Piezoelectric actuator and optical scanning apparatus having a plurality of piezoelectric layers

A piezoelectric actuator includes a plurality of piezoelectric layers, a plurality of electrodes between which each of the piezoelectric layers is placed so that the electrodes and the piezoelectric layers alternate with each other, and a substrate on which the plurality of piezoelectric layers and the plurality of electrodes are formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosures herein relate to a piezoelectric actuator and an optical scanning apparatus having a piezoelectric actuator.

2. Description of the Related Art

Piezoelectric actuators utilizing the characteristics of piezoelectric material that exhibits deformation in response to application of voltage have been known in the art.

Related-art actuators have piezoelectric material provided on a substrate as disclosed in Patent Document 1, for example. A piezoelectric device includes piezoelectric material and a pair of electrodes between which the piezoelectric material is placed. Drive voltage is applied to the pair of electrodes to deform the piezoelectric material.

Various electronic devices of today are required to have low power conservation. Reduction in power consumption is also required in electronic devices having piezoelectric actuators, for example. As a result, reduction in the drive voltage of piezoelectric actuators is also required.

Accordingly, there may be a need to provide a piezoelectric actuator and an optical scanning apparatus for which drive voltage can be reduced.

Patent Document

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a piezoelectric actuator and an optical scanning apparatus that substantially obviate one or more problems caused by the limitations and disadvantages of the related art.

A piezoelectric actuator includes a plurality of piezoelectric layers, a plurality of electrodes between which each of the piezoelectric layers is placed so that the electrodes and the piezoelectric layers alternate with each other, and a substrate on which the plurality of piezoelectric layers and the plurality of electrodes are formed.

An optical scanning apparatus for rotationally swinging a mirror support part supporting a mirror around a rotational axis through twist of twist beams that support the mirror support part on both ends thereof on the rotational axis includes two first drive beams disposed on respective sides of the mirror and the mirror support part, connection beams configured to connect one side of each of the first drive beams to the twist beams, a movable frame configured to surround the mirror, the mirror support part, the twist beams, the first drive beams, and the connection beams, and first drive units disposed on the first drive beams, respectively, wherein each the first drive units includes a plurality of piezoelectric layers, a plurality of electrodes between which each of the piezoelectric layers is placed so that the electrodes and the piezoelectric layers alternate with each other, and a substrate on which the plurality of piezoelectric layers and the plurality of electrodes are formed.

According to at least one embodiment, drive voltage is reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

In the following, a first embodiment will be described with reference to the accompanying drawings.FIG. 1is a drawing illustrating the configuration of a piezoelectric actuator according to the first embodiment.

A piezoelectric actuator10of the present embodiment includes a lower electrode20formed on a substrate11and a piezoelectric material12formed on the lower electrode20. The piezoelectric actuator10of the present embodiment further includes a middle electrode30formed on the piezoelectric material12, a piezoelectric material13formed on the middle electrode30, and an upper electrode40formed on the piezoelectric material13.

The piezoelectric actuator10is configured such that the middle electrode30is coupled to the ground, and the upper electrode40and the lower electrode20receive a drive signal for driving the piezoelectric actuator10. The upper electrode40and the lower electrode20are displaced in response to the voltage of the drive signal as it is supplied thereto.

The lower electrode20of the present embodiment is a film comprised of three layers. The lower electrode20of the present embodiment includes a first layer21, a second layer22, and a third layer23. In the lower electrode20of the present embodiment, the first layer21and the third layer23are LNO (LaNiO3) layers, each of which may be 30 nm in thickness. The second layer22of the present embodiment is a Pt thin film, which may be 150 nm in thickness.

Similarly, the middle electrode30of the present embodiment is a film comprised of three layers. The middle electrode30of the present embodiment includes a first layer31, a second layer32, and a third layer33. In the middle electrode30of the present embodiment, the first layer31and the third layer33are LNO (LaNiO3) layers, each of which may be 80 nm in thickness. The second layer32of the present embodiment is a Pt thin film, which may be 150 nm in thickness. As noted above, the first layer31and the third layer33of the middle electrode30of the present embodiment have a film thickness of 80 nm, which is not a limiting example. The film thickness of the first layer31and the third layer33may be 30 nm or more. This thickness of 30 nm is required to evenly grow an LNO thin film.

The upper electrode40of the present embodiment is a film comprised of two layers. The upper electrode40of the present embodiment includes a first layer41and a second layer42. In the upper electrode40of the present embodiment, the first layer41is an LNO (LaNiO3) layer, which may be 80 nm in thickness. The second layer42is a Pt thin film, which may be 100 nm in thickness.

The specific configuration of the present embodiment in which the first layers21,31and41and the third layers23and33are LNO (LaNiO3) thin films, and the second layers22,32and42are Pt thin films is not a limiting example. It suffices for the first layers21,31and41and the third layers23and33to be a thin film including a perovskite structure and the (110) orientation. SRO (Sr2RuO4) may be used for these layers. The second layers22,32and42may be a platinum group metal that is not Pt, and may be a thin film made of Ir, Os, or the like.

The piezoelectric materials12and13of the present embodiment are PZT (Lead titanium zirconium oxide) thin films. The piezoelectric material12and the piezoelectric material13are formed on the lower electrode20and the middle electrode30, respectively, by use of the sol-gel process. The substrate11of the present embodiment is a silicon substrate.

In the present embodiment, for the purpose of crystallizing the piezoelectric material12and the piezoelectric material13formed on the lower electrode20and the middle electrode30, respectively, the lower electrode20and the middle electrode30are formed by sputtering such that the crystal orientation in the vertical direction in the LNO surface is oriented predominantly in the (110) orientation by raising the temperature of the substrate11to more than 500 degrees Celsius. The lower electrode20and the middle electrode30of the present embodiment are formed in the above-noted condition for the purpose of crystallizing the PZT thin films to achieve satisfactory piezoelectric characteristics, thereby allowing a drive voltage to be reduced.

The third layer23of the lower electrode20and the third layer33of the middle electrode30in the present embodiment facilitate crystallization of the piezoelectric material12and the piezoelectric material13formed thereon. The first layer31of the middle electrode30and the first layer41of the upper electrode40in the present embodiment serve to suppress oxidization of the piezoelectric material12and the piezoelectric material13formed therebeneath.

In the following, a description will be given of the dielectric characteristics of the piezoelectric actuator10according to the present embodiment.FIG. 2is a drawing illustrating the piezoelectric actuator that is used to evaluate dielectric characteristics.

In the present embodiment, dielectric characteristics are evaluated by connecting the electrodes of the piezoelectric actuator10as illustrated inFIG. 2. In the piezoelectric actuator illustrated inFIG. 2, connection-purpose electrodes25,35and45are formed on the lower electrode20, the middle electrode30, and the upper electrode40, respectively. In the example illustrated inFIG. 2, an AC power supply50connects between the electrode35and a connection point between the electrode25and the electrode45. The AC power supply50applies a drive voltage to the piezoelectric actuator10.

FIG. 3is a drawing illustrating dielectric characteristics that are observed when the thickness of the LNO thin films of the piezoelectric actuator is changed. In the present embodiment, changes in the saturation polarization Pm, remnant polarization Pr, and coercive electric field Ec of the piezoelectric actuator10are small when the thickness of the LNO thin films is in a range of 30 nm to 100 nm, which is regarded as an indication of stable dielectric characteristics.

In consideration of the above, the thickness of the LNO thin films in the present embodiment is set equal to 30 nm which is the lower end of a range of 30 nm to 100 nm. It suffices for the film thickness of the LNO thin films of the present embodiment to be within a range between 30 nm and 100 nm.

In the following, a description will be given of displacement and drive voltage applied to the piezoelectric actuator10of the present embodiment.FIG. 4is a drawing illustrating the relationship between drive voltage and displacement.

FIG. 4depicts the relationship between a drive voltage and an amplitude of the swing (i.e., displacement) of a cantilever utilizing a related-art single-piezoelectric-layer actuator and the relationship between a drive voltage and an amplitude of the swing (i.e., displacement) of a cantilever utilizing the piezoelectric actuator10.

InFIG. 4, a dotted line represents the relationship between a drive voltage and an amplitude of the swing of a cantilever utilizing the related-art piezoelectric actuator, and a solid line represents the relationship between a drive voltage and an amplitude of the swing of a cantilever utilizing the piezoelectric actuator10of the present embodiment. The drive voltage illustrated inFIG. 4is an alternating voltage of 250 Hz. The amplitude of the swing was measured by use of a Doppler vibration meter or the like.

As illustrated InFIG. 4, the cantilever utilizing the piezoelectric actuator10of the present embodiment can provide about the same amplitude of the swing as the cantilever utilizing the related-art piezoelectric actuator by use of approximately half the drive voltage applied to the related-art piezoelectric actuator. Specifically, in order to obtain the amplitude of the swing that is 4 um, the cantilever utilizing the related-art piezoelectric actuator may need a drive voltage of approximately 45 V. On the other hand, the cantilever utilizing the piezoelectric actuator10produces a swing amplitude of 4 um by use of a drive voltage of approximately 20 V. The use of the piezoelectric actuator10of the present embodiment thus achieves reduction in drive voltage.

FIG. 5is a drawing illustrating drive voltage applied to a piezoelectric actuator. InFIG. 5, dotted-line waves represent drive voltage applied to the related-art piezoelectric actuator, and solid-line waves represent drive voltage applied to the piezoelectric actuator10of the present embodiment.

InFIG. 5, the amplitude of the drive voltage applied to the piezoelectric actuator10is V1, and the amplitude of the drive voltage applied to the related-art piezoelectric actuator is V2. In this case, V1is approximately equal to V2/2.

In this manner, the use of the piezoelectric actuator10of the present embodiment serves to reduce the drive voltage by about a half, compared with the related-art single-piezoelectric-layer actuator.

The present embodiment is directed to an example in which the number of piezoelectric material layers provided in the piezoelectric actuator10is two. This example is non-limiting. The piezoelectric actuator10of the present embodiment may have four piezoelectric material layers or six piezoelectric material layers.

Second Embodiment

In the following, a second embodiment will be described with reference to the accompanying drawings. The second embodiment is directed to an optical scanning apparatus utilizing the piezoelectric actuator10of the first embodiment. In the second embodiment, elements having the same or similar functional configurations as those of the first embodiment are referred to by the same or similar numerals, and a description thereof will be omitted.

FIG. 6is a drawing illustrating an optical scanning apparatus according to the second embodiment.

An optical scanning apparatus100of the present embodiment includes a mirror110, a mirror support part120, twist beams130A and130B, connection beams140A and140B, first drive beams150A and150B, a movable frame160, second drive beams170A and170B, and a fixed frame180. The first drive beams150A and150B of the present embodiment are provided with drive units151A and151B, respectively. The second drive beams170A and170B are provided with drive units171A and171B, respectively.

The mirror support part120of the present embodiment has slits122formed therein that extend along the circumference of the mirror110. The slits122serve to reduce the weight of the mirror support part120and to absorb stress while transmitting twist from the twist beams130A and130B to the mirror110.

In the optical scanning apparatus100of the present embodiment, the mirror110is supported on the surface of the mirror support part120, which is connected to one end of each of the twist beams130A and130B situated on either side thereof. The twist beams130A and130B constitute a swing axis, and extend along the axial direction to support the mirror support part120at both ends on the axis. The twist beams130A and130B twist to swing the mirror110supported on the mirror support part120, thereby scanning the light shining on and reflected by the mirror110. The twist beams130A and130B are connected to and supported by the connection beams140A and140B, respectively, and are thus ultimately connected to the first drive beams150A and150B.

The first drive beams150A and150B, the connection beams140A and140B, the twist beams130A and130B, the mirror support part120, and the mirror110are surrounded by the movable frame160. Each of the first drive beams150A and150B has one end thereof supported by the movable frame160. The other end of the first drive beam150A extends on the inner side thereof to be connected to the connection beams140A and140B. The other end of the first drive beam150B also extends on the inner side thereof to be connected to the connection beams140A and140B.

The first drive beams150A and150B form a pair, and are placed on both sides of the mirror110and the mirror support part120in the direction perpendicular to the direction in which the twist beams130A and130B extend.

The drive units151A and151B are formed on the surfaces of the first drive beams150A and150B, respectively. The drive units151A and151B each include the lower electrode20, the piezoelectric material12, the middle electrode30, the piezoelectric material13, and the upper electrode40formed on the surfaces of the first drive beams150A and150B, respectively. In the drive units151A and151B, the piezoelectric materials exhibit expansions and contractions in response to the polarity of drive voltage applied between the middle electrode30and both the lower electrode20and the upper electrode40. Drive voltages having different polarities may be applied to the first drive beams150A and150B, respectively. In such a case, the first drive beams150A and150B oscillate to move in opposite vertical directions on the right and left sides of the mirror110, so that the mirror110rotationally swings around the swing or rotation axis that is provided by the twist beams130A and130B. The direction in which the mirror110rotationally swings around the axis of the twist beams130A and130B is hereinafter referred to as a horizontal direction. Resonant oscillation may be used for horizontal drive exerted by the first drive beams150A and150B, thereby achieving high-speed swinging of the mirror110.

One end of each of the second drive beams170A and170B is connected to an exterior side of the movable frame160. The second drive beams170A and170B form a pair, and are placed on the right-hand side and left-hand side of the movable frame160, respectively. The second drive beam170A includes beams each extending in parallel to the first drive beam150A. Each of the beams is connected at one end thereof to an adjacent one of the beams so that the series-connected beams are arranged in a zigzag form. The other end of the second drive beam170A is connected to an interior side of the fixed frame180. Similarly, the second drive beam170A also includes beams each extending in parallel to the first drive beam150B. Each of the beams is connected at one end thereof to an adjacent one of the beams so that the series-connected beams are arranged in a zigzag form. The other end of the second drive beam170B is connected to an interior side of the fixed frame180.

The drive units171A and171B are formed on the surfaces of the second drive beams170A and170B, respectively, in rectangular forms that do not have a curved part. The drive unit171A includes the lower electrode20, the piezoelectric material12, the middle electrode30, the piezoelectric material13, and the upper electrode40formed on the surface of the second drive beam170A. The drive unit171B includes the lower electrode20, the piezoelectric material12, the middle electrode30, the piezoelectric material13, and the upper electrode formed on the surface of the second drive beam170B.

Drive voltages having different polarities are applied to adjacent rectangular units of the drive units171A and171E on the second drive beams170A and170B, so that adjacent rectangular beams are bent in opposite vertical directions, thereby transmitting accumulated vertical movements of the individual rectangular beams to the movable frame160. Through these movements, the second drive beams170A and170B swing the mirror110in the vertical direction perpendicular to the horizontal direction. Resonant oscillation may be used for vertical drive exerted by the second drive beams170A and170B.

The drive unit171B includes drive units171DL,171CL,171BL, and171AL in this order from left to right toward the movable frame160. The drive unit171A on the right-hand side includes drive units171AR,171BR,171CR, and171DR in this order from left to right from the movable frame160. In this case, the drive units171Ax and the drive units171Cx (i.e., four units in total) are driven by a single common waveform, and the drive units171Bx and the drive units171Dx (i.e., four units in total) are driven by a single common waveform that has a different phase than the former waveform, thereby achieving vertical swinging motion. The drive units171Ax,171Bx,171Cx, and171Dx of the present embodiment each include the piezoelectric material12, the piezoelectric material13, the lower electrode20, the middle electrode30, and the upper electrode40similarly to the drive units171A and171B.

In the optical scanning apparatus100of the present embodiment, the piezoelectric actuator10of the first embodiment having two piezoelectric material layers is used as the drive units151A,151B,171A, and171B as described above. With this arrangement, the present embodiment can decrease by half the drive voltage applied to the151A,151B,171A, and171B.

In the optical scanning apparatus100of the present embodiment, a piezoelectric sensor191is provided on the connection beam140B to detect an angle of the mirror110in the horizontal direction when the mirror110rotationally swings in the horizontal direction.

In the present embodiment, the piezoelectric sensor191may detect the angle of the mirror110in the horizontal direction, so that the drive voltage may be controlled based on the detected results. In the optical scanning apparatus100of the present embodiment, a drive wire is provided to supply a piezoelectric-sensor drive voltage for driving the piezoelectric sensor191, and a sensor wire is provided that extends from the piezoelectric sensor191. The drive wire and the sensor wire are connected to a set of terminals TA or TB. The sets of terminals TA and TB are used for connecting the optical scanning apparatus100to an optical scanning control apparatus200that will be described later.

In the present embodiment, the piezoelectric sensor195for detecting an angle of the mirror110in the vertical direction when the mirror110swings in the vertical direction may be situated on one of the rectangular beams of the second drive beam170A.

The optical scanning control apparatus200of the present embodiment will now be described by referring toFIG. 7.FIG. 7is a drawing illustrating the optical scanning control apparatus according to the second embodiment.

The optical scanning control apparatus200of the present embodiment includes the optical scanning apparatus100, a front-end IC (integrated circuit)400, an LD (laser diode)440, and a mirror driver IC500.

The front-end IC400of the present embodiment processes video signals supplied thereto, and sends the processed signals to the LD440. Further, the front-end IC400of the present embodiment supplies a signal for controlling the swinging of the mirror110to the optical scanning apparatus100.

The front-end IC400of the present embodiment includes a video signal processing unit410, an LD driver420, and a mirror controlling unit430. The video signal processing unit410separates the synchronizing signals, luminance signal, and chromaticity signals from each other included in the supplied video signals. The video signal processing unit410supplies the luminance signal and the chromaticity signals to the LD driver420, and supplies the synchronizing signals to the mirror controlling unit430.

The LD driver420controls the LD440based on the signals supplied from the video signal processing unit410.

The mirror controlling unit430controls the swinging of the mirror110based on the synchronizing signals and the output of the piezoelectric sensor191output from the mirror driver IC500. More specifically, the mirror controlling unit430uses the mirror driver IC500to produce drive voltages (i.e., drive signals) for driving the drive units151A and151B of the optical scanning apparatus100

The mirror driver IC500of the present embodiment includes phase inverting units510and511and a noise removal unit600.

The phase inverting units510and511invert the phases of the drive signals supplied from the mirror controlling unit430. Specifically, the phase inverting unit510inverts the phase of the drive signal supplied to the drive unit151A to produce the phase-inverted signal, which is supplied as the drive signal to the drive unit151B. The phase inverting unit511inverts the phase of the drive signal supplied to the drive unit171A to produce the phase-inverted signal, which is supplied as the drive signal to the drive unit171B.

The noise removal unit600of the present embodiment reduces noise included in the output of the piezoelectric sensor191. The noise included in the output of the piezoelectric sensor191is generated by crosstalk with the drive signals supplied to the drive units151A,151B,171A, and171B due to the length and distance of the drive wires.

The noise removal unit600removes noise received from the drive signals supplied to the drive units151A and151B. The optical scanning control apparatus200of the present embodiment may be provided with a noise removal unit that removes noise received from the drive signals supplied to the drive units171A and171B. The noise removal unit for the drive units171A and171B may have the same configuration as the noise removal unit600.

The noise removal unit600of the present embodiment includes gain and phase adjusting units520and530, an adder circuit540, a buffer550, and a subtraction circuit560.

The gain and phase adjusting units520and530generate, from the drive signals supplied to the drive units151A and151B, respectively, signals equivalent to noises included in the output of the piezoelectric sensor191. In the following description, the drive signal supplied to the drive unit151A is referred to as a drive signal1, and the drive signal supplied to the drive unit151B is referred to as a drive signal2.

The gain and phase adjusting unit520of the present embodiment generates a signal equivalent to noise included in the output of the piezoelectric sensor191when the drive signal1is applied to the drive unit151A. The gain and phase adjusting unit530of the present embodiment generates a signal equivalent to noise included in the output of the piezoelectric sensor191when the drive signal2is applied to the drive unit151B.

The adder circuit540obtains the sum of the outputs of the gain and phase adjusting units520and530, and the obtained sum is then inverted. In the present embodiment, the outputs of the gain and phase adjusting units520and530are added together, and the resulting sum is inverted. With this arrangement, a signal equivalent to noises included in the output of the piezoelectric sensor191is generated when the drive signals1and2are simultaneously supplied to the drive units151A and151B, respectively.

The buffer550amplifies the output of the piezoelectric sensor191. In the present embodiment, only one piezoelectric sensor, i.e., the piezoelectric sensor191, is provided in the optical scanning apparatus100. The piezoelectric sensor191outputs an electric current responsive to the displacement of the connection beam140B propagating from the twist beam130B in response to the angle of the mirror110in the horizontal direction.

The subtraction circuit560subtracts the output of the adder circuit540from the output of the buffer550. The output of the buffer550of the present embodiment is a signal that includes both noise and the output of the piezoelectric sensor191. The output of the adder circuit540is a signal that is equivalent to the noise included in the output of the piezoelectric sensor191. Subtracting the output of the adder circuit540from the output of the buffer550thus serves to remove the noise from the output of the piezoelectric sensor191. The output of the subtraction circuit560is supplied as the output of the noise removal unit600to the mirror controlling unit430of the front-end IC400. Based on the output of the noise removal unit600, the mirror controlling unit430produces drive signals.

Control of the drive signals in the present embodiment as described above ensures that the swing of the mirror110is properly controlled.

In the present embodiment, the piezoelectric sensor191may also include the lower electrode20, the piezoelectric material12, the middle electrode30, the piezoelectric material13, and the upper electrode40.

In the optical scanning control apparatus200of the present embodiment as described above, the piezoelectric actuator10of the first embodiment is used as the drive units151A,151B,171A, and171B, thereby allowing a reduction to be made in the drive voltage supplied to the mirror110. Further, the piezoelectric sensor191of the present embodiment has the configuration of the piezoelectric actuator10of the first embodiment, thereby allowing the sensor output to be increased. Moreover, in the present embodiment, the removal of noise from the sensor output ensures the provision of a highly accurate sensor output.

Third Embodiment

In the following, a third embodiment will be described with reference to the accompanying drawings. The third embodiment differs from the first and second embodiments in that the upper electrode and the lower electrode of a piezoelectric actuator are electrically connected to the substrate. In the description of the third embodiment in the following, differences from the first embodiment will be described. The same or similar elements as those of the first embodiment are referred to by the same or similar reference symbols, and a description thereof will be omitted.

FIG. 8is a drawing illustrating the configuration of a piezoelectric actuator according to the third embodiment. The piezoelectric actuator10A of the present embodiment has the upper electrode40and the lower electrode20electrically connected to the ground, and has the middle electrode30that receives a drive signal for driving the piezoelectric actuator10A. The middle electrode30is displaced in response to the voltage of the drive signal as it is supplied thereto.

In the piezoelectric actuator10A of the present embodiment, the upper electrode40and the lower electrode20are electrically connected to the substrate11through an interconnection60. A connection-purpose electrode61is formed on the upper electrode40of the present embodiment. A connection-purpose electrode62is formed on the lower electrode20. A connection-purpose electrode63is formed on the substrate11of the present embodiment. The upper electrode40, the lower electrode20, and the substrate11of the present embodiment are connected together through the electrodes61,62, and63and the interconnection60.

In the following, a description will be given of the optical scanning apparatus utilizing the piezoelectric actuator10A of the present embodiment by referring toFIG. 9.FIG. 9is a drawing illustrating an optical scanning apparatus according to the third embodiment.

In the present embodiment, the fact that noises generated by the drive wires for supplying drive signals to the drive units171A and171B are included in the output of the piezoelectric sensor195through the substrate11is taken into account, thereby resulting in the arrangement in which the piezoelectric actuator10A is utilized as the drive units171A and171B for the purpose of noise reduction.

Namely, in respect of the drive units171A and171B of the present embodiment, the upper electrode40and the lower electrode20formed on the surfaces of the second drive beams170A and170B are connected to the substrate11through the interconnection60.

In the optical scanning apparatus100A of the present embodiment, the piezoelectric actuator10A of the present embodiment is used as the drive units171A and171B, thereby reducing noise included in the output of the piezoelectric sensor195for detecting a vertical angle. The above-noted noise in the present embodiment is generated by crosstalk due to the length and distance of the drive wires for supplying drive signals.

In the following, a description will be given of the interconnection60of the present embodiment by referring toFIG. 10andFIG. 11, which are enlarged views of a portion91and a portion92ofFIG. 9, respectively.

FIG. 10is an enlarged view of the portion91.

FIG. 10illustrates an interconnection60BC connecting the upper electrode40and the lower electrode20to the substrate11in the drive units171BL and171CL included in the drive unit171B.

The drive unit171BL has an upper electrode40B and a lower electrode20B. The upper electrode40B is connected to the interconnection60BC through a contact hole61B. The lower electrode20B is connected to the interconnection60BC through a contact hole62B. The interconnection60BC to which the upper electrode40B and the lower electrode20B are connected is connected to the substrate11through a contact hole63BC.

The drive unit171CL has an upper electrode40C and a lower electrode20C. The upper electrode40C is connected to the interconnection60BC through a contact hole61C. The lower electrode20C is connected to the interconnection60BC through a contact hole62C. The interconnection60BC to which the upper electrode40C and the lower electrode20C are connected is connected to the substrate11through the contact hole63BC.

Accordingly, the drive units171BL and171CL have the upper electrode40and the lower electrode20thereof connected to the substrate11through the interconnection60BC, so that the potential of the upper electrode40and the lower electrode20is set equal to the potential of the substrate11.

FIG. 11is an enlarged view of the portion92.

FIG. 11illustrates an interconnection60AB connecting the upper electrode40and the lower electrode20to the substrate11in the drive units171AL and171BL.FIG. 11illustrates an interconnection60CD connecting the upper electrode40and the lower electrode20to the substrate11in the drive units171CL and171DL included in the drive unit171B.

The drive unit171AL has an upper electrode40A and a lower electrode20A. The upper electrode40A is connected to the interconnection60AB through a contact hole61a. The lower electrode20A is connected to the interconnection60AB through a contact hole62a. The interconnection60AB to which the upper electrode40A and the lower electrode20A are connected is connected to the substrate11through a contact hole63AB.

In the drive unit171BL, the upper electrode40B is connected to the interconnection60AB through a contact hole61b. The lower electrode20B is connected to the interconnection60AB through a contact hole62b.

Accordingly, the drive units171AL and171BL have the upper electrode40and the lower electrode20thereof connected to the substrate11through the interconnection60AB, so that the potential of the upper electrode40and the lower electrode20is set equal to the potential of the substrate11.

The drive unit171DL has an upper electrode40D and a lower electrode20D. The upper electrode40D is connected to the interconnection60CD through a contact hole61d. The lower electrode20D is connected to the interconnection60CD through a contact hole62d. The interconnection60CD to which the upper electrode40D and the lower electrode20D are connected is connected to the substrate11through a contact hole63CD.

In the drive unit171CL, the upper electrode40C is connected to the interconnection60CD through a contact hole61c. The lower electrode20C is connected to the interconnection60CD through a contact hole62c.

Accordingly, the drive units171CL and171DL have the upper electrode40and the lower electrode20thereof connected to the substrate11through the interconnection60CD, so that the potential of the upper electrode40and the lower electrode20is set equal to the potential of the substrate11.

In the present embodiment, the upper electrode40B of the drive unit171BL is connected to the substrate11through the contact holes61B and61b, and the lower electrode20B is connected to the substrate11through the contact holes62B and62b. Further, the upper electrode40C of the drive unit171CL of the present embodiment is connected to the substrate11through the contact holes61C and61c, and the lower electrode20C is connected to the substrate11through the contact holes62C and62c.

In the present embodiment, each of the upper electrode40and the lower electrode20is connected through a plurality of connecting points to the substrate11in the piezoelectric actuator10A, thereby suppressing the generation of uneven electrical resistance at the connecting points.

FIGS. 12A through 12Fare drawings illustrating the waveforms of the output of a piezoelectric sensor that detects an angle with respect to the vertical axis.

FIGS. 12A and 12Dillustrate the waveforms of the output of the piezoelectric sensor195observed when the peak-to-peak potential difference of a drive voltage is 10 Vp-p.FIGS. 12B and 12Eillustrate the waveforms of the output of the piezoelectric sensor195observed when the peak-to-peak potential difference of a drive voltage is 20 Vp-p.FIGS. 12C and 12Fillustrate the waveforms of the output of the piezoelectric sensor195observed when the peak-to-peak potential difference of a drive voltage is 40 Vp-p.

FIGS. 12A, 12B, and 12Cillustrate cases in which the piezoelectric actuator10A is not used, andFIGS. 12D, 12E, and 12Fillustrate cases in which the piezoelectric actuator10A is used.

As illustrated inFIGS. 12A, 12B, and 12C, the waveform of the output of the piezoelectric sensor195has distortion that increases with an increase in the drive voltage.

In the case of the piezoelectric actuator10A being used, on the other hand, no distortion occurs as illustrated inFIGS. 12D, 12E, and 12F.

In this manner, noise included in the output of the piezoelectric sensor195is reduced in the optical scanning apparatus100A of the present embodiment.

Although the present embodiment has been described with reference to the example in which the upper electrode40and the lower electrode20of the piezoelectric actuator10A are electrically connected to the substrate11, this is not a limiting example. For example, the middle electrode30may be connected to the substrate11serving as a ground, and a drive signal may be supplied to the upper electrode40and the lower electrode20.

Although the invention has been described by referring to embodiments, the invention is not limited to the configurations of these embodiments. Various variations and modifications may be made without departing from the scope of the present invention, and may be made in accordance with applications.

The present application is based on Japanese priority applications No. 2012-213500 filed on Sep. 27, 2012 and No. 2013-174661 filed on Aug. 26, 2013 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.