer member 260
(having a connecting portion CN and a thermal collecting portion
FL), and a second light-absorbing layer (e.g., an SiO.sub.2 layer)
272.
[0061] The pyroelectric capacitor 230 comprises a lower electrode
(the first electrode) 234, a pyroelectric material layer 232, and
an upper electrode (the second electrode) 236. The lower electrode
of the pyroelectric capacitor 230 has an extending portion RX that
extends around the pyroelectric material layer in plan view (in
plan view as seen from the direction perpendicular to the surface
of the substrate), this extending portion RX having
light-reflecting properties by which at least a part of the light
that has been transmitted through a thermal collecting portion FL
of the thermal transfer member 260 is reflected. The "extending
portion" can also alternatively be called a "jutting portion" or an
"augmented portion."
[0062] The first light-absorbing layer 270 is formed between the
thermal transfer member 260 (specifically, the thermal collecting
portion FL of the thermal transfer member 260) and the extending
portion RX in the lower electrode of the heat-detecting element
(the pyroelectric capacitor 230), and is connected to the thermal
transfer member 260 (specifically, the thermal collecting portion
FL of the thermal transfer member 260).
[0063] The second light-absorbing layer 272 is formed on the
thermal transfer member 260 (specifically, the thermal collecting
portion FL of the thermal transfer member 260, and is connected to
the thermal transfer member 260 (specifically, the thermal
collecting portion FL of the thermal transfer member 260).
[0064] Namely, the lower electrode 234 comprises a material with
excellent conductivity (for example, a metallic material); the
light reflectance of metallic materials and the like is generally
high. Accordingly, much of the light that is incident on the
surface of the extending portion RX of the lower electrode 234,
which is a constituent element of the pyroelectric capacitor 230,
is reflected, this reflected light then being absorbed in either
the first light-absorbing layer 270 or the second light-absorbing
layer 272. The incident light can accordingly be used without
waste, and can be converted to heat. A part of the light that
arrives at the surface of the support member 215 may also possibly
be reflected and absorbed in either the first light-absorbing layer
270 or the second light-absorbing layer 272. In this regard as
well, the incident light can be used efficiently.
[0065] In the example of FIGS. 1A and 1B, the extending portion RX
in the lower electrode 234 is formed so as to jut to the periphery
of the thermal transfer member 260 in plan view. The extending
portion RX can be made to jut farther out than the periphery of the
thermal transfer member 260, or, conversely, can also be made to
stop jutting while inside the periphery of the thermal transfer
member 260. However, the effect of efficiently reflecting light
that has been transmitted through the thermal collecting portion FL
of the thermal transfer member 260 is weakened when the extending
portion RX in the lower electrode 234 has too small a surface area.
Therefore, the extending portion RX is preferably formed to jut at
least to the periphery (near the periphery) of the thermal transfer
member 260, in plan view. Also, it is preferable, from the
viewpoint of effectively utilizing the incident light, that the
extending portion RX be provided around the pyroelectric material
layer 232 in plan view. The extending portion RX is further
preferably provided around the entirety.
[0066] The lower electrode 234, comprising a metallic material and
also having high thermal conductivity, therefore also exerts the
effect of efficiently transferring to the pyroelectric material
layer 232 heat that, for example, has been generated at places
distant from the pyroelectric material layer 232 in the first
light-absorbing layer 270. That is, since the lower electrode 234,
for example, extends broadly on the support member 215, it is
therefore possible to efficiently transfer to the pyroelectric
material layer 232 heat that has been generated in a broad range in
the first light-absorbing layer 270. In this regard, it can be said
that the lower electrode 234 also serves as a thermal transfer
member (that is, as a thermal transfer member which can be said to
be, for example a second thermal transfer member, distinct from the
thermal transfer member 260 formed on the upper part of the
pyroelectric capacitor 230, which can then be said to be the first
thermal transfer member).
[0067] The base part (base) is constituted by the substrate 10 and
the multilayer structure 100. This base part (base) supports the
element structure 160 that includes the support member 215 and the
pyroelectric capacitor 230 in the cavity 102. In addition, a
transistor, resistor, or other semiconductor element can be formed,
for example, in the region of the silicon (Si) substrate 10 that
overlaps with the heat-detecting element (pyroelectric capacitor
230) as seen in plan view (e.g., refer to the example of FIG.
6).
[0068] As described above, an etching stopper film (e.g., an
Si.sub.3N.sub.4 film) 130a is provided on the surface of the
multilayer structure 100 that is formed on the substrate 10. In
addition, etching stopper films (e.g., Si.sub.3N.sub.4 films) 130b
to 130d are formed on the back surface of the support member
(membrane) 215. The etching stopper films 130a to 130d have the
role of preventing removal of layers other than the targets of
etching in the step in which the sacrificial layer (not shown in
FIG. 1, refer to designation 101 in FIG. 3) is etched in order to
form the cavity 102. However, the etching stopper film is not
necessary, in some cases, depending on the material that
constitutes the support member (membrane) 215.
[0069] In addition, the pyroelectric capacitor 230 that is part of
the element structure 160 is supported above the cavity 102 by the
support member (membrane) 215 which is also part of the element
structure 160.
[0070] The support member (membrane) 215 can be formed by
patterning a three-layer laminate of a silicon oxide film
(SiO)/silicon nitride film (SiN)/silicon oxide film (SiO) (this is
only an example and does not limit the invention). The support
member (membrane) 215 is configured and arranged to stably support
the pyroelectric capacitor 230, and thus the total thickness of the
support member (membrane) 215 is set to be sufficient to provide
the necessary mechanical strength.
[0071] An oriented film (not shown in the drawings) is formed on
the surface of the support member (membrane) 215, and the
pyroelectric capacitor 230 is formed on this oriented film. As
described above, the pyroelectric capacitor 230 comprises a lower
electrode (first electrode) 234, a pyroelectric material layer
(e.g., a pyroelectric body PZT layer; lead zirconate titanate
layer) 232 that is formed on the lower electrode, and an upper
electrode (second electrode) 236 that is formed on the pyroelectric
material layer 232.
[0072] Each of the lower electrode (first electrode) 234 and the
upper electrode (second electrode) 236 can be formed, for example,
by laminating three layers of metal film. For example, a
three-layer structure may be used in which iridium (Ir), iridium
oxide (IrO.sub.x) and platinum (Pt) are formed by patterning, for
example, in sequence from a location farthest from the pyroelectric
material layer (PZT layer) 232. As described above, PZT (Pb(Zi,
Ti)O.sub.3; lead zirconate titanate) may be used as the
pyroelectric material layer 232.
[0073] When heat is transferred to the pyroelectric material layer
(pyroelectric body), a change in electrical polarity arises in the
pyroelectric material layer 232 as a result of the ensuing
pyroelectric effect (pyroelectric effect). By detecting the current
that accompanies this change in the degree of electrical polarity,
it is possible to detect the intensity of the incident light.
[0074] This pyroelectric material layer 232 can be formed into a
film, for example, by sputtering or MOCVD. The film thickness of
the lower electrode (first electrode) 234 and the upper electrode
(second electrode) 236 is, for example, about 0.4 .mu.m, and the
film thickness of the pyroelectric material layer 232 is, for
example, about 0.1 .mu.m.
[0075] The pyroelectric capacitor 230 is covered by the insulating
layer 250 and the first light-absorbing layer 270. A first contact
hole 252 is provided on the insulating layer 250. The first contact
hole 252 is used for connecting the electrode 226 of the upper
electrode (second electrode) 236 to the upper electrode (second
electrode) 236.
[0076] Also, the second contact hole 254 is provided in the first
light-absorbing layer 270 (and the insulating layer 250). The
second contact hole 254 is provided through the first
light-absorbing layer 270 and the insulating layer 250. This second
contact hole 254 is used in order to connect the thermal transfer
member 260 to the upper electrode 236 of the pyroelectric capacitor
230. Specifically, the second contact hole 254 (where the filled
portion is indicated by the reference designation 228 in the
drawing) can be filled with the same material that constitutes the
thermal transfer member 260 (e.g., aluminum nitride (AlN) or
aluminum oxide (AlO.sub.x)), and, as a result, a connecting portion
CN is configured in the thermal transfer member 260.
[0077] The portion of the thermal transfer member 260 that extends
over the first light-absorbing layer 270 has a thermal collecting
portion FL with a planarized surface and the connecting portion CN
in the portion that connects the thermal collecting portion FL with
the upper electrode (second electrode) 236 in the pyroelectric
capacitor 230.
[0078] The thermal collecting portion FL of the thermal transfer
member 260, for example, has the role of collecting the heat that
has been generated over a wide region and transferring it to the
pyroelectric capacitor 230 that is used as the heat-detecting
element. The thermal collecting portion FL, for example, can also
be formed in a configuration in which it has a level surface on the
first light-absorbing layer 270 that has been planarized. In this
case, the "thermal collecting portion" may also be referred to as a
"flat part" or "planar part".
[0079] As described above, the thermal transfer member 260 can
comprise a material that has high thermal conductivity and is
optically transmissive (for example, semi-transmissive) to the
light of a desired band of wavelength, and can comprise, for
example, aluminum nitride (AlN), aluminum oxide (AlO.sub.x), or the
like. It is also possible for the material in the thermal
collecting portion FL to be different from the material 228 in the
connecting portion CN (for example, the material of the contact
plug embedded in the contact hole 254).
[0080] FIG. 1B (as well as FIG. 1A) illustrates the existence of a
relationship W0<W1<W2, where W0 is the width of the
connecting portion CN, W1 is the width of the pyroelectric material
layer 232, and W2 is the width of the thermal collecting portion FL
of the thermal transfer member 260. The width of the lower
electrode (first electrode) 234 of the pyroelectric capacitor 230
is also set to be W2. In other words, as depicted in FIG. 1A, the
periphery (outer edge) of the thermal transfer member 260 is
substantially matched in plan view to the periphery (outer edge) of
the lower electrode (first electrode) 234.
[0081] As illustrated in FIG. 1B, a distance H1 between the upper
surface of the second light-absorbing layer 272 and the surface of
the extending portion RX of the lower electrode (first electrode)
234 of the pyroelectric capacitor 230 is set to n(.lamda.1/4) ("n"
is an integer 1 or greater), where .lamda.1 is a first wavelength
and .lamda.2 is a second wavelength. A first optical resonator (a
.lamda.1/4 optical resonator) is thereby configured between the
upper surface of the second light-absorbing layer 272 and the
surface of the extending portion RX of the lower electrode (first
electrode) 234. Because the film thickness of the lower electrode
(first electrode) 234 is sufficiently thin, the thickness thereof
can be ignored without any particular problem, and accordingly the
above-described distance H1 can be considered to be the total film
thickness combining the film thickness H2 of the first
light-absorbing layer 270 and the film thickness H3 of the second
light-absorbing layer 272.
[0082] The distance H3 between the lower surface of the second
light-absorbing layer 272 and the upper surface of the second
light-absorbing layer 272 (that is, the film thickness H3 of the
second light absorbing layer 272) can be set to n(.lamda.2/4). A
second optical resonator (a .lamda.2/4 optical resonator) is
thereby configured between the lower surface of the second
light-absorbing layer 272 and the upper surface of the second
light-absorbing layer 272. Because the film thickness of the
thermal collecting portion FL in the thermal transfer member 260 is
sufficiently thin, the thickness thereof can be ignored without any
particular problem, and accordingly the resonator length of the
second optical resonator can be considered to be the film thickness
H3 of the second light-absorbing layer 272. The effect of
constituting the first optical resonator and the second optical
resonator will be described later. The light-reflecting layer 235
and the thermal collecting portion FL of the thermal transfer
member 260 are disposed in parallel with each other. Accordingly, a
parallel between the upper surface of the light-reflecting layer
235 and the upper surface of the second light-absorbing layer 272
can be maintained.
Layout Configuration of Pyroelectric Infrared Detector
[0083] Next, the layout configuration will be described with
reference to FIG. 1A. As shown in FIG. 1A, the support member
(membrane) 215 has a mounting part 210 that carries the
pyroelectric capacitor 230 and two arms that hold the mounting part
210 over the cavity (thermal isolation cavity) 102, specifically, a
first arm 212a and a second arm 212b. The pyroelectric capacitor
230 is formed on the mounting part 210 in the support member
(membrane) 215. In addition, as described above, the configuration
of the element structure 160 includes the support member (membrane)
215, the pyroelectric capacitor 230, the first light-absorbing
layer 270, the thermal transfer member 260, and the second
light-absorbing layer 272.
[0084] The first arm 212a and the second arm 212b, as described
above, can be formed in long thin shapes by processing involving
patterning a three-layer laminated film consisting of a silicon
oxide film (SiO), a silicon nitride film (SiN), and a silicon oxide
film (SiO). The reason that long thin shapes are produced is to
increase thermal resistance and to control heat dissipation (heat
release) from the pyroelectric capacitor 230.
[0085] The wide distal end part 232a of the first arm 212a is
supported above the cavity 102 by a first post 104a (circular
member as seen in plan view, represented by a broken line in FIG.
1A). In addition, wiring 229a is formed on the first arm part 212a
that connects one end (reference symbol 228) to the lower electrode
(first electrode) 234 of the pyroelectric capacitor 230 and the
other end 231a to the first post 104a.
[0086] The first post 104a, for example, is provided between the
structure 100 that includes the insulating layer shown in FIG. 1B
and the distal end part 232a of the first arm part 212a. This first
post 104a is constituted by a multilayer wiring structure that has
been processed into a pillar shape that is selectively formed in
the cavity 102 (composed of an interlayer insulating layer and a
conductive layer that constitutes wiring for connecting the
elements such as transistors provided on the underlying silicon
substrate 10 with the pyroelectric capacitor 230).
[0087] Similarly the second arm part 212b is supported above the
cavity 102 by a second post 104b (in FIG. 1A, a circular member as
seen in plan view, represented by a broken line). The broad distal
end part 232b in the second arm part 212b is supported over the
cavity 102 by a second post 104b (in FIG. 1A, a circular member as
seen in a plan view, represented by a broken line). In addition,
wiring 229b is formed on the second arm part 212b that connects one
end (reference symbol 226) to the upper electrode (second
electrode) 236 of the pyroelectric capacitor 230 and the other end
231b to the second post 104b.
[0088] The second post 104b, for example, is provided between the
structure 100 that includes the insulating layer shown in FIG. 1B
and the distal end part 232b of the second arm part 212b. This
second post 104b may be constituted by a multilayer wiring
structure that has been processed into a pillar shape selectively
in the cavity 102 (composed of an interlayer insulating layer and a
conductive layer that constitutes wiring for connecting the
elements such as transistors provided on the underlying silicon
substrate 10 with the pyroelectric capacitor 230).
[0089] In the example shown in FIG. 1A, the first post 104a and the
second post 104b are used in order to hold the element structure
160 including the support member 215 and the pyroelectric capacitor
230 above the cavity 102. With this configuration, it is useful if
a plural number of pyroelectric capacitors 230 used as
heat-detecting elements are disposed at high density in a shared
cavity 102 (in other words, when forming a heat-detecting element
array). However, this configuration is only an example and does not
limit the present invention. For example, in the example shown in
FIG. 6, a single space 102 is formed for each of the individual
heat-detecting elements (pyroelectric capacitor) 230, and the
support member (membrane) 215 may be supported by the structure 100
including the insulating layer surrounding the cavity 102.
[0090] In FIG. 1A, the pyroelectric capacitor 230 is disposed in a
middle region of the mounting unit 210 in the support member 215,
and the pyroelectric capacitor 230 has a substantially square shape
in plan view. FIG. 1A illustrates the existence of a relationship
W0<W1<W2, where W0 is the width in the connecting portion CN
of the thermal transfer member 260, W1 is the width of the
pyroelectric material layer 232 in the pyroelectric capacitor 230,
and W2 is the width of the thermal collecting portion FL of the
thermal transfer member 260 and the width of the lower electrode
(first electrode) 234.
[0091] Consequently, the surface area of the collecting portion FL
of the thermal transfer member 260 as seen in plan view (from a
direction perpendicular to the surface of the substrate 10; i.e.,
as seen perpendicularly from above) is greater than the surface
area of the connecting portion CN. In addition, the surface area of
the collecting portion FL of the thermal transfer member 260 as
seen in plan view is greater than the surface area of the
pyroelectric capacitor 230.
[0092] In addition, as shown in FIG. 1A, the first light-absorbing
layer 270 and the second light-absorbing layer 272 are formed
around the pyroelectric capacitor 230 used as the heat-detecting
element, which is on the support member (membrane) 215, as seen in
plan view. Consequently, the heat that is generated over a large
region of the first light-absorbing layer 270 and the second
light-absorbing layer 272 is efficiently transmitted directly to
the pyroelectric capacitor 230, or indirectly via the thermal
transfer member 260.
[0093] In other words, the heat that is generated over a large
region of the first light-absorbing layer 270 and the second
light-absorbing layer 272 is collected from all directions (in
other words, from all sides) in the pyroelectric capacitor 230. In
this case, the pyroelectric capacitor 230 is disposed below the
middle of the roughly square-shaped thermal transfer member 260, as
seen in plan view. Thus, the heat that is collected via the thermal
transfer member 260 from all directions is transferred to the upper
electrode (second electrode) 236 of the pyroelectric capacitor 230
through the shortest possible distance via the connecting portion
CN. Thus, much of the heat is efficiently collected from a wide
area, and the heat can be transferred to the upper electrode
(second electrode) 236 of the pyroelectric capacitor 230 through
the shortest possible distance while minimizing loss. Thus, the
photodetection sensitivity of the thermal detector 200 can be
additionally increased. In addition, the response rate of the
thermal detector can be additionally improved.
[0094] Since the extending portion RX of the lower electrode (first
electrode) 234 in the pyroelectric capacitor 230 also has the
effect of transferring heat, as has been described above, the heat
that is generated in a large region of, for example, the first
light-absorbing layer 270 is collected in the pyroelectric material
layer 232 from every direction, through the extending portion RX.
The effect of efficiently transferring to the pyroelectric material
layer 232 heat that has been generated at places distant from the
pyroelectric material 232 in the first light-absorbing layer 270 is
also obtained.
[0095] Absorption is also more efficient in this embodiment,
because heat is generated by the two light-absorbing films 270,
272. The heat can be directly transferred to the heat-detecting
element 230 via the first light-absorbing layer 270. The thermal
detector can accordingly detect at a further improved degree of
sensitivity compared to the infrared detection element recited in
Japanese Patent No. 3339276 and the infrared solid-state imaging
element recited in Japanese Patent Application Republication No.
99/31471. Also, the heat-detecting element 230 is connected to the
thermal transfer member 260 in this embodiment. The response speed
is accordingly as high as that of the infrared detection element
recited in Patent Reference 1. The response speed obtained in this
embodiment is even higher than that of the infrared solid-state
imaging element recited in Patent Reference 2, because the thermal
transfer member 260 is directly connected to the heat-detecting
element 230.
Operation of Pyroelectric Infrared Detector
[0096] The thermal detector 200 according to this embodiment
presented in FIGS. 1A and 1B operates in the manner described
below.
[0097] Namely, a part of the light (for example, infrared light)
that is incident on the thermal detector 200 is first absorbed in
the second light-absorbing layer 272, and the remainder thereof
arrives at the thermal transfer member 260 without being absorbed.
The thermal transfer member 260 is optically transmissive to light
in a band of wavelength in which the thermal detector 200 has
detection sensitivity, and is, for example, translucent to infrared
light. For example, a part of the arriving light is reflected in
the thermal transfer member 260, and the remainder thereof is
transmitted through the thermal transfer member 260. The part of
the light that is transmitted through the thermal transfer member
260 is absorbed in the first light-absorbing layer 270, and the
remaining light arrives at the surface of the support member
(membrane) 215, as well as at the surface of the extending portion
RX of the lower electrode (first electrode) 234 of the pyroelectric
capacitor 230 serving as a heat-detecting element formed on the
support member (membrane) 215.
[0098] Much of (for example, the majority of) the light that is
incident on the extending portion RX of the lower electrode (first
electrode) 234 of the pyroelectric capacitor 230 is reflected on
the surface thereof, and then absorbed into at least one of the
first light-absorbing layer 270 and the second light-absorbing
layer 272, thus generating heat in either the first light-absorbing
layer 270 or the second light-absorbing layer 272. In other words,
the presence of the extending portion RX of the lower electrode
(first electrode) 234 reduces the occurrence of incident light
being transmitted through the support member (membrane) 215 and
escaping downward; a greater amount of incident light can
accordingly be converted to heat, such that light can be used
efficiently.
[0099] Light that is reflected by the surface of the support member
(membrane) 215 is also absorbed into at least one of the first
light-absorbing layer 270 and the second light-absorbing layer 272,
thus generating heat in either the first light-absorbing layer or
the second light-absorbing layer. For example, in a case in which
the first light-absorbing layer 270 comprises a layer of SiO.sub.2
(refractive index: 1.45) and the support member (membrane) 215
comprises a layer of SiN (refractive index: 2.0), the refractive
index of the film constituting the support member (membrane) 215
(in other words, the refractive index of the support member 215) is
greater than the refractive index of the first light-absorbing
layer 270, and therefore almost all the light that arrives at the
support member (membrane) 215 will be reflected by the surface of
the support member (membrane) 215.
[0100] It is also effective to further provide, for example, a
titanium (Ti) film, or other metal film, as a constituent element
of the support member (membrane) 215 (particularly preferably
provided to the surface by which light is reflected), increasing
the light reflectance in the surface of the support member
(membrane) 215. The light that is reflected by the surface of the
support member (membrane) 215 is absorbed in the first
light-absorbing layer 270 or the second light-absorbing layer
272.
[0101] The following is an example of how, in a case in which the
incident light exhibits such behaviour as described above, heat is
generated in the first light-absorbing layer 270 and the second
light-absorbing layer 272, and of how the generated heat is
transferred to the pyroelectric capacitor 230, which is a
heat-detecting element.
[0102] Namely, a part of the light that is incident on the thermal
detector 200 is first absorbed in the second light-absorbing layer
272, heat then being generated in the second light-absorbing layer.
Light that is reflected by the thermal transfer member 260 is also
absorbed in the second light-absorbing layer 272, thus generating
heat in the second light-absorbing layer 272.
[0103] A part of the light that is transmitted through (passes
through) the thermal transfer member 260 is absorbed in and
generates heat in the first light-absorbing layer 270. The
remaining light arrives at the surface of the extending portion RX
of the lower electrode (first electrode) of the pyroelectric
capacitor 230, and also at the surface of the support member
(membrane) 215.
[0104] As described above, much of (for example, the majority of)
the light that is incident on the surface of the extending portion
RX of the lower electrode (first electrode) is reflected, and this
reflected light is then absorbed in the first light-absorbing layer
270 or the second light-absorbing layer 272. The incident light can
accordingly be used without waste, and can be converted to
heat.
[0105] The extending portion RX of the lower electrode (first
electrode) of the pyroelectric capacitor 230 also has the effect of
collecting heat; heat generated in a wide range of the first
light-absorbing layer 270 can therefore be efficiently collected in
the pyroelectric material layer 232.
[0106] Since part of the light that arrives at the surface of the
support member (membrane) 215 is also reflected, and then absorbed
in the first light-absorbing layer 270 or the second
light-absorbing layer 272, the incident light is also effectively
utilized in this regard.
[0107] The heat that has been generated by the second
light-absorbing layer 272 is efficiently transferred to the
pyroelectric capacitor 230 that is used as the heat-detecting
element via the thermal transfer member 260, and the heat that has
been generated by the first light-absorbing layer 270 is
efficiently transferred to the pyroelectric capacitor 230, directly
or via the thermal transfer member 260.
[0108] Specifically, the thermal collecting portion of the thermal
transfer member 260 is formed so as to broadly cover the
heat-detecting element 230, and thus most of the heat that is
generated by the first light-absorbing layer 270 and the second
light-absorbing layer 272 can be transferred efficiently to the
heat-detecting element, regardless of the site at which it was
generated. For example, even heat that has been generated at a
location distant from the pyroelectric capacitor 230 can be
efficiently transferred to pyroelectric capacitor 230, which is a
heat-detecting element, via the thermal transfer member 260 having
high thermal conductivity.
[0109] In addition, because the thermal collecting portion FL of
the thermal transfer member 260 and the pyroelectric capacitor 230
are connected by the connecting portion CN of the thermal transfer
member 260, the heat that is transmitted via the thermal collecting
portion FL of the thermal transfer member 260 can be directly
transmitted to the pyroelectric capacitor 230 via the connecting
portion CN. Moreover, because the pyroelectric capacitor 230 that
is used as the heat-detecting element is positioned under (directly
under) the thermal transfer member 260 (provided in positions that
are superimposed as seen in plan view), it is possible, for
example, to connect the pyroelectric capacitor 230 and the middle
part of the thermal transfer member 260 via the shortest possible
distance, as seen in plan view. Thus, the loss occurring with heat
transfer can be decreased, and an increase in footprint can be
minimized.
[0110] In this manner, in accordance with the thermal detector
described in FIGS. 1A and 1B (in this case a pyroelectric-type
infrared light detector), the heat that has been generated over a
large region in two (a plurality of) light-absorbing layers 270,
272 can be efficiently transferred to the pyroelectric capacitor
230 which is used as the heat-detecting element. Thus, the light
detection sensitivity of small-size thermal detectors
(pyroelectric-type infrared photodetectors) can be greatly
increased. Moreover, the time required for light transfer is
decreased, and so the response rate of the thermal detector
(pyroelectric-type infrared photodetector) can be increased.
[0111] The light-reflecting effects and heat-collecting effects of
the extending portion RX of the lower electrode (first electrode)
234 of the pyroelectric capacitor 230 also increase the detection
efficiency of the thermal detector.
[0112] In addition, with the thermal detector (pyroelectric-type
infrared photodetector) described in FIGS. 1A and 1B, the first
light-absorbing layer 270 and the second light-absorbing layer 272
are formed surrounding the pyroelectric capacitor 230 used as the
heat-detecting element as seen in plan view on the support member
215 (or the mounting part 210 thereof). As a result, the heat that
is generated over a large region of the first light-absorbing layer
270 and the second light-absorbing layer 272 is extremely
efficiently transferred to the pyroelectric capacitor 230 used as
the heat-detecting element, either directly or indirectly via the
thermal transfer member 260. Thus, the light detection sensitivity
of the thermal detector (pyroelectric-type infrared photodetector)
can be additionally increased, and the response rate of the thermal
detector (pyroelectric-type infrared photodetector) can be
additionally increased.
[0113] The thermal detector recited in FIGS. 1A and 1B (the
pyroelectric infrared detector) also has a first optical resonator
for a first wavelength .lamda.1 configured between the surface of
the second light-absorbing layer 272 and the surface of the
extending portion RX of the lower electrode (first electrode) 234
of the pyroelectric capacitor 230, and also has a second optical
resonator for a second wavelength .lamda.2, which is different from
the first wavelength .lamda.1, configured between the lower surface
of the second light-absorbing layer 272 and the upper surface of
the second light-absorbing layer 272. Namely, the film thicknesses
of the first light-absorbing layer 270 and the second
light-absorbing layer 272 are adjusted to constitute two optical
resonators having different resonance wavelengths.
[0114] As has been described above, the light that is reflected by
the extending portion RX of the lower electrode (first electrode)
234 of the pyroelectric capacitor 230 is absorbed into at least one
of the first light-absorbing layer 270 and the second
light-absorbing layer 272, but constituting the first optical
resonator can increase the effective absorptivity in each
light-absorbing layer at this time.
[0115] The first optical resonator can be, for example, a so-called
.lamda./4 optical resonator. Namely, the film thicknesses of the
first light-absorbing layer 270 and the second light-absorbing
layer 272 are adjusted such that the distance H1 between the
surface of the extending portion RX of the lower electrode (first
electrode) 234 of the pyroelectric capacitor 230 and the upper
surface of the second light-absorbing layer 272 (the total
thickness H1 of the first light-absorbing layer 270 and the second
light-absorbing layer 272, when the film thickness of the lower
electrode 234 can be ignored) satisfies the relationship
n(.lamda.1/4) (n is an integer equal to or greater than 1), where
.lamda.1 is the first wavelength. The light of the wavelength
.lamda.1 that is incident and the light of the wavelength .lamda.1
that is reflected by the extending portion RX of the lower
electrode 234 are thereby cancelled out due to mutual interference,
thus increasing the effective absorptivity in the first
light-absorbing layer 270 and the second light-absorbing layer
272.
[0116] Since the extending portion RX of the lower electrode 234
comprises a material that is highly reflective of light, much of
the incident light can be reflected upward, and optical resonance
is accordingly prone to occur.
[0117] As for the light that is reflected by the surface of the
support member (membrane) 215, since mutual interference occurs
with the incident light, resonance in the first optical resonator
is also prone to occur.
[0118] Moreover, as described above, the light that has been
reflected at the thermal transfer member 260 is absorbed at the
second light-absorbing layer 272, but by constituting the second
optical resonator, effective absorption in the second
light-absorbing layer 272 can be increased, in this case. A
so-called .lamda./4 optical resonator, for example, may be used as
the second optical resonator.
[0119] Specifically, taking the second wavelength as .lamda.2, the
second optical resonator can be constituted by setting the distance
between the bottom surface of the second light-absorbing layer 272
and the top surface of the second light-absorbing layer 272
(specifically, the film thickness of the second light-absorbing
layer) to n(.lamda.2/4). As a result, incident light of wavelength
.lamda.2 and light of wavelength .lamda.2 that has been reflected
at the bottom surface of the second light-absorbing layer
(interface between the first light-absorbing layer 270 and the
second light-absorbing layer 272) are cancelled out due to mutual
interference, thereby increasing the effective absorption at the
second light-absorbing layer 272.
[0120] Moreover, by having a configuration involving two optical
resonators, the wavelength bandwidth of light that can be detected
by the thermal detector can be increased as a result of peaks
synthesis because a resonance peak is produced at the two different
wavelengths. In other words, the wavelength bandwidth (wavelength
range) that can be detected by the thermal detector can be
increased.
Preferred Example of Thermal Transfer Member
[0121] A preferred example of the thermal transfer member (thermal
transfer layer) is described below. As described above, with the
thermal detector 200 of this embodiment, a structure is used in
which the heat collecting portion FL in the thermal transfer member
260 is sandwiched by the first light-absorbing layer 270 and the
second light-absorbing layer 272. Thus, in addition, the thermal
collecting portion FL of the thermal transfer member 260 can
collect even heat that has been generated at positions that are far
from the pyroelectric capacitor 230 that is used as the
heat-detecting element. As a result, it is preferable for the
thermal collecting portion to have a large surface area as seen in
plan view. Given this situation, it is preferable for the thermal
transfer member 260 to be constituted by a material that is
transmissive to light and allows light of at least some of the
wavelengths that are in the desired wavelength range to pass, so
that light that is incident from above the thermal detector 200 is
absorbed by both the first light-absorbing layer 270 and the second
light-absorbing layer 272.
[0122] Specifically, the thermal transfer member 260 is preferably
constituted by a material that has thermal conductivity and light
transmissivity and has favorable thermal transfer properties. The
thermal transfer member 260 can be constituted, for example, by
aluminum nitride (AlN) or aluminum oxide (AlO.sub.x). The aluminum
oxide is also referred to as alumina, and Al.sub.2O.sub.3 may also
be used, for example.
[0123] FIG. 2A is a diagram that show an example of the spectral
characteristics (light reflection characteristics and light
transmission characteristics) of the alumina plate in the
far-infrared light wavelength range and FIG. 2B is a diagram that
shows an example of the detection sensitivity of the thermal
detector when two optical resonators are configured.
[0124] Although the far-infrared light wavelength range is not
particularly strictly defined, the wavelength range of far-infrared
light is generally about 4 .mu.m to about 1000 .mu.m. Infrared
light is radiated by all bodies, and bodies having high
temperatures radiate intense infrared light. The wavelength of peak
radiation is inversely proportional to temperature, and the peak
wavelength of infrared light radiated by a body at room
temperature, 20.degree. C., is about 10 .mu.m.
[0125] FIG. 2A shows the reflectance and transmittance of an
alumina plate in the wavelength range of 4 .mu.m to 24 .mu.m. The
horizontal axis is wavelength (.mu.m), and the vertical axis is
relative intensity (arbitrary units: a.u.). In FIG. 2, the
characteristic line Q1 indicating transmittance is represented as a
dashed-dotted line, and the characteristic curve Q2 indicating
reflectance is indicated as a solid line. Characteristic curve Q3
which shows the results of adding the reflectance and the
transmittance is represented by a dotted line.
[0126] As shown in FIG. 2A, the reflectance varies widely in
accordance with wavelength. On the other hand, the transmittance is
nearly zero in the wavelength range of 6 .mu.m and above.
[0127] Considering the transmittance and reflectance for light of
wavelength 4 .mu.m, the transmittance is 0.2 (in other words, 20%),
and the reflectance is 0.5 (in other words, 50%). Considering the
transmittance and reflectance for light of wavelength 12 .mu.m, the
transmittance is nearly 0 (0%), and the reflectance is about 0.43
(43%).
[0128] Considering these spectral characteristics, the first
wavelength .lamda.1 described above can be set to 4 .mu.m, and the
second wavelength .lamda.2 can be set to 12 .mu.m. In this case, if
the film thickness of the first light-absorbing layer 270 can be 3
.mu.m, for example, then the film thickness of the second
light-absorbing layer 272 can be 1 .mu.m, for example.
[0129] When alumina having the spectral characteristics shown in
FIG. 2A is used as the material for the thermal transfer member
260, about 50% of the light having wavelengths of the first
wavelength .lamda.1 (=4 .mu.m) contained in the incident light is
reflected by the thermal transfer member 260 that is formed from
alumina, and about 20% of light having a wavelength of the first
wavelength .lamda.1 (=4 .mu.m) contained in the incident light
passes through the thermal transfer member 260.
[0130] The light of wavelength .lamda.1 that has passed through the
thermal transfer member 260 reaches the support member (membrane)
215 and is reflected at the surface thereof, then moves upwards
towards the second light-absorbing layer 272, where some of this
light is reflected at the top surface of the second light-absorbing
layer 272 (interface between the atmosphere and the second
light-absorbing layer 272) and is directed downwards again. In this
manner, resonance can arise at wavelength .lamda.1 in the first
optical resonator.
[0131] In addition, about 43% of the light of wavelength .lamda.2
(=12 .mu.m) contained in the incident light is reflected by the
thermal transfer member 260 (almost no transmitted light), and the
reflected light moves upwards through the second light-absorbing
layer 272. Some of this light is reflected at the top surface of
the second light-absorbing layer 272 (interface between the
atmosphere and the second light-absorbing layer 272), and is again
directed downwards. In this manner, resonance can be made to arise
at wavelength .lamda.2 in the second optical resonator.
[0132] As a result of the generation of optical resonance as
described above, the effective light absorption in the first
light-absorbing layer 270 and the second light-absorbing layer 272
can be increased.
[0133] As shown in FIG. 2B, the wavelength range in which the
thermal detector has detection sensitivity can be increased. FIG.
2B is a diagram showing an example of the detection sensitivity of
a thermal detector for a case in which two optical resonators are
constituted. In the example shown in FIG. 2B, the resonance peak P1
produced by the first optical resonator appears at wavelength
.lamda.1 (e.g., .lamda.1=4 .mu.m), and the resonance peak P2
produced by the second optical resonator appears at wavelength
.lamda.2 (e.g., .lamda.2=12 .mu.m). By synthesizing these peak
characteristics, the detection sensitivity P3 of the thermal
detector 200 is widened. In other words, a thermal detector 200 is
realized that has detection sensitivity over a broad range of
wavelengths. Similar effects can be obtained when aluminum nitride
(AlN) is used as the material for the thermal transfer member
260.
[0134] In this manner, in accordance with the thermal detector of
this embodiment, the heat that is generated at locations distant
from the heat-detecting element can be efficiently and rapidly
collected in the pyroelectric capacitor 230 that is used as the
heat-detecting element through the thermal collecting portion FL of
the thermal transfer member (thermal transfer layer) 260. In
addition, by utilizing interference between light wavelengths
(optical resonance), it is possible to increase the effective
absorption of light at the first light-absorbing layer 270 and the
second light-absorbing layer 272. It is also possible to widen the
wavelength range in which the thermal detector has detection
sensitivity.
Thermal Detector Manufacturing Method
[0135] The thermal detector manufacturing method is described below
with reference to FIGS. 3 to 5. First, FIGS. 3A to 3E will be
discussed. FIGS. 3A to 3E are diagrams that show the steps of the
thermal detector manufacturing method up until formation of the
first light-absorbing layer.
[0136] In the step shown in FIG. 3A, a silicon substrate (which may
have elements such as transistors) is prepared, and a structure 100
including an insulating layer (e.g., a multilayer wiring structure)
is formed on the silicon substrate 10. An etching stopper film 130a
is then formed on the structure 100 including the insulating layer,
and a sacrificial layer (e.g., an SiO.sub.2 layer) 101 is then
formed.
[0137] In the step of FIG. 3B, an etching stopper film 130b is
formed on the sacrificial layer 101. Next, a thick film that will
serve as the support member (membrane) 215 (e.g., a thick film
composed of a three-layer laminated film) is formed.
[0138] In the step of FIG. 3C, the support member (membrane) 215 is
laminated with the lower electrode (first electrode) 234, the
pyroelectric material layer (PZT layer) 232, and the upper
electrode (second electrode) 236, forming the pyroelectric
capacitor 230 serving as the heat-detecting element. At this time,
the lower electrode (first electrode) 234 of the pyroelectric
capacitor 230 is formed so as to have an extending portion RX that
extends on the support member (membrane) 215.
[0139] The method for forming the pyroelectric capacitor 230, for
example, can be an atomic layer CVD method. Next, the insulating
layer 250 is formed so that it covers the pyroelectric capacitor
230. The insulating layer 250 can be formed, for example, by a CVD
method. Next, the insulating layer 250 is patterned.
[0140] In the step of FIG. 3D, the first contact hole 252 is formed
in the insulating layer 250 that covers the pyroelectric capacitor
230, and a metal material layer is then deposited, whereupon the
metal material layer is patterned in order to form the electrode
(and wiring) 226 that connects with the upper electrode (second
electrode) 236. In the step of FIG. 3D, wiring (not shown in) and
an electrode that connects to the lower electrode (first electrode)
are formed together.
[0141] In the step of FIG. 3E, the first light-absorbing layer
(e.g., SiO.sub.2 layer) 270 is formed by a CVD method. Next, this
surface is planarized by, for example, chemical mechanical
polishing (CMP).
[0142] FIGS. 4A to 4C are diagrams illustrating the principal steps
in the method for producing the thermal detector, until the
patterning of the first light-absorbing layer and the second
light-absorbing layer. In the step of FIG. 4A, a second contact
hole 254 is formed in the first light-absorbing layer 270. A
thermal transfer member (heat transfer layer) 260 is then formed by
the subsequent deposition and patterning of a material that has
high thermal conductivity and optical transparency, such as
aluminum oxide (alumina: AlO.sub.x), or aluminum nitride (AlN). The
thermal transfer member 260 possesses a thermal collecting portion
FL and a connecting portion CN. The second contact hole 254 is
filled in with alumina or another material. The portion 228 that is
filled in with the alumina or other material constitutes the
connecting portion CN. The light-reflecting layer 235 and the
thermal collecting portion FL of the heat transfer member 260 are
disposed in parallel with each other.
[0143] In the step of FIG. 4B, a material layer that will form the
second light-absorbing layer (e.g., SiO.sub.2 layer) is deposited
and patterned on the first light-absorbing layer 270. As a result,
the second light-absorbing layer 272 is formed. In the step of FIG.
4C, the first light-absorbing layer 270 is patterned.
[0144] FIGS. 5A and 5B are diagrams that show the steps up to
completion of the thermal detector in the thermal detector
manufacturing method. In the step of FIG. 5A, the support member
(membrane) 215 is patterned. As a result, the mounting part 210,
the first arm part 212a, and the second arm part 212b are formed.
In FIG. 5A, the reference symbol OP is used for the portions that
are removed by patterning (openings).
[0145] In the step of FIG. 5B, the sacrificial layer 101 is
selectively removed by, for example, wet etching. As a result, the
cavity (thermal isolation cavity) 102 is formed. The mounting part
210 of the support member 215 is separated from the base part
(substrate 10, structure 100 including insulating layer, and
etching stopper film 130a) by the cavity 102. Consequently, release
of heat through the support member 215 is inhibited. The thermal
detector is completed in this manner.
Embodiment 2
[0146] Referring now to FIG. 6, a thermal detector in accordance
Embodiment 2 will now be explained. In view of the similarity
between the first and second embodiments, the parts of the second
embodiment that are similar or identical to the parts of the first
embodiment will be given the same reference numerals as the parts
of the first embodiment. Moreover, the descriptions of the parts of
the second embodiment that are identical to the parts of the first
embodiment may be omitted for the sake of brevity.
[0147] FIG. 6 is a diagram showing another example of the thermal
detector. With the thermal detector 200 shown in FIG. 6, the cavity
102 is formed for each individual heat-detecting element, and the
support member (membrane) 215 is supported by the structure (part
of the base part) that surrounds the cavity 102. In addition, a
circuit constituent element (in this case, a MOS transistor) is
formed in the region overlapping the heat-detecting element as seen
in plan view. This MOS transistor is connected via multilayer
wiring to the pyroelectric capacitor 230 that is used as the
heat-detecting element. In the example of FIG. 6, the thermal
transfer member 260 is utilized as wiring.
[0148] Specifically, a source layer (S) and a drain layer (D) are
formed in the substrate (silicon substrate) 10. In addition, a gate
insulating film INS and a gate electrode G (e.g., a polysilicon
gate electrode) are formed on the substrate 10. As a result, a MOS
transistor that serves as the circuit constituent element is
formed.
[0149] The structure 100 including the insulating layer is formed
on the substrate 10. The base (base) is constituted by the
substrate 10 and the structure 100 including the insulating
layer.
[0150] The structure 100 including the insulating layer is
constituted by a multilayered structure, more specifically, a
multilayer wiring structure. The multilayer wiring structure
comprises a first insulating layer 100a, a second insulating layer
100b, a third insulating layer 100c, a first contact plug CP1, a
first layer wiring M1, a second contact plug CP2, a second layer
wiring M2, and a third contact plug CP3. Part of the third
insulating layer 100c is selectively removed to form the cavity
(thermal isolation cavity part) 102.
[0151] The pyroelectric capacitor 230 is formed as the
heat-detecting element on the mounting part 210 of the support
member (membrane) 215. In addition, the thermal transfer member 260
is formed between the first light-absorbing layer 270 and the
second light-absorbing layer 272.
[0152] The element structure 160 is constituted by the support
member (membrane) 215, the pyroelectric capacitor 230, the first
light-absorbing layer 270, the second light-absorbing layer 272,
the thermal transfer member 260, a fourth contact plug CP4, a third
layer wiring M3, and a fifth contact plug CP5. As described above,
the thermal transfer member 260 also functions as part of the
wiring that connects the pyroelectric capacitor 230 that is used as
the heat-detecting element to the other elements (in this case, a
CMOS transistor that is formed on the substrate 10).
[0153] Specifically, as described above, the thermal transfer
member 260 can be constituted by a metal compound such as AlN or
AlO.sub.x, but because materials having metals as primary
components also have favorable electrical conductivity, the thermal
transfer member 260 can also be utilized as wiring (or part of the
wiring) that connects the heat-detecting element to other elements.
By using the thermal transfer member 260 as wiring, it is not
necessary to provide separate wiring, and the production steps can
be simplified.
Thermal Detection Device
[0154] FIG. 7 is a circuit diagram that shows an example of a
circuit configuration for the thermal detector (thermo-optical
detection array) including the thermal detector according to any of
the illustrated embodiments. In the example of FIG. 7, a plurality
of photodetecting cells (specifically, thermal detectors 200a to
200d) are disposed two-dimensionally. In order to select single
photodetecting cells from among the plurality of photodetecting
cells (thermal detectors 200a to 200d), scan lines (W1a, W1b, etc.)
and data lines (D1a, D1b, etc.) are provided.
[0155] The thermal detector 200a that serve as a single
photodetecting cell has an element-selection transistor Mla and a
piezoelectric capacitor ZC that serves as the thermo-optical
detecting element 5. The potential relationship of the two poles of
the piezoelectric capacitor ZC can be inverted by switching the
potential that is applied to PDr1 (by inverting this potential, it
is not necessary to provide a mechanical chopper). Other
photodetecting cells are similarly configured.
[0156] The potential of the data line D1a can be initialized by
turning on a reset transistor M2. When reading a detection signal,
the read transistor M3 is ON. The current that is generated as a
result of the pyroelectric effect is converted to voltage by an I/V
conversion circuit 510, amplified by an amplifier 600, and
converted to digital data by an A/D converter 700.
[0157] In this embodiment, a plurality of thermal detectors is
disposed two-dimensionally (for example, disposed in the form of an
array along two respective perpendicular axes (X-axis and Y-axis)),
thereby realizing a thermal detection device (thermal-type optical
array sensor).
Electronic Instrument
[0158] FIG. 8 is a diagram showing an example of the configuration
of an electronic instrument. Examples of the electronic instrument
include an infrared sensor device, a thermographic device, and an
on-board automotive night-vision camera or surveillance camera.
[0159] As shown in FIG. 8, the electronic instrument comprises an
optical system 400, a sensor device 410 (corresponding to the
thermal detector 200 in the previous embodiment), an image
processing part 420, a processing part 430, a memory component 440,
an operation component 450, and a display part 460. The electronic
instrument of this embodiment is not restricted to the
configuration of FIG. 8, and various modified embodiment are
possible in which some of the constituent elements (e.g., the
optical system, operational, part, or display part) are omitted and
other constituent elements are added.
[0160] The optical system 400 includes one or a plurality of lenses
and driving parts for driving these lenses. Imaging and the like of
the subject is carried out on the sensor device 410. In addition,
focus adjustment may be carried out as necessary.
[0161] The sensor device 410 has a configuration in which the
photodetectors of the embodiments described above are laid out
two-dimensionally, and a plurality of lines (scan lines (or word
lines)) and a plurality of columns (data lines) are provided. The
sensor device 410 can also comprise line selection circuits (line
drivers), a read circuit for reading data from the photodetectors
via the columns, an A/D converter, and the like, in addition to the
photodetectors that are laid out two-dimensionally. Because data is
sequentially read from photodetectors that are laid out
two-dimensionally, a captured image of the subject can be
processed.
[0162] Based on the digital image data (pixel data) from the sensor
device 410, the image processing part 420 carries out various image
processing operations such as image correction processing. The
image processing part 420 corresponds to the control part that
processes the output of the sensor device 410 (thermal detector
200). The processing part 430 carries out control of the respective
elements of the electronic instrument and overall control of the
electronic instrument. This processing part 430 is realized, for
example, in a CPU or the like. The memory component 440 stores
various types of information, and, for example, functions as a work
space for the processing part 430 or the image processing part 420.
The operation component 450 is used as an interface for a user to
operate the electronic instrument and can be worked, for example,
in the form of various buttons, a GUI (graphical user interface)
screen, or the like.
[0163] The display part 460 displays the GUI screen, images that
have been captured by the sensor device 410, and the like, and is
worked in the form of various types of displays, such as a liquid
crystal display or organic EL display.
[0164] By using the thermal detector of a single cell as a sensor
such as an infrared light sensor in this manner and by disposing
the thermal detector of each cell along two perpendicular axes, a
sensor device (thermo-optical detecting device) 410 can be
configured. When this is done, a thermal (light) distribution image
can be captured. By using this sensor device 410, it is possible to
configure an electronic instrument such as a thermographic device,
or an on-board automotive night-vision camera or surveillance
camera.
[0165] As described previously, the thermal detector according to
the present invention has high light detection sensitivity. Thus,
the performance of the electronic instrument in which the thermal
detector is mounted is increased.
[0166] FIG. 9 is a diagram showing another example of the
configuration of the electronic instrument. The electronic
instrument 800 of FIG. 9 comprises a thermal detector 200 and an
acceleration detection element 503 which are mounted in a sensor
unit 600. The sensor unit 600 also can carry a gyro sensor or the
like. Various types of physical quantities can be measured by the
sensor unit 600. The various detection signals that are output from
the sensor unit 600 are processed by a CPU 700. The CPU 700
corresponds to the control part for processing the output of the
thermal detector 200.
[0167] As described above, in accordance with at least one
embodiment of the present invention, for example, the detection
sensitivity of a thermal detector can be dramatically improved.
[0168] In addition, in the embodiments described above, although a
pyroelectric capacitor is used as the heat-detecting element, a
thermopile element or bolometer element may be used instead.
[0169] In addition, in the embodiments described above, an infrared
detector that detects infrared light is used as an example of a
thermal detector. However, it will be apparent from this disclosure
that the thermal detector according to the present invention may be
configured and arranged to detect other type of light such as
terahertz light, for example.
[0170] In addition, in the embodiments described above, an infrared
detector that detects infrared light is used as an example of a
thermal detector. However, it will be apparent from this disclosure
that the thermal detector according to the present invention may be
configured and arranged to detect other type of light such as
terahertz light, for example.
GENERAL INTERPRETATION OF TERMS
[0171] In understanding the scope of the present invention, the
term "comprising" and its derivatives, as used herein, are intended
to be open ended terms that specify the presence of the stated
features, elements, components, groups, integers, and/or steps, but
do not exclude the presence of other unstated features, elements,
components, groups, integers and/or steps. The foregoing also
applies to words having similar meanings such as the terms,
"including", "having" and their derivatives. Also, the terms
"part," "section," "portion," "member" or "element" when used in
the singular can have the dual meaning of a single part or a
plurality of parts. Also as used herein to describe the above
embodiments, the following directional terms "top", "bottom",
"upper", "lower", "forward", "rearward", "above", "downward",
"vertical", "horizontal", "below" and "transverse" as well as any
other similar directional terms refer to those directions of the
thermal detector when the thermal detector is oriented as shown in
FIG. 1B. Finally, terms of degree such as "substantially", "about"
and "approximately" as used herein mean a reasonable amount of
deviation of the modified term such that the end result is not
significantly changed. For example, these terms can be construed as
including a deviation of at least .+-.5% of the modified term if
this deviation would not negate the meaning of the word it
modifies.
[0172] While only selected embodiments have been chosen to
illustrate the present invention, it will be apparent to those
skilled in the art from this disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. Furthermore,
the foregoing descriptions of the embodiments according to the
present invention are provided for illustration only, and not for
the purpose of limiting the invention as defined by the appended
claims and their equivalents. All modifications such as described
above may be understood to fall within the scope of the invention.
Terms disclosed together with different equivalent or broader terms
in at least one instance in the specification or drawings, for
example, may be replaced by these different terms at any place in
the specification or drawings.
* * * * *