Optical scanning devices, electronic devices

Abstract

The purpose of the present invention is to reduce the noise of a signal used for detecting the deflection angle of a movable mirror.　This optical scanning device includes a mirror, a driving part, a detection part, and a dummy capacitance part. The detection part generates capacitance between a movable electrode related to the movement of the driving part and a fixed electrode unrelated to the movement of the driving part. The dummy capacitance part generates dummy capacitance between a first electrode and a second electrode. The movable electrode, the fixed electrode, the first electrode, and the second electrode are provided in the same active layer (53) and separate from each other, and the active layer (53) is disposed to face a common support layer (51) with an insulating layer (52) interposed therebetween. First parasitic capacitance (Cs-R) generated between the active layer (53) in which the fixed electrode is provided and the support layer (51) and second parasitic capacitance (Cs-L) generated between the active layer (53) in which the first electrode is provided and the support layer (51) are approximately equivalent. Capacitance (Cv) of the detection part and the first parasitic capacitance (Cs-R) are connected in series to constitute a first signal path, and dummy capacitance (Cd) and the second parasitic capacitance (Cs-L) are connected in series to constitute a second signal path.

Description

[Technical Field]

[0001] The present disclosure relates to an optical scanning device and an electronic device. [Background technology]

[0002] Optical scanning devices that scan incident laser light in two-dimensional directions are known. Conventional examples of optical scanning devices are described in, for example, Patent Document 1 and Non-Patent Document 1 listed below. In such optical scanning devices, it is necessary to detect the deflection angle of the movable mirror that scans the laser light, but noise is likely to be mixed into the signal used for this purpose. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-245890 [Non-Patent Document 1] Hee-Moon Jeong et al., “Slow scanning electromagnetic MEMS scanner for laser display”, Proc. SPIE6887, MOEMS and Maniaturized Systems VII, 688704 (8 February 2008). Summary of the Invention [Problem to be solved by the invention]

[0004] One of the objectives of a specific aspect of the present disclosure is to reduce noise in a signal used to detect the deflection angle of a movable mirror. [Means for solving the problem]

[0005] [1] An optical scanning device according to one aspect of the present disclosure includes: (a) a mirror having a reflective surface; (b) a drive unit that oscillates the mirror; (c) a detection unit that detects the movement of the drive unit based on a change in capacitance; and (d) a dummy capacitance unit that generates a dummy capacitance that is approximately equivalent to the capacitance in an initial state of the detection unit; (e) the detection unit has a movable electrode whose position varies in accordance with the movement of the drive unit and a fixed electrode that is not affected by the movement of the drive unit, and is configured to generate the capacitance between the movable electrode and the fixed electrode; and (f) the dummy capacitance unit has a first electrode and a second electrode, and is configured to generate the dummy capacitance between the first electrode and the second electrode. (g) the movable electrode, the fixed electrode, the first electrode, and the second electrode are provided in an active layer, which is the same semiconductor layer, and are separated from each other, and the active layer is disposed opposite a support layer, which is a common semiconductor layer, with an insulating layer sandwiched therebetween; (h) a first parasitic capacitance generated between the active layer, on which the fixed electrode is provided, and the support layer is approximately equivalent to a second parasitic capacitance generated between the active layer, on which the first electrode is provided, and the support layer; and (i) the capacitance of the detection unit and the first parasitic capacitance are connected in series to form a first signal path, and the dummy capacitance and the second parasitic capacitance are connected in series to form a second signal path. [2] An electronic device according to one aspect of the present disclosure is an electronic device including the optical scanning device described above in [1].

[0006] According to the above configuration, it is possible to reduce noise in the signal used to detect the deflection angle of the movable mirror. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view showing the configuration of an optical scanning device (optical deflector) according to the first embodiment. [Figure 2] 2A is an enlarged view of the deflection angle detection section, and FIG. 2B is an enlarged view of the dummy comb-teeth structure section. [Figure 3] 3A is an enlarged view of a detection pad, and FIG. 3B is an enlarged view of a dummy detection pad. [Figure 4]FIG. 4 is an enlarged view of the vicinity of the read signal input pad. [Figure 5] FIG. 5 is a schematic cross-sectional view taken along line aa in FIG. [Figure 6] FIG. 6 is a diagram for explaining the location where parasitic capacitance occurs. [Figure 7] FIG. 7 is a plan view for explaining capacitance components formed in each portion of the optical scanning device. [Figure 8] Fig. 8(A) is a cross-sectional view showing the connections at locations where capacitance components are formed in an optical scanning device, and Fig. 8(B) is an equivalent circuit diagram showing the connections at each capacitance component. [Figure 9] Figure 9(A) is a waveform diagram showing an example of a read signal, Figure 9(B) is a waveform diagram showing an example of a voltage signal Vout1, Figure 9(C) is a waveform diagram showing an example of a voltage signal Vout2, and Figure 9(D) is an enlarged waveform diagram showing an example of a differential signal between voltage signals Vout1 and Vout2. [Figure 10] 10(A) to 10(G) are process diagrams showing an example of a method for manufacturing an optical scanning device. [Figure 11] 11(A) to 11(F) are process diagrams showing an example of a method for manufacturing an optical scanning device. [Figure 12] FIG. 12 is a plan view showing the configuration of the optical scanning device according to the second embodiment. [Figure 13] FIG. 13 is a partially enlarged view of the optical scanning device shown in FIG. [Figure 14] FIG. 14 is a partially enlarged view of the optical scanning device shown in FIG. [Figure 15] 15(A) and 15(B) are partial cross-sectional views of an optical scanning device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] (First embodiment) FIG. 1 is a plan view showing the configuration of an optical scanning device (optical deflector) 1 of the first embodiment. In this embodiment, the surface on which the laser light to be scanned is incident is called the front surface, and the surface on the opposite side is called the back surface. FIG. 1 shows a plan view seen from the front surface side. As shown in the figure, the optical scanning device 1 of this embodiment has a roughly bilaterally symmetrical structure in a plan view.

[0009] The optical scanning device 1 mainly comprises a reflecting unit (mirror) 2, a torsion bar 3, an inner piezoelectric actuator 4, an inner frame 5, an outer piezoelectric actuator (drive unit) 6, and an outer frame (frame) 7. The left-right direction in the figure is defined as the X-axis, the up-down direction as the Y-axis, and the thickness direction of the optical scanning device 1 (the direction perpendicular to the paper surface) as the Z-axis. These axes intersect at right angles at the center o of the optical scanning device 1.

[0010] The reflecting unit 2 is a movable mirror having a reflecting surface that is approximately circular in plan view, and is configured to be able to swing around the Y-axis and the X-axis by the inner piezoelectric actuator 4 and the outer piezoelectric actuator 6. By reflecting the laser light by such a reflecting unit 2, the laser light incident on the reflecting unit 2 can be scanned in two dimensions.

[0011] In a plan view, one torsion bar 3 is provided above and one below the reflector 2. The torsion bars 3 extend from the reflector 2 along the Y-axis direction and are connected to the inner periphery of the inner frame 5. The torsion bars 3 are also connected to the upper and lower ends of the left and right inner piezoelectric actuators 4.

[0012] The inner piezoelectric actuator 4 and the outer piezoelectric actuator 6 are provided on the left and right sides of the reflecting section 2 in a plan view.

[0013] The inner piezoelectric actuators 4 are connected to each other and have a shape that is close to an ellipse extending along the Y axis in plan view as a whole.

[0014] The outer piezoelectric actuators 6 are interposed between the inner frame 5 and the outer frame 7. Each outer piezoelectric actuator 6 includes a plurality of piezoelectric cantilevers 13. Of the piezoelectric cantilevers 13, those closest to the reflecting section 2 and those farthest from the reflecting section 2 have shorter lengths in the Y-axis direction than the other piezoelectric cantilevers 13. Furthermore, the closer each piezoelectric cantilever 13 is to the reflecting section 2, the smaller its width in the X-axis direction is.

[0015] The inner frame portion 5 surrounds the reflecting portion 2 and the torsion bar 3. The inner frame portion 5 has a shape that is close to an ellipse extending along the Y axis as a whole in a plan view.

[0016] The drive pads 15 and the drive GND pads 16 are provided on the upper left and right sides of the outer frame portion 7 in a plan view. The drive pads 15 have multiple circular portions in a plan view. The drive pads 15 and the drive GND pads 16 are electrically and physically connected to the outside via bonding wires (not shown) when the optical scanning device 1 is packaged.

[0017] The drive pad 15 and drive GND pad 16 on the right side of the figure are used to supply a drive voltage to the inner piezoelectric actuator 4 on the right side of the figure. Similarly, the drive pad 15 and drive GND pad 16 on the left side of the figure are used to supply a drive voltage to the inner piezoelectric actuator 4 on the left side of the figure. Each inner piezoelectric actuator 4 is interposed between the torsion bar 3 and the inner frame part 5, and by twisting the torsion bar 3, the reflecting part 2 is oscillated around the Y axis at a first frequency. Resonance is used for this oscillation. The first frequency is, for example, 15 kHz to 25 kHz.

[0018] A drive voltage of the second frequency is applied to each outer piezoelectric actuator 6 via the drive pad 15 and the drive GND pad 16. This causes the reflecting section 2 to oscillate around the X axis at the second frequency. Resonance is not used for the oscillation around the X axis. The second frequency is lower than the first frequency described above, and is set to, for example, 60 Hz.

[0019] Laser light incident on the reflecting unit 2 from a light source (not shown) is reflected in a direction according to the deflection angle (deflection angle) around the X-axis and the Y-axis of the reflecting unit 2. The reflection direction (deflection direction) changes from moment to moment according to the change in the deflection angle of the reflecting unit 2. As a result, the laser light reflected by the reflecting unit 2 is scanned around the Y-axis at a first frequency and around the X-axis at a second frequency.

[0020] The deflection angle detection unit (detection unit) 20 detects the deflection angle of the reflector 2 by detecting the movement associated with the non-resonant vibration of the outer piezoelectric actuator 6 as a change in electrostatic capacitance, and is configured to include a fixed electrode 20a and a movable electrode 20b. The fixed electrode 20a is configured integrally with the outer frame 7. The fixed electrode 20a has a comb-tooth electrode 20c, as shown in an enlarged view in FIG. 2(A). The movable electrode 20b has a comb-tooth electrode 20d, as shown in an enlarged view in FIG. 2(A). The comb-tooth electrodes 20c and 20d are arranged so that their electrode branches are alternately arranged one by one along the X-axis direction. The position of the comb-tooth electrode 20c of the fixed electrode 20a does not change regardless of the movement of the outer piezoelectric actuator 6, while the position of the comb-tooth electrode 20d of the movable electrode 20b changes in response to the movement of the outer piezoelectric actuator 6. A capacitance component (electrostatic capacitance) is formed between the comb-tooth electrode 20c and the comb-tooth electrode 20d, and the magnitude of the capacitance component changes in accordance with the change in the position of the comb-tooth electrode 20d.

[0021] The dummy comb-tooth structure 21 is a part provided in pair with the deflection angle detection unit 20, and includes a fixed electrode 21a and a movable electrode 21b. The fixed electrode 21a is formed integrally with the outer frame 7. The movable electrode 21b has a comb-tooth electrode 21d, as shown in an enlarged view in FIG. 2(B). In the dummy comb-tooth structure 21, the fixed electrode 21a is not provided with a comb-tooth electrode. Therefore, no capacitance component is formed in the dummy comb-tooth structure 21. The dummy comb-tooth structure 21 is provided to balance the weight between the left and right outer piezoelectric actuators 6.

[0022] The dummy comb-tooth structure 21 and the deflection angle detection unit 20 are electrically and physically separated from each other by the Si layer 53 (see FIG. 5 described later), which is the active layer, via a groove 17 provided between each of the fixed electrodes 20 a and 21 a. The groove 17 reaches the SiO layer 52, thereby electrically and physically separating them.

[0023] The detection pad 22 is connected to the fixed electrode 20a and is located at the lower right end in the figure. The detection GND pad 24 is located above the detection pad 22 in the figure. As shown in an enlarged view in FIG. 3(A), the detection pad 22 has a comb-tooth electrode 22a. Island-shaped dummy electrode branches 24a are provided between each electrode branch of the comb-tooth electrode 22a. The dummy electrode branches 24a are not connected to the detection GND pad 24 or the like and are isolated in an island-like manner. The comb-tooth electrode 22a and each dummy electrode branch 24a form a comb-tooth structure 26. This comb-tooth structure 26 is a portion that balances with the dummy detection portion 27 and ensures that the etching areas are equal. The detection GND pad 24, comb-tooth electrode 22a, and dummy electrode branches 24a are electrically and physically isolated from each other by grooves 17 in the Si layer 53.

[0024] The dummy detection pad 23 is connected to the fixed electrode 21a and is located at the lower left end in the figure. The detection GND pad 25 is located above the dummy detection pad 23 in the figure. As shown in the enlarged view in FIG. 3B, a comb-tooth electrode (first electrode) 23a is connected to the dummy detection pad 23, and a comb-tooth electrode (second electrode) 25a is connected to the detection GND pad 25. These comb-tooth electrodes 23a and 25a form a dummy detection unit (dummy capacitance unit) 27. The comb-tooth electrodes 23a and 25a are electrically and physically isolated from each other by the groove 17 in the Si layer 53. The magnitude of the capacitance component (dummy capacitance) formed by this dummy detection unit 27 is designed to be approximately equivalent to the capacitance component formed by the comb-tooth electrodes 20c and 20d of the deflection angle detection unit 20 in the initial state. Note that the initial state refers to a state in which no fluctuation occurs in the outer piezoelectric actuator 6. The dummy detector 27 is formed on the outer frame 7 so that the capacitance component does not change depending on the deflection angle.

[0025] The read signal input pad 28 is located on the left end of the drawing, above the detection GND pad 25. The read signal input pad 29 is located on the right end of the drawing, above the detection GND pad 24. These read signal input pads 28, 29 are used to input a signal (read signal) used to read the deflection angle. Figure 4 shows an enlarged plan view of the vicinity of the read signal input pad 28. Although not shown enlarged, the signal input pad 29 has a similar structure.

[0026] Fig. 5 is a schematic cross-sectional view corresponding to the direction of line aa shown in Fig. 1. In Fig. 5, the structure of the optical scanning device 1 is exaggerated to make it easier to understand the laminated structure and the configuration of each part. The optical scanning device 1 of this embodiment has a basic structure in which an SiO2 (silicon dioxide) layer 52 serving as an etching stop layer is provided on one side (upper side in the figure) of an Si (silicon) layer 51 serving as a support layer for holding the reflecting part 2 etc., and an Si layer 53 serving as an active layer for forming elements is provided thereon.

[0027] Specifically, the optical scanning device 1 includes, from the bottom up in the figure, an SiO layer 50 as an insulating layer, a Si layer 51 as a support layer that holds the elements, an SiO layer (BOX layer) 52 as an etching stop layer, a Si layer 53 as an active layer for forming the elements, an SiO layer 54 as an insulating layer for the upper piezoelectric drive unit, a Pt (platinum) layer 55 as a lower electrode layer, a PZT (lead zirconate titanate) layer 56 as a piezoelectric layer, and a Pt layer 57 as an upper electrode layer. Each of these layers is patterned into a predetermined shape.

[0028] As shown in the figure, the reflective portion 2 is constructed by stacking an SiO2 layer 52, an Si layer 53, an SiO2 layer 54, and a Pt layer 55 on a reinforcing rib layer 60 formed by partially etching an Si layer 51.

[0029] The left and right inner piezoelectric actuators 4 as resonant drive units are configured by laminating a Si layer 53, a SiO2 layer 54, a Pt layer 55, a PZT layer 56, and a Pt layer 57. Similarly, the left and right outer piezoelectric actuators 6 as non-resonant drive units each have a piezoelectric cantilever 13 configured by laminating a Si layer 53, a SiO2 layer 54, a Pt layer 55, a PZT layer 56, and a Pt layer 57.

[0030] The fixed electrode 20a and its comb-tooth electrode 20c, and the movable electrode 20b and its comb-tooth electrode 20d that constitute the deflection angle detection unit 20 are each made of a Si layer 53. In other words, the fixed electrode 20a and the movable electrode 20b are formed on the same semiconductor layer. This allows the Si layer 51, which serves as a support layer, to be used as the base of the element. The comb-tooth electrode 20d of the movable electrode 20b is connected to the detection GND pad 24 by the Si layer 53, which is surrounded by a groove. The comb-tooth electrode 20c of the fixed electrode 20a is integrated with the outer frame portion 7.

[0031] Similarly, the comb-tooth electrode 21 d constituting the dummy comb-tooth structure 21 is made of a Si layer 53 .

[0032] The left and right detection GND pads 24, 25 are provided on a Si layer 53 laminated on an SiO2 layer 50, a Si layer 51, and an SiO2 layer 52. The left and right signal reading signal input pads 28, 29 are configured to expose the Si layer 51 on the same side as the reflecting surface of the reflecting section 2 by etching down to the SiO2 layer 52 on the Si layer 51 as a support layer. This allows electrical connection to the Si layer 51 from the top side (the side where the laser light is incident) of the optical scanning device 1.

[0033] FIG. 6 is a diagram illustrating the locations where parasitic capacitance occurs. FIG. 6 shows a plan view of the optical scanning device 1 from the rear side, with four locations 71, 72, 73, and 74 where parasitic capacitance occurs indicated in dark gray. The optical scanning device 1 of this embodiment utilizes an SOI (Silicon on Insulator) structure as shown in FIG. 5. Therefore, parasitic capacitance is generated in the location where the Si layer 51, which serves as the support layer, and the Si layer 53, which serves as the active layer, overlap, because the SiO2 layer 52 is sandwiched between the layers. The locations 71 and 72 correspond to the areas where the drive pad 15 and the drive GND pad 16, etc. are formed, respectively. The locations 73 and 74 correspond to the areas where the fixed electrodes 20a and 21a, etc. are formed, respectively. The locations 73 and 74 are separated by the groove 17 described above.

[0034] 7 is a plan view for explaining capacitance components formed in each part of the optical scanning device. In FIG. 7, the plan view shown in FIG. 1 is reduced in size to show the locations where capacitance components are formed. The capacitance component corresponding to the region where the drive pad 15 and the drive GND pad 16 are formed on the upper left side of the drawing is denoted as C r-L The capacitance component corresponding to the region where the drive pad 15 and the drive GND pad 16 are formed on the upper right side of the figure is C r-R Furthermore, the capacitance components (first parasitic capacitance, second parasitic capacitance) corresponding to the regions where the fixed electrodes 20a, 21a, etc. are formed are respectively represented as C s-L , C s-R Furthermore, the capacitance component (electrostatic capacitance of the detection unit) formed in the deflection angle detection unit 20 is defined as C v The capacitance component (dummy capacitance) formed in the dummy detection unit 27 is defined as Cd Let's say.

[0035] FIG. 8A is a cross-sectional view showing the connection relationship of the portions forming the capacitance components in the optical scanning device. Here, the portions related to the capacitance components are shown in a deformed manner for ease of understanding. As shown in the figure, the capacitance component C s-L is formed on the signal path leading from the Si layer 51, which is the support layer, to the dummy detection pad 23. s-R is formed on the signal path leading from the Si layer 51, which is the support layer, to the detection pad 22. r-L Toyo Quantity component C r-R are connected from the Si layer 51, which is the support layer, to the detection GND pad 24. It is formed on the signal path. Also, the capacitance component (dummy capacitance) C d is formed in the dummy detection section 27 and connected to the detection GND pad 24 (i.e., GND potential). v is formed in the deflection angle detection unit 20 and connected to the detection GND pad 24 (that is, GND potential).

[0036] FIG. 8B is an equivalent circuit diagram showing the connection relationship of each capacitance component. As shown in the figure, the capacitance component C s-L and the capacitance component C d are connected in series, and the capacitance component C s-R and the capacitance component C v are connected in series, and these are connected in parallel. In addition, a capacitance component C r-R and C r-L are connected in parallel to each other. In the figure, the circuit connection lines shown by solid lines represent connections via the Si layer 53, which is the active layer, and the circuit connection lines shown by dotted lines represent connections via the Si layer 51, which is the support layer.

[0037] The read signal input from the read signal input pad 28 is transferred to each capacitance component C via the Si layer 51 of the support layer. s-L , C s-R , C r-R , C r-LEach capacitance component C r-R , C r-L The read signal that passes through the s-L , C s-R The read signal passing through each capacitance component C d , C v It reaches the GND potential via

[0038] The dummy detection pad 23 is connected to a capacitance component C s-L and the capacitance component C d The voltage signal V divided by out1 The detection pad 22 provides a capacitance component C s-R and the capacitance component C v and pressure division The generated voltage signal V out2 Therefore, these voltage signals V out1 , V out2 By taking the difference between the two, it is possible to obtain a signal in which the common in-phase noise components are cancelled out. This improves the accuracy of detecting the deflection angle. In addition, there is no need to add a new layer as a support layer (foundation), which helps to reduce costs.

[0039] FIG. 9(A) is a waveform diagram showing an example of a read signal, and FIG. 9(B) is a waveform diagram showing an example of a voltage signal V ou t1 9(C) is a waveform diagram showing an example of the voltage signal V out2 9(D) is a waveform diagram showing an example of the voltage signal V out1 , V out2 Here, a read signal, which is an input voltage at a certain time t, is V in (t), the noise is N(t), and the voltage signal V out1 (t), V out2 If the differential signal of (t) is v(t), it can be expressed as follows: V out1 (t)=V in (t)+N(t) V out2 (t)=V in (t)+v(t)+N(t) V out2(t)-V out1 (t)=v(t)

[0040] When the deflection angle detection unit 20 is in the initial position, the capacitance component C v and the capacitance component C d are approximately equal and the equivalent circuit is symmetrical, so theoretically, the voltage signal V out1 and the voltage signal V ou t2 The deflection angle detection unit 20 operates and the capacitance component C v If we consider the case where decreases, that is, the impedance increases, the voltage division law gives us the voltage signal V out2 is the voltage signal V out1 It increases relative to the capacitance component C v The opposite occurs when the voltage signal V out1 and the voltage signal V out2 By taking the difference between the capacitance component C and the capacitance component C, the common noise component is cancelled out, and the change in voltage due to the deflection angle detection unit 20 can be detected. v Since varies according to the frequency of the outer piezoelectric actuator 6, which is the non-resonant driving part, the impedance also varies periodically, and accordingly the voltage signal V out2 The capacitance also changes periodically. Since there are two points per period where the capacitance is at its maximum, the fluctuation period 90 of the differential signal is twice the drive frequency. Also, the change 91 in the differential signal corresponds to the change in the deflection angle.

[0041] 10(A) to 10(G) and 11(A) to 11(F) are process diagrams showing an example of a method for manufacturing an optical scanning device. Hereinafter, an example of the method for manufacturing the optical scanning device 1 will be briefly described with reference to the respective drawings.

[0042] First, a substrate having a laminate of an SiO2 layer 50, an Si layer 51, an SiO2 layer 52, an Si layer 53, and an SiO2 layer 54 is prepared (FIG. 10(A)), and a Pt layer 55 is formed on one side of the SiO2 layer 54 (the side not in contact with the Si layer 53) (FIG. 10(B)). Next, a PZT layer 56 is formed on one side of the Pt layer 55 (the side not in contact with the SiO2 layer 54) (FIG. 10(C)), and a Pt layer 57 is formed on one side of the PZT layer 56 (the side not in contact with the Pt layer 55) (FIG. 10(D)). Note that any known method may be used for forming the films.

[0043] Next, the Pt layer 57 and the PZT layer 56 are patterned into a predetermined shape (FIG. 10(E)). Any known method may be used for this patterning. As an example, in this embodiment, a method is used in which a mask pattern is formed using a resist film (photosensitive film), followed by etching, and then the resist film is peeled off (the same applies to patterning in each of the subsequent steps).

[0044] Next, the Pt layer 55 is patterned into a predetermined shape (FIG. 10(F)), and then the SiO2 layer 54 is patterned into a predetermined shape (FIG. 10(G)). Furthermore, the Si layer 53 is patterned into a predetermined shape (FIG. 11(A)), and then the SiO2 layer 52 is patterned into a predetermined shape (FIG. 11(B)).

[0045] Next, the SiO2 layer 50 on the back side is patterned into a predetermined shape (FIG. 11(C)), then the Si layer 51 is patterned into a predetermined shape (FIG. 11(D)), and further a rib portion 60 is formed (FIG. 11(E)). After that, the SiO2 layer 52 is patterned into a predetermined shape (FIG. 11(F)). With the above steps, the optical scanning device 1 according to the above embodiment is completed.

[0046] According to the first embodiment as described above, it is possible to reduce noise in the signal used to detect the deflection angle of the movable mirror.

[0047] The optical scanning device 1 according to the first embodiment described above can be applied to any electronic device that requires laser light scanning. For example, it can be applied to a pico-projector used in a head-up display or a wearable device. It can also be applied to a device that changes the light distribution pattern in response to the presence of oncoming vehicles, preceding vehicles, pedestrians, or various objects when irradiating light ahead of a vehicle. It can also be applied to an object detection device such as LiDAR (Light Detection and Ranging). It can also be applied to various MEMS sensors, such as acceleration sensors, angular velocity sensors, pressure sensors, and electromyography sensors.

[0048] (Second embodiment) Fig. 12 is a plan view of the optical scanning device according to the second embodiment, as viewed from the rear side. Figs. 13 and 14 are partial enlarged views of the optical scanning device shown in Fig. 12. The overall configuration of the optical scanning device 1a according to the second embodiment is the same as that of the optical scanning device 1 according to the first embodiment, with only the structure of the Si layer 51, which is the support layer, being different. Hereinafter, a description of the commonalities between the optical scanning device 1a according to the second embodiment and the optical scanning device 1 according to the first embodiment will be omitted, and the structure of the Si layer 51, which is related to the differences, will be described in detail.

[0049] As shown in the figure, the Si layer 51 of the optical scanning device 1a has a capacitance component C s-L , capacitive component C s-RA plurality of through holes 80 are provided in a region overlapping with the Si layer 53, which is an active layer constituting the semiconductor device (i.e., a region related to the generation of parasitic capacitance). In the illustrated example, the through holes 80 are arranged in rows in the left-right and up-down directions in the figure, but the arrangement of the through holes 80 is not limited to this. The region where the through holes 80 are arranged corresponds to the above-mentioned regions 73 and 74 (see FIG. 6). Similarly, a plurality of through holes 81 are provided in the above-mentioned regions 71 and 72, i.e., the regions where the drive pad 15 and the drive GND pad 16 are formed. Regarding the size of each of the through holes 80 and 81, for example, when each is substantially square as illustrated, one side can be about 50 μm to 150 μm.

[0050] 15(A) and 15(B) are partial cross-sectional views of the optical scanning device of the second embodiment. FIG. 15(A) is a cross-sectional view corresponding to line aa in FIG. 13, and FIG. 15(B) is a cross-sectional view corresponding to line bb in FIG. 13. As shown in FIG. 15(A), the through-hole 80 is formed by partially removing the Si layer 51, which serves as a support layer, so as to reach the SiO layer (BOX layer) 52. On the other hand, as shown in FIG. 15(B), the Si layer 51, which serves as a support layer, is not removed in the portion where the through-hole 80 does not exist, and the SiO layer (BOX layer) 52 is not exposed. Although not shown, each through-hole 81 has a similar structure. Such through-holes 80 and 81 can be formed during the process of etching the Si layer 51 (see FIG. 11(E)) during the manufacturing process of the optical scanning device 1 described in the first embodiment. The Si layer 51, which is a support layer, also plays a role in ensuring the mechanical strength of the optical scanning device 1a, so by limiting its removal to partial removal by the through holes 80 and 81, it is possible to prevent a decrease in the mechanical strength.

[0051] By providing each through hole 80, the overlapping area between the Si layer 51 as the support layer and the Si layer 53 as the active layer can be reduced, so that the capacitance component C s-L and capacitance component C s-R This reduces the value of the capacitance component C vand the capacitance component C s-R Since the difference between the voltages is small, the amount of change in voltage caused by the deflection angle detection unit 20 can be made larger.

[0052] Specifically, the capacitance component C v It is difficult to increase the value of the capacitance C because the electrodes are formed in a direction perpendicular to the support layer, etc., while the parasitic capacitance generated by the overlapping portion between the Si layer 53 as the active layer and the Si layer 51 as the support layer is formed in a direction parallel to the support layer, etc., and therefore the value is likely to be large. v is about 1 pF, while the capacitance component C s-R In principle, the capacitance component C v and the capacitance component C s -R Ratio to (C s-R / C v When the capacitance component C is close to 1, the change in the voltage due to the deflection angle detection unit 20 reaches a maximum value. s-R becomes smaller, so C s-R / C v As the value approaches 1, the voltage change can be made larger.

[0053] (Modified embodiment) The present disclosure is not limited to the above-described embodiments and can be modified in various ways within the scope of the present disclosure. For example, the resonant drive unit in each of the above-described embodiments may be used in a non-resonant drive manner, or the non-resonant drive unit may be used in a resonant drive manner. While the above-described embodiments illustrate the use of piezoelectric drive actuators, electrostatic drive actuators or electromagnetic drive actuators may also be used. The capacitive component of the dummy detection unit is formed using comb-tooth electrodes, but it may also be formed using parallel plate electrodes. While the above-described embodiments illustrate the use of two read signal input pads, it may also be formed using one, three, or more. The read signal may also be applied from the opposite side (the movable electrode side). While the planar shape of each of the through holes 80 and 81 is illustrated as an example of a substantially square, this is not limited thereto and may be various planar shapes, such as a circle, a triangle, or a hexagon. The planar shapes of the through holes 80 and 81 do not all have to be the same; different planar shapes may also be present. [Explanation of symbols]

[0054] 1: optical scanning device, 2: reflecting part (movable mirror), 3: torsion bar, 4: inner piezoelectric actuator, 5: inner frame part, 6: outer piezoelectric actuator, 7: outer frame part (frame), 13: piezoelectric cantilever, 15: driving pad, 16: driving GND pad, 17: groove, 20: deflection angle detection part, 20a: fixed electrode, 20b: movable electrode, 20c, 20d: comb-tooth electrodes, 21: dummy comb-tooth structure part, 21a: fixed electrode, 21b: movable electrode, 22: detection pad , 22a: comb-tooth electrode, 23: dummy detection pad, 23a: comb-tooth electrode, 24: detection GND pad, 24a: dummy electrode branch, 25: detection GND pad, 25a: comb-tooth electrode, 26, 27: comb-tooth structure portion, 28, 29: read signal input pad, 50: SiO2 layer, 51: Si layer, 52: SiO2 layer (BOX layer), 53: Si layer, 54: SiO2 layer, 55: Pt layer, 56: PZT (lead zirconate titanate) layer, 57: Pt layer, 80, 81: through holes

Claims

1. a mirror having a reflective surface; a driving unit that swings the mirror; a detection unit that detects the movement of the drive unit based on a change in capacitance; a dummy capacitance section that generates a dummy capacitance that is approximately equivalent to the capacitance in an initial state of the detection section; Including, the detection unit has a movable electrode whose position varies in accordance with the movement of the drive unit and a fixed electrode that is not related to the movement of the drive unit, and is configured to generate the capacitance between the movable electrode and the fixed electrode; the dummy capacitance section has a first electrode and a second electrode, and is configured to generate the dummy capacitance between the first electrode and the second electrode; the movable electrode, the fixed electrode, the first electrode, and the second electrode are provided in an active layer that is the same semiconductor layer and are separated from each other; the active layer is disposed opposite to a support layer, which is a common semiconductor layer, with an insulating layer interposed therebetween; a first parasitic capacitance occurring between the active layer provided with the fixed electrode and the support layer is substantially equivalent to a second parasitic capacitance occurring between the active layer provided with the first electrode and the support layer; the capacitance of the detection unit and the first parasitic capacitance are connected in series to form a first signal path, and the dummy capacitance and the second parasitic capacitance are connected in series to form a second signal path; Optical scanning device.

2. the first signal path and the second signal path are connected in parallel, the active layer has a detection pad for obtaining a voltage division between the capacitance of the detection section and the first parasitic capacitance, and a dummy detection pad for obtaining a voltage division between the dummy capacitance and the second parasitic capacitance, 2. The optical scanning device according to claim 1.

3. the support layer has a signal input pad configured to be exposed on the same side as the reflective surface of the mirror; 3. The optical scanning device according to claim 1 or 2.

4. a planar area of ​​the fixed electrode and a planar area of ​​the first electrode are substantially equal; 3. The optical scanning device according to claim 1 or 2.

5. the movable electrode and the fixed electrode each have a comb-teeth electrode, and the electrostatic capacitance is generated between the comb-teeth electrodes; 3. The optical scanning device according to claim 1 or 2.

6. the first electrode and the second electrode each have a comb-teeth electrode, and the dummy capacitance is generated between the comb-teeth electrodes; 3. The optical scanning device according to claim 1 or 2.

7. a read signal is input to the support layer, and a deflection angle of the mirror is obtained based on a difference between a divided voltage between the capacitance of the detection unit and the first parasitic capacitance and a divided voltage between the dummy capacitance and the second parasitic capacitance; 3. The optical scanning device according to claim 1 or 2.

8. the support layer has a plurality of through holes each reaching the insulating layer at a portion related to generation of the first parasitic capacitance and the second parasitic capacitance, 3. The optical scanning device according to claim 1 or 2.

9. An electronic device comprising the optical scanning device according to claim 1 or 2.

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