U.S. patent application number 11/131089 was filed with the patent office on 2005-09-22 for micro-actuator utilizing electrostatic and lorentz forces, and micro-actuator device, optical switch and optical switch array using the same.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Akagawa, Keiichi, Ishizuya, Tohru, Suzuki, Junji, Suzuki, Yoshihiko.
Application Number | 20050206986 11/131089 |
Document ID | / |
Family ID | 26622373 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050206986 |
Kind Code |
A1 |
Akagawa, Keiichi ; et
al. |
September 22, 2005 |
Micro-actuator utilizing electrostatic and lorentz forces, and
micro-actuator device, optical switch and optical switch array
using the same
Abstract
The movable part 21 is fastened to the substrate 11 via flexure
parts 27a and 27b, and can move upward and downward with respect to
the substrate 11. The substrate 11 also serves as a fixed
electrode. The movable part 21 has second electrode parts 23a and
23b which can generate an electrostatic force between these
electrode parts and the substrate 11 by means of a voltage that is
applied across these electrode parts and the substrate 11, and a
current path 25 which is disposed in a magnetic field, and which
generates a Lorentz force when a current is passed through this
current path. A mirror 12 which advances into and withdraws from
the light path is disposed on the movable part 21. As a result, the
mobility range of the movable part can be broadened, and the power
consumption can be reduced, without applying a high voltage or
sacrificing small size.
Inventors: |
Akagawa, Keiichi;
(Kamakura-shi, JP) ; Suzuki, Junji; (Tokyo,
JP) ; Ishizuya, Tohru; (Tokyo, JP) ; Suzuki,
Yoshihiko; (Funabashi-shi, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 5TH AVE FL 16
NEW YORK
NY
10001-7708
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
26622373 |
Appl. No.: |
11/131089 |
Filed: |
May 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11131089 |
May 16, 2005 |
|
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|
10792427 |
Mar 2, 2004 |
|
|
|
10792427 |
Mar 2, 2004 |
|
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PCT/JP02/09023 |
Sep 5, 2002 |
|
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Current U.S.
Class: |
359/224.1 |
Current CPC
Class: |
G02B 2006/12104
20130101; G02B 6/3584 20130101; B81B 2201/045 20130101; B81B 3/0037
20130101; B81B 2203/053 20130101; G02B 6/3546 20130101; B81B
2203/0109 20130101; G02B 6/3514 20130101; G02B 6/357 20130101; G02B
6/3572 20130101; G02B 6/358 20130101 |
Class at
Publication: |
359/224 |
International
Class: |
B41J 002/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2001 |
JP |
2001-282421 |
Dec 3, 2001 |
JP |
2001-368060 |
Claims
1. A microactuator comprising: one substrate including a first
electrode part; a movable part which is movably disposed with
respect to the substrate, and which includes a second electrode
part such that an electrostatic force is generated between the
second electrode part and the first electrode part when a voltage
is applied across the first electrode part and the second electrode
part; and a current path which is disposed in a magnetic field such
that a Lorentz force is generated when current is passed through
the current path; wherein the movable part is mechanically
connected to the substrate via a spring part.
2. The microactuator according to claim 1, wherein the movable part
comprises a thin film.
3. The microactuator according to claim 1, wherein the current path
is positioned such that the Lorentz force is generated in a
direction that causes the movable part to move into a first
position where the electrostatic force is increased.
4. The microactuator according to claim 3, wherein the movable part
is movable between the first position and a second position in
which the electrostatic force decreases or disappears; and wherein
a returning force which urges the movable part to the second
position is generated when the movable part is displaced from the
second position.
5. The microactuator according to claim 4, wherein the first
electrode part and the second electrode part face each other;
wherein a gap between the first electrode part and the second
electrode part is narrower in the first position than in the second
position; and wherein the returning force is generated by the
spring part.
6. An optical switch comprising: the microactuator according to
claim 1; and a mirror which is disposed on the movable part.
7. An optical switch array comprising a plurality of the optical
switches according to claim 6; wherein the plurality of optical
switches are disposed in a two-dimensional configuration.
8. The optical switch array according to claim 7, further
comprising a circuit which includes a plurality of switching
elements, and wherein said circuit controls the current and the
voltage for respective rows and columns of the optical switches in
response to row selection signals and column selection signals for
each row and column of the plurality of optical switches.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a Continuation application of
U.S. patent application Ser. No. 10/792,427, filed on Mar. 2, 2004,
which is a Continuation of PCT International Application No.
PCT/JP02/09023, filed Sep. 5, 2002, which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to a microactuator, a
microactuator device, an optical switch and an optical switch
array.
BACKGROUND ART
[0003] As advances have been made in micro-machining techniques,
the need for microactuators has increased in various fields.
Optical switches which switch light paths utilized in optical
communications, etc., may be cited as one example of a field in
which microactuators are used. For instance, the optical switch
disclosed in Japanese Patent Application Kokai No. 2001-42233 may
be cited as one example of such an optical switch.
[0004] Microactuators generally have a fixed part, and a movable
part that can be moved by a specified force, and are held in a
specified position by the above-mentioned specified force. In
conventional microactuators, an electrostatic force is often used
as the above-mentioned specified force. For example, in the case of
the microactuator that moves a micro-mirror used in the optical
switch disclosed in Japanese Patent Application Kokai No.
2001-42233, the movable part can be moved to an upper position
(position in which the micro-mirror reflects the incident light) or
a lower position (position in which the micro-mirror allows the
incident light to pass through "as is"), and can be held in these
positions, by an electrostatic force.
[0005] In such microactuators that utilize an electrostatic force,
a first electrode part is disposed on the fixed part, a second
electrode part is disposed on the movable part, and an
electrostatic force is generated between the first and second
electrode parts by applying a voltage across these electrode
parts.
[0006] However, in the case of conventional microactuators using an
electrostatic force as described above, the movable part is moved
by an electrostatic force and held in a specified position by an
electrostatic force; accordingly, it is difficult to broaden the
range of mobility of the movable part.
[0007] The electrostatic force F1 that acts between parallel
flat-plate electrodes is as shown in the following Equation (1),
where .epsilon. is the dielectric constant, V is the potential
difference, d is the interelectrode distance, and S is the
electrode surface area.
F1=.epsilon..times.V.sup.2.times.S/(2d.sup.2) (1)
[0008] As is seen from Equation (1), the electrostatic force F1
decreases abruptly in inverse proportion to the square of the
inter-electrode distance d as the inter-electrode distance d
increases. Accordingly, in the case of the above-mentioned
conventional microactuators, it becomes difficult to move the
movable part when the inter-electrode distance d exceeds a certain
distance, so that it is difficult to broaden the mobility range of
the movable part. Furthermore, if the potential difference (voltage
across the electrodes) V is increased in an attempt to obtain a
sufficient electrostatic force F1 in the case of a large
inter-electrode distance d, problems occur in terms of the
dielectric strength, and a high-voltage generating part is
required. Furthermore, if the electrode surface area S is increased
in an attempt to obtain a sufficient electrostatic force F1 in the
case of a large inter-electrode distance d, the dimensions of the
device are increased, so that miniaturization, which is the whole
idea of a microactuator, is lost.
[0009] According, as a result of research, the present inventor
conceived of the use of Lorentz force instead of electrostatic
force in a microactuator.
[0010] It is known that the Lorentz force F2 (N) is as shown in the
following Equation (2), where B is the magnetic flux density (T), L
is the length of the electric wire (m), and I is the current
(A).
F2=I.times.B.times.L (2)
[0011] Since there is no term that stipulates the position of the
electric wire in Equation (2), the Lorentz force F2 that is
generated at a constant magnetic flux density does not vary even if
the position of the electric wire changes.
[0012] The Lorentz force can be caused to act on the movable part
in a microactuator by installed a current path corresponding to the
above-mentioned electric wire in the movable part, applying a
magnetic field to this current path, and causing a current to flow
through this current path. Even if the mobility range of the
movable part is broadened compared to that of a conventional
device, the application of a substantially uniform magnetic field
in this range can easily be accomplished, for example, by using a
magnet or the like. Accordingly, even if the mobility range of the
movable part is broadened, a constant force can be caused to act on
the movable part regardless of the position of the movable part.
Specifically, if such a Lorentz force is used instead of an
electrostatic force in a microactuator, a constant driving force
can be obtained (in principle) regardless of the position of the
movable part (unlike a case in which an electrostatic force which
shows a variation in the driving force according to the position of
the movable part is used).
[0013] For example, in the case of an inter-electrode distance of
50 .mu.m, an electrode shape of 50 .mu.m square, a voltage of 5 V
and a dielectric constant of 1, the electrostatic force F1
according to the above-mentioned Equation (1) is 0.1 nN. On the
other hand, if a current path with a length of 50 .mu.m is created
in a 50 .mu.m square electrode, and a magnetic field with a
magnetic flux density of 0.1 T is applied, a Lorentz force of 5 nN
is generated when a current of 1 mA is caused to flow. In order to
obtain a force of 5 nN or greater using an electrostatic force, the
inter-electrode distance must be set at 7 .mu.m or less, or else
the electrode shape must be set at 350 .mu.m or greater.
Accordingly, it is seen that the Lorentz force is more advantageous
for obtaining the same driving force.
[0014] Furthermore, for example, if a 20 mm square
neodymium-iron-boron-ty- pe magnet is disposed in a position that
is separated from the microactuator by a distance of 2 mm, a
magnetic flux density of 0.1 T can easily be obtained.
[0015] Thus, the use of a Lorentz force instead of an electrostatic
force in a microactuator makes it possible to broaden the mobility
range of the movable part without applying a high voltage or
sacrificing small size.
[0016] However, it has been demonstrated that a new problem arises
in cases where a Lorentz force is used instead of an electrostatic
force in a microactuator. Specifically, in cases where a Lorentz
force is used instead of an electrostatic force, the movable part
is moved to a specified position by means of this Lorentz force,
and the movable part continues to be held in this position by the
Lorentz force. Accordingly, since the current used to generate the
Lorentz force must be constantly caused to flow in a continuous
manner, the power consumption is conspicuously increased.
[0017] For instance, in the case of an application involving a
large-scale optical switch, several tens of thousands of actuators
are installed in a single optical switch device. Accordingly, there
is a strong demand for a reduction in the power consumption of the
respective actuators. For example, in the case of an optical switch
with 100.times.100 channels, it is essential that (for example) MOS
switches for selecting the channels be manufactured on a
semiconductor substrate. Assuming that the resistance of one MOS
switch is 10 k.OMEGA., then in a case where a current of 1 mA is
caused to flow continuously through this switch, the power
consumption of one MOS switch is 10 mW. In a case where the total
number of MOS switches is 10,000, the power consumption is as high
as 100 W. As a result, the amount of heat generated is excessively
large, so that there are problems in terms of practical use.
DISCLOSURE OF THE INVENTION
[0018] The present invention was devised in order to solve such
problems. The object of the present invention is to provide a
microactuator, microactuator device, optical switch and optical
switch array which can broaden the mobility range of the movable
part and reduce the power consumption without applying a high
voltage or sacrificing small size.
[0019] As a result of further research, the present inventor
discovered that the above-mentioned object can be achieved by
constructing a microactuator so that the utilization of an
electrostatic force and the utilization of a Lorentz force can be
coupled. Specifically, the present inventor discovered that the
above-mentioned object can be achieved in a microactuator which
comprises a fixed part and a movable part that is disposed so that
this movable part can move with respect to the above-mentioned
fixed part, by respectively disposing on the fixed part and movable
part electrode parts which are used in order to make it possible to
cause an electrostatic force to act on the movable part, and
disposing in the movable part a current path which is used to cause
a Lorentz force to act on the movable part.
[0020] By using such means, for example, it is possible to move the
movable part by means of a Lorentz force alone in cases where the
distance between the electrode part of the movable part and the
electrode part of the fixed part is large, and to hold the movable
part by means of an electrostatic force alone in cases where the
distance between the electrode part of the movable part and the
electrode part of the fixed part is decreased. As a result, the
mobility range of the movable part can be broadened, and the power
consumption can be reduced, without applying a high voltage or
sacrificing small size.
[0021] In the case of driving by an electrostatic force, since the
charging-discharging of a capacitor is performed electrically,
power consumption occurs only during charging and discharging,
i.e., at points in time at which there is a change in the voltage.
Accordingly, in cases where the movable part does not move
frequently, so that the period for which the movable part is held
in a specified position (a position which is such that the distance
between the electrode part of the fixed part and the electrode part
of the movable part is small) is relatively long, as in a
microactuator used in an optical switch, etc., the power
consumption can be greatly reduced if the force that is used to
hold the movable part in the specified position is generated only
by an electrostatic force. For example, in a case where the
inter-electrode capacitance is 10 pF, the voltage is 5 V and the
movement of the movable part occurs once per minute, the power
consumption of electrostatic driving is 4.2 pW. In a case where the
number of such microactuators used is 10,000, the total power
consumption of electrostatic driving is 42 nW. Furthermore, in the
case of a position where the distance between the electrode part of
the fixed part and the electrode part of the movable part is small,
an electrostatic force of a sufficient magnitude can be obtained
even if the voltage across the two electrode parts is relatively
low and the electrode surface area is relatively small.
[0022] In the case of driving by a Lorentz force, a constant
driving force can be obtained regardless of the position of the
movable part; accordingly, if the movable part is moved by means of
such a Lorentz force, the mobility range can be broadened. The
power consumption of such a Lorentz force is as follows: for
example, assuming that the resistance of the on-chip MOS switches
for selecting the channels is 10 k.OMEGA. as in the example
described above, then, in a case where a current of 1 mA is caused
to flow through this MOS switch for 10 msec each minute
(corresponding to the movement period of the movable part), the
power consumption of Lorentz force driving is 1.7 .mu.W. In a case
where the number of microactuators is 10,000, the total power
consumption of Lorentz force driving is 17 mW, so that the power
consumption is greatly reduced compared to the power consumption of
100 W that occurs in the case of the above-mentioned constant
Lorentz force driving. Almost all of the total power consumption is
accounted for by the Lorentz force; however, this is not a major
problem in practical terms.
[0023] Thus, by mounting both a device that generates an
electrostatic force and a device that generates a Lorentz force in
a microactuator, it is possible (for example) to reduce the power
consumption by generating the force that is used to hold the
movable part in a specified position by means of an electrostatic
force, and to drive the microactuator by means of a Lorentz force
in cases where the gap between the movable electrode and the fixed
electrode is large, so that the mobility range can be broadened
while preventing the application of a high voltage and an increase
in the electrode surface area.
[0024] The present invention was devised on the basis of the novel
findings obtained as a result of the above-mentioned research
conducted by the present inventor.
[0025] Specifically, the first invention that is used in order to
achieve the object is a microactuator (a) which comprises a fixed
part and a movable part that is disposed so that this movable part
can move with respect to the fixed part, (b) in which the fixed
part has a first electrode part, and (c) in which the movable part
has a second electrode part that can generate an electrostatic
force between this second electrode part and the first electrode
part by means of a voltage applied across the first electrode part
and this second electrode part, and a current path that is disposed
in a magnetic field and that generates a Lorentz force when current
is passed through this current path.
[0026] The second invention that is used in order to achieve the
object is the first invention, which is further characterized by
the fact that the movable part is constructed from a thin film.
[0027] In this invention, since the movable part is formed by a
thin film, the size and weight of the movable part can be reduced,
and the power consumption can be reduced. Furthermore, since the
movable part can be manufactured by a semiconductor process, the
manufacturing cost can be reduced, and the formation of an array is
easy.
[0028] The third invention that is used in order to achieve the
object is the first invention or second invention, which is further
characterized by the fact that the current path is disposed so that
a Lorentz force can be generated in a direction that causes the
movable part to move into a first position where the electrostatic
force is increased.
[0029] In this invention, since the Lorentz force that is required
in order to move the movable part into a position where the movable
part is held can be efficiently applied, the power consumption for
generating this Lorentz force can be reduced.
[0030] The fourth invention that is used in order to achieve the
object is the third invention, which is further characterized by
the fact that the movable part is disposed so that this movable
part can move between the first position and a second position in
which the electrostatic force drops or disappears, and so that a
returning force which tends to return the movable part to the
second position is generated.
[0031] In this invention, the movable part can move to a position
that is not reached by the electrostatic force; accordingly, the
mobility range of the movable part can be broadened. Furthermore,
since the movable part is moved by the returning force when the
movable part moves into the second position, no electric power is
required for this movement.
[0032] The fifth invention that is used in order to achieve the
object is the fourth invention, which is further characterized by
the fact that (a) the first electrode part and the second electrode
part are disposed facing each other, (b) the movable part is
mechanically connected to the fixed part via a spring part that
possesses spring properties so that the gap between the first and
second electrode parts narrows when the movable part is positioned
in the first position, and so that the gap widens when the movable
part is positioned in the second position, and (c) the returning
force is generated by the spring part.
[0033] In this invention as well, the movable part can move to a
position that is not reached by the electrostatic force;
accordingly, the mobility range of the movable part can be
broadened. Furthermore, since the movable part is moved by the
returning force when the movable part moves into the second
position, no electric power is required for this movement.
[0034] The sixth invention that is used in order to achieve the
object is the first invention or second invention, wherein the
fixed part has a third electrode part, and the movable part has a
fourth electrode part that can generate an electrostatic force
between this fourth electrode part and the third electrode part by
means of a voltage applied across this fourth electrode part and
the third electrode part.
[0035] In this invention, the mobility range of the movable part
can be further broadened.
[0036] The seventh invention that is used to achieve the object is
the sixth invention, which is further characterized by the fact
that the second electrode part is also used as the fourth electrode
part.
[0037] In this invention, since the construction is simple, the
weight of the movable part can be reduced; furthermore, since the
number of manufacturing processes required is also reduced, the
manufacturing cost can be reduced.
[0038] The eighth invention that is used to achieve the object is
the sixth invention or seventh invention, which is further
characterized by the fact that the current path is disposed so that
a Lorentz force can be generated in respective directions which are
such that the movable part is respectively moved into a first
position where the electrostatic force that is generated between
the first and second electrode parts is increased, and the
electrostatic force that is generated between the third and fourth
electrode parts drops or disappears, and a second position where
the electrostatic force that is generated between the first and
second electrode parts drops or disappears, and the electrostatic
force that is generated between the third and fourth electrode
parts increases.
[0039] In this invention, since the Lorentz force that is required
in order to move the movable part into a position where the movable
part is held can be efficiently applied, the power consumption that
is required in order to generate this Lorentz force can be
reduced.
[0040] The ninth invention that is used in order to achieve the
object is the eighth invention, which is further characterized by
the fact that the movable part is disposed so that a returning
force that tends to return the movable part to a specified position
between the first and second positions is generated.
[0041] In this invention, since the movable part is moved by the
returning force when the movable part moves into the specified
position, no electric power is required for this movement.
[0042] The tenth invention that is used in order to achieve the
object is the ninth invention, which is further characterized by
the fact that (a) the first electrode part is disposed facing the
second electrode part on one side with respect to the movable part,
(b) the third electrode part is disposed facing the fourth
electrode part on the other side with respect to the movable part,
(c) the movable part is mechanically connected to the fixed part
via a spring part that possesses spring properties so that a first
gap between the first and second electrode parts narrows and a
second gap between the third and fourth electrode parts widens when
the movable part is positioned in the first position, and so that
the first gap widens and the second gap narrows when the movable
part is positioned in the second position, and (d) the returning
force is generated by the spring part.
[0043] In this invention as well, since the movable part is moved
by the returning force when the movable part moves into the
specified position, no electric power is required for this
movement.
[0044] The eleventh invention that is used in order to achieve the
object is a microactuator device which is characterized by the fact
that this device comprises the microactuator of any of the first
through fifth inventions, a magnetic field generating part that
generates the magnetic field, and a control part that controls the
voltage that is applied across the first and second electrode parts
and the current that flows through the current path.
[0045] In this invention, the magnitude of the Lorentz force and
the timing of the generation of this Lorentz force can be
controlled; accordingly, the microactuator can be driven under
appropriate conditions.
[0046] The twelfth invention that is used in order to achieve the
object is the eleventh invention, which is further characterized by
the fact that (a) the control part controls the voltage and the
current so that the movable part is caused to move into the first
position by the Lorentz force or by the Lorentz force and the
electrostatic force when the movable part is moved into the first
position, and (b) the control part controls the voltage so that the
movable part is held in the first position by the electrostatic
force, and controls the current so that this current does not flow,
at least in a steady holding state in which the movable part is
held in the first position.
[0047] In this invention, electric power that is used to generate
the Lorentz force is required only when the movable part is moved
into the first position; since only an electrostatic force is
utilized in order to hold the movable part in the first position,
the power consumption required for holding can be reduced.
[0048] The thirteenth invention that is used in order to achieve
the object is a microactuator device which is characterized by the
fact that this device comprises the microactuator of any of the
sixth through tenth inventions, a magnetic field generating part
that generates the magnetic field, and a control part that controls
the voltage that is applied across the first and second electrode
parts, the voltage that is applied across the third and fourth
electrode parts, and the current that flows through the current
path.
[0049] In this invention, the magnitude of the Lorentz force and
the timing of the generation of this Lorentz force can be
controlled; accordingly, the microactuator can be driven under
appropriate conditions.
[0050] The fourteenth invention that is used in order to achieve
the object is the thirteenth invention, which is further
characterized by the fact that (a) the control part controls the
voltage that is applied across the first and second electrode
parts, the voltage that is applied across the third and fourth
electrode parts and the current that flows through the current path
so that the movable part is caused to move into the first position
by the Lorentz force or by the Lorentz force and the electrostatic
force between the first and second electrode parts when the movable
part is moved into the first position, (b) the control part
controls the voltage that is applied across the first and second
electrode parts, the voltage that is applied across the third and
fourth electrode parts and the current that flows through the
current path so that the movable part is caused to move into the
second position by the Lorentz force or by the Lorentz force and
the electrostatic force between the third and fourth electrode
parts when the movable part is moved into the second position, (c)
the control part controls the voltage that is applied across the
first and second electrode parts and the voltage that is applied
across the third and fourth electrode parts so that the movable
part is held in the first position by the electrostatic force
between the first and second electrode parts, and controls the
current so that this current does not flow, at least in a steady
holding state in which the movable part is held in the first
position, and (d) the control part controls the voltage that is
applied across the first and second electrode parts and the voltage
that is applied across the third and fourth electrode parts so that
the movable part is held in the second position by the
electrostatic force between the third and fourth electrode parts,
and controls the current so that this current does not flow, at
least in a steady holding state in which the movable part is held
in the second position.
[0051] In this invention, electric power that is used to generate
the Lorentz force is required only when the movable part is moved
into the first position; since only an electrostatic force is
utilized in order to hold the movable part in the first position,
the power consumption required for holding can be reduced.
[0052] The fifteenth invention that is used in order to achieve the
object is an optical switch which is characterized by the fact that
this optical switch comprises the microactuator of any of the first
through tenth inventions, and a mirror which is disposed on the
movable part.
[0053] The sixteenth invention that is used in order to achieve the
object is an optical switch array which is characterized by the
fact that this optical switch array comprises a plurality of the
optical switches that constitute the fifteenth invention, and said
plurality of optical switches are disposed in a two-dimensional
configuration.
[0054] The seventeenth invention that is used in order to achieve
the object is the sixteenth invention, which is further
characterized by the fact that this optical switch array comprises
a circuit which contains a plurality of switching elements, and
which controls the current and the voltage for optical switches in
selected rows and columns in response to row selection signals for
each row of the plurality of optical switches and column selection
signals for each column of the plurality of optical switches.
BRIEF DESCRIPTION OF THE DRAWINGS
[0055] FIG. 1 is a schematic structural diagram which shows one
example of an optical switch system comprising an optical switch
array that constitutes a first working configuration of the present
invention.
[0056] FIG. 2 is a schematic plan view which shows one of the
optical switches constituting the optical switch array shown in
FIG. 1.
[0057] FIG. 3 is a schematic sectional view along line X1-X2 in
FIG. 2.
[0058] FIG. 4 is a schematic sectional view along line Y1-Y2 in
FIG. 2.
[0059] FIG. 5 is a schematic sectional view corresponding to FIG.
3.
[0060] FIG. 6 is a timing chart which shows the relationship
(varying over time) of the current used for the Lorentz force, the
voltage used for the electrostatic force and the position of the
mirror in one of the optical switches constituting the optical
switch array shown in FIG. 1.
[0061] FIG. 7 is an electrical circuit diagram which shows the
optical switch array shown in FIG. 1.
[0062] FIG. 8 is a timing chart which shows the signals that are
supplied to the respective terminals in FIG. 7.
[0063] FIG. 9 is a schematic sectional view which shows in model
form the respective processes of the optical switch array shown in
FIG. 1.
[0064] FIG. 10 is a schematic sectional view which shows in model
form other respective processes of the optical switch array shown
in FIG. 1.
[0065] FIG. 11 is a schematic plan view which shows one of the
optical switches constituting an optical switch array that
constitutes a second working configuration of the present
invention.
[0066] FIG. 12 is a schematic sectional view along line X3-X4 in
FIG. 11.
[0067] FIG. 13 is a schematic sectional view along line Y3-Y4 in
FIG. 11.
[0068] FIG. 14 is a schematic sectional view corresponding to FIG.
12.
[0069] FIG. 15 is another schematic sectional view corresponding to
FIG. 12.
[0070] FIG. 16 is a timing chart which shows the relationship
(varying over time) of the current used for the Lorentz force, the
voltage used for the electrostatic force and the position of the
mirror in one of the optical switches shown in FIG. 11.
[0071] FIG. 17 is an electrical circuit diagram which shows the
optical switch array constituting a second working configuration of
the present invention.
[0072] FIG. 18 is a timing chart which shows the signals that are
supplied to the respective terminals in FIG. 17.
BEST MODE FOR CARRYING OUT THE INVENTION
[0073] Microactuators constituting working configurations of the
present invention, as well as microactuator devices, optical
switches and optical switch arrays using these microactuators, will
be described below with reference to the figures.
[0074] [First Working Configuration]
[0075] FIG. 1 is a schematic structural diagram which shows one
example of an optical switch system comprising an optical switch
array 1 that constitutes a first working configuration of the
present invention. For convenience of description, X, Y and Z axes
that are mutually perpendicular are defined as shown in FIG. 1 (the
same is true of figures described later). The surface of the
substrate 11 of the optical switch array 1 is parallel to the XY
plane. Furthermore, for convenience of description, the + side in
the direction of the Z axis is referred to as the upper side, and
the - side in the direction of the Z axis is referred to as the
lower side.
[0076] As is shown in FIG. 1, this optical switch system comprises
an optical switch array 1, M optical fibers 2 used for light input,
M optical fibers 3 used for light output, N optical fibers 4 used
for light output, a magnet 5 used as a magnetic field generating
part that generates a magnetic field (as will be described later)
for the optical switch array 1, and an external control circuit 6
which sends control signals used to realize light path switching
states indicated by light path switching state command signals to
the optical switch array 1 in response to these light path
switching state command signals. In the example shown in FIG. 1,
M=3 and N=3; however, M and N may respectively be arbitrary
numbers.
[0077] In the present working configuration, as is shown in FIG. 1,
the magnet 5 is a plate-form permanent magnet which is magnetized
so that the + side in the direction of the Y axis is the N pole,
and the - side in the direction of the Y axis is the S pole. This
magnet 5 is disposed on the underside of the optical switch array
1, and generates a magnetic field indicated by the lines of
magnetic force 5a for the optical switch array 1. Specifically, the
magnet 5 generates a substantially uniform magnetic field which is
oriented toward the - side along the direction of the Y axis with
respect to the optical switch array 1. Of course, it would also be
possible to use (for example) a permanent magnet of some other
shape or an electromagnet, etc., as the magnetic field generating
part instead of the magnet 5.
[0078] As is shown in FIG. 1, the optical switch array 1 comprises
a substrate 11 and M.times.N mirrors 12 which are disposed on the
substrate 11. The M optical fibers 2 used for light input are
disposed in a plane parallel to the XY plane so that these optical
fibers guide incident light in the direction of the X axis from one
side of the substrate 11 in the direction of the X axis. The M
optical fibers 3 used for light output are disposed on the other
side of the substrate 11 so that these optical fibers respectively
face the M optical fibers 2 used for light input, and are disposed
in a plane parallel to the XY plane so that light that advances in
the direction of the X axis without being reflected by any of the
mirrors 12 of the optical switch array 1 is incident on these
optical fibers. The N optical fibers 4 used for light output are
disposed in a plane parallel to the XY plane so that light that is
reflected by any of the mirrors 12 of the optical switch array 1
and that therefore advances in the direction of the Y axis is
incident on these optical fibers. The M.times.N mirrors 12 are
disposed on the substrate 11 in the form of a two-dimensional
matrix so that these mirrors can be moved rectilinearly in the
direction of the Z axis by microactuators (described later) in a
manner that allows the mirrors to advance into and withdraw from
the respective intersection points between the exit light paths of
the M optical fibers 2 used for light input and the entry light
paths of the optical fibers 4 used for light output. In the present
example, furthermore, the orientation of the mirrors 12 is set so
that the normal of these mirrors forms a 45.degree. angle with the
X axis in the plane parallel to the XY plane. Of course, this angle
may be appropriately altered, and in cases where the angle of the
mirrors 12 is altered, the orientation of the optical fibers 4 used
for light output may be set in accordance with this angle.
Furthermore, in this example, the mechanism that drives the mirrors
12 is a micro actuator.
[0079] In this optical switch system, the light path switching
principle itself is the same as the light path switching principle
of a conventional two-dimensional optical switch.
[0080] Next, the structure of one of the optical switches used as a
unit element in the optical switch array 1 shown in FIG. 1 will be
described with reference to FIGS. 2 through 5. FIG. 2 is a
schematic plan view which shows one optical switch. FIG. 3 is a
schematic sectional view along line X1-X2 in FIG. 2. FIG. 4 is a
schematic sectional view along line Y1-Y2 in FIG. 2. FIG. 5 is a
schematic sectional view corresponding to FIG. 3, and shows a state
in which the mirror 12 is held on the lower side. Furthermore, FIG.
3 shows a state in which the mirror 12 is held on the upper
side.
[0081] Besides the above-mentioned mirror 12 and the
above-mentioned substrate 11 used as a fixed part, this optical
switch comprises a movable plate 21 used as a movable part which is
disposed so that this part can move with respect to the substrate
11. A recessed part 13 constituting a region into which the movable
plate 21 advances is formed on the substrate 11. In the present
working configuration, a semiconductor substrate such as a silicon
substrate is used as the substrate 11, and the portion of the
substrate 11 that faces the movable plate 21 constitutes a first
electrode part. Of course, it would also be possible to form a
first electrode part separately from the substrate 11 by means of a
metal film, etc., on the substrate 11.
[0082] The movable plate 21 is formed by a thin film, and comprises
a lower-side insulating film 22, two second electrode parts 23a and
23b which are formed on the lower-side insulating film 22, portions
of wiring patterns 24a and 24b which are formed on the lower-side
insulating film 22 and which are respectively used for the
electrical connection of the electrode parts 23a and 23b to
specified locations on the substrate 11, a coil layer 25 which is
formed on the lower-side insulating film 22 and which is used as a
current path that is disposed in the magnetic field generated by
the magnet 5 shown in FIG. 1 and that generates a Lorentz force
when a current is passed through this coil layer, and an upper-side
insulating film 26 which covers the upper sides of the
above-mentioned elements. The second electrode parts 23a and 23b
can generate an electrostatic force between these electrode parts
23a and 23b and the substrate 11 (which constitutes the
above-mentioned first electrode part) by means of a voltage that is
applied across these electrode parts and the substrate 11.
[0083] For example, SiN films or SiO.sub.2 films, etc., can be used
as the insulating films 22 and 26. Furthermore, for example, metal
films, etc., such as Al films can be used as the electrode parts
23a and 23b, wiring patterns 24a and 24b and coil layer 25.
Furthermore, since the electrode parts 23a and 23b, portions of the
wiring patterns 24a and 24b and coil layer 25 are covered by the
upperside insulating film 26, these parts should actually be shown
by hidden lines in FIG. 2; however, for convenience of graphic
illustration, the parts hidden by the upper-side insulating film 26
are also indicated by solid lines. However, the portion of the coil
layer 25 that is hidden by the mirror 12 is indicated by hidden
lines.
[0084] In the present working configuration, both end portions of
the movable plate 21 in the direction of the X axis are
mechanically connected to the peripheral parts of the recessed part
13 in the substrate 11 via flexure parts 27a and 27b used as spring
parts that have spring properties, and anchoring parts 28a and 28b,
in that order. The flexure parts 27a and 27b and anchoring parts
28a and 28b are constructed by the lower-side insulating film 22,
the remaining portions of the above-described wiring patterns 24a
and 24b, wiring patterns 29a and 29b that are respectively used for
the electrical connection of the coil layer 25 to specified
locations on the substrate 11, and the upper-side insulating film
26, all of which extend "as is" as continuations of the movable
plate 21. Furthermore, the wiring patterns 29a and 29b extend "as
is" as continuations of the metal film, etc., constituting the coil
layer 25. In the anchoring parts 28a and 28b, the wiring patterns
24a, 24b, 29a and 29b are respectively electrically connected to
specified locations on the substrate 11 via holes (not shown in the
figures) formed in the lower-side insulating film 22. The wiring
patterns 24a and 24b are electrically connected in common by wiring
(not shown in the figures) formed on the substrate 11.
[0085] As is shown in FIG. 2, the flexure parts 27a and 27b have a
meandering shape as seen in a plan view. As a result, the movable
plate 21 can move upward and downward (in the direction of the Z
axis). Specifically, in the present working configuration, the
movable plate 21 can move between an upper position (second
position) (see FIGS. 3 and 4) to which the movable plate 21 is
returned by spring force (returning force) of the flexure parts 27a
and 27b when no electrostatic force or Lorentz force is acting on
the movable plate 21, and a lower position (first position) (see
FIG. 5) in which the movable plate 21 advances into the recessed
part 13 of the substrate 11 and contacts the bottom part of this
recessed part 13. In the upper position shown in FIGS. 3 and 4, the
gap between the second electrode parts 23a and 23b of the movable
plate 21 and the substrate 11 used as the first electrode part is
widened, so that the electrostatic force that can be generated
between these parts drops or disappears. In the lower position
shown in FIG. 5, the gap between the second electrode parts 23a and
23b of the movable plate 21 and the substrate 11 used as the first
electrode part is narrowed, so that the electrostatic force that
can be generated between these parts is increased.
[0086] The coil layer 25 is disposed so that a Lorentz force can be
generated in a direction (downward direction) that causes the
movable plate 21 to move into the lower position shown in FIG. 5,
where the above-mentioned electrostatic force is increased. In
concrete terms, in the present working configuration, since a
magnetic field which is oriented toward the - side is generated
along the direction of the Y axis by the magnet 5 shown in FIG. 1
as described above, the coil layer 25 is disposed so that this
layer extends along the direction of the X axis as shown in FIG.
1.
[0087] The mirror 12 is fastened to the upper surface of the
movable plate 21 in an upright attitude. As was described above,
the orientation of the reflective surface of the mirror 12 is set
so that the normal of this reflective surface forms an angle of
45.degree. with the X axis in the plane parallel to the XY
plane.
[0088] A microactuator which drives the mirror 12 is formed by the
constituent elements other than the mirror 12 in the structure of
the above-mentioned optical switch.
[0089] Next, one example of the control method used, and the
operation of the optical switch accomplished by this control
method, will be described with reference to FIG. 6, with a focus on
a single optical switch. FIG. 6 is a timing chart which shows the
relationship (varying over time) of the current that flows through
the coil layer 25 of one optical switch and gives rise to a Lorentz
force (hereafter referred to as the "current used for the Lorentz
force"), the voltage that is applied across the first electrode
part (substrate 11) of this optical switch and the second electrode
parts 23a and 23b of the movable plate 21, and that gives rise to
an electrostatic force between these parts (hereafter referred to
as the "voltage used for the electrostatic force"), and the
position of the mirror 12 of this optical switch (and accordingly,
the position of the movable plate 21).
[0090] Initially, it is assumed that the current used for the
Lorentz force is zero and that the voltage used for the
electrostatic force is zero, so that the mirror 12 is held in the
upper position as shown in FIGS. 3 and 4 by the spring force of the
flexure parts 27a and 27b. In this state, as is shown in FIG. 3,
the incident light is reflected by the mirror 12 and advances
toward the front with respect to the plane of the page.
[0091] Afterward, at time T1, control is initiated in order to
switch the position of the mirror 12 to the lower position shown in
FIG. 5. Specifically, at time T1, the current used for the Lorentz
force is set at +I. Here, +I is a current that generates a
downward-oriented Lorentz force in the coil layer 25 that is
stronger than the spring force of the flexure parts 27a and
27b.
[0092] The mirror 12 is gradually lowered by this Lorentz force,
and stops at time T2 at which the movable plate 21 contacts the
substrate 11, so that the mirror 12 is held in the lower position
shown in FIG. 5.
[0093] The mirror 12 does not continue to be held in the lower
position by the Lorentz force "as is"; at time T3, the voltage used
for the electrostatic force is set at V, and at time T4, the
current used for the Lorentz force is reduced to zero. Here, V is a
voltage that generates an electrostatic force that is stronger than
the spring force of the flexure parts 27a and 27b, at least when
the mirror 12 is positioned in the lower position. In the period
T2-T3, the mirror 12 is held in the lower position by the Lorentz
force alone; in the period T3-T4, the mirror 12 is held in the
lower position by the Lorentz force and the electrostatic force,
and from time T4 on, the mirror 12 is held in the lower position by
the electrostatic force alone. The period T2-T4 is a so-called
lower-side holding transition period in which the holding of the
mirror 12 in the lower position is switched from the Lorentz force
to the electrostatic force, while the period from time T4 on is a
so-called steady period of lower-side holding.
[0094] During the period in which the mirror 12 is held in the
lower position, as is shown in FIG. 5, the incident light passes
through "as is" without being reflected by the mirror 12, and
constitutes the emitted light.
[0095] Subsequently, at time T5, control is initiated in order to
switch the position of the mirror 12 to the upper position shown in
FIGS. 3 and 4. Specifically, at time T5, the voltage used for the
electrostatic force is reduced to zero. As a result, the mirror 12
is returned to the upper position shown in FIGS. 3 and 4 relatively
quickly by the spring force of the flexure parts 27a and 27b, and
continues to be held in the upper position by this spring
force.
[0096] Thus, when the gap between the second electrode parts 23a
and 23b of the movable plate 21 and the substrate 11 (first
electrode part) is large, the mirror 12 is moved into the lower
position against the spring force of the flexure parts 27a and 27b
by a Lorentz force whose magnitude does not depend on the position
of the mirror 12 (i.e., the position of the movable plate 21).
Accordingly, the mobility range of the movable plate 21 can be
broadened without applying a high voltage or sacrificing small size
in order to increase the electrostatic force. Furthermore, in the
steady state of holding in the lower position, where the gap
between the second electrode parts 23a and 23b of the movable plate
21 and the substrate 11 (first electrode part) narrows, the mirror
12 is held in the lower position by the electrostatic force alone;
accordingly, the power consumption can be reduced.
[0097] Furthermore, in the example described above, the voltage
used for the electrostatic force is set at V at time T3 between
time T2 and time T4; however, the voltage used for the
electrostatic force may be set at V at any point in time during the
period T1-T4, or the voltage used for the electrostatic force may
be set at V prior to time T1. Moreover, if the electrostatic force
that is generated when the voltage used for the electrostatic force
is set at V is smaller than the spring force of the flexure parts
27a and 27b when the movable plate 21 is positioned in the upper
position, then the voltage used for the electrostatic force may
also be set at V during the upper-side holding period after the
movable plate 21 has moved into the upper position following time
T5. The voltage refresh period on the right side in the example
shown in FIG. 8 (described later) corresponds to such a case.
[0098] The optical switch array 1 shown in FIG. 1 has a plurality
of optical switches of the type shown in FIGS. 2 through 5 as the
above-mentioned unit elements; these optical switches are disposed
in a two-dimensional matrix. Furthermore, the circuit shown in FIG.
7, which contains a plurality of switching elements, is mounted on
the optical switch array 1 shown in FIG. 1 in order to realize the
above-mentioned control for each of these optical switches using a
small number of control lines. FIG. 7 is an electrical circuit
diagram which shows the optical switch array 1.
[0099] In FIG. 7, nine optical switches are disposed in three rows
and three columns in order to simplify the description. Of course,
there are no restrictions on these numbers; for example, the
principle is the same in a case where there are optical switches
disposed in 100 rows and 100 columns.
[0100] In terms of the electrical circuit involved, the single
optical switch shown in FIGS. 2 through 5 may be viewed as a single
capacitor (corresponding to a composite capacitor in which a
capacitor formed by the second electrode 23a and first electrode
(substrate 11) and a capacitor formed by the second electrode 23b
and first electrode (substrate 11) are connected in parallel), and
a single coil (corresponding to the coil layer 25). In FIG. 7, the
capacitors and coils of the optical switches in m rows and n
columns are respectively designated as Cmn and Lmn. For example,
the capacitor and coil of the optical switch at the upper left
(first row, first column) in FIG. 7 are respectively designated as
C11 and L11.
[0101] In the circuit shown in FIG. 7, in order to reduce the
number of control lines, column selection switches Mmnb and Mmnd
and row selection switches Mmna and Mmnc are respectively provided
for the capacitors Cmn and coils Lmn. One end of each capacitor Cmn
is connected to one end of the corresponding row selection switch
Mmna, the other end of this row selection switch Mmna is connected
to one end of the corresponding column selection switch Mmnb, and
the other end of this column selection switch Mmnb is connected to
one end of a voltage control switch MC1 and one end of a voltage
control switch MC2. The other end of each capacitor Cmn is
connected to ground. The other end of the voltage control switch
MC1 is connected to a clamping voltage VC, and the other end of the
voltage control switch MC2 is connected to ground.
[0102] Furthermore, one end of each coil Lmn is connected to one
end of the corresponding row selection switch Mmnc, the other end
of this row selection switch Mmnc is connected to one end of the
corresponding column selection switch Mmnd, and the other end of
this column selection switch Mmnd is connected to one end of a
current control switch MC3. The other end of each coil Lmn is
connected to ground. The other end of the current control switch
MC3 is connected to one end of a current source I1 that supplies
the above-mentioned current +I, and the other end of the current
source I1 is connected to ground.
[0103] The column selection switches Mmnb and Mmnd, row selection
switches Mmna and Mmnc, voltage control switches MC1 and MC2 and
current control switch MC3 used as switching elements can be
constructed from (for example) N-type MOS transistors formed on the
substrate 11 in cases where a silicon substrate is used as the
substrate 11.
[0104] The gates of the row selection switches M11a, M11c, M12a,
M12c, M13a and M13c of the first row are connected to a terminal
V1. Similarly, the gates of the row selection switches of the
second row are connected to a terminal V2, and the gates of the row
selection switches of the third row are connected to a terminal
V3.
[0105] The gates of the column selection switches M11b, M11d, M21b,
M21d, M31b and M31d of the first column are connected to a terminal
H1. Similarly, the gates of the column selection switches of the
second column are connected to a terminal H2, and the gates of the
column selection switches of the third column are connected to a
terminal H3.
[0106] Next, one example of a timing chart of the voltages that are
applied to the respective terminals V1, V2, V3, H1, H2, H3, C1, C2
and C3 is shown in FIG. 8. In FIG. 8, the time period prior to time
t1 is a voltage refresh period in which the capacitors Cmn of all
of the optical switches are biased to a clamping voltage VC.
Accordingly, during this period, the terminals V1, V2, V3, H1, H2
and H3 are all at a high level, and all of the column selection
switches Mmnb and Mmnd and row selection switches Mmna and Mmnc are
in a conductive state. Furthermore, during this period, the
terminal C1 is at a high level, and the terminal C2 is at a low
level, so that the voltage control switch MC1 is in a conductive
state, and the voltage control switch MC2 is in a non-conductive
state. Furthermore, the terminal C3 is at a low level, so that the
current control switch MC3 is in a non-conductive state. During the
voltage refresh period, the mirrors 12 are held in either the upper
position or the lower position. In the example shown in FIG. 8, the
mirrors 12 are held in the lower position during the voltage
refresh period prior to time t1.
[0107] Incidentally, in the present working configuration, the
signals (voltages) that are applied to the terminals V1, V2, V3,
H1, H2, H3, C1, C2 and C3 are supplied as control signals from the
external control circuit 6 shown in FIG. 1. For example, the
external control circuit 6 investigates optical switches whose
position state is to be altered from the current position state on
the basis of light path switching state command signals, and
successively sets state alteration periods one at a time for each
of the optical switches whose state is to be altered. In cases
where there are no optical switches whose position state is to be
altered from the current position state, the above-mentioned
voltage refresh period is set. Furthermore, in cases where a
plurality of state alteration periods are set (that is, in cases
where the number of optical switches whose position state is to be
altered from the current position state is two or greater), voltage
refresh periods may be set between the respective state alteration
periods, or such voltage refresh periods may be omitted. For
example, in a case where the number of optical switches whose
position state is to be altered from the current position state is
three, a sequence of state alteration period.fwdarw.voltage refresh
period.fwdarw.state alteration period.fwdarw.voltage refresh
period.fwdarw.state alteration period may be set, or state
alteration periods may be continuously set. Furthermore, in the
respective set state alteration periods, signals that are applied
to the terminals V1, V2, V3, H1, H2, H3, C1, C2 and C3 are supplied
so that the above-mentioned control shown in FIG. 6 is realized in
accordance with the commanded light path switching states for the
corresponding optical switches. Moreover, it goes without saying
that the external control circuit 6 may also be mounted on the
optical switch array 1.
[0108] FIG. 8 shows an example in which a sequence of voltage
refresh period.fwdarw.state alteration period for the optical
switch of row 1 column 1.fwdarw.voltage refresh period is set by
the external control circuit 6. In the example shown in FIG. 8, the
mirrors 12 are held in the lower position during the voltage
refresh period prior to time t1. At time t1, a state alteration
period for the optical switch of row 1 column 1 is initiated, and
the terminals V2, V3, H2 and H3 are placed at a low level, so that
the capacitors other than the capacitor C11 are isolated. Next, at
time t3, the terminal C2 is placed at a high level, so that the
charge of C11 is discharged, and the voltage used for the
electrostatic force is reduced to zero. This time t3 corresponds to
time T5 in FIG. 6. As a result, the electrostatic force is
eliminated, so that the mirror 12 moves to the upper position shown
in FIGS. 3 and 5, and is held in this position. Next, at time t4,
the terminal C2 is placed at a low level, and at time t5, the
terminal C1 is placed at a high level. Subsequently, at time t6,
this state alteration period is ended, and a voltage refresh period
is initiated.
[0109] During the period extending from time t1 to time t6, the
holding of the mirrors 12 of the optical switches other than the
optical switch of row 1 column 1 in the lower position is
accomplished by the voltage that is generated by the charges
remaining in the respective capacitors. Accordingly, it is
desirable that the respective capacitors be manufactured so that
there is little charge leakage when the MOS switches are in a
non-conductive state.
[0110] Next, one example of the method used to manufacture the
optical switch array 1 constituting the present working
configuration will be described with reference to FIGS. 9 and 10.
The respective diagrams shown in FIGS. 9 and 10 are schematic
sectional views that illustrate this manufacturing process in model
form, and correspond to FIG. 4.
[0111] First, MOS transistors (not shown in the figures) that
constitute the switches Mmna, Mmnb, Mmnc, Mmnd, MC1, MC2 and MC3
shown in FIG. 7 are formed by an ordinary MOS process on a silicon
substrate 31 that is to form the above-mentioned substrate 11.
Furthermore, the wiring (not shown in the figures) that is
necessary in order to realize the circuit shown in FIG. 7 is formed
on the silicon substrate 31. An SiO.sub.2 film 32 is formed on the
surface of the substrate 31 in this state. Next, an SiN film 33
that is to form the lower-side insulating film 22 is formed on top
of the SiO.sub.2 film 32. Furthermore, holes used for connection
are formed by a photo-etching method in the SiO.sub.2 film 32 and
SiN film 33 in locations where the wiring patterns 24a, 24b, 29a
and 29b are to be connected to the MOS transistors formed on the
substrate 31. An A1 film 34 that is to form the electrode parts 23a
and 23b, wiring patterns 24a, 24b, 29a and 29b and coil layer 25 is
formed by a vapor deposition method, etc., on the substrate 31 in
this state; this film is then patterned to form the shapes of these
parts. Afterward, an SiN film 35 that is to form the upper-side
insulating film 26 is formed, and the SiN films 33 and 35 are
patterned into the shapes of the movable plate 21, flexure parts
27a and 27b and anchoring parts 28a and 28b by a photo-etching
method (FIG. 9(a)).
[0112] Next, an SiO.sub.2 film 36 is formed on the substrate 31 in
the state shown in FIG. 9(a). Then, this film 36 is removed in the
location where the mirror 12 is to be formed in the SiO.sub.2 film
36, and the SiO.sub.2 films 32 and 36 are removed in the locations
where etching holes are to be formed in the SiO.sub.2 films 32 and
36 (FIG. 9(b)).
[0113] Next, the substrate in the state shown in FIG. 9(b) is
thickly coated with a resist 37. Here, the resist 37 is exposed and
developed so that a region where the mirror 12 is grown is formed
in the resist 37 (FIG. 9(c)). Subsequently, Au, Ni or some other
metal 38 that is to form the mirror 12 is grown by electroplating
(FIG. 10(a)).
[0114] Next, after the resist 37 has been removed, a KOH solution
is injected via the etching holes, and portions of the substrate 31
are removed (FIG. 10(b)). Finally, the remaining SiO.sub.2 films 32
and 36 are removed. As a result, the optical switch array 1 of the
present working configuration is completed.
[0115] [Second Working Configuration]
[0116] FIG. 11 is a schematic plan view which shows one optical
switch used as a unit element in an optical switch array
constituting a second working configuration of the present
invention. In FIG. 11, the upper electrode part 41 should actually
be indicated by a solid line; however, in order to facilitate
understanding, this electrode part 41 is indicated by an imaginary
line. FIG. 12 is a schematic sectional view along line X3-X4 in
FIG. 11. FIG. 13 is a schematic sectional view along line Y3-Y4 in
FIG. 11. FIG. 14 is a schematic sectional view corresponding to
FIG. 12, and shows a state in which the mirror 12 is held in the
upper position. FIG. 15 is a schematic sectional view corresponding
to FIG. 12, and shows a state in which the mirror 12 is held in the
lower position. Furthermore, like the above-mentioned FIGS. 3 and
4, FIGS. 12 and 13 show a state in which the movable plate 21 is
positioned in the position to which this movable plate 21 is
returned by the spring force (returning force) of the flexure parts
27a and 27b when no electrostatic force or Lorentz force acts on
the movable plate 21; in the present working configuration, this
position is called the neutral position.
[0117] In FIGS. 11 through 15, element that are the same as
elements in FIGS. 1 through 5 or that correspond to such elements
are labeled with the same symbols, and a redundant description is
omitted.
[0118] The optical switch array of the present working
configuration can be used instead of the optical switch array 1 in
the optical switch system shown in FIG. 1. The optical switch array
of the present working configuration differs from the optical
switch array 1 shown in FIG. 1 in that an upper electrode part
(third electrode part) 41 that is disposed above the movable plate
21 is added in the single optical switches that are used as unit
elements.
[0119] The upper electrode part 41 is formed using polysilicon as
the material of this part. In FIGS. 11 through 15, 42a and 42b
indicate upper electrode anchoring parts, 43a and 43b indicate
rising parts, and 44 indicates a through-hole that is formed in the
central portion of the upper electrode part 41. The upper electrode
part 41 is constructed as an integral unit with the rising parts
43a and 43b and upper electrode anchoring parts 42a and 42b, and is
mechanically connected to the peripheral portions of the recessed
part 13 in the substrate 11 via the rising parts 43a and 43b and
upper electrode anchoring parts 42a and 42b in that order. Thus,
since the upper electrode part 41 is fastened to the substrate 11,
the upper electrode part 41 constitutes a fixed part together with
the substrate 11.
[0120] In the present working configuration, the electrode parts
23a and 23b of the movable plate 21 act not only as second
electrode parts that are capable of generating an electrostatic
force between these electrode parts and the first electrode part
(substrate 11), but also as fourth electrode parts that are capable
of generating an electrostatic force between these electrode parts
and the upper electrode part (third electrode part) 41. Of course,
instead of such a combined use, it would also be possible (for
example) to form a metal film, etc., constituting such a fourth
electrode part on top of the insulating film 26 in the movable
plate 21, and to form a further insulating film on top of this
fourth electrode part.
[0121] Furthermore, in the present working configuration, the
movable plate 21 is devised so that this movable plate can move
between an upper position (second position) (see FIG. 14) in which
the movable plate 21 moves upward from the above-mentioned neutral
position and contacts the upper electrode part 41, and a lower
position (first position) (see FIG. 15) in which the movable plate
21 advances into the recessed part 13 of the substrate 11, and
contacts the bottom part of this recessed part. In the upper
position shown in FIG. 14, the gap between the second electrode
parts 23a and 23b of the movable plate 21 and the substrate 11 used
as a first electrode part is widened, so that the electrostatic
force that can be generated between these electrode parts drops or
disappears, and the gap between the second electrode parts 23a and
23b of the movable plate 21 and the upper electrode part (third
electrode part) 41 is narrowed, so that the electrostatic force
that can be generated between these electrode parts is increased.
On the other hand, in the lower position shown in FIG. 15, the gap
between the second electrode parts 23a and 23b of the movable plate
21 and the substrate 11 used as a first electrode part is narrowed,
so that the electrostatic force that can be generated between these
electrode parts is increased, and the gap between the second
electrode parts 23a and 23b of the movable plate 21 and the upper
electrode part (third electrode part) 41 is widened, so that the
electrostatic force that can be generated between these electrode
parts drops or disappears.
[0122] In the present working configuration, the first electrode
part (substrate 11) and the upper electrode part 41 used as a third
electrode part are electrically connected in common. As a result,
with reference to the second electrode parts 23a and 23b of the
movable plate 21, the same voltage is simultaneously applied across
the second electrode parts 23a and 23b of the movable plate 21 and
the first electrode part (substrate 11), and across the second
electrode parts 23a and 23b of the movable plate 21 and the upper
electrode part 41 used as a third electrode part. Of course, it
would also be possible to devise the system so that the first
electrode part (substrate I1) and upper electrode part 41 used as a
third electrode part are not electrically connected, and so that
voltages can be applied independently across the second electrode
parts 23a and 23b of the movable plate 21 and the first electrode
part (substrate 11), and across the second electrode parts 23a and
23b of the movable plate 21 and the upper electrode part 41 used as
a third electrode part.
[0123] Furthermore, a microactuator which drives the mirror 12 is
formed by the constituent elements other than the mirror 12 in the
structure of the optical switch shown in FIGS. 11 through 15.
[0124] Next, one example of the control method used in the present
working configuration, and the operation of the optical switch
accomplished by this control method, will be described with
reference to FIG. 16, with a focus on a single optical switch. FIG.
16 is a timing chart which shows the relationship (varying over
time) of the current that flows through the coil layer 25 of one
optical switch and gives rise to a Lorentz force (hereafter
referred to as the "current used for the Lorentz force"), the same
voltage that is applied across the first electrode part (substrate
11) of this optical switch and the second electrode parts 23a and
23b of the movable plate 21 and across the second electrode parts
23a and 23b of the movable plate 21 of this optical switch and the
upper electrode part (third electrode part), and that gives rise to
respective electrostatic forces between these parts (hereafter
referred to as the "voltage used for the electrostatic force"), and
the position of the mirror 12 of this optical switch (and
accordingly, the position of the movable plate 21).
[0125] Initially, it is assumed that the current used for the
Lorentz force is zero and that the voltage used for the
electrostatic force is V, so that the mirror 12 is held in the
upper position shown in FIG. 14 by the electrostatic force between
the electrode parts 23a and 23b of the movable plate 21 and the
upper electrode part 41. In this case, the voltage V is set so that
the electrostatic force between the electrode parts 23a and 23b and
the upper electrode part 41 is stronger than the spring force of
the flexure parts 27a and 27b. In this state, the incident light is
reflected by the mirror 12 and advances toward the front with
respect to the plane of the page as shown in FIG. 14.
[0126] Subsequently, at time T1, control is initiated in order to
switch the position of the mirror 12 to the lower position shown in
FIG. 15. Specifically, at time T1, the voltage used for the
electrostatic force is reduced to zero. As a result, the mirror 12
is caused to return to the neutral position shown in FIGS. 12 and
13 relatively quickly by the spring force of the flexure parts 27a
and 27b.
[0127] Subsequently, at time T2, the current used for the Lorentz
force is set at +I. Here, +I is a current that generates a
downward-oriented Lorentz force that is stronger than the spring
force of the flexure parts 27a and 27b in the coil layer 25.
[0128] The mirror 12 is gradually lowered by this Lorentz force,
and stops at time T3, at which the movable plate 21 contacts the
substrate 11; the mirror 12 is then held in the lower position
shown in FIG. 15.
[0129] The mirror 12 does not continue to be held "as is" in the
lower position by this Lorentz force; after the voltage used for
the electrostatic force is set at V at time T4, the current used
for the Lorentz force is reduced to zero at time T5. Here, the
voltage V is the same as the value described above; this voltage V
is set at a voltage which generates an electrostatic force that is
stronger than the spring force of the flexure parts 27a and 27b
when the mirror 12 is positioned in the lower position. During the
period T3-T4, the mirror 12 is held in the lower position only by
the Lorentz force; during the period T4-T5, the mirror 12 is held
in the lower position by the Lorentz force and the electrostatic
force, and during the period from time T5 on, the mirror 12 is held
in the lower position only by the electrostatic force. The period
T3-T5 is a so-called lower-side holding transition period in which
the holding of the mirror 12 in the lower position is switched from
the Lorentz force to the electrostatic force, and the period from
time T5 on is a so-called steady period of lower-side holding.
[0130] During the period in which the mirror 12 is held in the
lower position, as is shown in FIG. 15, the incident light passes
through "as is" to form emitted light without being reflected by
the mirror 12.
[0131] Subsequently, at time T6, control is initiated in order to
switch the position of the mirror 12 to the upper position shown in
FIG. 14. Specifically, at time T6, the voltage used for the
electrostatic force is reduced to zero. As a result, the mirror 12
is returned to the neutral position shown in FIGS. 12 and 13
relatively quickly by the spring force of the flexure parts 27a and
27b.
[0132] Subsequently, at time T7, the current used for the Lorentz
force is set at -I. Here, -I is a current that generates an
upward-oriented Lorentz force that is stronger than the spring
force of the flexure parts 27a and 27b in the coil layer 25.
[0133] The mirror 12 is gradually raised by this Lorentz force, and
stops at time T8, at which the movable plate 21 contacts the upper
electrode part 41; the mirror 12 is then held in the upper position
shown in FIG. 14.
[0134] The mirror 12 does not continue to be held "as is" in the
upper position by this Lorentz force; after the voltage used for
the electrostatic force is set at V at time T9, the current used
for the Lorentz force is reduced to zero at time T10. During the
period T8-T9, the mirror 12 is held in the upper position only by
the Lorentz force; during the period T9-T10, the mirror 12 is held
in the upper position by the Lorentz force and the electrostatic
force, and during the period from time T10 on, the mirror 12 is
held in the upper position only by the electrostatic force. The
period T8-T10 is a so-called upper-side holding transition period
in which the holding of the mirror 12 in the upper position is
switched from the Lorentz force to the electrostatic force, and the
period from time T10 on is a so-called steady period of upper-side
holding.
[0135] Thus, when the gap between the second electrode parts 23a
and 23b of the movable plate 21 and the substrate 11 (first
electrode part) is large, the mirror 12 is moved into the lower
position against the spring force of the flexure parts 27a and 27b
by a Lorentz force whose magnitude does not depend on the position
of the mirror 12 (i.e., the position of the movable plate 21).
Furthermore, when the gap between the second electrode parts 23a
and 23b of the movable plate 21 and the upper electrode part 41
(third electrode part) is large, the mirror 12 is moved into the
upper position against the spring force of the flexure parts 27a
and 27b by a Lorentz force whose magnitude does not depend on the
position of the mirror 12. Accordingly, the mobility range of the
movable plate 21 can be broadened without applying a high voltage
or sacrificing small size in order to increase the electrostatic
force. Furthermore, in the steady state of holding in the lower
position, where the gap between the second electrode parts 23a and
23b of the movable plate 21 and the substrate 11 (first electrode
part) narrows, and the steady state of holding in the upper
position, where the gap between the second electrode parts 23a and
23b of the movable plate 21 and the upper electrode part 41 (third
electrode part) narrows, the mirror 12 is held in the lower
position or upper position by the electrostatic force alone;
accordingly, the power consumption can be reduced.
[0136] Furthermore, in the last example described above, the
voltage used for the electrostatic force is set at V at time T4
between time T3 and time T5; however, the voltage used for the
electrostatic force may be set at V at any point in time during the
period T1-T4. Similarly, in the last example described above, the
voltage used for the electrostatic force is set at V at time T9
between time T8 and time T10; however, the voltage used for the
electrostatic force may be set at V at any point in time during the
period T6-T9.
[0137] The optical switch array 1 of the present working
configuration has a plurality of optical switches of the type shown
in FIGS. 11 through 15 as the above-mentioned unit elements, and
these optical switches are disposed in a two-dimensional matrix.
Furthermore, the circuit shown in FIG. 17, which contains a
plurality of switching elements, is mounted on the optical switch
array 1 of the present working configuration in order to realize
the above-mentioned control for each of these optical switches
using a small number of control lines. FIG. 17 is an electrical
circuit diagram which shows the optical switch array of the present
working configuration. In FIG. 17, elements that are the same as in
FIG. 7, or that correspond to such elements, are labeled with the
same symbols, and a redundant description is omitted.
[0138] The circuit shown in FIG. 17 differs from the circuit shown
in FIG. 7 in that a current control switch MC4 and a current source
I2 that supplies the above-mentioned current -I are added. One end
of the current control switch MC4 is connected to the second end of
each column selection switch Mmnd, and the other end of the current
control switch MC4 is connected to one end of the current source
I2. The other end of the current source I2 is connected to ground.
The gate of the current control switch MC4 is connected to a
terminal C4.
[0139] Furthermore, in FIG. 17, the capacitors Cmn of the optical
switches in m rows and n columns correspond to composite capacitors
in which the capacitors formed by the second electrode 23a and
first electrode (substrate 11), the capacitors formed by the second
electrode 23b and first electrode (substrate 11), the capacitors
formed by the second electrode 23a and upper electrode part 41
(third electrode part) and the capacitors formed the second
electrode 23b and upper electrode part 41 are connected in
parallel.
[0140] Next, one example of a timing chart of the voltages that are
applied to the respective terminals V1, V2, V3, H1, H2, H3, C1, C2,
C3 and C4 is shown in FIG. 18. In FIG. 18, the period prior to time
t1 is a voltage refresh period in which the capacitors Cmn of all
of the optical switches are biased to a clamping voltage VC.
Accordingly, during this period, the terminals V1, V2, V3, H1, H2
and H3 are all at a high level, so that all of the column selection
switches Mmnb and Mmnd and row selection switches Mmna and Mmnc are
in a conductive state. Furthermore, during this period, the
terminal C1 is at a high level, and the terminal C2 is at a low
level, so that the voltage control switch MC1 is in a conductive
state, and the voltage control switch MC2 is in a non-conductive
state. Furthermore, the terminals C3 and C4 are at a low level, so
that the current control switches MC3 and MC4 are in a
non-conductive state. During the voltage refresh period, the
mirrors 12 are held in either the upper position or the lower
position.
[0141] In the present working configuration, incidentally, the
signals (voltages) that are applied to the terminals V1, V2, V3,
H1, H2, H3, C1, C2, C3 and C4 are supplied as control signals from
an external control circuit corresponding to the external control
circuit 6 shown in FIG. 1. Like the external control circuit 6
shown in FIG. 1, this external control circuit investigates optical
switches whose position state is to be altered from the current
position state (for example) on the basis of light path switching
state command signals, and successively sets state alteration
periods one at a time for each of the optical switches whose state
is to be altered. In cases where there are no optical switches
whose position state is to be altered from the current position
state, the above-mentioned voltage refresh period is set.
Furthermore, in cases where a plurality of state alteration periods
are set (that is, in cases where the number of optical switches
whose position state is to be altered from the current position
state is two or greater), voltage refresh periods may be set
between the respective state alteration periods, or such voltage
refresh periods may be omitted. For example, in a case where the
number of optical switches whose position state is to be altered
from the current position state is three, a sequence of state
alteration period.fwdarw.voltage refresh period.fwdarw.state
alteration period.fwdarw.voltage refresh period.fwdarw.state
alteration period may be set, or state alteration periods may be
continuously set. Furthermore, in the respective set state
alteration periods, signals that are applied to the terminals V1,
V2, V3, H1, H2, H3, C1, C2, C3 and C4 are supplied so that the
above-mentioned control shown in FIG. 6 is realized in accordance
with the commanded light path switching states for the
corresponding optical switches. Moreover, it goes without saying
that the external control circuit 6 may also be mounted on the
optical switch array 1.
[0142] FIG. 18 shows an example in which a sequence of voltage
refresh period.fwdarw.state alteration period for the optical
switch of row 1 column 1.fwdarw.voltage refresh period is set by
the external control circuit 6. In the example shown in FIG. 18,
during the voltage refresh period prior to time t1, the mirror 12
is held in either the upper position or the lower position. At time
t1, a state alteration period is initiated for the optical switch
of row 1 column 1; the terminals V2, V3, H2 and H3 are placed at a
low level, so that the capacitors other than the capacitor C11 are
isolated. Nest, at time t3, the terminal C2 is placed at a high
level, so that the charge in C11 is discharged, and the voltage
used for the electrostatic force is reduced to zero. As a result,
the electrostatic force is eliminated, so that the mirror 12 moves
into the neutral position shown in FIGS. 12 and 13. Next, after the
terminal C2 is placed at a low level at time t4, the terminal C3 is
placed at a high level at time t5, so that a current +I is caused
to flow through the coil L11. In cases where the direction of
movement is the opposite direction, C4 is placed at a high level
instead of C3, so that a current -I is caused to flow. Next, at
time t6, the terminal C1 is placed at a high level, so that the
capacitor C11 is again charged to a clamping voltage VC, thus
causing clamping to be performed. Next, at time t7, the terminal C3
is placed at a low level, so that the current to the coil L11 is
stopped. Subsequently, at time t8, this state alteration period is
ended, and a voltage refresh period is initiated.
[0143] Furthermore, the optical switch array of the present working
configuration can basically be manufactured in the same manner as
the optical switch array 1 of the above-mentioned first working
configuration. In the present working configuration, since an upper
electrode part 41 is added, alterations may be appropriately made,
such as the formation of the upper electrode part 41 following the
formation of a sacrificial layer corresponding to the gap between
the movable plate 21 and upper electrode part 41.
[0144] In the respective working configurations described above, if
a high voltage were to be applied across the electrode parts, it
would be necessary to increase the withstand voltage of the MOS
transistors in FIGS. 7 and 8. However, MOS transistors that have a
high withstand voltage have a large planar size, so that chip
miniaturization becomes difficult. On the other hand, in the
respective working configurations described above, there is no need
to apply a high voltage across the electrode parts; accordingly,
MOS transistors with a small planar size can be used. In this
respect as well, miniaturization can be achieved.
[0145] Respective working configurations of the present invention
were described above. However, the scope of the present invention
is not limited by these working configurations.
[0146] For example, the respective working configurations described
above were examples of optical switch arrays in which a plurality
of optical switches were disposed in a two-dimensional
configuration. However, the present invention may also comprise a
single optical switch. Furthermore, the respective working
configurations described above were examples in which the
microactuator of the present invention was applied to an optical
switch; however, there are no limitations on the application of
this microactuator.
[0147] Industrial Applicability
[0148] The microactuator and microactuator device of the present
invention can be used to drive devices with an extremely small
structure such as devices manufactured by micro-machining. For
example, the optical switch and optical switch array of the present
invention can be used in optical communications, etc.
* * * * *