Patent Description:
There is known an optical scanning apparatus that scans incident laser beam in a two-dimensional direction. A prior art example of an optical scanning apparatus is disclosed in, for example, the following Patent Document <NUM> and the Non-Patent Document <NUM>. In such an optical scanning apparatus, it is necessary to detect the deflection angle of a movable mirror that scans the laser beam, but noise is likely to be mixed into the signal used in the process.

In a specific aspect, it is an object of the present disclosure to reduce noise of the signal used to detect the deflection angle of a movable mirror.

According to the above configurations, it is possible to reduce noise of the signal used to detect the deflection angle of a movable mirror.

<FIG> is a plane view showing the configuration of an optical scanning apparatus (optical deflector) <NUM> according to a first embodiment. In the present embodiment, the surface into which the laser beam to be scanned enters is defined as the front surface, and the surface on the opposite side thereof is defined as the back surface. <FIG> shows a plane view seen from the front surface side. As illustrated, the optical scanning apparatus <NUM> of the present embodiment has an almost bilaterally symmetrical structure in a plane view.

The optical scanning apparatus <NUM> is configured to include a reflecting section (mirror) <NUM>, a torsion bar <NUM>, inner piezoelectric actuators <NUM>, an inner frame section <NUM>, outer piezoelectric actuators (drive sections) <NUM>, and an outer frame section (frame) <NUM> as a main component. The horizontal direction in the figure is defined as the X axis, the vertical direction as the Y axis, and the thickness direction of the optical scanning apparatus <NUM> (direction perpendicular to the diagram sheet surface) as the Z axis.

The reflecting section <NUM> is a movable mirror having a substantially circular reflecting surface in a plane view, and is configured to be swingable around the Y-axis and the X-axis by the inner piezoelectric actuators <NUM> and the outer piezoelectric actuators <NUM>. By reflecting a laser beam by such reflecting section <NUM>, the laser beam incident on the reflecting section <NUM> can be scanned in a two-dimensional direction.

The torsion bar <NUM> is provided, in a plane view, above and below the reflecting section <NUM>. The torsion bar <NUM> extends along the Y-axis direction from the reflecting section <NUM> and is coupled to the inner periphery of the inner frame section <NUM>. Further, the torsion bar <NUM> is coupled to the upper and lower ends of the left and right inner piezoelectric actuators <NUM>.

The inner piezoelectric actuators <NUM> and the outer piezoelectric actuators <NUM> are provided one each on the left and right sides of the reflecting section <NUM> in a plane view.

The inner piezoelectric actuators <NUM> are coupled to each other, and have an overall shape close to an ellipse that extends along the Y-axis in a plane view.

The outer piezoelectric actuators <NUM> are interposed between the inner frame section <NUM> and the outer frame section <NUM>. Each of the outer piezoelectric actuators <NUM> is configured to include a plurality of piezoelectric cantilevers <NUM>. Among the piezoelectric cantilevers <NUM>, the one closest to the reflecting section <NUM> and the one farthest from the reflecting section <NUM> have shorter lengths in the Y-axis direction than the other piezoelectric cantilevers <NUM>. Further, each piezoelectric cantilever <NUM> has a width in the X-axis direction that becomes relatively small as it is located closer to the reflecting section <NUM>.

The inner frame section <NUM> surrounds the reflecting section <NUM> and the torsion bar <NUM>. The inner frame section <NUM> has an overall shape close to an ellipse that extends along the Y-axis in a plane view.

A driving pad <NUM> and a driving GND pad <NUM> are respectively provided on the left and right upper sides of the outer frame section <NUM> in a plane view. The driving pad <NUM> has a plurality of circular portions in a plane view. The driving pad <NUM> and the driving GND pad <NUM> are electrically/physically connected to the outside via bonding wires (not shown) when the optical scanning apparatus <NUM> is packaged.

The driving pad <NUM> and the driving GND pad <NUM> on the right side in the figure are used to supply a drive voltage to the inner piezoelectric actuator <NUM> on the right side in the figure. Similarly, the driving pad <NUM> and the driving GND pad <NUM> on the left side in the figure are used to supply a drive voltage to the inner piezoelectric actuator <NUM> on the left side in the figure. Each inner piezoelectric actuator <NUM> is interposed between the torsion bar <NUM> and the inner frame section <NUM>, and oscillates the reflecting section <NUM> around the Y axis at a first frequency by twisting the torsion bar <NUM>. Resonance is used for this oscillation. The first frequency is, for example, <NUM> to <NUM>.

Each outer piezoelectric actuator <NUM> is supplied with a drive voltage of a second frequency via the driving pad <NUM> and the driving GND pad <NUM>. Thereby, the reflecting section <NUM> oscillates 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, <NUM>.

Laser beam that enters the reflecting section <NUM> from a light source (not shown) is reflected in a direction according to the swing angle (deflection angle) of the reflecting section <NUM> around the X-axis and the Y-axis. The reflecting direction (deflecting direction) changes moment by moment according to changes in the swing angle of the reflection section <NUM>. Thereby, the laser beam reflected by the reflection section <NUM> is scanned around the Y-axis at the first frequency and scanned around the X-axis at the second frequency.

A deflection angle detection section (a detection section) <NUM> is for detecting the deflection angle of the reflection section <NUM> by detecting the movement accompanying non-resonant vibration by the outer piezoelectric actuators <NUM> as a change of a 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 section <NUM>. This fixed electrode 20a has a comb teeth electrode 20c, as shown in an enlarged view in <FIG>. The movable electrode 20b has a comb teeth electrode 20d, as shown in an enlarged view in <FIG>. The comb teeth electrode 20c and the comb teeth electrode 20d are arranged so that each other's electrode branches form a line one by one in turn along the X-axis direction. The position of the comb teeth electrode 20c of the fixed electrode 20a does not change regardless of the movement of the outer piezoelectric actuators <NUM>, and the position of the comb teeth electrode 20d of the movable electrode 20b changes in relation to the movement of the outer piezoelectric actuators <NUM>. A capacitance component (capacitance) is formed between the comb teeth electrode 20c and the comb teeth electrode 20d, and its magnitude changes in accordance with the positional change of the comb teeth electrode 20d.

A dummy comb teeth structure section <NUM> is a portion provided in a pair with the deflection angle detection section <NUM>, and is configured to include a fixed electrode 21a and a movable electrode 21b. The fixed electrode 21a is configured integrally with the outer frame section <NUM>. The movable electrode 21b has a comb teeth electrode 21d, as shown in an enlarged view of <FIG>. In the dummy comb teeth structure section <NUM>, the fixed electrode 21a is not provided with a comb teeth electrode. Therefore, no capacitance component is formed in the dummy comb teeth structure section <NUM>. The dummy comb teeth structure section <NUM> is provided to balance the weight between the left and right outer piezoelectric actuators <NUM>.

The dummy comb teeth structure section <NUM> and the deflection angle detection section <NUM> are electrically and physically separated from each other by a groove <NUM> provided between the respective fixed electrodes 20a and 21a, at a Si layer <NUM> which is an active layer (refer to <FIG>, which will be described later). The groove <NUM> reaches a SiO<NUM> layer <NUM> and is electrically and physically separated from the SiO<NUM> layer <NUM>.

A detection pad <NUM> is connected to the fixed electrode 20a and is arranged at the lower right end in the figure. A detection GND pad <NUM> is arranged above the detection pad <NUM> in the figure. As shown in an enlarged view in <FIG>, the detection pad <NUM> has a comb teeth electrode 22a. Further, an island-shaped dummy electrode branch 24a is provided between the respective electrode branches of the comb teeth electrode 22a. The dummy electrode branches 24a are not connected to the detection GND pad <NUM>, etc., and are separated into island shapes. A comb teeth structure section <NUM> is configured by the comb teeth electrode 22a and each dummy electrode branch 24a. This comb teeth structure section <NUM> is a part to maintain a balance with the dummy detection section <NUM> and to equalize the etching area. The detection GND pad <NUM>, the comb teeth electrode 22a, and the dummy electrode branch 24a are electrically and physically separated from each other by the groove <NUM> at the Si layer <NUM>.

A dummy detection pad <NUM> is connected to the fixed electrode 21a and is arranged at the lower left end in the figure. A detection GND pad <NUM> is arranged above the dummy detection pad <NUM> in the figure. As shown in an enlarged view in <FIG>, a comb teeth electrode (first electrode) 23a is connected to the dummy detection pad <NUM>, and a comb teeth electrode (second electrode) 25a is connected to the detection GND pad <NUM>, and a dummy detection section (a dummy capacitance section) <NUM> is configured by these comb teeth electrodes 23a and 25a. The comb teeth electrodes 23a and 25a are electrically and physically separated from each other by the groove <NUM> at the Si layer <NUM>. The size of the capacitance component (dummy capacitance) formed by the dummy detection section <NUM> is designed so that it becomes approximately equivalent to the capacitance component formed by the comb teeth electrode 20c and the comb teeth electrode 20d of the deflection angle detection section <NUM> in the initial state. Here, note that the initial state refers to a state in which the outer piezoelectric actuator <NUM> does not fluctuate. The dummy detection section <NUM> is formed in the outer frame section <NUM> so that the capacitance component does not change due to the deflection angle.

A read signal input pad <NUM> is arranged above the detection GND pad <NUM> on the left end side in the figure. A read signal input pad <NUM> is arranged above the detection GND pad <NUM> on the right end side in the figure. These read signal input pads <NUM> and <NUM> are used to input signals (read signals) used for reading the deflection angle. <FIG> shows an enlarged plane view of the vicinity of the read signal input pad <NUM>. Here, note that although an enlarged view is omitted, the read signal input pad <NUM> has a similar structure.

<FIG> is a schematic cross-sectional view corresponding to the a-a line direction shown in <FIG>. Here, note that in <FIG>, the structure of the optical scanning apparatus <NUM> is illustrated in a modified manner in order to make it easier to understand the laminated structure and the configuration of each section. The optical scanning apparatus <NUM> of the present embodiment has a basic structure in which the SiO<NUM> (silicon dioxide) layer <NUM> as an etching stop layer on one side (upper side in the figure) of the Si (silicon) layer <NUM> as a support layer to retain the reflective section <NUM>, etc. is provided, and in which the Si layer <NUM> as an active layer for forming elements is provided thereon.

Specifically, the optical scanning apparatus <NUM> is configured to include, in order from the bottom in the figure, a SiO<NUM> layer <NUM> as an insulating layer, the Si layer <NUM> as a support layer that holds the element, the SiO<NUM> layer (box layer) <NUM> as an etching stop layer, the Si layer <NUM> as an active layer for forming an element, a SiO<NUM> layer <NUM> as an insulating layer to insulate from the piezoelectric driving section on the upper layer side, a Pt (platinum) layer <NUM> as a lower electrode layer, a PZT (lead zirconate titanate) layer <NUM> as a piezoelectric layer, and a Pt layer <NUM> as an upper electrode layer. Each of these layers is patterned into a predetermined shape.

As shown in the figure, based on a reinforcing rib layer <NUM> formed by etching the Si layer <NUM> halfway, the reflective section <NUM> is configured by laminating the SiO<NUM> layer <NUM>, the Si layer <NUM>, the SiO<NUM> layer <NUM>, and the Pt layer <NUM>.

The left and right inner piezoelectric actuators <NUM> as a resonance driving section is configured by laminating the Si layer <NUM>, the SiO<NUM> layer <NUM>, the Pt layer <NUM>, the PZT layer <NUM>, and the Pt layer <NUM>. Similarly, each piezoelectric cantilever <NUM> of the left and right outer piezoelectric actuators <NUM> as a non-resonant driving section is configured by laminating the Si layer <NUM>, the SiO<NUM> layer <NUM>, the Pt layer <NUM>, the PZT layer <NUM>, and the Pt layer <NUM>.

The fixed electrode 20a and its comb teeth electrode 20c, and the movable electrode 20b and its comb teeth electrode 20d, which constitute the deflection angle detection section <NUM>, are each composed of the Si layer <NUM>. That is, the fixed electrode 20a and the movable electrode 20b are formed in the same semiconductor layer. Thereby, the Si layer <NUM> as a support layer can be used as a base of the element. The comb teeth electrode 20d of the movable electrode 20b is connected to the detection GND pad <NUM> through the Si layer <NUM> surrounded by a groove. The comb teeth electrode 20c of the fixed electrode 20a is integrated with the outer frame section <NUM>.

Similarly, the comb teeth electrode 21d that constitutes the dummy comb teeth structure section <NUM> is composed of the Si layer <NUM>.

The left and right detection GND pads <NUM> and <NUM> are provided on the Si layer <NUM> which is stacked on the SiO<NUM> layer <NUM>, the Si layer <NUM>, and the SiO<NUM> layer <NUM>. Further, each of the left and right signal reading signal input pads <NUM> and <NUM> is configured to expose the Si layer <NUM> on the same side as the reflective surface of the reflective section <NUM> by etching up to the SiO<NUM> layer <NUM> on the Si layer <NUM> as a support layer. This allows electrical connection to the Si layer <NUM> from the upper surface side of the optical scanning apparatus <NUM> (the side on which the laser beam is incident).

<FIG> is a diagram for explaining the portion in which parasitic capacitance is generated. In <FIG>, a plane view of the optical scanning apparatus <NUM> viewed from the back side is shown, and four portions <NUM>, <NUM>, <NUM>, and <NUM> where parasitic capacitance is generated are shown in dark gray. Since the optical scanning apparatus <NUM> of the present embodiment uses an SOI (Silicon on Insulator) structure as shown in <FIG>, at a portion where the Si layer <NUM> which is a support layer and the Si layer <NUM> which is an active layer overlap, an SiO<NUM> layer <NUM> is sandwiched between each layer, thereby parasitic capacitance is formed. The portions <NUM> and <NUM> correspond to regions in which the driving pad <NUM>, the driving GND pad <NUM>, etc. are formed, respectively. The portions <NUM> and <NUM> correspond to regions in which the fixed electrodes 20a and 21a are formed, respectively. The portion <NUM> and the portion <NUM> are separated by the groove <NUM> described above.

<FIG> is a plane view for explaining capacitance components formed in each portion of the optical scanning apparatus. <FIG> is a scaled-down version of the plane view shown in <FIG>, and shows locations where capacitance components are formed. The capacitance component corresponding to the formation region of the driving pad <NUM>, driving GND pad <NUM>, etc. on the upper left side in the figure is defined as Cr-L. The capacitance component corresponding to the formation region of the driving pad <NUM>, driving GND pad <NUM>, etc. on the upper right side of the figure is defined as Cr-R. Further, the capacitance components (first parasitic capacitance, second parasitic capacitance) corresponding to the formation regions of fixed electrodes 20a, 21a, etc. are defined as Cs-L and Cs-R, respectively. Further, the capacitance component formed at the deflection angle detection section <NUM> (capacitance of the detection section) is defined as Cv. The capacitance component (dummy capacitance) formed at the dummy detection section <NUM> is defined as Cd.

<FIG> is a cross-sectional view showing the connection relationship of locations forming capacitance components in the optical scanning apparatus. Here, for ease of understanding, portions related to capacitance components are shown in a modified manner. As shown in the figure, the capacitance component Cs-L is formed on a signal path leading from the Si layer <NUM> which is a support layer, to the dummy detection pad <NUM>. The capacitance component Cs-R is formed on a signal path leading from the Si layer <NUM> which is a support layer, to the detection pad <NUM>. The capacitance component Cr-L and the capacitance component Cr-R are each formed on a signal path leading from the Si layer <NUM> which is a support layer, to the detection GND pad <NUM>. Further, the capacitance component (dummy capacitance) Cd is formed in the dummy detection section <NUM> and is connected to the detection GND pad <NUM> (i.e., GND potential). Further, the capacitance component (detection capacitance) Cv is formed at the deflection angle detection section <NUM> and is connected to the detection GND pad <NUM> (i.e., GND potential).

<FIG> is an equivalent circuit diagram showing the connection relationship of each capacitance component. As shown, the capacitance component Cs-L and the capacitance component Cd are connected in series, the capacitance component Cs-R and the capacitance component Cv are connected in series, and these are connected in parallel. Further, the capacitance components Cr-R and Cr-L are connected in parallel to these signal paths (first signal path, second signal path), respectively. Here, note that in the figure, circuit connection lines indicated by solid lines represent connections through the Si layer <NUM> which is an active layer, and circuit connection lines indicated by dotted lines represent connections through the Si layer <NUM> which is a support layer.

A read signal input from the read signal input pad <NUM> is input in parallel to each capacitance component Cs-L, Cs-R, Cr-R, and Cr-L via the Si layer <NUM>, which is a support layer. The read signal passing through each capacitance component Cr-R and Cr-L reaches the GND potential as it is, but the read signal passing through each capacitance component Cs-L and Cs-R reaches the GND potential via each capacitance component Cd and Cv.

From the dummy detection pad <NUM>, a voltage signal Vout1 which is divided by the capacitance component Cs-L and the capacitance component Cd, is obtained. From the detection pad <NUM>, a voltage signal Vout2 which is divided by the capacitance component Cs-R and the capacitance component Cv, is obtained. Therefore, by obtaining the difference between these voltage signals Vout1 and Vout2, it is possible to obtain a signal in which a common in-phase noise components are canceled. Thus, this improves the accuracy of deflection angle detection. Further, since there is no need to add a new layer as a support layer (foundation), cost increase can be suppressed.

<FIG> is a waveform diagram showing an example of the read signal, <FIG> is a waveform diagram showing an example of the voltage signal Vout1, <FIG> is a waveform diagram showing an example of the voltage signal Vout2, and <FIG> is an enlarged waveform diagram showing an example of a differential signal between voltage signals Vout1 and Vout2. Here, when defining a read signal which is an input voltage at a certain time "t" as Vin(t), noise as N(t), and a differential signal between the voltage signals Vout1(t) and Vout2(t) as v(t), these parameters can be expressed as follows. <MAT> <MAT> <MAT>.

When the deflection angle detection section <NUM> is at the initial position, the capacitance component Cv and the capacitance component Cd are approximately equal and the equivalent circuit is symmetrical, therefore, the voltage signal Vout1 and the voltage signal Vout2 are theoretically equal. Considering a case where the deflection angle detection section <NUM> operates and the capacitance component Cv decreases, that is, a case where the impedance increases, the voltage signal Vout2 increases relative to the voltage signal Vout1 based on Voltage Division Rule. The opposite phenomenon occurs when the capacitance component Cv increases. Therefore, by obtaining the difference between the voltage signal Vout1 and the voltage signal Vout2, the common noise component is canceled out, and the change in voltage due to the deflection angle detection section <NUM> can be detected. In detail, as shown in <FIG>, since the capacitance component Cv changes according to the frequency of the outer piezoelectric actuator <NUM>, which is a non-resonant driving section, the impedance also changes periodically, and accordingly, the voltage signal Vout2 also changes periodically. Since there are two points where the capacitance is maximum per period, the fluctuation cycle <NUM> of the differential signal is twice the driving frequency. Further, a change amount <NUM> of the differential signal corresponds to a change amount of the deflection angle.

<FIG> and <FIG> are process diagrams showing an example of a method for manufacturing the optical scanning apparatus. Hereinafter, an example of a method for manufacturing the optical scanning apparatus <NUM> will be briefly described with reference to each figure.

First, a substrate in which the SiO<NUM> layer <NUM>, the Si layer <NUM>, the SiO<NUM> layer <NUM>, the Si layer <NUM>, and the SiO<NUM> layer <NUM> are stacked is prepared (<FIG>), and a Pt layer <NUM> is formed on one side of the SiO<NUM> layer <NUM> (the side not in contact with the Si layer <NUM>) (<FIG>). Next, a PZT layer <NUM> is formed on one side of the Pt layer <NUM> (the side not in contact with the SiO<NUM> layer <NUM>) (<FIG>), and further, a Pt layer <NUM> is formed on one side of the PZT layer <NUM> (the side not in contact with the Pt layer <NUM>) (<FIG>). Here, note that any known method may be used for the film formation method.

Next, the Pt layer <NUM> and the PZT layer <NUM> are patterned into a predetermined shape (<FIG>). Here, any known method may be used for this patterning. As an example, in the present embodiment, a method is used in which a mask pattern is formed using a resist film (photoresist film), etching is performed, and then the resist film is peeled off (the same applies to the patterning in each subsequent step).

Next, the Pt layer <NUM> is patterned into a predetermined shape (<FIG>), and then the SiO<NUM> layer <NUM> is patterned into a predetermined shape (<FIG>). Further, the Si layer <NUM> is patterned into a predetermined shape (<FIG>), and then the SiO<NUM> layer <NUM> is patterned into a predetermined shape (<FIG>).

Next, the SiO<NUM> layer <NUM> on the back surface side is patterned into a predetermined shape (<FIG>). Then the Si layer <NUM> is patterned into a predetermined shape (<FIG>), and the rib portion <NUM> is further formed (<FIG>). Thereafter, the SiO<NUM> layer <NUM> is patterned into a predetermined shape (<FIG>). Through the above steps, the optical scanning apparatus <NUM> according to the embodiment described above is completed.

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

The optical scanning apparatus <NUM> according to the first embodiment described above can be applied to any electronic equipment that requires laser beam scanning. For example, it can be applied to pico-projectors used in head-up displays and wearable devices. Further, the present disclosure can be applied to an apparatus that changes the light distribution pattern depending on the presence of an oncoming vehicle, a preceding vehicle, a pedestrian, or various objects when irradiating light toward the front of an own vehicle. Alternatively, the present disclosure can be applied to an object detection apparatus such as LiDAR (Light Detection And Ranging). Further, the present disclosure can be applied to various MEMS sensors such as an acceleration sensor, an angular velocity sensor, a pressure sensors, or a myoelectric sensor.

<FIG> is a plane view from the back side of an optical scanning apparatus according to a second embodiment. Further, <FIG> and <FIG> are partial enlarged views of the optical scanning apparatus shown in <FIG>, respectively. Here, note that the overall configuration of the optical scanning apparatus 1a according to the second embodiment is the same as the optical scanning apparatus <NUM> according to the first embodiment described above, and only the structure of the Si layer <NUM> which is a support layer is different. Hereinafter, regarding the optical scanning apparatus 1a according to the second embodiment, the description of common features with the optical scanning apparatus <NUM> of the first embodiment will be omitted, and the structure of the Si layer <NUM> which is different, will be described in detail.

As shown in the figure, the Si layer <NUM> of the optical scanning apparatus 1a is provided with a plurality of through holes <NUM> in a region overlapping with the Si layer <NUM> (that is, a portion related to the generation of parasitic capacitance), where the Si layer <NUM> which is an active layer that comprises capacitance component Cs-L and capacitance component Cs-R that are capacitance components corresponding to the formation regions of fixed electrodes 20a, 21a, etc. In the illustrated example, the through holes <NUM> are arranged in rows in the horizontal and vertical directions in the figure, but the arrangement of the through holes <NUM> is not limited thereto. The region where each through hole <NUM> is arranged corresponds to the above-described portions <NUM> and <NUM> (refer to <FIG>). Further, a plurality of through holes <NUM> are similarly provided in the portions <NUM> and <NUM> described above, that is, in the regions where the driving pad <NUM> and the driving GND pad <NUM> are formed. With regard to the size of each of the through holes <NUM> and <NUM>, for example, when each is approximately square as shown in the figure, one side thereof can be approximately <NUM> to <NUM>.

<FIG> are partial cross-sectional views of the optical scanning apparatus of the second embodiment. <FIG> is a cross-sectional view taken along line a-a shown in <FIG>, and <FIG> is a cross-sectional view taken along line b-b shown in <FIG>. As shown in <FIG>, the through hole <NUM> is formed by partially removing the Si layer <NUM> which is a support layer, to reach the SiO<NUM> layer (BOX layer) <NUM>. On the other hand, as shown in <FIG>, at the portion where the through hole <NUM> does not exist, the Si layer <NUM> which is a support layer is not removed, and the SiO<NUM> layer (BOX layer) <NUM> is not exposed. Here, although not shown, each through hole <NUM> has a similar structure as the through hole <NUM>. These through holes <NUM> and <NUM> can be formed during the process of etching the Si layer <NUM> (refer to <FIG>) in the manufacturing process of the optical scanning apparatus <NUM> described in the first embodiment. Since the Si layer <NUM> which is a support layer also has a role of ensuring mechanical strength of the optical scanning apparatus 1a, by only partially removing the layer to form the through holes <NUM> and <NUM>, a decrease in mechanical strength can be prevented.

By providing each through hole <NUM>, it is possible to reduce the overlapping area between the Si layer <NUM> which is a support layer, and the Si layer <NUM> which is an active layer. Thereby, the values of the capacitance component Cs-L and the capacitance component Cs-R , which are parasitic capacitance, can be reduced. This reduces the difference between the capacitance component Cv which is the capacitance component to be detected and the capacitance component Cs-R. Thereby, the voltage change due to the deflection angle detection section <NUM> can be made greater.

In detail, it is difficult to increase the value of the capacitance component Cv which is the capacitance component to be detected because the electrodes are formed in a direction perpendicular to the support layer or the like. On the other hand, since the parasitic capacitance caused by the overlap between the Si layer <NUM> which is an active layer and the Si layer <NUM> which is a support layer is formed in a direction parallel to the support layer, etc., its value tends to increase. When through holes <NUM> are not provided, the capacitance component Cv is, for example, about <NUM> pF, whereas the capacitance component Cs-R may be about several tens of pF. In principle, when the ratio of the capacitance component Cv to the capacitance component Cs-R (Cs-R/Cv) is around <NUM>, amount of voltage change due to the deflection angle detection section <NUM> reaches its maximum value. As the capacitance component Cs-R decreases, the value of Cs-R/Cv approaches <NUM>, thereby the amount of voltage change can be made greater.

Claim 1:
An optical scanning apparatus comprising:
a mirror having a reflective surface;
a driving section that swings the mirror;
a detection section that detects the movement of the driving section by change of a capacitance; and
a dummy capacitance section that generates a dummy capacitance that is approximately equivalent to the capacitance in an initial state of the detection section;
wherein the detection section has a movable electrode whose position changes in relation to the movement of the driving section and a fixed electrode whose position does not change in relation to the movement of the driving section, and is configured such that the capacitance is generated between the movable electrode and the fixed electrode,
wherein the dummy capacitance section is configured to include a first electrode and a second electrode, and is configured to generate the dummy capacitance between the first electrode and the second electrode,
wherein the movable electrode, the fixed electrode, the first electrode, and the second electrode are provided in an active layer formed in the same semiconductor layer, and are each separated,
wherein the active layer is arranged to face a support layer which is a common semiconductor layer, with an insulating layer in between,
wherein a first parasitic capacitance that occurs between the active layer provided with the fixed electrode and the supporting layer, and a second parasitic capacitance that occurs between the active layer provided with the first electrode and the supporting layer, are approximately equivalent, and
wherein the capacitance of the detection section 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.