JP2014127681A - Polarization method of piezoelectric rotation angle sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization method for increasing output of a piezoelectric rotation angle sensor in a light deflector.SOLUTION: The light deflector includes a piezoelectric actuator for rotating a mirror part combined with a rectangular frame around a prescribed axial line, and the piezoelectric rotation angle sensor for outputting a voltage corresponding to the amount of expansion and contraction of a substrate layer 26 while having a lower electrode layer 29, a piezoelectric film layer 30, and an upper electrode layer 31 laminated in this order from the lower side on the substrate layer 26. The directions of electric fields facing the lower electrode layer 29 and the upper electrode layer 31 are set as positive and negative directions respectively, a positive polarization process and a negative polarization process for separately impressing polarization processing voltages generated by electric fields of positive and negative directions, the absolute value of which is larger than that of the coercive electric field of the piezoelectric film layer 30, between both electrode layers 29, 30 are alternately implemented so as to include the positive polarization process at least twice and the negative polarization process at least once.

Description

  The present invention relates to a polarization method of a piezoelectric rotation angle sensor in an optical deflector.

  2. Description of the Related Art A piezoelectric drive type optical deflector manufactured using MEMS (Micro Electro Mechanical Systems) technology is known. For example, the optical deflectors disclosed in Patent Documents 1 and 2 enable a mirror unit that reflects light incident from a certain direction, a support made of a rectangular frame, and the mirror unit to be rotatable about a predetermined axis. A coupling unit coupled to the support and a piezoelectric rotation angle sensor for detecting the rotation angle of the mirror unit are provided.

  In the optical deflector of Patent Document 1, the piezoelectric rotation angle sensor is formed so as to surround the peripheral portion of the mirror portion via a slit, and is coupled to the support body together with the mirror portion via a common torsion bar. ing.

  In the optical deflector of Patent Document 2, the mirror unit is coupled to the support via a torsion bar and a cantilever actuator, and the piezoelectric rotation angle sensor is disposed at the end of the actuator on the torsion bar side. Yes.

  In the above optical deflector, in order to increase the output of the piezoelectric rotation angle sensor, the ferroelectric used in the piezoelectric rotation angle sensor is subjected to polarization treatment, and the ferroelectric dipole It is effective to align the direction of the moment.

JP 2011-150055 A JP 2010-197994 A

  Therefore, as a polarization method for the piezoelectric film layer made of the ferroelectric of the piezoelectric rotation angle sensor in the optical deflector, a unidirectional DC voltage generated in the piezoelectric film layer with an electric field larger than the coercive electric field is applied to the piezoelectric film layer. It is conceivable to apply for several minutes.

  However, simply applying a unidirectional DC voltage for several minutes has a limit in the amount of increase in output of the piezoelectric sensor, and a technique for further increasing this is desired.

  An object of the present invention is to provide a polarization method that further increases the output of a piezoelectric rotation angle sensor in an optical deflector.

  The polarization method of the piezoelectric rotation angle sensor according to the present invention includes a mirror part that reflects light incident from a certain direction, a support, and the mirror part coupled to the support so as to be rotatable about a predetermined axis. A coupling portion having an expansion / contraction surface that expands / contracts according to a rotation angle of the mirror portion, a piezoelectric actuator that rotates the mirror portion around the predetermined axis, and an expansion / contraction surface of the coupling portion that are stacked in order from the bottom. The piezoelectric rotation angle in an optical deflector comprising a lower electrode layer, a piezoelectric film layer, and an upper electrode layer, and a piezoelectric rotation angle sensor that outputs a voltage corresponding to the amount of expansion / contraction of the expansion / contraction surface as an inter-electrode voltage. A polarization method of a sensor, wherein an absolute value of the piezoelectric film layer is obtained when a direction of an electric field directed to the lower electrode layer and the upper electrode layer is set to a positive direction and a negative direction in a thickness direction of the piezoelectric film layer, respectively. Greater than absolute value of coercive electric field A positive polarization process and a negative polarization process in which a polarization voltage that generates a positive and negative electric field is applied between the electrode layers, respectively, so that the positive polarization process includes at least twice and the negative polarization process includes at least one time. Further, the present invention is characterized by being alternately performed.

  According to the present invention, in the optical deflector configured as described above, the positive and negative polarization processes are alternately performed so that the piezoelectric layer of the piezoelectric rotation angle sensor includes the positive polarization process at least twice and the negative polarization process at least once. By implementing, the output of the piezoelectric rotation angle sensor can be further increased.

  In the polarization method of the piezoelectric rotation angle sensor, the polarization process can be terminated by the positive polarization process.

  According to this polarization method, the output of the piezoelectric rotation angle sensor can be increased by ending the polarization process with the positive polarization process, compared to when ending the polarization process with the negative polarization process.

  In the polarization method of the piezoelectric rotation angle sensor, the piezoelectric actuator constitutes the coupling portion, and a dividing groove that divides the lower electrode layer, the piezoelectric film layer, and the upper electrode layer on the substrate layer provides a proximal end side. The lower electrode layer, the piezoelectric film layer, and the upper electrode layer in the non-actuator part are divided into an actuator part and a non-actuator part on the tip side, and the lower electrode layer, the piezoelectric film layer, and the upper electrode layer of the piezoelectric rotation angle sensor The surface on the piezoelectric rotation angle sensor side of the substrate layer in the non-actuator portion can constitute the stretchable surface.

  According to this polarization method, the substrate layer is formed in common to the actuator portion on the proximal end side and the non-actuator portion on the distal end side through the lower side of the dividing groove in the piezoelectric actuator, and the stretchable surface is the substrate in the non-actuator portion. Since the layer is on the same side as the lower electrode layer of the actuator unit, the piezoelectric rotation angle sensor detects the expansion and contraction of the expansion and contraction surface with high followability to the expansion and contraction of the substrate layer in the actuator unit. Accuracy is improved.

The block diagram of an optical scanner. The enlarged view of the principal part of the piezoelectric actuator with a sensor, and its vicinity range. III-III arrow sectional drawing of FIG. FIG. 4 is a cross-sectional view taken along arrow IV-IV in FIG. 2. VV arrow sectional drawing of FIG. The figure explaining positive polarization and negative polarization with the structure of a piezoelectric rotation angle sensor. The figure which shows the hysteresis curve of the electric field strength-polarization amount of PZT selected as a material of the piezoelectric film layer of a piezoelectric rotation angle sensor. The figure which shows the relationship between the deflection angle of a mirror part in the non-polarization state of the piezoelectric film layer of a piezoelectric rotation angle sensor, and the output of a piezoelectric rotation angle sensor. The figure which investigated the change of the output voltage ratio of a piezoelectric rotation angle sensor when a positive polarization process and a negative polarization process were alternately repeated with respect to a piezoelectric rotation angle sensor.

  The configuration of the optical deflector 1 will be described with reference to FIG. The optical deflector 1 is manufactured using MEMS technology. The optical deflector 1 emits reflected light 92 as scanning light by increasing or decreasing a reflection angle at a constant frequency with respect to incident light 91 from the laser light source 90 as light incident from a certain direction.

  The control unit 95 receives various input signals including the detection signal of the sensor region 7 from the optical deflector 1 and controls the linear piezoelectric actuators 5 and 8 based on the input signals. The control unit 95 further controls on / off of the laser light source 90 and, in some cases, the amount of light of the laser light source 90, thereby adjusting the alignment pattern of the scanning light. A portion including the optical deflector 1, the laser light source 90, and the control unit 95 is equipped as an optical scanner 96 in, for example, a projector, a barcode reader, a laser printer, a laser headlamp, or a head-up display.

  For convenience of explanation, the top, bottom, left and right of the optical deflector 1 are defined. The top, bottom, left and right of the optical deflector 1 are the top, bottom, left and right in the front view of the optical deflector 1 of FIG. Note that the vertical and horizontal directions defined for the convenience of description of the optical deflector 1 do not define the vertical and horizontal directions in the actual use of the optical deflector 1. Further, the optical deflector 1 is not limited to being used in a vertical (vertical) position in actual use, but may be used while being inclined with respect to a horizontal plane or a vertical plane.

  The optical deflector 1 includes a mirror unit 2, two torsion bars 3, a rectangular frame 4, one piezoelectric actuator 5, and three piezoelectric actuators 8, and the circular mirror unit 2 is disposed at the center of the optical deflector 1. The incident light 91 from the laser light source 90 is received by the mirror surface on the front side (the front side and the back side of the optical deflector 1 are referred to as “front side” and “back side”, respectively), and the axis of the torsion bar 3 The reflected light 92 is emitted in a direction corresponding to the rotation angle around the. The axis of the torsion bar 3 is also the rotation axis of the mirror unit 2. The two torsion bars 3 have their axes aligned on the same diameter of the mirror part 2, and the tip part is coupled to the periphery of the mirror part 2 from the left and right sides of the mirror part 2.

  On the right side of the mirror portion 2, the piezoelectric actuators 5 and 8 are respectively disposed above and below the base end portion of the right torsion bar 3, and the front end side is coupled to the base end portion of the right torsion bar 3. On the left side of the mirror portion 2, the two piezoelectric actuators 8 are respectively disposed above and below the base end portion of the left torsion bar 3, and the front end side is coupled to the base end portion of the left torsion bar 3.

  The piezoelectric actuator 5 has a proximal-side actuator portion 6a and a distal-side non-actuator portion 6b. The structural difference between the piezoelectric actuator 5 and the piezoelectric actuator 8 is that the piezoelectric actuator 5 has a non-actuator portion 6b, whereas the piezoelectric actuator 8 does not have a non-actuator portion 6b, and the whole is an actuator portion. Is a point.

  The piezoelectric actuator 5 is configured such that the front side of the non-actuator portion 6b occupying the front end side area is a sensor region 7, and the non-actuator portion 6b loses its function as a piezoelectric actuator and functions as a piezoelectric sensor instead.

  The rectangular frame 4 surrounds the mirror part 2, the torsion bar 3, and the piezoelectric actuators 5 and 8 from the outside. The piezoelectric actuators 5 and 8 are coupled to the proximal end portion of the torsion bar 3 at the distal end portion, and coupled to the upper side portion or the lower side portion of the rectangular frame 4 at the proximal end portion. The torsion bar 3 and the piezoelectric actuators 5 and 8 correspond to a coupling unit that couples the mirror unit 2 to a rectangular frame 4 as a support so as to be rotatable around a predetermined axis.

  The structure of the piezoelectric actuator 5 will be described with reference to FIGS. For convenience of explanation, the length direction, the width direction, and the thickness direction of the piezoelectric actuator 5 are defined. The length direction of the piezoelectric actuator 5 is a direction (vertical direction in FIG. 2) along the center line of the piezoelectric actuator 5 between the distal end side and the proximal end side of the piezoelectric actuator 5.

  The thickness direction of the piezoelectric actuator 5 is a direction that penetrates the optical deflector 1 between the front side and the back side (perpendicular to the paper surface in FIG. 2). The width direction of the piezoelectric actuator 5 is a direction (left and right direction in FIG. 2) perpendicular to both the length direction and the thickness direction. The thickness direction of the piezoelectric actuator 5 coincides with the stacking direction of each layer when the optical deflector 1 is manufactured by the MEMS technology.

  Here, the length (dimension between the tip end and the base end) of the piezoelectric actuator 5 is defined as La, and the width of the piezoelectric actuator 5 is defined as Wa.

  In FIG. 2, the non-actuator portion 6 b occupies the tip portion of the piezoelectric actuator 5. The non-actuator portion 6b is between the distal end of the piezoelectric actuator 5 and a position separated by La / 3 from the distal end toward the proximal end in the length direction, and has a length less than La / 3.

  For convenience of explanation, numbers 1 to 5 are assigned in order from the inside of the piezoelectric actuator 5 to the respective sections whose width is Wa / 5 when the piezoelectric actuator 5 is divided into five equal parts in the width direction. The element parts 101-103 are each arrange | positioned to the division of the numbers 1-3 in the non-actuator part 6b. The conducting wire portions 111 to 113 are wired in sections 1 to 3 on the surface of the actuator portion 6a of the piezoelectric actuator 5, connected to the element portions 101 to 103 at one end, and reach the base end of the piezoelectric actuator 5 at the other end. Furthermore, it is connected to a corresponding electrode pad (not shown) of the rectangular frame 4 or other support frame (not shown).

  Strictly speaking, Wa is the width of the portion that functions as the piezoelectric actuator in the piezoelectric actuator 5 (not the width of the substrate layer 26 in FIG. 4 described later, but the width of the lower electrode layer 29 to the upper electrode layer 31). It becomes a little narrower than the width of the piezoelectric actuator 5.

  Among the element units 101 to 103, the element unit 102 is selected as the piezoelectric rotation angle sensor. The element portions 101 and 103 on both sides of the element portion 102 are ground portions that act as electromagnetic shields. In addition, it can replace with the element part 102 and the element part 101 can also be selected as a piezoelectric rotation angle sensor.

  The reason why the element unit 101 or 102 is selected as the piezoelectric rotation angle sensor is based on the results of experiments by the inventors (for details, refer to Japanese Patent Application No. 2012-199364 of the present applicant). According to the experiment, the sensor No. 1-No. 5 and sensor No. 5 respectively. 1-No. As a result of a pseudo examination of the output of sensor 5, sensor No. 3-No. It was found that the output of 5 could not reproduce the actual resonance frequency. Therefore, sensor No. 1-No. When the outputs of 5 are added, the output of a simple piezoelectric sensor increases. 3-No. As shown in FIG. 5, since the total output includes an output component that cannot reproduce the actual resonance frequency, it has been found that a shift occurs in the peak position of the resonance frequency. Therefore, it is advantageous that the element unit 101 or 102 is used as a piezoelectric rotation angle sensor. The total output of the element units 101 and 102 may be used as the output of the piezoelectric rotation angle sensor.

  When shortening the length of the element parts 101 to 103, the position of one end of the element parts 101 to 103 is fixed to the position of the coupling end with the torsion bar 3, and the position of the other end is variable according to the length. The length is shortened by bringing the other end closer to one end. This is because the piezoelectric components of the element units 101 to 103 have a larger output component in a portion closer to one end side closer to the torsion bar 3 than the other end side.

  In order to ensure the output of the piezoelectric actuator 5, the length of the element portions 101 to 103 is set to be less than La / 3 of the length of the piezoelectric actuator 5, but the output of the piezoelectric rotation angle sensor decreases as the length decreases. Therefore, in order to secure a minimum output exceeding the allowable value, the element units 101 to 103 are preferably La / 6 (= La / (3 × 2)) or more.

  FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2 and shows the structure when the sensor region 7 is formed while leaving the functional layer of the piezoelectric actuator 5 as it is. After being manufactured as the piezoelectric actuator 8, the piezoelectric actuator 5 is divided into an actuator portion 6a on the proximal end side and a non-actuator portion 6b on the distal end side by forming a dividing groove 12 in FIG. The non-actuator part 6b is further etched to form a plurality of element parts 101 to 103 separated from each other in the width direction.

The piezoelectric actuator 5 has a structure before formation of a dividing groove 12 in FIG. 5 described later, in order from a lower layer to an upper layer, a substrate layer 26 of Si (silicon: 40 μm), a thermal oxide film of SiO ₂ (silicon dioxide: 500 nm). Layer 27, Ti (titanium: 50 nm, TiO _x instead of Ti) lower electrode adhesion layer 28, Pt (platinum: 150 nm) lower electrode layer 29, PZT (lead zirconate titanate: 3 μm) piezoelectric film It has a layer 30, an upper electrode layer 31 of Pt (platinum: 150 nm), an interlayer insulating film adhesion layer 32 of Ti (titanium: 50 nm), and an interlayer insulating film layer 33 of SiO ₂ (silicon dioxide: 500 nm). For example, ADPR (Arc Discharged Reactive Ion Plating) is adopted as a method of forming the piezoelectric film layer 30. The lower electrode adhesion layer 28 and the upper interlayer insulating film adhesion layer 32 are interposed between the two in order to improve the adhesion between the Pt layer and the SiO ₂ layer.

  The element portions 101 to 103 are made of Al (aluminum: 500 nm) or Au (gold: 500 nm), and the upper electrode layer below the interlayer insulating film layer 33 through a contact hole formed in the interlayer insulating film layer 33. 31 is in contact.

  Although the element units 101 to 103 have the same structure, the element units 101 and 103 are connected to the ground via the conductor parts 111 and 113, and only the element part 102 is input to the control unit 95 via the conductor part 112. Connected to the terminal. As a result, only the element unit 102 functions as a piezoelectric rotation angle sensor.

  4 is a cross-sectional view taken along the line IV-IV in FIG. 2, and the conductive wire portions 111 to 113 are made of Al (aluminum: 500 nm) or Au (gold: 500 nm), similar to the element portions 101 to 103, and It is formed on the surface of the insulating film layer 33.

  In FIG. 5 as a cross-sectional view taken along the line V-V in FIG. 2, a broken line H indicates a boundary line between the torsion bar 3 and the piezoelectric actuator 5 or 8. The dividing groove 12 extends in the width direction at a predetermined position in the length direction of the piezoelectric actuator 5. The piezoelectric film layer 30, the upper electrode layer 31, and the interlayer insulating film adhesion layer 32 of the piezoelectric actuator 5 are divided into the actuator portion 6a and the non-actuator portion 6b by the dividing groove 12.

  In the dividing groove 12, a total of three Al layers are formed as connecting lines so as to cover the side wall and the bottom wall. The three connection lines connect the element parts 101 to 103 of the non-actuator part 6b and the conductor parts 111 to 113 of the actuator part 6a to each other.

  Next, the structure and polarization processing of the piezoelectric rotation angle sensor 50 will be described with reference to FIG. In FIG. 6, the piezoelectric rotation angle sensor 50 means the element unit 102 selected as the piezoelectric rotation angle sensor. As described above, instead of only the element unit 102, only the element unit 101 or both of the element units 101 and 102 may be selected as the piezoelectric rotation angle sensor. In this case, the structure of FIG. 6 means the element unit 101 or the element units 101 and 102 selected as the piezoelectric rotation angle sensor.

  Since the thermal oxide film layer 27, the lower electrode adhesion layer 28, and the interlayer insulating film adhesion layer 32 in FIGS. 3 to 5 are not main elements in the function of the piezoelectric rotation angle sensor 50, FIG. Above, omitted. The actual piezoelectric rotation angle sensor 50 also includes a thermal oxide film layer 27, a lower electrode adhesion layer 28, and an interlayer insulating film adhesion layer 32. Since the lower electrode layer 29 of the piezoelectric rotation angle sensor 50 is also the lower electrode layer 29 of the actuator unit 6a and is connected to the ground, the voltage of the lower electrode layer 29 is zero.

  In the polarization process of the piezoelectric film layer 30, a voltage is applied to the upper electrode layer 31 via an electrode pad (not shown) on the surface side of the rectangular frame 4. The upper electrode layer 31 becomes an output unit of the piezoelectric rotation angle sensor 50 after the polarization process, and a voltage corresponding to the rotation angle of the mirror unit 2 is output.

  As shown in FIG. 6A, in the piezoelectric rotation angle sensor 50, when a positive voltage is applied to the upper electrode layer 31, each PZT molecule 51 of the piezoelectric film layer 30 has a positive electrode and a negative electrode respectively connected to the lower electrode. It faces toward the layer 29 side and the upper electrode layer 31 side. As shown in FIG. 6B, in the piezoelectric rotation angle sensor 50, when a negative voltage is applied to the upper electrode layer 31, each PZT molecule 51 of the piezoelectric film layer 30 has a positive electrode and a negative electrode respectively connected to the upper electrode. It faces toward the layer 31 side and the lower electrode layer 29 side.

  The electric field direction from the upper electrode layer 31 to the lower electrode layer 29 in the piezoelectric film layer 30 is defined as positive as shown in FIG. 6A, and the lower electrode layer in the piezoelectric film layer 30 as shown in FIG. The direction of the electric field from 29 to the upper electrode layer 31 is negative. Furthermore, a polarization process that generates a positive electric field in the piezoelectric film layer 30 as shown in FIG. 6A is called a positive polarization process, and a negative electric field is generated in the piezoelectric film layer 30 as shown in FIG. 6B. The polarization process to be performed is called negative polarization process.

  Before describing specific polarization processing of the piezoelectric rotation angle sensor 50 having the above-described configuration, the sensor function of the piezoelectric rotation angle sensor 50 will be schematically described.

  During the operation of the optical scanner 96 (FIG. 1), the piezoelectric actuator 5 and the piezoelectric actuator 8 have a triangular waveform that increases and decreases at a predetermined frequency only on the positive side of the upper electrode layer 31 (only on the negative side. Unipolar drive) A polarization voltage having a rectangular waveform or a sine waveform is applied. As a result, in the entire actuator portion 6a and the piezoelectric actuator 8 of the piezoelectric actuator 5, the piezoelectric film layer 30 is contracted and released in the length direction of the piezoelectric actuator 5 and the piezoelectric actuator 8, and the piezoelectric actuator 5 and the piezoelectric actuator 8 are thus released. Rotates the tip portion around the axis of the torsion bar 3 at the predetermined frequency.

  Each torsion bar 3 is reciprocally rotated at the base end portion by receiving a driving force reciprocally rotating around the axis from the piezoelectric actuator 5 or 8 coupled to both sides of the base end portion. The portion 2 reciprocates around the axis of the torsion bar 3 at the predetermined frequency.

  On the other hand, in the non-actuator portion 6b of the piezoelectric actuator 5, the surface on the lower electrode layer 29 side of the substrate layer 26 expands and contracts as an expansion / contraction surface (strictly speaking, since it is unipolar drive, the amount of contraction is increased or decreased within a range of 0 or more. ), The piezoelectric film layer 30 of the piezoelectric rotation angle sensor 50 expands and contracts in the length direction of the piezoelectric actuator 5, and the mirror electrode 2 rotates on the upper electrode layer 31 of the piezoelectric rotation angle sensor 50. A voltage corresponding to the corner is output. This voltage is sent to the control unit 95 as an output of the piezoelectric rotation angle sensor 50.

Next, the coercive electric field of the material of the piezoelectric film layer 30 will be described with reference to FIG. FIG. 7 shows the electric field hysteresis for the material. In FIG. 7, the positive / negative of the electric field strength on the horizontal axis is matched with the direction of the electric field in FIGS. 6 (a) and 6 (b). One coercive electric field exists on the positive side and one on the negative side, and the absolute values of the coercive electric fields Ec and -Ec are both 5 V / μm. The absolute value of the saturation polarization amount (= ± about 5 μC / cm ² ) is about 40 V / m.

  Referring to FIG. 8, when the piezoelectric rotation angle sensor 50 is used without the polarization treatment of the piezoelectric film layer 30, the vibration frequency of the mirror unit 2, the deflection angle of the mirror unit 2, and the output of the piezoelectric rotation angle sensor 50. Will be described. The deflection angle (= rotation angle) is 0 ° when the mirror portion 2 is facing directly in front, the deflection angle of one and the other with respect to the true front is positive and negative, and the mirror portion around the axis of the torsion bar 3 The absolute value of the deflection angle of 2 is shown.

  The deflection angle of the mirror unit 2 is a resonance frequency determined by the mass of the mirror unit 2, the torsion bar 3 and the piezoelectric actuators 5 and 8, the rigidity of the torsion bar 3 and the piezoelectric actuators 5 and 8, etc. (resonance frequency = 15 in FIG. 8). .889 kHz) (maximum deflection angle = about 5 ° in FIG. 8), and decreases rapidly with distance from the resonance frequency. The output of the piezoelectric rotation angle sensor 50 is substantially proportional to the deflection angle of the mirror unit 2 and is maximum at the resonance frequency of the mirror unit 2 (maximum output voltage = about 125 mV in FIG. 8). The output voltage of the piezoelectric rotation angle sensor 50 indicated by the vertical axis in FIG. 8 is the output voltage of the piezoelectric rotation angle sensor 50 at the maximum deflection angle at each frequency, in other words, the piezoelectric rotation angle at each frequency. This is the maximum output voltage of the sensor 50.

  When the piezoelectric film layer 30 is not polarized, the output voltage of the piezoelectric rotation angle sensor 50 is low as shown in FIG. If the output voltage of the piezoelectric rotation angle sensor 50 at a frequency sufficiently away from the resonance frequency is a noise voltage, in FIG. 8, the noise voltage = 24 mV, and the S / N ratio = 125/24 = 5.2.

  With reference to FIG. 9, the polarization method of the piezoelectric rotation angle sensor 50 in the optical deflector 1 will be described. In FIG. 9, the horizontal axis represents the cumulative polarization cycle number, and the vertical axis represents the output voltage ratio (output voltage ratio at the resonance frequency) of the piezoelectric rotation angle sensor 50 at the cumulative polarization cycle number in increments of 0.5.

  Each half cycle corresponds to one execution of the positive polarization process or the negative polarization process (FIG. 6). One cycle corresponds to the execution of a set of one positive polarization process and one negative polarization process regardless of the order of the positive and negative polarization processes. A positive polarization process and a negative polarization process are alternately performed on the sample of the piezoelectric rotation angle sensor 50, and the output voltage ratio of the piezoelectric rotation angle sensor 50 for each half cycle is examined. Each characteristic line in FIG. 9 is obtained by placing marks at corresponding positions and connecting the marks “♦” and the marks “■” sequentially with a solid line and a broken line.

  In FIG. 9, the characteristic of the solid line is that the marks “♦” are connected in order, and in each cycle, the positive polarization process is executed in the first half cycle, and the negative polarization process is executed in the subsequent half cycle. Experimental results are shown. The broken line connects the “■” marks in order. In each cycle, the negative polarization process is executed in the first half cycle, and the positive polarization process is executed in the subsequent half cycle. .

  In FIG. 9, when the cumulative number of polarization cycles = 0 as the starting point of the solid line and the broken line, the mark “◆” and the mark “■” overlap, and the starting point is relative to the sample of the piezoelectric rotation angle sensor 50. This means that the polarization process has not been performed once, that is, the piezoelectric film layer 30 is in the non-polarized state of FIG. In FIG. 9, the reason why the vertical axis is normalized not by the output voltage of the piezoelectric rotation angle sensor 50 but by the output voltage ratio is that the output voltage of the piezoelectric rotation angle sensor 50 is different for each sample of the piezoelectric rotation angle sensor 50. This is because, although the variation is relatively large, the output voltage ratio has a small variation for each sample of the piezoelectric rotation angle sensor 50, so that the effect of the polarization method can be generally shown.

  In each polarization process, the inventor manually operates the apparatus to apply a positive voltage to the upper electrode layer 31 of the piezoelectric rotation angle sensor 50 in the positive polarization process and a negative voltage in the negative polarization process. Was carried out. The applied voltage is a voltage at which an electric field of approximately 1.7 times or more of the coercive electric field Ec of + and − is applied to the piezoelectric film layer 30 in the positive and negative polarization processes, in other words, the sign is the same and the absolute value is the resistance. The voltage applied was an electric field that was approximately 1.7 times or more of the absolute value of the electric field | ± Ec |. The application time was about 3 seconds for both the positive polarization treatment and the negative polarization treatment.

  The following was found from the experimental graph of FIG.

  (A) If the polarization process includes at least three consecutive half cycles of performing at least the positive polarization process, the negative polarization process, and the positive polarization process in order, the output voltage of the piezoelectric rotation angle sensor 50 The ratio is increased with respect to the output voltage ratio (= 1) of the piezoelectric rotation angle sensor 50 when the process is completed by only one negative polarization process, only one positive polarization process, or only one cycle of polarization process. Is recognized.

(B) In each cycle after the cumulative number of polarization cycles = 1, the output voltage ratio of the piezoelectric rotation angle sensor 50 is higher at the end of the positive polarization process in both the solid line experimental results and the broken line experimental results. It is higher than at the end of the negative polarization process. That is, in the solid line experimental results, the output voltage ratio of the piezoelectric rotation angle sensor 50 is higher when the cumulative polarization cycle number = 1.5 than when the cumulative polarization cycle number = 2. Further, in the experimental result indicated by the broken line, the output voltage ratio of the piezoelectric rotation angle sensor 50 is higher when the cumulative polarization cycle number = 2 than when the cumulative polarization cycle number = 1.5.

  Based on the knowledge of (a) and (b) above, in the polarization processing of the piezoelectric rotation angle sensor 50 of the optical deflector 1, the polarization processing starts from the positive polarization processing and the cumulative number of polarization cycles becomes 1.5. Carried out.

  Thereby, the change in the output voltage of the piezoelectric rotation angle sensor 50 with respect to the lengthwise expansion / contraction amount of the piezoelectric actuator 5 during the reciprocating rotation of the mirror unit 2, that is, the piezoelectric rotation angle with respect to the change in the rotation angle of the mirror unit 2. The change in the output voltage of the sensor 50 can be increased as compared with the piezoelectric rotation angle sensor 50 by a normal polarization process. Therefore, the S / N ratio of the output of the piezoelectric rotation angle sensor 50 during the resonance vibration of the mirror unit 2 can be increased more than that of the piezoelectric rotation angle sensor 50 by the normal polarization process.

  In the polarization process of the piezoelectric rotation angle sensor 50 of the optical deflector 1, the polarization process starting from the negative polarization process and the cumulative polarization cycle number = 2 is performed, or the cumulative polarization cycle number = 2.5 or more. In addition, even if the cumulative number of polarization cycles is terminated by the positive polarization process, the output and the S / N ratio of the piezoelectric rotation angle sensor 50 are increased more than those of the piezoelectric rotation angle sensor 50 by the normal polarization process. be able to.

  Although the present invention has been described with respect to the embodiments, the present invention is not limited to the embodiments, and can be implemented with various modifications.

  In the optical deflector 1 of the embodiment, since the mirror unit 2 rotates only around one axis, only one piezoelectric rotation angle sensor 50 is provided, but the mirror unit has two axes perpendicular to each other. When a piezoelectric rotation angle sensor is provided for each rotation angle detected around each axis, the present invention is applicable to any piezoelectric rotation angle sensor polarization method. Can do.

  In the embodiment, the unipolar positive voltage is applied to the upper electrode layers 31 of the piezoelectric actuators 5 and 8 to drive the piezoelectric actuators 5 and 8, but the unipolar negative voltage is applied to the upper electrode layers 31. Can be applied to drive the piezoelectric actuators 5 and 8. In that case, a negative voltage is output to the upper electrode layer 31 of the piezoelectric rotation angle sensor 50.

DESCRIPTION OF SYMBOLS 1 ... Optical deflector, 2 ... Mirror part, 3 ... Torsion bar (connection part), 4 ... Rectangular frame (support body), 5 ... Piezoelectric actuator, 8 ... Piezoelectric actuator , 26 ... substrate layer, 29 ... lower electrode layer, 30 ... piezoelectric film layer, 31 ... upper electrode layer, 50 ... piezoelectric rotation angle sensor.

Claims (3)

A mirror that reflects light incident from a certain direction;
A support;
A coupling portion having a telescopic surface that couples the mirror portion to the support so as to be rotatable around a predetermined axis, and expands and contracts according to a rotation angle of the mirror portion;
A piezoelectric actuator for rotating the mirror portion around the predetermined axis;
A piezoelectric rotation angle that has a lower electrode layer, a piezoelectric film layer, and an upper electrode layer that are sequentially stacked on the expansion / contraction surface of the coupling portion, and outputs a voltage corresponding to the expansion / contraction amount of the expansion / contraction surface as an inter-electrode voltage. A polarization method of the piezoelectric rotation angle sensor in an optical deflector comprising a sensor,
The absolute value is larger than the absolute value of the coercive electric field of the piezoelectric film layer when the directions of the electric fields directed to the lower electrode layer and the upper electrode layer in the thickness direction of the piezoelectric film layer are respectively positive and negative. A positive polarization process and a negative polarization process in which a polarization voltage that generates an electric field in the positive and negative directions is applied between the electrode layers, respectively, so that the positive polarization process is included at least twice and the negative polarization process is included at least once. The method of polarization of a piezoelectric rotation angle sensor, which is performed alternately. In the polarization method of the piezoelectric rotation angle sensor according to claim 1,
A polarization method for a piezoelectric rotation angle sensor, characterized in that the polarization process ends with a positive polarization process. In the polarization method of the piezoelectric rotation angle sensor according to claim 1 or 2,
The piezoelectric actuator constitutes the coupling portion and is divided into a proximal-side actuator portion and a distal-side non-actuator portion by a dividing groove for dividing the lower electrode layer, the piezoelectric film layer, and the upper electrode layer on the substrate layer. Divided,
The lower electrode layer, the piezoelectric film layer, and the upper electrode layer in the non-actuator portion constitute the lower electrode layer, the piezoelectric film layer, and the upper electrode layer of the piezoelectric rotation angle sensor,
A polarization method of a piezoelectric rotation angle sensor, wherein a surface of the substrate layer in the non-actuator portion on the piezoelectric rotation angle sensor side constitutes the expansion / contraction surface.