JP2013186224A - Optical reflection element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical reflection element capable of improving a resonance frequency of an operation mode which vibrates to a normal line direction of a movable plate without causing a reduction in amplitude in the rotation operation of the movable plate.SOLUTION: There is provided an optical reflection element which comprises: a first side 11a parallel to a first axis 18; a square external frame having a second side 11b parallel to a second axis 19 which is almost orthogonal to the first axis 18; a first drive part having a meander shape which extends from the inside of one first side 11a of the external frame and is provided with at least one or more piezoelectric actuators; a strip-shaped support beam extending from an approximately middle point of the inside of one first side 11a of the external frame to a direction of the second axis 19; and a movable plate 15 which is connected to the support beam 12 and the drive part and has a reflection surface at the central part.

Description

  The present invention relates to an optical reflection element used for an optical scanning projector or the like.

  Optical reflection elements that scan a light beam emitted from a laser and project an image on a screen have been put into practical use. Such an optical reflection element scans an actuator provided with a mirror part, reflects a light beam by the mirror part and projects it onto a screen, and a raster scanning method is used as a scanning method of the actuator. FIG. 11 is a perspective view showing the configuration of a conventional optical reflection element that is scanned by a raster scan method.

  In FIG. 11, the conventional optical reflecting element includes a rectangular outer frame 1, a pair of meander-shaped first drive units 2 that extend from the inner side of the short side of the outer frame 1 and include at least one piezoelectric actuator, 1 and a rectangular movable plate 3 connected at a side parallel to the short side of the outer frame.

  The movable plate 3 includes a rectangular middle frame 4 connected to the first drive unit 2 at a side parallel to the short side of the outer frame 1, a second drive unit 5 including at least one piezoelectric actuator, The mirror unit 7 includes a reflecting surface connected to the second driving unit 5 by a pair of torsion bars 6.

  The movable plate 3 rotates around the first axis 8 parallel to the long side direction of the outer frame 1 through the approximate center of the mirror unit 7, and the mirror unit 7 passes through the approximate center of the outer frame 1. By rotating around the second axis 9 parallel to the short side direction, the mirror portion 7 is scanned with the light beam irradiated and reflected in two axes, and an image is projected on the screen.

  Note that Patent Document 1 is known as prior art document information relating to the invention of this application.

JP 2009-169290 A

  In the optical reflection element as described above, it is important to increase the deflection angle. In order to realize the raster scan method, it is necessary to drive the movable plate 3 around the first axis 8 in a sawtooth wave shape including harmonic components. In order to improve the vibration characteristics, it is necessary to increase the resonance frequency of the natural vibration mode in which the movable plate rotates around the first axis 8. If possible, it is desirable that the resonance frequency be at least 500 Hz.

  However, in the above-described conventional configuration, in addition to the vibration mode in which the movable plate 3 rotates around the first axis 8, the mode in which the movable plate 3 vibrates in the normal direction of the reflecting surface or the movable plate 3 is the second mode. There are various vibration modes, such as a mode of rotating around the axis 9. If an attempt is made to improve the amplitude of the rotational motion around the first axis 8 of the movable plate 3 or to improve the resonant frequency of the vibration mode of the rotational motion, the resonant frequency of the other vibration mode may decrease, As a result, the operation becomes unstable at the time of scanning, which makes it difficult to control the movable plate 3 or is easily affected by disturbance vibrations, resulting in deterioration of vibration resistance.

  Therefore, the present invention provides an operation mode in which the movable plate oscillates in the normal direction of the reflecting surface without causing a decrease in amplitude in the rotational operation around the first axis 8 of the movable plate 3, and the movable plate has the second axis 9. An object of the present invention is to provide an optical reflecting element capable of improving the resonance frequency of a mode that rotates around.

  In order to achieve the above object, the present invention provides a rectangular outer shape having a first side parallel to the first axis and a second side parallel to the second axis substantially orthogonal to the first axis. A frame, a meander-shaped first drive unit including at least one piezoelectric actuator extending from the inside of the first side of the outer frame, and the inner side of the other first side of the outer frame. A strip-shaped support beam extending from the substantially middle point in the second axial direction, and a movable plate connected to the support beam and the drive unit and having a reflection surface at the center portion are provided.

  The present invention selects the vibration of the movable plate in the normal direction of the reflecting surface with bending compared to the rotational movement around the first axis of the movable plate with torsion, by the support beam having higher bending rigidity than torsional rigidity. The operation mode in which the movable plate vibrates in the normal direction of the reflecting surface without causing a decrease in amplitude in the rotational operation around the first axis of the movable plate, and the movable plate is around the second axis. Since the resonance frequency of the mode that rotates in the direction can be improved, the controllability and vibration resistance of the optical reflecting element can be improved.

The top view of the optical reflective element in Example 1 of this invention Sectional drawing of the piezoelectric actuator in the AA line of the same FIG. The figure which shows the drive of the optical reflection element Sectional view of the support beam along line BB in FIG. The top view of the optical reflective element in Example 2 of this invention Sectional drawing in the 2nd axis | shaft 19 of the same FIG. (A)-(e) Sectional drawing which shows the manufacturing method of the optical reflective element by Example 2 of this invention Overall view of movable plate in embodiment 3 of the present invention Overall view of optical reflecting element in Example 4 of the present invention Diagram showing drive of the movable plate A perspective view of a conventional optical reflecting element

Example 1
Embodiment 1 of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a plan view of an optical reflecting element in Embodiment 1 of the present invention. As shown in FIG. 1, the optical reflecting element according to the first embodiment of the present invention is parallel to a first side 11 a parallel to the first axis 18 and a second axis 19 that is substantially orthogonal to the first axis 18. A rectangular outer frame 11 having a second side 11b, and a strip-shaped support beam 12 extending in the direction of the second axis 19 from a substantially middle point inside one first side 11a of the outer frame 11. And a meander-shaped first drive unit 13 extending from the inside of the other first side 11a of the outer frame, and a movable member having a reflection surface 14 at the center and connected to the support beam 12 and the drive unit 13. A plate 15 is provided. Further, the meander-shaped first driving unit 13 includes a piezoelectric actuator 16 and a bending unit 17, and realizes a rotating operation around the second axis 19 in the movable plate 15.

  Next, the composition of the members of the optical reflecting element in Example 1 of the present invention will be described below.

  The optical reflecting element according to the first embodiment of the present invention uses an elastic member such as silicon having a high elastic strength, mechanical strength, and high Young's modulus as a substrate material.

  FIG. 2 is a sectional view of the piezoelectric actuator 16 taken along the line AA in FIG. The piezoelectric actuator 16 includes a silicon oxide film 21 stacked on the silicon base material 20, a lower electrode layer 22 stacked on the silicon oxide film 21, a piezoelectric layer 23 stacked on the lower electrode layer 22, The upper electrode layer 24 is laminated on the piezoelectric layer 23.

The material of each layer is platinum for the lower electrode layer 22, gold for the upper electrode layer 24, lead zirconate titanate (Pb (Zr _x , Ti _1-x ) O ₃ , and x = 0. 525) or the like. In addition, these can be collectively formed by a thin film process such as vapor deposition, sol-gel, CVD, or sputtering, and a fine pattern can be accurately processed by an etching technique using a photolithography technique.

  The movable plate 15 is made of a base material 20 such as silicon, and has a reflecting surface 14 at the center. The reflective surface 14 is a reflective film for reflecting light such as a laser beam, and a metal thin film mainly composed of silver is formed by a thin film process such as vapor deposition or sputtering.

  Next, a driving method according to the first embodiment of the present invention using the piezoelectric actuator 16 will be described.

  A voltage having a plurality of frequency components is applied to the piezoelectric actuator 16 portion of the first drive unit 13 shown in FIG. As a result, the piezoelectric actuator 16 is displaced so as to curve downward or convex upward.

  At this time, the phases of the voltages applied to the adjacent piezoelectric actuators 16 are reversed, so that each is driven symmetrically. That is, the adjacent piezoelectric actuators 16 are displaced in directions different by 180 degrees.

  In this manner, in the meander structure, the adjacent piezoelectric actuators 16 are displaced in directions different by 180 degrees, so that the displacement is accumulated around the rotation axis, and the displacement of the movable plate 15 can be obtained as shown in FIG.

  Next, the resonance frequency of the operation mode in which the movable plate 5 vibrates in the normal direction of the reflecting surface 14 without causing a decrease in amplitude in the rotational operation around the second axis 19 of the movable plate 15 which is the point of the present invention. The effect of the support beam 12 for improving the above will be described.

The torsional moment T generated between the surface in contact with the movable plate 15 and the surface in contact with the outer frame 11 is caused by the torsional deformation of the support beam 12 when the first driving unit 13 rotates the movable plate 15 by the rotation angle Ψ. Can be described as being twisted by the rotational angle Ψ. When the length of the support beam 12 in the direction of the second side 11b of the outer frame 11 is l, the torsion angle θ per unit length is expressed by the equation (1) θ = Ψ / l (1)
The relationship between the torsion angle θ per unit length and the torsion moment T is expressed by the following equation (2): T = G · Ip · θ (2)
It can be expressed as. At this time, G is a transverse elastic coefficient of the support beam 12, Ip is a cross-sectional secondary pole moment of the support beam 12, and G · Ip obtained by multiplying these is called torsional rigidity. As shown in the equation (2), the torsional rigidity is a physical index indicating the difficulty of twisting. The transverse elastic modulus of the support beam 12 is a value determined by the material, and the cross-sectional secondary pole moment is determined by the structure. FIG. 4 is a cross-sectional view of the support beam 12 taken along the line BB in FIG. The length of the outer frame 11 in the direction of the first side 11a is a, the thickness of the support beam 12 in the normal direction of the reflecting surface 14 is b, and these relationships are expressed by the following expression (3): a <b (3)
Is satisfied, the cross-sectional secondary pole moment Ip is expressed by the following equation (4): Ip = f · a ^ 3 · b (4)
It is represented by At this time, f is a coefficient obtained by a series solution in elasticity theory, fluctuates in the ratio of a and b, f = 0.290 when b / a = 5, and b / a = 10 f = 0.313, and as b / a increases, the value approaches 1/3.

On the other hand, the bending deformation of the support beam 12 when the movable plate 15 is displaced in the normal direction of the reflection surface 14 is obtained by changing the bending moment generated in the support beam 12 and the line segment CC connecting the position b / 2 in FIG. And the curvature radius ρ of the surface parallel to the reflecting surface 14 accompanying the bending deformation of the support beam 12, the equation (5) M = E · I · 1 / ρ (5)
Can be expressed as At this time, E is a longitudinal elastic modulus of the material of the support beam 12, I is a cross-sectional secondary moment of the support beam 12, and E · I obtained by multiplying these is called bending rigidity. As shown in the equation (5), the bending stiffness is a physical index indicating difficulty in bending. Generally, as the rigidity increases, the resonance frequency of the structure also increases. Therefore, in order to improve the resonance frequency of the operation mode accompanied by the displacement of the movable plate 15 in the normal direction of the reflecting surface 14, it is necessary to increase the bending rigidity of the structure. The longitudinal elastic modulus of the support beam 12 is a value determined by the material, and the cross-sectional secondary moment is determined by the structure. The cross-sectional second moment is calculated by using the formulas (6) and I = 1/12 · a · b ^ 3 (6)
It is represented by

  Here, if the structure of the support beam 12 is designed so that the value of b is larger than the value of a, I can be selectively increased compared to Ip, and the bending stiffness can be selectively compared with the torsional stiffness. Can be increased.

  Therefore, the resonance frequency of the operation mode in which the movable plate 15 vibrates in the normal direction of the reflecting surface 14 without causing a decrease in amplitude in the rotational operation around the second axis 19 of the movable plate 15 which is the object of the present invention. Can be improved.

  In addition, when the bending rigidity of the support beam 12 is higher than the bending rigidity of the driving beam, the bending rigidity of the support beam 12 is dominant in the bending rigidity of the optical reflecting element, and this effect can be enhanced. Further, as the value of b is designed to be larger than the value of a, the bending rigidity is more selectively improved than the torsional rigidity.

(Example 2)
The arrangement of the first drive unit 13 and the support beam 12 which are different points between the second embodiment of the present invention and the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 5 shows a plan view of an optical reflecting element in Embodiment 2 of the present invention. As shown in FIG. 5, the optical reflecting element according to the second embodiment of the present invention is parallel to the first side 11 a parallel to the first axis 18 and the second axis 19 substantially orthogonal to the first axis 18. A rectangular outer frame 11 having a second side 11b, a pair of meander-shaped first drive parts 13 extending from the inside of the first side 11a of the outer frame 11, and a first of the outer frame 11 A pair of strip-shaped support beams 12 extending from a substantially middle point inside the side 11 a toward the second axis 19 of the outer frame 11, a reflection surface 14 at the center, and a support beam 12 and a drive unit 13. It has a movable plate 15 to be connected. FIG. 6 shows a cross-sectional view in the direction of the second axis 19. As shown in FIG. 6, the support beam 12 is located below the first drive unit 13.

  Next, the manufacturing method of the optical reflective element in Example 2 is demonstrated below.

First, as shown in FIG. 7 (a), a lower metal made of Pt is formed on one surface on a substrate 20 composed of a Si substrate 20a, an Si substrate 20c, a Si substrate 20e and a sacrificial layer 20b made of SiO ₂ and a sacrificial layer 20d. The layer 22, the piezoelectric film 23 made of PZT, and the upper metal layer 24 made of Au are sequentially laminated by sputtering or the like.

  Next, by using the elastic resin layer as an etching mask, a part of the lower metal layer 22 made of Pt, the piezoelectric film 23 made of PZT, and the upper metal layer 24 made of Au is removed by ICP dry etching, and FIG. ), The piezoelectric actuator 16 is formed.

  Next, as shown in FIG. 7C, a reflective film containing Ag as a main component is formed, and the reflective surface 14 is formed.

  Next, as shown in FIG. 7D, the Si substrate 20a and the Si substrate 20e are etched to form the support beam 12 and the first drive unit 13. However, at this time, the support beam 12 and the first drive unit 13 are connected via the sacrificial layer 20b.

Finally, as shown in FIG. 7E, the sacrificial layer 20b and the sacrificial layer 20d made of SiO ₂ are etched to separate the support beam 12 and the first driving unit 13 from each other.

  By the process as described above, a structure in which the support beam 12 is positioned below the first driving unit 13 can be realized.

  The driving force in the piezoelectric actuator is proportional to the area of the piezoelectric body, and the larger the driving force, the larger the deflection angle can be obtained in the optical reflecting element. In the configuration of the second embodiment of the present invention, since the first drive unit 13 and the support beam 12 are arranged in the vertical direction, the support beam 12 can be provided while increasing the area of the drive unit. As a result, the bending rigidity can be increased without increasing the element size, and the optical reflecting element can be miniaturized.

(Example 3)
The configuration of the movable plate 30, which is a difference between the third embodiment of the present invention and the first embodiment of the present invention, will be described with reference to the drawings.

  FIG. 8 shows a plan view of the movable plate 30. As shown in FIG. 8, the movable plate 30 includes a third side 30 a parallel to the first axis 18 and a fourth side 30 b parallel to the second axis 19 substantially orthogonal to the first axis 18. A rectangular frame-shaped support body 31, a pair of second drive parts 32 whose outer ends are supported by opposing portions inside the support body 31, and the inner parts of each of the second drive parts 32 The end is provided with a mirror part 34 supported on the first shaft 18. The second drive unit 32 includes a bending unit 35, a piezoelectric actuator 36, and a diaphragm 37, and the mirror unit 34 has the reflection surface 14.

  Next, the composition of the movable plate 30 will be described below.

  The movable plate 30 is made of an elastic member having elasticity, mechanical strength and high Young's modulus such as silicon as a substrate material. The piezoelectric actuator 36 includes a silicon oxide film 21 stacked on the silicon base material 20, a lower electrode layer 22 stacked on the silicon oxide film 21, and a lower portion, like the piezoelectric actuator 16 described in FIG. A piezoelectric layer 23 laminated on the electrode layer 22 and an upper electrode layer 24 laminated on the piezoelectric layer 23 are provided.

  Next, the operation of the movable plate 30 will be described below.

  First, an alternating voltage having a resonance frequency of the optical reflection element is applied to the piezoelectric actuator 36 portion of the second drive unit 32 shown in FIG. As a result, the piezoelectric actuator 36 is displaced so as to be curved downward or convex upward.

  At this time, the adjacent diaphragm 37 is driven symmetrically with the piezoelectric actuator 36 by the principle of resonance. That is, the diaphragm 37 is displaced and driven in a direction different from the piezoelectric actuator 36 by 180 degrees.

  As described above, in the meander structure, the adjacent diaphragm 37 and the piezoelectric actuator 36 are displaced in directions different by 180 degrees, so that the displacement is accumulated around the second axis 33 and the displacement of the mirror portion 34 can be obtained.

  In the structure of the third embodiment of the present invention, since the movable plate 30 includes the second driving unit 32 in the direction of the second axis 33, the mirror unit 34 can be rotated simultaneously by two axes. A single optical reflecting element can be used for scanning by a raster scan method, and the system can be miniaturized.

Example 4
A configuration of the movable plate 40 which is a difference between the fourth embodiment of the present invention and the first embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 9, the optical reflecting element according to the fourth embodiment of the present invention is parallel to the third side 40 a parallel to the first axis 18 and the second axis 33 substantially orthogonal to the first axis 18. A rectangular frame-shaped support body 41 having a second side 40b, first support portions 42a and 42b, first arms 43a and 43b, second arms 44a and 44b, and connecting portions 45a and 45b. There are two tuning fork vibrators 46a and 46b. Further, one end of the first support portions 42a and 42b is fixed to the support body 41, and one end of the two second support portions 48a and 48b is fixed to the vibration centers 47a and 47b of the tuning fork vibrators 46a and 46b. The other support part 48a, 48b has a mirror part 34 including a reflection surface 14 for reflecting light such as a laser beam at the other end. In addition, two tuning fork vibrators 46a and 46b are arranged opposite to the mirror part 34, and two vibration centers 47a and 47b and the second shaft 33 of the mirror part 34 are arranged on the same straight line. .

  Next, a driving method according to the fourth embodiment of the present invention using the piezoelectric actuator 49 will be described.

  FIG. 10 illustrates how the movable plate 40 is driven. Tuning fork vibrators 46a and 46b are arranged opposite to each other on the same line of the second shaft 33 of the mirror part 34 with the mirror part 34 as the center, and the first arms 43a and 43b of the two tuning fork vibrators 46a and 46b are connected to the second arm. A voltage is applied to the piezoelectric actuator 49 so that the phases of the arms 44a and 44b bend in directions different from each other by 180 degrees. Using the vibration energy of the two tuning fork vibrators 46a and 46b, torsional vibration can be caused in the torsional vibrator constituted by the second support part 48a, the mirror part 34, and the second support part 48b. By this torsional vibration, repetitive rotational vibration of the mirror part 34 is realized.

  In the structure according to the fourth embodiment of the present invention, the movable plate 40 can be rotated in the direction of the second axis 33, and the mirror part 34 can be rotated simultaneously at two axes. As a result, a raster scanning method can be used with a single optical reflecting element, and the system can be miniaturized.

  The optical reflecting element of the present invention is useful for an image projection apparatus such as a projector, a head-up display, and a head-mounted display.

DESCRIPTION OF SYMBOLS 11 Outer frame 11a 1st edge | side 11b 2nd edge | side 12 Support beam 13 1st drive part 14 Reflecting surface 15, 30, 40 Movable plate 16, 36, 49 Piezoelectric actuator 17, 35 Curved part 18 1st axis | shaft 19 Second shaft 20 Base material 21 Oxide film 22 Lower electrode layer 23 Piezoelectric layer 24 Upper electrode layer 30a, 40a Third side 30b, 40b Fourth side 31, 41 Support body 32 Second drive unit 34 Mirror unit 37 Diaphragm 42a, 42b 1st support part 43a, 43b 1st arm 44a, 44b 2nd arm 45a, 45b Connection part 46a, 46b Tuning fork vibrator 47a, 47b Vibration center 48a, 48b 2nd support part

Claims (6)

A rectangular outer frame having a pair of first sides parallel to the first axis and a pair of second sides parallel to the second axis substantially orthogonal to the first axis;
A meander-shaped first drive unit including at least one or more piezoelectric actuators extending from the inside of one first side of the outer frame;
A strip-shaped support beam extending in a second axial direction from a substantially middle point inside the other first side of the outer frame;
An optical reflection element comprising: the support beam and a movable plate connected to the drive unit and having a reflection surface at a central portion. A rectangular outer frame having a pair of first sides parallel to the first axis and a pair of second sides parallel to the second axis substantially orthogonal to the first axis;
A pair of meander-shaped first drive units each including at least one or more piezoelectric actuators extending from the inside of each first side of the outer frame;
A support beam extending in a second axial direction from a substantially middle point inside each first side of the outer frame;
A movable plate connected to the drive beam and the support beam having a reflective surface in the center;
The optical reflecting element according to claim 1, wherein the support beam is located below the first driving unit. The movable plate is
A rectangular support having a pair of third sides parallel to the first axis and a pair of fourth sides parallel to the second axis;
A pair of meander-shaped second drive parts each including at least one or more piezoelectric actuators extending in the second axial direction from the inside of each third side of the support;
3. The optical reflection element according to claim 1, further comprising a mirror portion having a reflection surface at a central portion and connected to the second driving portion. 4. The movable plate is
A rectangular support having a pair of third sides parallel to the first axis and a pair of fourth sides parallel to the second axis;
A pair of first support portions each having one end supported on the inner side of each fourth side of the support;
Two tuning fork vibrators having a first arm and a second arm supported on each other end of the pair of first support portions;
A pair of second support portions each supported at one end at the vibration center of the two tuning fork vibrators;
These two tuning fork vibrators are placed facing each other,
The optical reflection element according to claim 1, further comprising a mirror portion having a rotation axis arranged on the same line as the vibration center of the two tuning fork vibrators. The support beam is
5. The optical reflecting element according to claim 1, wherein the optical reflecting element has a bending rigidity larger than that of the first driving unit. The support beam is
The optical reflecting element according to any one of claims 1 to 5, wherein a dimension in the thickness direction is 10 times or more a dimension in the width direction.

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