JP5187836B2 - Sensor sensitivity adjusting means and sensor manufacturing method - Google Patents

Description

  The present invention relates to a sensor sensitivity adjusting means for adjusting the sensitivity of a sensor using resonance vibration of a piezoelectric element such as a vibration gyro, an acceleration sensor, and a pressure sensor, and a method for manufacturing the sensor.

  A sensor that uses a piezoelectric vibrator and detects angular velocity, acceleration, pressure, and the like by detecting a vibration mode, a change in resonance frequency, and the like is used in various applications. For example, a piezoelectric vibration gyro is an angular velocity sensor using a dynamic phenomenon in which when an angular velocity is applied to an object having velocity, a Coriolis force is generated in the object itself in a direction perpendicular to the velocity direction. Specifically, in a system in which the vibration in the direction orthogonal to the vibration of the drive vibration mode generated by applying an electrical signal, that is, the magnitude of the detected vibration mode can be electrically detected, the drive is performed in advance. In the state where the vibration mode is excited, if the angular velocity about the axis parallel to the intersection line between the vibration surface of the drive vibration mode and the vibration surface of the detection vibration mode is given, the detection vibration mode is set by the action of the Coriolis force described above. Generated and detected as an output voltage. Since the detected output voltage is proportional to the magnitude and angular velocity of the driving vibration mode, the magnitude of the angular velocity can be obtained from the magnitude of the output voltage in a state where the magnitude of the driving vibration mode is constant.

  As a piezoelectric vibrator, a basic operation principle of a piezoelectric vibration gyro will be described by taking a tuning fork type piezoelectric vibrator having two arms as an example. FIG. 3 is a diagram showing the shape and vibration mode of a tuning fork type piezoelectric vibrator, FIG. 3 (a) is a perspective view of the tuning fork type piezoelectric vibrator, and FIG. 3 (b) is a diagram showing in-plane vibration. 3 (c) is a diagram showing out-of-plane vibration. In FIG. 3, 50 is a tuning fork type piezoelectric vibrator, 51 is a base portion, and 52a and 52b are arm portions. The arrows in FIG. 3 indicate the displacement direction of the arm, that is, the direction of vibration. In-plane vibration is vibration in a direction parallel to the plane including the axes of the two arm portions, and out-of-plane vibration is perpendicular to the in-plane vibration. Vibration.

  This tuning fork type piezoelectric vibrator is made of a piezoelectric material, and an electrode coupled to vibration modes of in-plane vibration and out-of-plane vibration is arranged on the surface, thereby enabling excitation and detection. More specifically, when a driving signal having a frequency close to the resonance frequency of the in-plane vibration mode is applied to the electrode and the tuning fork vibration mode is excited, and an angular velocity is applied to the longitudinal axis of the vibrator, the vibrator , A Coriolis force proportional to the angular velocity works to generate an out-of-plane vibration mode. If an electric signal generated by this out-of-plane vibration mode is taken out from the detection electrode, an electric signal proportional to the angular velocity can be obtained, and it can function as a piezoelectric vibration gyro.

  FIG. 4 is a perspective view showing an example of a conventional electrode structure of the tuning fork type piezoelectric vibrator. The drive electrodes to which the drive signal is applied are the main drive parts 11a and 11b installed on the arm parts 101a and 101b, which are vibration parts, the drive output pads 11e and 11f to which the drive voltage is applied, and the drive voltage of the drive output pad. The drive electrodes 11c and 11d lead to the main drive unit, respectively. The detection electrodes face the main drive units 11a and 11b, respectively, and detect detection signals with the main detection units 12a and 12b installed on the arm units 101a and 101b, respectively. The detection output pads 12e and 12f to be taken out and detection lead-out portions 12c and 12d for guiding the signal of the main detection unit to the detection output pad, respectively, are provided. Main reference installed on the arm portions 101a and 101b respectively facing the 11b The reference potential of the reference output pad 13d and the reference output pad 13d of 13a and 13b and the reference potential is applied consists mainly reference portion 13a, and the reference lead portion 13c leading to 13b.

  Sensors using piezoelectric vibrators such as the above-described piezoelectric vibration gyro can be configured at a lower cost and smaller than sensors using other mechanical vibration mechanisms, so as sensors for detecting portable small devices and small devices, Widely used. However, in recent years, with the further miniaturization of these portable devices and the high integration of functions, there is an increasing demand for further miniaturization and cost reduction.

  One of the issues to be solved in miniaturization of sensors is high-efficiency correction to cope with the relative increase in variations in processing accuracy and assembly accuracy of piezoelectric vibrators that occur with miniaturization. There is a need to consider means. These variations affect variations in resonance frequency such as the drive vibration mode and detection vibration mode of the piezoelectric vibrator, and greatly affect variations in detection sensitivity of the sensor.

  Conventionally, there are two methods for adjusting the variation in detection sensitivity: a method of adjusting on the vibrator side and a method of adjusting on the sensor circuit side. After the piezoelectric vibrator is assembled, the vibration is adjusted by mechanical processing or the like. It has been performed by a method of converging to a certain range of variation on the child side and finally adjusting with high accuracy on the circuit side.

  FIG. 5 is a circuit diagram showing an example of a circuit configuration of a piezoelectric vibration gyro using the piezoelectric vibrator of FIG. 4 described above. In FIG. 5, drive output pads 11 e and 11 f of drive electrodes of the tuning fork type piezoelectric vibrator 100 are connected to the self-excited oscillation circuit 103 and excited at the resonance frequency of the piezoelectric vibrator 100. The reference output pad 13d of the reference electrode is connected to the reference potential. The charge generated in the detection output pad 12e or 12f of the detection electrode is amplified and converted into a voltage by a charge amplifier 102 having a feedback capacitor 106 connected as a feedback load between the input and output terminals of the operational amplifier. Further, the signal is rectified and amplified by the synchronous detection circuit 104 and the low-pass filtering (LPF) circuit 105 and output as a DC voltage. The sensor sensitivity is determined from the drive amplitude of the piezoelectric vibrator 100, the detection sensitivity of the piezoelectric vibrator 100, the amplification factor of the charge amplifier 102, the amplification factor of the synchronous detection circuit 104, and the amplification factor of the LPF circuit 105.

  Patent Document 1 discloses a method for adjusting sensor sensitivity on the circuit side, in which a variable amplifier using a variable resistor is provided on the output side of the synchronous detection circuit, and sensitivity adjustment is performed by adjusting the variable resistor.

  On the other hand, as an adjustment method on the vibrator side, a method of trimming a part of the main drive parts 11a and 11b of the drive electrode or a part of the main detection parts 12a and 12b of the detection electrode with a laser to lower the sensitivity is used. It is shown in Patent Document 2.

JP 2007-93233 A JP 2006-105659 A

  In the sensitivity adjustment method of Patent Document 1, a variable resistor is required outside the sensor circuit that is normally made into an IC, so that it is difficult to reduce the size. In addition, the variable resistor can be designed by taking it into the IC, but in this case, the IC becomes complicated and becomes an obstacle to cost reduction.

  Furthermore, as an adjustment method on the circuit side, a method of adjusting the drive amplitude of the piezoelectric vibrator by changing the drive voltage of the self-excited oscillation circuit 103 and a method of adjusting the amplification factor of the LPF circuit 105 are general. These are methods for adjusting the resistance value with a trimming resistor or adjusting the voltage and the resistance value with an analog switch IC, which hinders downsizing and cost reduction.

  On the other hand, in the adjustment method on the vibrator side shown in Patent Document 2 or the like, the feedback capacitor 106 of the charge amplifier 102 has a coupling capacitance between the detection electrode and the drive electrode of the piezoelectric vibrator 100 or between the detection electrode and the reference electrode. This is effective when the coupling capacity is large, but a problem arises when the coupling capacity is small. This is because when the main drive part of the drive electrode and the main detection part of the detection electrode are disconnected, the mutual coupling capacitance decreases, and as a result, the amplification factor of the charge amplifier 102 increases. That is, since the amplification factor of the charge amplifier is determined by the ratio of the input capacitance and the feedback capacitance, the amplification factor of the sensor circuit increases, and the decrease in detection sensitivity due to the reduction in the electrode area of the piezoelectric vibrator 100 is offset.

  Therefore, the problem of the present invention is that it is possible to reduce the size and the price, and the feedback capacitance of the charge amplifier is smaller than the coupling capacitance between the drive electrode and the detection electrode and the coupling capacitance between the detection electrode and the reference electrode. It is an object to provide a sensor sensitivity adjusting means and a sensor manufacturing method capable of adjusting the sensor sensitivity even when the sensor sensitivity is small.

To achieve the above object, the sensor sensitivity adjusting means of the present invention comprises a piezoelectric material, a drive electrode for vibrating at a resonance frequency, a detection electrode for detecting a signal, a reference electrode maintained at a constant potential, And a charge amplifier circuit that amplifies a minute signal output detected by the detection electrode of the piezoelectric vibrator, and the drive electrode is disposed in a vibration portion of the piezoelectric vibrator. The drive unit includes a drive output pad to which a drive voltage is applied, and a drive lead-out unit connected to the drive output pad and the main drive unit, and the detection electrode is disposed in the vibration portion so as to face the main drive unit. And a detection output pad for extracting a detection signal, a detection output pad connected to the main detection unit, and a detection lead-out unit connected to the main detection unit. The reference electrode faces the main drive unit. A reference output pad to which a reference potential is applied, a reference output pad connected to the reference output pad and the main reference part, and a part of the detection extraction part. Between a part of the reference drawer part, between a part of the detection drawer part and a part of the drive drawer part, or between a part of the reference drawer part and a part of the drive drawer part. , A counter electrode pair facing each other and having capacitance is formed, and the charge amplifier circuit is changed by deleting at least part of the counter electrode pair and changing the capacitance The sensitivity of the sensor is adjusted and the sensor is manufactured by performing this adjustment.

  Trimming by laser irradiation may be used as means for removing a part of the counter electrode pair.

  In the present invention, not the electrode part directly formed on the vibration part of the piezoelectric vibrator such as the main drive part, the main detection part, and the main reference part as described above, but the lead part connected to the electrode part or the output pad. By providing a counter electrode pair having a coupling capacity between the electrodes, and removing a part of the counter electrode pair by a method such as laser trimming, the drive amplitude and detection sensitivity of the piezoelectric vibrator are not affected. In addition, the gain of the charge amplifier circuit can be changed, and the sensor sensitivity can be adjusted.

  As a result, it is possible to reduce the size and price, and even when the feedback capacitance of the charge amplifier is smaller than the coupling capacitance between the drive electrode and the detection electrode or the coupling capacitance between the detection electrode and the reference electrode. A sensor sensitivity adjusting means and a sensor manufacturing method capable of adjusting the sensor sensitivity are obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram for explaining a first embodiment of a sensor sensitivity adjusting means according to the present invention, and is a perspective view showing an electrode structure of a tuning fork type piezoelectric vibrator 110 used in the present embodiment. . Also in the present embodiment, as in the conventional tuning-fork type piezoelectric vibrator shown in FIG. 4, the drive electrodes to which the drive signal is applied are the main drive parts installed on the arm parts 101a and 101b, which are the vibration parts, respectively. 11a and 11b, drive output pads 11e and 11f to which a drive voltage is applied, and drive lead-out portions 11c and 11d that guide the drive voltage of the drive output pad to the main drive unit, respectively, and detection electrodes are connected to the main drive units 11a and 11b. Main detection units 12a and 12b installed on the respective arm units 101a and 101b facing each other, detection output pads 12e and 12f for extracting detection signals, and detection extraction units 12c and 12d for guiding the signals of the main detection units to the detection output pads, respectively. The reference electrodes for applying a reference potential to the detection electrodes and the drive electrodes are the main drive units 11a and 11b. Main reference portions 13a and 13b installed on the arm portions 101a and 101b, respectively, a reference output pad 13d to which a reference potential is applied, and a reference lead portion 13c for guiding the reference potential of the reference output pad to the main reference portion. It is made up of. Note that the output pad and the lead-out portion of each electrode are disposed on the base portion where the piezoelectric vibrator does not vibrate.

  However, in FIG. 1, a part of the detection drawer 12 c and a part of the drive drawer 11 c and a part of the detection drawer 12 d and a part of the drive drawer 11 d are opposed to each other. Counter electrode pairs 14a and 14b having capacitance are formed. Here, each of the counter electrode pairs 14a and 14b constitutes an interdigital electrode by a plurality of electrode fingers in order to increase the capacitance.

  In the sensor circuit of FIG. 5, only the charge amplifier 102 connected to one of the detection output pads 12e or 12f is shown, but in the actual sensor circuit, it is shown in Patent Document 1 and Patent Document 2. It is desirable that a charge amplifier is connected to each of the detection output pads 12e and 12f by a circuit similar to the above, and both outputs are input to the synchronous detection circuit 104 through a differential amplifier. Therefore, in the piezoelectric vibrator of the present embodiment, the counter electrode pairs 14a and 14b are arranged symmetrically.

  When a part of the electrode fingers of the counter electrode pairs 14a and 14b is cut by, for example, laser trimming, the coupling capacitance between the drive electrode and the detection electrode is reduced, the amplification factor of the charge amplifier 102 is increased, and the entire sensor is Sensitivity increases. Further, since the counter electrode pairs 14a and 14b are arranged in a portion where the piezoelectric vibrator 110 does not vibrate, the vibration amplitude and detection sensitivity of the piezoelectric vibrator are not affected.

  FIG. 2 is a diagram for explaining a second embodiment of the sensor sensitivity adjusting means according to the present invention, and is a perspective view showing an electrode structure of a tuning-fork type piezoelectric vibrator 120 used in the present embodiment. . Also in the present embodiment, similarly to the tuning-fork type piezoelectric vibrator shown in FIG. 1, main drive units 11a and 11b, main detection units 12a and 12b respectively installed on the arm units 101a and 101b, which are vibration units, Main reference portions 13a and 13b, drive output pads 11e and 11f installed at the base of the piezoelectric vibrator, drive drawer portions 11c and 11d, detection output pads 12e and 12f, detection lead portions 12c and 12d, reference output pad 13d, It has the electrode part of the reference | standard drawer | drawing-out part 13c.

  However, in the present embodiment, the detection drawer 12c and the detection drawer 12d are not only connected to the main detection unit and the detection output pad, but are also installed on the side facing the reference drawer. In the portion, counter electrode pairs 15a and 15b having capacitances are formed to face each other between a part of the detection lead part and a part of the reference lead part 13c. Again, the counter electrode pairs 15a and 15b each constitute an interdigital electrode with a plurality of electrode fingers in order to increase the capacitance.

  Also in the present embodiment, when a part of the electrode fingers of the counter electrode pair 15a and 15b is cut by laser trimming, the coupling capacitance between the reference electrode and the detection electrode is reduced, and the amplification factor of the charge amplifier 102 is increased. The sensitivity of the entire sensor increases. Further, since the counter electrode pairs 15a and 15b are arranged at the base portion where the piezoelectric vibrator 120 does not vibrate, the vibration amplitude and detection sensitivity of the piezoelectric vibrator are not affected.

  As described above, according to the present invention, it is possible to obtain a sensor sensitivity adjusting means and a sensor manufacturing method capable of adjusting the sensor sensitivity without affecting the vibration amplitude and the detection sensitivity of the piezoelectric vibrator. The sensitivity adjustment means can be reduced in size and price compared with the method of adjusting in the sensor circuit.

  Needless to say, the present invention is not limited to the above-described embodiment. For example, a counter electrode pair is provided between a part of the reference lead part and a part of the drive lead part. Also good. Further, the present invention is not limited to a piezoelectric vibration gyro, but also in an acceleration sensor or a pressure sensor using a piezoelectric vibrator by piezoelectric resonance vibration, a counter electrode pair is provided on an electrode portion provided other than the vibration portion, and the electrostatic Sensitivity can be adjusted by adjusting the capacity. The design of the piezoelectric vibrator form and electrode structure can be changed according to the application.

The figure for demonstrating 1st embodiment of the sensor sensitivity adjustment means by this invention, and the perspective view which shows the electrode structure of the tuning fork type piezoelectric vibrator used for this embodiment. The figure for demonstrating 2nd embodiment of this invention, and the perspective view which shows the electrode structure of the tuning fork type piezoelectric vibrator used for this embodiment. FIG. 3A is a perspective view of the tuning fork type piezoelectric vibrator, FIG. 3B is a diagram showing in-plane vibration, and FIG. 3C is an out of plane view. The figure which shows a vibration. The perspective view which shows an example of the conventional electrode structure of a tuning fork type piezoelectric vibrator. The circuit diagram which shows an example of the circuit structure of the piezoelectric vibration gyro using a piezoelectric vibrator.

Explanation of symbols

11a, 11b Main driver 11c, 11d Drive drawer 11e, 11f Drive output pads 12a, 12b Main detector 12c, 12d Detection drawer 12e, 12f Detection output pads 13a, 13b Main reference 13c Reference drawer 13d Reference output pad 14a, 14b, 15a, 15b Counter electrode pair 50, 100, 110, 120 Piezoelectric vibrators 52a, 52b, 101a, 101b Arm unit 102 Charge amplifier 103 Self-excited oscillation circuit 104 Synchronous detection circuit 105 LPF circuit 106 Feedback capacitance

Claims (4)

A piezoelectric vibrator made of a piezoelectric material, having a drive electrode for vibrating at a resonance frequency, a detection electrode for detecting a signal, and a reference electrode maintained at a constant potential, and detection from the detection electrode of the piezoelectric vibrator And a charge amplifier circuit for amplifying a small signal output, wherein the drive electrode is a main drive unit installed in a vibrating portion of the piezoelectric vibrator, a drive output pad to which a drive voltage is applied, and the drive output pad And a driving lead part connected to the main driving part, the detection electrode being opposed to the main driving part, a main detection part installed in the vibration part, a detection output pad for extracting a detection signal, and the detection output The reference electrode comprises a pad and a detection lead part connected to the main detection part, and the reference potential is applied to the reference electrode and the main reference part installed in the vibration part facing the main drive part. A reference output pad, and a reference drawer connected to the reference output pad and the main reference unit, between a part of the detection drawer and a part of the reference drawer, or one of the detection drawers Between each other and at least one of the reference drawer part and part of the drive drawer part. A counter electrode pair is formed, and at least a part of the counter electrode pair is deleted to change the capacitance, thereby changing an amplification factor of the charge amplifier circuit and adjusting sensitivity of the sensor. Sensor sensitivity adjustment means.   The sensor sensitivity adjusting means according to claim 1, wherein trimming by laser irradiation is used as means for deleting a part of the counter electrode pair. A piezoelectric vibrator made of a piezoelectric material, having a drive electrode for vibrating at a resonance frequency, a detection electrode for detecting a signal, and a reference electrode maintained at a constant potential, and detection from the detection electrode of the piezoelectric vibrator And a charge amplifier circuit for amplifying a small signal output, wherein the drive electrode has a main drive unit installed in a vibrating portion of the piezoelectric vibrator, a drive output pad to which a drive voltage is applied, and the drive electrode A drive output pad and a drive drawer connected to the main drive unit, the detection electrode facing the main drive unit, a main detection unit installed in the vibration part, and a detection output pad for extracting a detection signal; The detection output pad and a detection lead portion connected to the main detection portion, the reference electrode facing the main drive portion and the main reference portion installed in the vibration portion and a reference potential A reference output pad to be applied and a reference lead portion connected to the reference output pad and the main reference portion, between a part of the detection lead portion and a part of the reference lead portion, or the detection lead Between at least one of a part and a part of the drive drawer, or between a part of the reference drawer and a part of the drive drawer. A counter electrode pair having a capacitance is formed, and at least a part of the counter electrode pair is deleted to change the capacitance, thereby changing the amplification factor of the charge amplifier circuit and adjusting the sensitivity of the sensor. A method for manufacturing a sensor.   4. The sensor manufacturing method according to claim 3, wherein trimming by laser irradiation is used as means for deleting a part of the counter electrode pair.

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