JP2003057575A - Micromirror device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a micromirror device which can slant a mirror widely with a low voltage. SOLUTION: This micromirror device has the mirror 33, torsion springs 35 and 36 which support the mirror 33 so that the mirror can slant to an upper substrate 27, a lower substrate 21 which is arranged opposite to the reverse surface of the mirror, a projection part 34 which is provided on the top surface of the lower substrate 21, and lower electrodes 22 and 23 which are formed on the external surface of the projection part 34. The torsion spring 36 has a >=1.8 aspect ratio of the height and width in section per perpendicular to its length.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micromirror device that can be used for optical switching elements for communication, measuring instruments, displays, scanners and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art FIG. 34 is a schematic perspective view showing a conventional micromirror device. In this micromirror device, as shown in the figure, a rotatable support portion 2 is provided on a substrate 1, and a base portion 3 is rotatably provided on the support portion 2 via a hinge 7. A frame 4 is provided on the base 3 via a torsion spring (not shown), a mirror 5 is provided on the frame 4 via a torsion spring (not shown), and a portion of the substrate 1 facing the mirror 5 is provided. A plurality of lower electrodes 6 are provided. By applying a voltage to these lower electrodes 6, the mirror 5 can be attracted by electrostatic force and the mirror 5 can be tilted in any direction.

The micromirror device shown in FIG. 34 is manufactured by a surface micromachining technique. That is, the growth of the polycrystalline silicon layer and the silicon oxide (SiO 2
2) Layer formation and patterning of each layer are performed to alternately deposit a polycrystalline silicon layer and a silicon oxide layer, and finally to immerse in a buffer hydrofluoric acid or the like to dissolve the silicon oxide layer, The movable portion is formed by removing the silicon oxide layer. This silicon oxide layer, for example, the silicon oxide layer 11 shown in FIG. 35, is called a sacrificial layer because it exists to form a movable portion and a gap.

In the micromirror device shown in FIG. 34, after forming a patterned layer composed of a silicon oxide layer and polycrystalline silicon, the silicon oxide layer is removed by buffered hydrofluoric acid, whereby the support portion 2 and the base portion are removed. 3, the frame body 4 and the mirror 5 are formed. When a micromirror device is manufactured by this method, if a large number of mirror patterns are formed, the silicon oxide layer 1 that is a sacrificial layer will be formed.
There is an advantage that a large number of mirrors 5 are formed only by removing 1.

[0005]

However, in the above micromirror device, the electrodes of the mirror 5 and the lower electrode 6 are arranged in parallel, and the gap between the electrodes is large. Since the electrostatic force applied to the mirror 5 is inversely proportional to the square of the gap between the electrodes, a high voltage was required to cause a large tilt in the mirror 5.

Further, in such a micromirror device, since the mirror 5 is made of polycrystalline silicon, internal strain remains due to crystal growth conditions, which causes deformation of the mirror 5. Due to this deformation, when collimated light is incident, it is reflected as a beam having a distorted beam profile. Therefore, for example, when this micromirror device is used as an optical switch for switching from the input optical fiber to the output optical fiber, there is a large loss when the collimated beam emitted from the input fiber enters the output fiber after being reflected.

Therefore, in order to reduce the loss due to the deformation of the mirror 5, the surface distribution of the voltage between the lower electrode 6 and the electrode of the mirror 5 capable of compensating the deformation is stored in advance in the memory of the computer, and based on this. The distribution of the electrostatic force applied to the mirror 5 is controlled to correct the deformation of the mirror 5. However, such correction is very troublesome.

Further, since the torsion spring that gives the restoring force of the mirror 5 is made of polycrystalline silicon and the polycrystalline silicon has a large number of crystal grain boundaries, when the repeated force acts, the crystal grain boundaries undergo fatigue fracture. Cause of. Therefore, repeated application of fatigue causes rapid fatigue, resulting in a problem of life.

Further, since the supporting portion 2 supporting the mirror 5 is also made of polycrystalline silicon, there is a problem that the supporting portion 2 is deformed by the fluctuation of the electrostatic force applied to the mirror 5. In addition, since the printed wiring for energizing each lower electrode 6 is formed on the front surface side of the substrate 1, when a large number of mirrors 5 are arranged to form an array, the required wiring pattern width becomes narrow. Moreover, since it is necessary to avoid the supporting portion 2 for wiring, there is a problem that the degree of freedom of wiring is low.

An object of the present invention is to provide a micromirror device that can tilt a mirror greatly at a low voltage.

[0011]

In order to achieve the above object, a micromirror device of the present invention comprises a mirror, a plurality of torsion springs for tiltably supporting the mirror with respect to an upper substrate, and a lower surface of the mirror. A lower substrate arranged in the same manner, a convex portion provided on the upper surface of the lower substrate so as to face the central portion of the mirror, and a plurality of lower electrodes formed on the outer surface of the convex portion.

According to this micromirror device, by forming the convex portion, at least a part of the mirror and the lower electrode can be brought close to each other, and the voltage required for tilting the mirror can be reduced.

The torsion spring may have a height / width aspect ratio of 1.8 or more in a cross section perpendicular to the longitudinal direction thereof. In this case, while maintaining the mirror support strength by the torsion spring,
Since the tilting of the mirror becomes easier, the voltage required for tilting the mirror can be reduced.

A recess may be formed on the upper surface of the lower substrate at a position around the protrusion and facing the outer peripheral edge of the mirror. In this case, the mirror can be tilted until the outer peripheral edge of the mirror enters the concave portion, so that the tilting range of the mirror can be expanded and the mirror is less likely to contact the lower substrate, preventing the mirror from being broken. it can.

A fulcrum protrusion made of an insulator may be formed on the convex portion so as to face the center of the mirror.
In this case, the fulcrum protrusion can prevent the mirror from being excessively displaced downward, and the mirror electrode and the lower electrode are not short-circuited, so that the mirror electrode and the lower electrode can be prevented from being damaged.

The torsion spring may have a meandering portion, and the upper substrate may be formed with a position regulating portion for regulating the displacement range of the torsion spring. In this case, the position control unit prevents excessive displacement of the torsion spring and mirror, and
Damage to the torsion spring can be prevented.

The mirror, the torsion spring, and the upper substrate may be integrally formed of a silicon single crystal, and the silicon single crystal may be bonded to a spacer formed on the lower substrate. In this case, the flatness of the mirror can be increased and the life of the torsion spring can be extended.

Wiring patterns may be formed on a lower surface of the lower substrate, and the wiring patterns and the lower electrodes may be electrically connected to each other through through holes formed in the lower substrate. In this case, the degree of freedom of wiring to the lower electrode is increased, and not only the wiring becomes easy, but also the pattern width of the wiring can be widened.

The method for manufacturing a micromirror device of the present invention comprises the following steps: a first oxide layer, a first single crystal silicon layer, a second oxide layer, and a second oxide layer on a supporting substrate.
Forming a single crystal silicon layer in order; forming a groove penetrating the second single crystal silicon layer, the second oxide layer, and the first single crystal silicon layer; a polycrystalline silicon layer in the groove Forming a mirror and a torsion spring with the second single crystal silicon layer by etching the second single crystal silicon layer;
Removing the polycrystalline silicon layer in the groove; etching a portion of the first single crystal silicon layer located below the torsion spring through the groove; and the first oxide layer and the Removing the second oxide layer to make the torsion spring independent. According to this manufacturing method, the mirror and the torsion spring can be easily integrally molded.

[0020]

1 is an exploded perspective view showing a first embodiment of a micromirror device according to the present invention, FIG. 2 is a perspective view showing a mirror support structure, and FIG. 3 is a sectional view taken along line AA of FIG. Is. The present invention is not limited to the following embodiments, and various modifications may be made without departing from the spirit of the present invention.

As shown in the figure, the crystal orientation is (100)
Lower substrate (lower electrode substrate) 2 made of single crystal silicon
A rectangular projecting portion 34 is provided in the center of 1, and lower electrodes 22 are provided near the four corners on the upper surface of the projecting portion 34, respectively. A plurality of lower electrodes 23 are also provided around the protrusion 34 at intervals (8 in this example).
Individual). On the lower surface of the lower substrate 21, patterned wiring 24
And the lower electrode 23 and the wiring 24 are formed on the lower substrate 2
1 are electrically connected to each other through through holes 25.

AuSn is formed on both sides of the upper surface of the lower substrate 21.
A solder portion 26 made of is provided. In addition, SOI
On the lower surface of an upper substrate (mirror forming substrate) 27 made of a (Silicon On Insulator) substrate, columns 28 made of single crystal silicon having a crystal orientation of (100) are provided. The upper width of the pillar 28 is, for example, 1 mm, and the lower width is 300 mm.
μm. Three layers of Ti / Pt / Au are provided under the pillar 28.
And a support post 28 is provided on the lower substrate 2.
It is joined to the first solder portion 26. As a result, the upper substrate 27 is bonded to the lower substrate 21.

A silicon oxide layer 30 is provided on the upper surface of the upper substrate 27, a base 31 made of single crystal silicon is provided on the silicon oxide layer 30, and an annular frame 32 is provided inside the base 31. Further, a mirror 33 is provided inside the frame body 32. Three Ti / Pt / Au layers are formed on the surface of the mirror 33 to impart conductivity. A mirror 33 is supported by the support column 28. For example, the distance between the lower electrode 22 and the mirror 33 is set to 20 μm, and the distance between the lower electrode 23 and the mirror 33 is set to 40 μm.

The base 31 and the frame 32 are connected to each other by a torsion spring 35 at two positions separated by 180 °, and the frame 32 and the mirror 33 are connected by a torsion spring 36 at two positions separated by 180 °. There is. The torsion springs 35 and 36 have the same shape. The line connecting the torsion springs 35 and the line connecting the torsion springs 36 are orthogonal to each other. The base 31, the frame 32, the mirror 33, and the torsion springs 35 and 36 are integrally formed of single crystal silicon.

When the height of the cross section of each of the torsion springs 35 and 36 is a and the width thereof is b, the aspect ratio a / b between the height a and the width b is an important parameter. The aspect ratio a / b is preferably 1.8 or more, more preferably 2.5 to 8, and most preferably about 3. When the aspect ratio a / b is 1.8 or more, the torsion springs 35 and 36 are more likely to be twisted, and the torsion springs 35 and 36 are less likely to bend due to the weight of the mirror 33 and the electrostatic force F. Therefore, the attitude control of the mirror 33 can be performed with higher accuracy. This effect will be described below.

The torsion spring 35 not only functions as a spring that gives a restoring force of torsion, but also functions as a support portion that supports the weight of the mirror 33. For this reason, bending stress is applied to the torsion spring 35 by the self-weight of the mirror 33 and the electrostatic force F for driving the mirror 33, and although the mirror 33 is firmly supported by the support column 28, it causes the bending of the mirror 33. Becomes When the height of the cross section of the torsion spring 35 is a, the width is b, the constant is β, and the shear elastic modulus of the single crystal silicon is G, the relational expression between the torsion angle θ of the torsion spring 35 and the torque T is expressed by the following equation. To be done. θ = T / βab ³ G

When the constant is α, the longitudinal elastic modulus of the single crystal silicon is E, and the moment of inertia of area of the torsion spring 35 is I, the relational expression between the bending deflection amount δ and the electrostatic force F is expressed by the following equation. It δ = Fα / EI The moment of inertia of area I is expressed by the following equation. I = ba ^3/12

Therefore, when the constant is A, the ratio δ / θ between the bending deflection amount δ and the twist angle θ is expressed by the following equation. δ / θ = Aβ (b / a) ² Therefore, by increasing the height a as compared with the width b, it becomes relatively easy to twist, and the self-weight of the mirror 33 and the deflection due to the electrostatic force F are reduced. .

In this micromirror device, the mirror 33 is arbitrarily provided by applying a negative electric field to the upper substrate 27 and a positive electric field to the lower electrodes 22 and 23, and by causing an asymmetric potential difference between the lower electrodes 22 and 23. Tilt in the direction of. For example, when a voltage of 60 V is applied to all electrodes on one side of the lower electrodes 22 and 23, the mirror 33 can be tilted by about 10 °.

In such a micromirror device, the electrostatic force applied to the mirror 33 is equal to the interelectrode gap 2
A protrusion 34 is formed on the upper surface of the lower substrate 21 so as to face the center of the mirror 33, although the protrusion 34 is inversely proportional to the power of the protrusion.
Since the lower electrode 22 is formed on the upper surface of the mirror 33, the distance between the mirror 33 and the lower electrode 22 can be reduced without narrowing the rotation range of the mirror 33. Therefore, the mirror 33 can be largely tilted with a low voltage.

Further, in this embodiment, since the mirror 33 is made of single crystal silicon which is harder than polycrystalline silicon, no internal strain remains in the mirror 33 and the deformation due to the internal strain is small. Therefore, when the collimated light is emitted, a distorted beam profile is not generated, and even when this micromirror device is used as an optical switch that switches the optical path from the input optical fiber to the output optical fiber, it is emitted from the input optical fiber. The loss when the collimated beam is incident on the output fiber after being reflected can be reduced. Therefore, it is not necessary to control the distribution of the electrostatic force applied to the mirror 33 to compensate for the deformation of the mirror 33.

Further, in this embodiment, since the torsion springs 35 and 36 for giving the restoring force of the mirror 33 are made of single crystal silicon, fatigue is unlikely to occur due to repeated force and the life is long. Further, since the SOI substrate is used as the upper substrate 27, the micromirror device can be easily manufactured.

Also, the support column 28 for supporting the mirror 33 is
Since it is made of hard single crystal silicon, the support column 28 is not deformed by the fluctuation of the electrostatic force applied to the mirror 33, and the attitude of the mirror 33 can be accurately controlled.
Further, since the upper substrate 27 provided with the mirror 33 is manufactured separately from the lower substrate 21 provided with the lower electrodes 22 and 23, sticking of the mirror does not occur during manufacturing.

Since the lower electrode 23 and the wiring 24 are connected by the through hole 25, the lower electrodes 22, 2
Since it is not necessary to avoid the wires 3 and the pillars 28 for wiring, the pattern width of the wires 24 for driving the mirror 33 can be increased, and the wiring flexibility and the wiring density can be increased.

A method of manufacturing the micromirror device shown in FIGS. 1 to 3 will be described. First, the crystal orientation is (10
Oxygen ions are implanted into the single crystal silicon substrate of 0) to form a silicon oxide layer 30 at a constant depth to form a SIMOX substrate. Single crystal silicon is epitaxially grown on the active layer of the SIMOX substrate to form an S layer having a thickness of about 10 μm.
An OI layer is formed and an SOI substrate is prepared.

Next, the SOI layer of the SOI substrate is doped with impurities so that the impurity concentration is 1 × 10 ^20, and the specific resistance is set to several thousandths of Ωcm. Next, three layers of Ti / Pt / Au reflective film are formed by lift-off. A double-sided aligner is used according to the mirror pattern on the front surface of the support substrate of the SOI substrate to form three layers of Ti /
The joint portion 29 made of Pt / Au is patterned. By performing back etching of the supporting substrate, the support 28
To form.

Next, ICP (inductively-coupled p
lasma) to etch the SOI layer to form a base 3
1, the frame 32, the mirror 33, and the torsion springs 35 and 36 are integrally formed. PCVD (plasma CV
After forming a silicon oxide layer (passivation film) on the surface by D) and protecting the surface, etching is performed with an etchant of KOH. For etching conditions, see H.S.
eidel et al., Anisotropic Etching of Crystalline Silico
n in Alkaline Solutions I., J. Electrochem. Soc.,
Vol.137, No.11 (1990) 3612-3626 and H. Seidel et al.,
Anisotropic Etching of Crystalline Silicon in Alka
line Solutions II., J. Electrochem. Soc., Vol.137,
No. 11 (1990) 3626 can be referred to.

A single crystal silicon substrate having a crystal orientation of (100) is etched with KOH to form protrusions 34, lower electrodes 22 and 23 are formed, and three layers of T are formed at the bottom of the step.
After forming the i / Pt / Au layer, the solder portion 26 is formed on the Ti / Pt / Au layer.

Next, through holes 25 are formed corresponding to the lower electrodes 23, and wirings 24 are formed on the back surface side of the single crystal silicon substrate. Then, the upper substrate 27 and the lower substrate 2
1 is aligned, and then the joint portion 29 is pressed against the solder portion 26 and heated at 390 ° C. to melt the solder in the solder portion 26 and the lower substrate 21 to the upper substrate 2.
Bond 7

According to this method for manufacturing a micromirror device, since the mirror 33 is formed of single crystal silicon,
Deformation due to internal strain is small, and since the torsion springs 35 and 36 are made of single crystal silicon, the life is extended with respect to repeated force.

FIG. 4 is a perspective view showing a part of another micromirror device according to the present invention. As shown in the figure, a lower silicon layer 41 made of single crystal silicon is provided on the pillar 28, and a silicon oxide layer 42 is provided on the lower silicon layer 41.
Is provided, an upper silicon layer 43 made of single crystal silicon is provided on the silicon oxide layer 42, and the base 31 is composed of the lower silicon layer 41, the silicon oxide layer 42, and the upper silicon layer 43.

The torsion spring 35 and the frame 32 are formed of the upper silicon layer 43. A horizontal holding portion 44 is provided below the torsion spring 35 in order to prevent the torsion spring 35 from being bent due to its own weight of the mirror 33 and electrostatic force F. The holding portion 44 is composed of a part of the lower silicon layer 41. When an excessive load is applied to the mirror 33, the tip of the torsion spring 35 comes into contact with the holding portion 44,
Restrict further displacement.

In such a micromirror device, since the torsion spring 35 is provided with the holding portion 44 for preventing the mirror 33 from bending due to its own weight or the electrostatic force F, the torsion spring 3 is provided.
Since it is not necessary to increase the ratio a / b of 5, the torsion spring 35 can be easily formed.

A method of manufacturing the micromirror device shown in FIG. 4 will be described with reference to FIGS. 5 (a) to 5 (d) and FIGS. 6 (a) to 6 (c). As shown in FIG. 5A, a silicon oxide layer 45 is formed on a supporting substrate 50 made of single crystal silicon in order.
A lower silicon layer 41, a silicon oxide layer 42, and an upper silicon layer 43 are formed, and a junction 29 is formed below the substrate having the five-layer structure.

Next, as shown in FIG. 5B, a groove (hole) 46 reaching the lower silicon layer 41 by etching.
To form. Next, as shown in FIG. 5C, a groove (hole) penetrating up to the silicon oxide layer 45 by etching.
47a and 47b are formed. In this case, first, the upper silicon layer 43 is etched with SF6 gas using ICP,
The silicon oxide layer 42 is reactively etched with a CF-based gas. After that, the lower silicon layer 41 is further etched by using ICP with SF6 gas to remove the silicon oxide layer 45 by C
Reactive etching is performed with an F-based gas.

Next, as shown in FIG. 5D, the groove 4
A polycrystalline silicon layer 48 is formed in 6, 47a and 47b. Next, as shown in FIG. 6A, the torsion spring 35 is formed by etching the upper silicon layer 43. In this case, the silicon oxide layer 42 serves as an etching stopper.

Next, as shown in FIG. 6B, three Ti / Pt / Au layers 49 are formed on the upper surface of the upper silicon layer 43.
To form. Next, as shown in FIG. 6C, the support substrate 50 is back-etched to support the pillars 28.
To form. In this case, the groove 47b is formed on the silicon oxide layer 45.
Since it penetrates through, the groove 47b portion of the lower silicon layer 41 is also etched, and the holding portion 44 is formed.

Next, the silicon oxide layers 42 and 45 are removed by immersing in buffered hydrofluoric acid to separate the root of the torsion spring 35 and the holding portion 44 from each other.

In the method of manufacturing the micromirror device, since the groove 47a penetrates the silicon oxide layers 42 and 45, when the silicon oxide layers 42 and 45 are removed by immersion in buffered hydrofluoric acid, the base portion is removed. Since it is possible to prevent the silicon oxide layers 42 and 45 from being removed in 31, the support substrate 50 (support 28), the lower silicon layer 41, and the upper silicon layer 43 are not separated in the base 31.

FIG. 7 is a perspective view showing a part of another micromirror device according to the present invention, and FIG. 8 is a sectional view showing a part of the micromirror device shown in FIG. As shown in the figure, a lower silicon layer 51 made of single crystal silicon is provided on the pillar 28, and Si-B- is formed on the lower silicon layer 51.
An intermediate layer 52 made of O and having a thickness of 10 μm is provided, an upper silicon layer 53 made of single crystal silicon is provided on the intermediate layer 52, and a base 31 is a lower silicon layer 51.
It is composed of an intermediate layer 52 and an upper silicon layer 53.

A lower electrode plate 54 is provided on a part of the lower silicon layer 51, and an upper electrode plate 55 is provided between the torsion spring 35 formed by the upper silicon layer 53 and the frame body 32. The width of the upper electrode plate 55, that is, the dimension in the direction of the line connecting both ends of the torsion spring 35 is 40 μm, and the length in the direction perpendicular thereto is 55 μm.

An input electrode 56 connected to the electrode of the lower electrode plate 54 is provided on the base 31, and an input electrode 57 connected to the electrode of the upper electrode plate 55 is provided on both sides of the torsion spring 35.

In this micromirror device, when a negative voltage is applied to the input electrode 56 and a positive voltage is applied to the input electrode 57, the upper electrode plate 55 can be tilted, so the mirror 33 should be tilted. You can

In such a micromirror device, since the thickness of the intermediate layer 52 is 10 μm, the gap between the lower electrode plate 54 and the upper electrode plate 55, that is, the interelectrode gap is 10 μm. Since the electrostatic force is inversely proportional to the square of the gap between the electrodes, the mirror 33 can be tilted more greatly. That is, the area of the upper electrode plate 55 is 1/6 of the area of the mirror 33, but the inter-electrode gap is 1/4 of the inter-electrode gap of 40 μm when no step is provided on the electrode portion of the lower substrate. Therefore, compared with the case where no step is provided in the electrode portion of the lower substrate,
The voltage applied to 7 can be half or less, that is, 40V.

Further, in this example, as shown in FIG. 1, a lower electrode is also provided on the projecting portion 34 of the lower substrate 21, and when this is also used, the voltage applied to the input electrodes 56 and 57 is, for example, It can be 25 V or less.

When manufacturing the micromirror device shown in FIGS. 7 and 8, Si—B—O is deposited on the SOI layer (lower silicon layer 51) of the SOI substrate, and epitaxial crystal growth is performed thereon. By stacking the SIMOX substrates on top of each other and sinking them (sintering), the SOI substrate and SI
Bonding with MOX substrate (Japanese Patent Laid-Open No. 61-2420)
If the substrate is manufactured by polishing and etching thereafter, the thickness of the intermediate layer 52 can be easily made 10 μm.

FIG. 9 is a view showing a part of another micromirror device according to the present invention. As shown, the base 31
A torsion spring 61 is provided between the frame 32 and the frame 32, and the torsion spring 61 intersects the frame 32 at right angles to the base 31.
Can be tilted around the direction line.

FIG. 10 is an exploded perspective view showing another micromirror device according to the present invention. As shown in the drawing, a lower substrate (lower electrode substrate) 71 made of single crystal silicon having a crystal orientation of (100) is provided with a protruding portion 72, a lower electrode 73 is provided on the protruding portion 72, and an upper surface of the lower substrate 71 is provided. The wiring 74 is provided in the. A lower electrode 73 is connected to the wiring 74, and a pillar 80 made of single crystal silicon is provided on the upper surface of the lower substrate 71.

A frame portion 79 made of single crystal silicon having a crystal orientation (100) is provided on the upper substrate (mirror forming substrate) 75, and a base portion 76 made of single crystal silicon is provided on the frame portion 79.
Is provided, and an annular frame 77 is provided inside the base 76. A mirror 78 is provided inside the frame 77, and three Ti / Pt / Au layers are provided on the surface of the mirror 78. The distance between the lower electrode 73 and the mirror 78 is 20 μm.
m.

Similar to the micromirror device shown in FIG. 1, the base portion 76 and the frame body 77 are connected to each other at two locations by a torsion spring (not shown).
7 and the mirror 78 are connected at two points by a torsion spring (not shown). Also, the column 80
The upper substrate 75 is attached to the lower substrate 71 by soldering, and the upper substrate 75 is bonded to the lower substrate 71.

In this micromirror device, S
The frame portion 79 can be formed by back-etching the support substrate of the OI substrate.
The frame 77 and the mirror 7 are formed by etching the I layer.
8. The torsion spring can be integrally formed.

FIG. 11 is an exploded perspective view showing another micromirror device according to the present invention. As shown in the drawing, the wiring 81 is provided on the lower surface of the lower substrate 71, that is, the lower surface of the paper of FIG. 11, and the through hole 82 that connects the lower electrode 73 and the wiring 81 is provided.

In this micromirror device, since the lower electrode 73 and the wiring 81 are connected by the through hole 82, there is no need to avoid the lower electrode 73 and the supporting column 80 for wiring, so that the mirror 78 is driven. Wiring 81
The pattern width of can be thickened.

FIG. 12 is an exploded perspective view showing another micromirror device according to the present invention. As shown in the figure, the lower electrode 92 is provided on the upper surface of the lower substrate (lower electrode substrate) 91 made of single crystal silicon having the crystal orientation (100), that is, the upper surface of the paper of FIG. 12, and the wiring 93 is provided on the lower substrate 91. The lower electrode 92 is connected to the wiring 93.

A frame portion 101 made of single crystal silicon having a crystal orientation (100) is formed on an upper substrate (mirror forming substrate) 94.
And a base portion 95 made of single crystal silicon is provided in the frame portion 101. An annular frame 96 is provided inside the base 95, a mirror 97 is provided inside the frame 96, and three Ti / Pt / Au layers are provided on the surface of the mirror 97. A protrusion 98 is provided on the back surface of the mirror 97.

Similar to the micromirror device shown in FIG. 1, the base 95 and the frame 96 are connected at two locations by a torsion spring (not shown), and the frame 9
6 and the mirror 97 are connected at two locations by a torsion spring (not shown). A base 95 made of single crystal silicon, a frame 96, a mirror 97, and a torsion spring are integrally formed.

Posts 102 are provided on both sides of the base 95, and the posts 102 are attached to the lower substrate 91 by soldering, and the upper substrate 94 is bonded to the lower substrate 91. That is, in this embodiment, the upper substrate 94 shown in FIG. 12 is turned upside down, that is, the front side and the back side are reversed, and the upper substrate 94 is bonded to the lower substrate 91.

In this micromirror device, since the protrusion 98 is provided on the back surface of the mirror 97, the gap between the lower electrode 92 and the electrode of the mirror 97, that is, the interelectrode gap, can be made small. As described above, since the electrostatic force is inversely proportional to the square of the gap between the electrodes, the mirror 97 can be tilted more greatly.

FIG. 13 is a perspective view showing a part of another micromirror device according to the present invention. As shown in the figure, a torsion spring 99 is provided between the base portion 76 and the frame body 77, and a holding portion 100 is provided to prevent the mirror 78 portion from being bent due to its own weight or electrostatic force F. .

A method of manufacturing the micromirror device shown in FIG. 13 will be described with reference to FIGS. 14 (a) to 14 (d) and FIGS.
5 (c) will be described. As shown in FIG. 14 (a),
A silicon oxide layer 112 is provided on a supporting substrate 111 made of single crystal silicon, and a silicon layer (SOI layer) 113 is provided on the silicon oxide layer 112. Below the SOI substrate, three layers of Ti / Pt / Au are provided. Joint part 11
4, an etching resist layer is formed on the silicon layer 113, and a groove (hole) 115 is further formed in the silicon layer 113.

Next, as shown in FIG. 14B, the surface of the silicon layer 113 is thermally oxidized to form the silicon oxide layer 11
After forming 6, the groove (hole) 117 reaching the support substrate 111 is formed by etching. In this case, first, the silicon oxide layer 116 is reactively etched with a CF gas, and then the silicon layer 113 is etched with SF6 gas using ICP. After that, the silicon oxide layer 112 is further added.
After reactive etching with CF-based gas, the supporting substrate 111 is etched with SF6 gas using ICP.

Next, as shown in FIG. 14C, a groove 118 is formed in the silicon oxide layer 116 by etching.
To form. Next, as shown in FIG. 14D, after the polycrystalline silicon layer 119 is formed on the surface, a part of the polycrystalline silicon layer 119 is removed by etching.

Next, as shown in FIG.
Silicon oxide layer (passivation film) on the surface by CVD
120 is formed. Next, as shown in FIG. 15B, the support substrate 111 is back-etched to form a frame portion 79. Next, as shown in FIG. 15C, the silicon oxide layers 112, 116 and 120 are removed by immersing in buffered hydrofluoric acid to form the torsion spring 99 and the holding portion 100.

In the method of manufacturing the micromirror device, since the groove 117 penetrates the silicon oxide layer 112, when the silicon oxide layer 112 is removed by immersing in the buffer hydrofluoric acid, the silicon oxide at the base 76 is removed. Since the layer 112 can be prevented from being removed, the support substrate 111 (frame portion 79) and the silicon layer 113 are not separated at the base portion 76.

In each of the embodiments described above, the SOI substrate is used as the substrate, that is, the upper substrate, but a SIMOX substrate may be used as the substrate. In each of the above-described embodiments, the silicon oxide layer 4 is used as the oxide layer.
Although 2, 45, the intermediate layer 52, and the silicon oxide layer 112 are used, other oxide layers may be used.

In each of the above-mentioned embodiments,
Although one mirror 33, 78 is provided on the upper substrate 27, 75, a large number of mirrors (array mirrors) may be provided on the upper substrate. In this case, wiring for driving the mirror is provided on the lower surface of the lower substrate. When the through hole is provided to connect the lower electrode and the wiring on the lower substrate, the pattern width of the wiring can be increased.

In each of the above-mentioned embodiments,
A substrate having a three-layer structure in which a silicon oxide layer 45 is provided on a supporting substrate 50 made of single crystal silicon and a lower silicon layer 41, a silicon oxide layer 42, and an upper silicon layer 43 are provided on the silicon oxide layer 45 was used. However, by depositing glass fine particles (soot) containing silica as a main component on one of two SIMOX substrates that have been subjected to epitaxial crystal growth, and then stacking (sintering) the other SIMOX substrate on top of each other. Alternatively, both SIMOX substrates may be bonded (see JP-A-61-242033), and then the substrates may be manufactured by polishing and etching.

Next, an embodiment will be described in which it is possible to prevent the mirror 33 and the protrusion 34 from contacting each other over a large area (referred to as pull-in).

Since the electrostatic force F is inversely proportional to the square of the distance d, the electrostatic force F tries to return the mirror 33 to the original position as soon as the mirror 33 approaches the predetermined distance on the protrusion 34 or less. The restoring force of the torsion springs 35 and 36 becomes much larger, and the mirror 33 and the protrusion 34 may come into contact with each other over a large area.

In this pull-in, since it is desired to reduce the voltage V to rotate the mirror 33, the tilt-in limit value is pulled in as the distance d is reduced as much as possible and the spring constants of the torsion springs 35 and 36 are reduced. The closer it is to the margin of the threshold at which it occurs, the more likely it is that it will occur. For this reason, high-precision voltage control must be performed within a few milliseconds so that the pull-in threshold value is not exceeded. The attitude control of the mirror 33 for several milliseconds corresponds to the switching time.

When the mirror 33 pulls in, the electrode of the mirror 33 and the lower electrode 22 may be short-circuited, and the electrode of the mirror 33 and the lower electrode 22 may be damaged. In the case of an array mirror, the spring constants of the torsion springs 35 and 36 of each mirror 33 are not uniform, so that the mirror 3
The electrostatic force F that causes the pull-in of 3 may be different.
In this case, the characteristics of the respective mirrors 33 are greatly different and are not practically used.

When the rotation of the mirror 33 becomes large, the edge (peripheral portion) of the mirror 33 and the lower substrate 2
Since point 1 and point 1 come into contact with each other at a point, stress concentrates instantaneously on the edge of the mirror 33, and the mirror 33 is easily broken. If the mirror 33 is thin and easily deformed, the distance d at which pull-in occurs tends to be smaller than the threshold value. Even if pull-in does not occur, the electrostatic force F
Thus, when the mirror 33 approaches the lower electrodes 22 and 23, that is, when the mirror 33 shifts toward the lower electrodes 22 and 23, the optical axis of the light beam incident on the mirror 33 shifts. The shift in the direction of the lower electrodes 22 and 23 must be kept as small as possible.

The present embodiment has been made to solve such a problem, and in order to achieve this object, in the present embodiment, a micromirror having a mirror and a lower substrate provided with a lower electrode. In the device, a protrusion made of an insulator is provided on a portion of the lower substrate where the lower electrode is provided.

FIG. 16 is a schematic sectional view showing the micromirror device according to this embodiment, and FIG. 17 is a schematic plan view showing the lower substrate of the micromirror device shown in FIG. As shown in the figure, a lower substrate (lower electrode substrate) 241 made of single crystal silicon having a crystal orientation of (100) has a height of 40 μm.
m protrusions 253 are provided, and the lower electrodes 242 are provided on the protrusions 253. A protrusion 243 having a surface of an insulator, a height of 5 μm, and a width of 3 μm is provided at the center of the protrusion 253, that is, the center of the lower electrode 242. A groove 244 is provided around the lower electrode 242, and an insulating film 245 is provided on the surface of the lower substrate 241 including the upper side wall of the groove 244 and the opening edge portion. The lower electrode 242 is provided on the insulating film 245.

An upper substrate (mirror forming substrate) 252 made of an SOI substrate is provided with columns 246 made of single crystal silicon having a crystal orientation of (100). The columns 246 are attached to the lower substrate 241, and the upper substrate is attached to the lower substrate 241. Two
52 is bonded.

A base 247 made of single crystal silicon having a thickness of about 10 μm is provided on the support column 246, an annular frame 248 is provided inside the base 247, and a mirror 249 is provided inside the frame 248. ing. On the surface of the mirror 249, electrodes made of three Ti / Pt / Au layers are provided. The pillar 246 supports the mirror 249 in space, and the distance between the lower electrode 242 and the mirror 249 is 20 μm. The base 247 and the frame 248 are connected at two locations by a torsion spring 250 similar to the torsion springs shown in FIGS. 4, 7, and 9, and the frame 248 and the mirror 249 are at two locations. The torsion springs 251 having the same shape as the torsion springs 250 are connected, and the line connecting the two torsion springs 250 and the line connecting the two torsion springs 251 are orthogonal to each other. Base 247 made of single crystal silicon having a thickness of about 10 μm, frame 2
48, mirror 249, torsion spring 250, 2
51 is integrally formed.

Next, a method of manufacturing the micromirror device shown in FIGS. 16 and 17 will be described. First, oxygen ions are implanted into a single crystal silicon substrate having a crystal orientation of (100), a silicon oxide layer is formed at a constant depth, and a SIM is formed.
As an OX substrate, epitaxially growing single crystal silicon on an active layer of a SIMOX substrate to form an SOI layer having a thickness of about 10 μm, an SOI substrate is prepared. Next, the SOI layer of the SOI substrate is doped with impurities so that the impurity concentration is 1 × 10 ^20, and the specific resistance is set to several thousandths of Ωcm. Next, three layers of Ti are lifted off.
A reflection film made of / Pt / Au is formed, and a three-layered joint made of Ti / Pt / Au is patterned on the back surface of the supporting substrate of the SOI substrate using a double-sided aligner in accordance with the mirror pattern on the surface. Next, ICP (inductivel
The SOI layer is etched using y-coupled plasma) to integrally form the base portion 247, the frame body 248, the mirror 249, and the torsion springs 250 and 251. Next, a silicon oxide layer (passivation film) is formed on the surface by PCVD (plasma CVD) to protect the surface, and then the support substrate of the SOI substrate is etched with an etchant of KOH to form the pillar 246.

A projection 243 is formed by anisotropic etching in the central portion of a single crystal silicon substrate having a crystal orientation of (100), and the projection 243 is masked to form a single crystal silicon substrate K.
Etching with OH to form a protrusion 253, forming a groove 244 around the protrusion 253 of the single crystal silicon substrate,
The insulating film 245 is formed by thermally oxidizing the surface of the single crystal silicon substrate, the surface of the protrusion 243 is used as an insulator, and the lower electrode 242 is formed on the insulating film 245. 3 layers of Ti / Pt /
After forming the Au layer, AuS on the Ti / Pt / Au layer
A solder part made of n is formed. Next, the lower substrate 24
After aligning 1 with the upper substrate 252, the solder in the solder portion is melted by heating at 390 ° C. with the joint portion pressed against the solder portion, and the upper substrate 252 is bonded to the lower substrate 241.

In this micromirror device, when a large voltage is applied symmetrically to the lower electrode 242, the mirror 249 moves toward the lower substrate 241 as shown in FIG. 18, that is, downward in the plane of FIG. Is in contact with the protrusion 243, the mirror 249 and the protrusion 253 do not contact each other over a large area, and pull-in does not occur.

When a large voltage is applied to the lower electrode 242 asymmetrically, as shown in FIG.
49 is greatly inclined, but the edge of the mirror 249 is groove 2
Since it is located inside 44, the edge of the mirror 249 does not come into contact with the lower substrate 241.

For example, a voltage of 95 V difference is applied to the lower electrode 24.
When given to all electrodes on one side of 2, mirror 249 could be tilted by 12 °. At this point, the mirror 249
The central portion of the mirror contacted the protrusion 243, and at the same time, the periphery of the mirror 249 contacted the edge of the groove 244 with a line.

Further, even if a voltage difference of 200 V was applied to the lower electrode 242, the mirror 249 was contacted only by the protrusion 243, and the contact area was small, so that pull-in did not occur. To demonstrate that pull-in is not happening,
When a voltage of 200V difference was applied to the lower electrode 242 and a voltage of several tens of V difference was applied to the lower electrode 242 asymmetrically, the mirror 249 could be rotated. Next,
Even if the lower electrode 242 is asymmetrically supplied with a voltage of 200 V, which is much larger than 95 V which gives the maximum rotation angle, and is rotated,
The voltage difference is 9 at the contact portion between the mirror 249 and the lower substrate 241.
As in the case of 5V, only the protrusion 243 and the upper edge of the groove 244 were present (see FIG. 20).

Further, since the edge of the mirror 249 did not collide with the lower electrode 242, the mirror 249 was never broken.

If the same experiment is performed without protrusions, pull-in occurs at a voltage difference of 70 V, so rotation control needs to be performed within a voltage difference of 65 V, and the movable rotation angle of the mirror is limited to ± 6 degrees. It was As described above, in the present invention, the movement of the mirror 249 is stopped at the edge of the groove 244 where the projection 243 and the insulating film 245 are formed, so that pull-in does not occur and short-circuit does not occur.

As described above, in this micromirror device, since the mirror 249 does not cause pull-in, the electrode of the mirror 249 and the lower electrode 242 are not short-circuited. 242 is not damaged. Further, in the case of an array mirror, the torsion spring 25 of each mirror 249 is
Even if the spring constants of 0 and 251 are not uniform, they can be put to practical use. Further, even when the rotation of the mirror 249 becomes considerably large, the mirror 249 does not come into contact with the lower substrate 241, so that the mirror 249 can be prevented from being broken.

Further, since the insulating film 245 is provided at least on the upper portion of the side wall of the groove 244 and the opening edge portion, even if the rotation of the mirror 249 becomes extremely large,
Even if the mirror 249 comes into contact with the lower substrate 241, the breakage of the mirror 249 can be reliably prevented.

FIG. 21 is a schematic plan view showing a lower substrate of another micromirror device according to the present invention, and FIG. 22 is a sectional view taken along line BB of FIG. As shown in the figure, the lower substrate 241
Is provided with a hole 261 penetrating the lower substrate 241.
An insulating film 262 is provided on the surface of the lower substrate 241 including the upper side wall of 61 and the opening edge portion.

Although the groove 244 and the hole 261 are provided as the recesses in the above embodiment, other recesses may be provided. Further, in the above-described embodiment, the protrusion 243 whose surface is made of an insulator is provided, but the protrusion entirely made of an insulator may be provided.

Further, in the above-described embodiment, the protrusion 243 having a height of 5 μm is provided. However, if the distance between the mirror and the protrusion when the voltage is not applied to the lower electrode is made smaller, the mirror 249 is moved to the lower electrode 242. Since it is possible to prevent the shift of the mirror 249 toward the lower electrode 242, the optical axis of the light beam incident on the mirror 249 does not shift.

23 to 27 show another more specific embodiment of the present invention. As shown in FIG. 27, the micromirror device of this embodiment has a lower substrate 300 and an upper substrate 301 joined in parallel.

As shown in FIG. 23, the lower substrate 300 has a convex portion 302 formed in the central portion of the upper surface thereof so as to face the central portion of the lower surface of the mirror 318. The convex portion 302 has a substantially square shape in a plan view, a substantially square upper horizontal surface 302b is formed at the center, and a lower horizontal lower surface 302a is formed around the horizontal upper surface 302b. Upper surface 3
A fulcrum protrusion 304 facing the center of the mirror 318 is formed at the center of 02b, and a slight gap is formed between the fulcrum protrusion 304 and the mirror 318. At least the surface of the fulcrum protrusion 304 is formed of an insulator.

Lower substrate 300 including outer surface of convex portion 302
At the center of the upper surface of each of the four lower electrodes 30 each having a fan shape so as to form a circle concentric with the mirror 318 in a plan view.
6 is formed. The material and the like of the lower electrode 306 are the same as those in the above-described embodiment. The center of the fan of the lower electrode 306 coincides with the fulcrum protrusion 304, and between the lower electrodes 306,
A gap 307 having a constant width is formed. Although not shown, through holes are formed in the lower substrate 300 below the lower electrode 306, and the lower electrode 306 is connected to a wiring pattern (not shown) formed on the lower surface of the lower substrate 300 through these through holes. Has been done.
The mirror 318 can be tilted by applying a voltage to the lower electrode 306 and the mirror 318 through the wiring pattern. At this time, if the mirror 318 is displaced downward by a predetermined value or more, the fulcrum protrusion 304 comes into contact with the center of the mirror 318 and becomes a fulcrum for tilting the mirror 318.

The number of lower electrodes 306 is four in this embodiment, but if the number is three or more, the mirror 318 can be tilted in any direction. However, considering the ease of wiring and the ease of control, four cases are preferable.

The ring portion 3 is formed on the upper surface of the lower substrate 300.
The concave portions 308 and 309 are respectively provided at two positions on the outer peripheral portion of the mirror 14 and at two positions on the outer peripheral portion of the mirror 318.
Are formed. The recess 308 is located at a position 90 ° away from the torsion spring 316 that supports the ring portion 314,
The recesses 309 are formed at positions separated by 90 ° from the torsion spring 316 that supports the mirror 318. Thereby, the tilting range of the mirror 318 and the ring portion 314 around the torsion spring 316 can be set large.

As shown in FIG. 24, the upper substrate 301
Is a central mirror 318, a ring portion 314 surrounding the outer periphery of the mirror 318, a base portion 312 surrounding the outer periphery of the ring portion 314, and a frame 322 formed on the outer peripheral edge.
However, it is integrally formed of silicon single crystal.
The frame 322 is formed via the silicon oxide film 320. 180 between the base portion 312 and the ring portion 314
It is connected by a pair of torsion springs 316, and the ring portion 314 and the mirror 318 are connected by a pair of torsion springs 316 at a position 90 ° apart from the previous torsion spring 316. These torsion springs 316 are also included in the mirror 31.
8, the ring portion 314, and the base portion 312 are integrally formed.

FIG. 25 shows details of the torsion spring 316. This figure shows a ring portion 314 and a base portion 31.
Although the torsion spring 316 for connecting to the No. 2 is shown, the one for connecting the ring portion 314 and the mirror 318 is exactly the same.

The torsion spring 316 has a base 3
12 is housed in a recess 332 formed in the base 12,
A base end portion 316a, a meandering portion 316b, and a stopper 316c formed at the tip of the meandering portion 316b,
The tip portion 316d extends from the stopper 316c and is connected to the ring portion 314. The base portion 316a and the tip portion 316d extend in the radial direction of the ring portion 314, and the meandering portion 316b extends in a direction perpendicular to the radial direction. The tip portion 316d passes through the slit 330 formed in the base portion 312. The width of the slit 330 is made sufficiently larger than the width of the tip portion 316d so as to allow the twist of the tip portion 316d.

The base end portion 316a, the meandering portion 316b, and the tip end portion 316d have substantially the same cross-sectional shape in the shape of a rectangle, and their height H (see FIG. 27) and width W (see FIG. 2).
5)), the aspect ratio H / W is 1.8 or more, more preferably 2.5 to 8, and most preferably about 3.
By adopting such an aspect ratio, it is possible to reduce the elasticity of the tip portion 316d in the twisting direction while increasing the support strength of the ring portion 314 in the vertical direction.
It is possible to tilt the mirror 318 with less power.

The stopper 316c of this embodiment has an isosceles triangular prism shape convex toward the ring portion 314,
A pair of position regulating parts 33 formed in the slit 330
There is a slight gap formed between 0a and 0a. Stopper 3
The width of 16c is smaller than the width of the slit 330. Therefore, even when the ring portion 314 is excessively displaced downward or in the direction away from the torsion spring 316,
The stopper 316c and the position restricting portion 330a come into contact with each other,
Suppress further displacement. As a result, the torsion spring 316 can be prevented from being damaged. Mirror 31
The same action can be obtained with the torsion spring 316 on the eight side.

FIG. 26 shows a modification of the stopper mechanism.
The stopper 316e in this example has a rectangular parallelepiped shape having a surface perpendicular to the tip portion 316d. At the opening edge of the slit 330 of the base portion 312, a pair of position restricting portions 330b protruding toward the stopper 316e are formed. The position restricting portion 330b has a substantially semicircular horizontal cross section, and a slight gap is formed between the position regulating portion 330b and the stopper 316e. Therefore, even when the ring portion 314 is excessively displaced downward or in the direction away from the torsion spring 316, the stopper 316e and the position restricting portion 33 are not provided.
0b comes into contact and suppresses further displacement. As a result, the torsion spring 316 can be prevented from being damaged. In addition, the stopper 316e and the position restricting portion 330b
Since it can slide in any direction along the surface perpendicular to the radial direction of the ring portion 314 while being in contact with the ring portion 31.
The tilting of No. 4 is hardly suppressed.

According to the micromirror device having the above structure, the stopper 316c or 316e for restricting the displacement amount of the torsion spring 316 and the position restricting portion 33 are provided.
0a or 330b is formed, the ring portion 31
4 and the mirror 318 can be prevented from being excessively displaced, and the torsion spring 316 can be prevented from being damaged.

The lower surface 302a and the upper surface 30
By forming the convex portion 302 having 2b and bringing the mirror center side of the lower electrode 306 closer to the mirror 318, it is possible to tilt the mirror 318 with a relatively low voltage.

Further, the recesses 308, 3 are formed in the lower substrate 300.
By forming 09, the tilt range of the ring portion 314 and the mirror 318 can be expanded while suppressing the thickness of the entire device. The recesses 308 and 309 may penetrate the lower substrate 300.

FIG. 28 shows still another embodiment of the present invention. In this embodiment, the convex portion 340 formed in the central portion of the lower substrate 300 has a conical shape, and the lower electrode 306 is also formed on the outer surface 340a thereof. Other configurations may be similar to those of the embodiment shown in FIGS.

FIG. 33 shows an embodiment obtained by partially modifying the embodiment shown in FIGS. 23 to 27. In this embodiment, the upper portion (that is, the central portion) of the convex portion 302, which includes the fulcrum protrusion 304 and the upper step surface 302b, is covered with an insulating layer, and the four lower electrodes 306 are provided on the lower step surface 302a and below it. It is formed only in the area.

Accordingly, in this embodiment, the convex portion 3
In a certain area centered on the vertex of 02, the convex portion 30
The lower electrode 306 is not formed on the outer peripheral surface of No. 2. In this embodiment, with the vertex (center) of the convex portion 302 as the center,
It is preferable that the lower electrode 306 is not formed in a circular region having a diameter of 1/5 to 1/2 of the diameter of the mirror. In that case, accurate control of the inclination angle can be performed more easily. Further, it is preferable that the lower electrode 306 is not formed in a range up to 50% of the height of the convex portion 302. The height of the convex portion 302 includes the height of the fulcrum protrusion 304.

As described above, the lower electrode 306 is formed on the convex portion 30.
When formed only on the annular portion excluding the upper portion (that is, the central portion) of 2, the inclination angle /
Although the ratio of the applied voltage decreases, there is an advantage that accurate control of the tilt angle can be easily performed in a relatively high voltage region (a region where the tilt angle is relatively large).

[0118]

Example [Experiment 1] Four types of examples of the present invention were prepared. All of the examples have the common structure shown in FIGS. 23 to 25 and FIG. 27, and the dimensions of each part are as shown in FIG. The respective examples differ only in the aspect ratio (H / W) of the cross section of the torsion spring, and 0.2, 1.
It was set to 2, 2.0 and 3.0. Using these examples,
The mirror tilt angle when 0 V was applied, and the voltage at which the pull-in phenomenon in which the mirror collides with the lower substrate (referred to as pull-in voltage) were measured. When applying the voltage, the voltage was applied only to the two lower electrodes corresponding to one side of the mirror. The results are shown in Fig. 29. As is clear from this graph, the sensitivity of each of the examples, that is, the inclination angle when 50 V was applied was almost the same, but the pull-in voltage was remarkably improved by increasing the aspect ratio.

[Experiment 2] Next, a micromirror device of a comparative example shown in FIG. 31 was prepared. The aspect ratio (H / W) of the torsion spring in this comparative example was set to 3.0. The comparative example is different from the example only in that the convex portion 302 is not formed, and other configurations are exactly the same as the example having the aspect ratio of 3.0.

Further, as Example 5, a micromirror device having the structure shown in FIG. 33 and having the dimensions of each part as shown in FIG. 30 was prepared. Various voltages were applied to these six types of micromirror devices, and the tilt angle of the mirror was measured. The results are shown in Fig. 32. As is apparent from this graph, by forming the convex portion 302 on the lower substrate as shown in FIGS. 30 and 33, the inclination angle can be increased even with the same applied voltage. It was also found that in the example of FIG. 33, it is easy to control the tilt angle especially when the tilt angle exceeds 4 °.

[0121]

According to the micromirror device of the present invention, since the convex portion is provided on the upper surface of the lower substrate so as to face the central portion of the mirror, and the lower electrode is formed on the outer surface of the convex portion,
At least part of the mirror and the lower electrode can be brought close to each other, and the voltage required for tilting the mirror can be reduced.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a micromirror device according to the present invention.

FIG. 2 is a perspective view showing a part of the micromirror device shown in FIG.

3 is a cross-sectional view taken along the line AA of FIG.

FIG. 4 is a perspective view showing a part of another micromirror device according to the present invention.

FIG. 5 is an explanatory view of the method for manufacturing the micromirror device shown in FIG.

FIG. 6 is an explanatory diagram of a method of manufacturing the micromirror device shown in FIG.

FIG. 7 is a perspective view showing a part of another micromirror device according to the present invention.

8 is a cross-sectional view showing a part of the micromirror device shown in FIG.

FIG. 9 is a diagram showing a part of another micromirror device according to the present invention.

FIG. 10 is an exploded perspective view showing another micromirror device according to the present invention.

FIG. 11 is an exploded perspective view showing another micromirror device according to the present invention.

FIG. 12 is an exploded perspective view showing another micromirror device according to the present invention.

FIG. 13 is a perspective view showing a part of the micromirror device shown in FIG.

FIG. 14 is an explanatory diagram of the method for manufacturing the micromirror device shown in FIGS. 12 and 13.

FIG. 15 is an explanatory view of the method for manufacturing the micromirror device shown in FIGS. 12 and 13.

FIG. 16 is a schematic cross-sectional view showing a micromirror device according to the present invention.

FIG. 17 is a schematic plan view showing a lower substrate of the micromirror device shown in FIG.

FIG. 18 is an operation explanatory diagram of the micromirror device shown in FIGS. 16 and 17;

FIG. 19 is an operation explanatory diagram of the micromirror device shown in FIGS. 16 and 17;

20 is an operation explanatory diagram of the micromirror device shown in FIGS. 16 and 17. FIG.

FIG. 21 is a schematic plan view showing a lower substrate of another micromirror device according to the present invention.

22 is a cross-sectional view taken along the line BB of FIG.

FIG. 23 is a plan view showing a lower substrate according to another embodiment of the present invention.

FIG. 24 is a plan view showing an upper substrate of another embodiment.

FIG. 25 is a plan view showing a stopper mechanism of a torsion spring.

FIG. 26 is a plan view showing a stopper mechanism of a torsion spring.

FIG. 27 is a vertical cross-sectional view of another embodiment.

FIG. 28 is a vertical sectional view showing still another embodiment.

FIG. 29 is a graph showing the effect of the present invention.

FIG. 30 is a sectional view showing an example of the present invention.

FIG. 31 is a cross-sectional view showing a comparative example.

FIG. 32 is a graph showing an experimental result by the apparatus of FIGS. 30 and 31.

FIG. 33 is a cross-sectional view of another embodiment.

FIG. 34 is a schematic perspective view showing a conventional micromirror device.

FIG. 35 is an explanatory diagram of a method for manufacturing the micromirror device shown in FIG. 34.

[Explanation of symbols]

21, 71, 91, 241, 300 Lower substrate 22, 23, 73, 92, 242, 306 Lower electrode 24, 74, 81, 93 Wiring pattern 25 Through hole 27, 75, 94, 252, 301 Upper substrate 28, 80 , 102, 246 columns 33, 78, 97, 249, 318 mirrors 34, 72, 98, 253 protrusions 35, 36, 99, 250, 251, 316 torsion springs 302 protrusions 304 fulcrum protrusions 330a, 330b position regulating portion 41 , 51 lower silicon layers 42, 45, 112 silicon oxide layers 43, 53 upper silicon layers

Continued front page    (72) Inventor Toru Maruno             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F-term (reference) 2H041 AA12 AB14 AC06 AZ02 AZ08                 2H045 AB02 AB06 AB13 AB73

Claims (11)

[Claims] 1. A micromirror device, comprising: a mirror; a plurality of torsion springs for tiltably supporting the mirror with respect to an upper substrate; a lower substrate arranged to face a lower surface of the mirror; and a lower substrate of the lower substrate. A micromirror device comprising: a convex portion provided on an upper surface so as to face a central portion of the mirror; and a plurality of lower electrodes formed on an outer surface of the convex portion. 2. The micromirror device according to claim 1, wherein the torsion spring has a height / width aspect ratio of 1.8 or more in a cross section perpendicular to the longitudinal direction thereof. Micro mirror device. 3. The micromirror device according to claim 1, wherein a concave portion is formed on the upper surface of the lower substrate at a position around the convex portion and facing an outer peripheral edge of the mirror. Micromirror device characterized by. 4. The micromirror device according to claim 1, wherein a fulcrum protrusion made of an insulator is formed on the convex portion so as to face the center of the mirror. . 5. The micromirror device according to claim 1, wherein the torsion spring has a meandering portion, and a position restricting portion for restricting a displacement range of the torsion spring is formed on the upper substrate. A micromirror device characterized in that 6. The micromirror device according to claim 1, wherein the mirror, the torsion spring, and the upper substrate are integrally formed of a silicon single crystal,
A micromirror device, wherein the silicon single crystal is bonded to a spacer formed on the lower substrate. 7. The micromirror device according to claim 1, wherein wiring patterns are formed on a lower surface of the lower substrate, and the wiring patterns and the lower electrodes are formed inside the lower substrate. A micromirror device, which is electrically connected through a through hole. 8. The micromirror device according to claim 1, wherein the upper substrate is an SOI substrate or a SIMOX substrate. 9. The micromirror device according to claim 1, wherein an insulating film is formed on at least an opening edge portion of the concave portion. 10. The micromirror device according to claim 1, wherein the apex of the convex portion is the center and the diameter of the mirror is 1
The micro-mirror device, wherein the lower electrode is not formed in a circular region having a diameter of / 5 to 1/2. 11. A method of manufacturing a micromirror device, comprising: a support substrate, a first oxide layer, a first single crystal silicon layer,
A step of sequentially forming a second oxide layer and a second single crystal silicon layer; a step of forming a groove penetrating the second single crystal silicon layer, the second oxide layer, and the first single crystal silicon layer Forming a polycrystalline silicon layer in the groove; etching the second single crystal silicon layer to form a mirror and a torsion spring with the second single crystal silicon layer; Removing a silicon layer; etching a portion of the first single crystal silicon layer located below the torsion spring through the groove; and removing the first oxide layer and the second oxide layer. Then, the method of manufacturing a micromirror device further comprises the step of making the torsion spring independent.