Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/097—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by vibratory elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/0802—Details

Definitions

• the present invention relates to a vibration-type piezoelectric acceleration sensor element and a vibration-type piezoelectric acceleration sensor using the element, for measuring acceleration, controlling attitude of a moving subject, and a control system for a moving subject such as a vehicle.
• Fig. 6 is a sectional view illustrating a makeup of a conventional acceleration sensor.
• strain-sensitive resistors 3 are provided at a part close to diaphragm 20 on the top surface of chip 1 formed with diaphragm 2.
• the other part of the top surface of chip 1 is provided with a semiconductor integrated circuit for calculating acceleration, and thin-film resistor 4 for adjusting the characteristic of the integrated circuit thereon.
• protective film 5 is formed at a part including at least the top part of thin-film resistor 4, but excluding the top part of strain-sensitive resistors 3.
• Applying acceleration causes weight 6 made of glass to become stressed, changing the resistance of strain-sensitive resistors 3. Measuring this change enables detecting acceleration.
• FIG. 7 is a block diagram illustrating a makeup of another conventional acceleration sensor.
• This acceleration sensor includes piezoelectric element 11 for outputting signals corresponding to acceleration; converter 12 for converting the impedance of output signals; filter 13 for removing unnecessary signals; and amplifier 14 for amplifying necessary signals.
• the sensor further includes alternating current (AC) signal output part 16 for outputting AC signals synchronized with the cycle of timing signals being externally input. Between AC signal output part 16 and piezoelectric element 1, capacitor 17 is connected in series.
• the voltage signals output from the acceleration sensor are to be introduced to measurement/operation unit 18 and controller 15, both equipped with a microprocessor.
• strain-sensitive resistor 3 or piezoelectric element 11 detects acceleration.
• the resistance changes by only a few percent and fluctuates largely.
• the resistance is influenced by the change in temperature of the signal process circuit, disabling precise detection of acceleration.
• it is presumably difficult to detect the component for such as static gravity acceleration due to the detection structure.
• a makeup for detecting a variation in speed by means of a strain of a semiconductor resistor is unable to detect acceleration due to such as static gravity.
• a vibration-type piezoelectric acceleration sensor element includes a frame; and a diaphragm, a support, and a retentive part, provided in the frame.
• the diaphragm includes a bottom electrode layer, a piezoelectric thin-film layer formed on the bottom electrode layer, and a top electrode layer formed on the piezoelectric thin-film layer.
• the support retains the diaphragm.
• the retentive part retains the support so that the support is reciprocable in the direction across the lamination of the respective layers of the diaphragm.
• Fig. 1 is a top view illustrating a makeup of a vibration-type piezoelectric acceleration sensor element according to an embodiment of the present invention.
• Fig. 2 is a perspective view illustrating a makeup of a diaphragm of the acceleration sensor element shown in Fig. 1.
• Fig. 3 is a schematic diagram illustrating a makeup of an acceleration sensor according to the embodiment of the present invention.
• Figs. 4A through 4F are sectional views illustrating a method of manufacturing the acceleration sensor element shown in Fig. 1.
• Fig. 5 is a schematic diagram illustrating a brake control system using the acceleration sensor shown in Fig. 3.
• Fig. 6 is a sectional view illustrating a makeup of a conventional acceleration sensor.
• Fig. 7 is a block diagram illustrating a makeup of another conventional acceleration sensor.
• Fig. 1 is a top view illustrating a makeup of a vibration-type piezoelectric acceleration sensor according to an embodiment of the present invention.
• Fig, 2 is a perspective view illustrating a makeup of a diaphragm in the acceleration sensor element.
• diaphragm 23A having a fundamental vibration is provided inside frame 31.
• Support 33 retains diaphragm 23A and changes the fundamental vibration of diaphragm 23A.
• Retentive part 32 retains support 33. Both support 33 and retentive part 32 are also provided inside frame 31.
• Diaphragm 23Ahaving a beam-shape includes bases 34A and 34B facing each other, where base 34A (a first end) is retained so as to be hung by frame 31; base 34B (a second end) , by support 33.
• Support 33 retained by frame 34 via retentive part 32 moves reciprocably in the direction across the lamination of the respective layers of diaphragm 23A to be after-mentioned, namely on a straight line in the direction from the front to the back side of Fig . 1.
• support 33 is retained by frame 31 at two positions on the right side, and one position on the left.
• the vibration-type piezoelectric acceleration sensor element (hereinafter, abbreviated as "element”) 35 in this makeup expands and contracts diaphragm 23A with a high responsivity and high sensitivity by acceleration, and thus detects acceleration with a high responsivity and high accuracy, without being influenced by the temperature change.
• providing weight 33A to add mass to support 33 further raises the sensitivity (conversion efficiency) .
• the displacement magnitude of support 33 due to acceleration increases, and diaphragm 23A expands and contracts proportionally, allowing acceleration to be detected with a high sensitivity.
• Arms 23B are provided for increasing the resonance sharpness of diaphragm 23A.
• Arms 23B increase the resonance sharpness by at least approximately two to three times, improving the detection accuracy.
• Each of Arms 23B includes parallel part 23C parallel with the direction from base 34A to base 34B, and connection part 23D vertical to parallel part 23C and connected to diaphragm 23A.
• Arms 23B are provided symmetrically with respect to diaphragm 23A.
• pairs of arms 23B are desirably provided symmetrically with respect to central axis 52 orthogonal to and bisecting diaphragm 23A.
• diaphragm 23A includes silicon (Si) layer 23 formed on silicon dioxide (Si0 2 ) layer 22, bottom electrode layer 24 formed on Si layer 23, and piezoelectric thin-film layer 25 formed on bottom electrode layer 24.
• Diaphragm 23A further includes drive electrode layer 26B and detection electrode layer 26A, both as top electrode layers formed on piezoelectric thin-film layer 25. Still, drive electrode layer 26B and detection electrode layer 26A are formed along a beam-like central part composing diaphragm 23A, all the way to frame 31, as shown in Fig. 1.
• drive electrode layer 26B and detection electrode layer 26A are desirably provided with terminal electrodes 51A and 51B at a predetermined part extending to frame 31, and are connected to a control circuit (not illustrated) .
• drive electrode layer 26B and detection electrode layer 26A both top electrode layers, extend to the outer edge of frame 31 along a beam-like central part of retentive part 32.
• Retentive part 32 desirably retains support 33 with a zigzag, beam-like spring as shown in Fig. 1. This causes diaphragm 23A to expand and to contract with a high responsivity and sensitivity by acceleration.
• drive electrode layer 26B and detection electrode layer 26A are desirably formed so as to be symmetrical with respect to central axis 52.
• FIG. 3 is a schematic diagram illustrating a makeup of a vibration- type piezoelectric acceleration sensor according to this embodiment of the present invention.
• detection signal line hereinafter, abbreviated as "line”
• drive signal line hereinafter, abbreviated as "line"
• line 36B are connected to detection electrode layer 26A and drive electrode layer 26B, respectively.
• Amplifying circuit 38 amplifies feeble signals, and also drives diaphragm 23A of element 35 shown in Fig. 2.
• Frequency/voltage (F/V) converter 39 converts the frequencies of input signals to voltage.
• Automatic gain control (AGC) circuit 40 controls the voltage level of output signals from amplifying circuit 38.
• Element 35 is mounted in vibration- type piezoelectric acceleration sensor (hereinafter, abbreviated as "sensor”) 41, with frame 31 retained. When sensor 41 is supplied with power, a certain signal such as a noise is input to amplifying circuit 38 to be amplified.
• the amplified signal is input to drive electrode layer 26B through line 36B to vibrate diaphragm 23A. Consequently, charge is excited from piezoelectric thin-film layer 25 to detection electrode layer 26A, and a signal is input from detection electrode layer 26A to amplifying circuit 38 through line 36A. Then, this closed-loop operation is repeated until element 35 enters a stable, steady state at the resonance frequency for the fundamental vibration.
• the resonance frequency signal for the fundamental vibration is input to F/V converter 39 to be converted to a predetermined voltage.
• F/V converter 39 functions as a detector for detecting the resonance frequency for the fundamental vibration of diaphragm 23A, the resonance frequency changes owing to expanding and contracting of diaphragm 23A due to the applied acceleration.
• AGC circuit 40 controls F/V converter 39 to operate accurately when the voltage output from amplifier 38 rises to cause strains in the signals.
• support 33 receives an inertial force caused by a reciprocable motion on a straight line, and this reciprocable motion causes diaphragm 23A oscillating in a steady state to expand and contract. Accordingly, the resonance frequency for the fundamental vibration of diaphragm 23A changes, which is detected according to acceleration.
• applying acceleration yields a high change rate for a resonance frequency, allowing acceleration to be detected with high accuracy, without being influenced by the temperature change.
• FIG. 4A through 4F are sectional views illustrating a method of manufacturing a vibration-type piezoelectric acceleration sensor element according to this embodiment of the present invention.
• these figures omit showing the detailed shape of diaphragm 23A.
• etching stopper 22 made of Si0 2 to stop etching on substrate 21 made of Si, and also Si layer 23 on etching stopper 22.
• the thickness of substrate 21 is to be 20 ⁇ ; etching stopper 22, 2 ⁇ m; Si layer 23, 300 ⁇ m .
• Fig. 4A form etching stopper 22 made of Si0 2 to stop etching on substrate 21 made of Si, and also Si layer 23 on etching stopper 22.
• the thickness of substrate 21 is to be 20 ⁇ ; etching stopper 22, 2 ⁇ m; Si layer 23, 300 ⁇ m .
• Ti titanium
• platinum platinum
• a thickness of 0.2 ⁇ m to form bottom electrode layer 24.
• piezoelectric thin-film layer 25 made of lead zirconate titanate (PZT) with a thickness of 2.5 ⁇ m.
• PZT lead zirconate titanate
• Ti layer with a thickness of 10 nm on piezoelectric thin-film layer 25 using a metal mask with vapor deposition so that the Ti layer has a predetermined pattern.
• gold gold with a thickness of 0.3 ⁇ m with vapor deposition to form top electrode layer 26 with a predetermined pattern.
• Forming piezoelectric thin-film layer 25 with PZT yields a high change rate with a resonance frequency due to acceleration, allowing acceleration to be detected with high accuracy, without being influenced by the temperature change.
• FIG. 4D form resist 27B with a predetermined pattern on the backside of substrate 21, and etch the backside of substrate 21, to form hole 29. Then as shown in Fig. 4E, etch again from the side of resist 27A to form side hole 30. Further, remove resist 27B, and as shown in Fig. 4F, form diaphragm 23A in a thin and beam-like form. Finally , remove resist 27A. In this way, element 35 including diaphragm 23A is formed.
• Fig. 5 is a schematic diagram of a brake control system using a vibration-type piezoelectric acceleration sensor according to the embodiment.
• Automobile body 42 On automobile body 42, front wheels 43A and 43B, rear wheels 48A and 48B, braking devices 44, steering wheel 45 , and brake control circuit (hereinafter, abbreviated as "controller") 46 are mounted.
• Automobile body 42 is traveling in traveling direction 47.
• Sensor 41 detects acceleration and controller 46 processes the output signals for the acceleration and transmits the processed signals to braking devices 44.
• Controller 46 controls so that front wheels 43A and 43B, and rear wheels 48A and 48B do not lock due to braking devices 44, enabling safe driving control. For example, turning steering wheel 45 to the left as shown by traveling direction 47 makes automobile body 42 turn to the left.
• controller 46 changes the effectiveness of the brakes for front wheel 43B and rear wheel 48B, which are on the outer edge of the tires in the rotating traveling direction, and front wheel 43A and rear wheel 48A, which are on the inner edge. This prevents an accident due to skids of the tires, controlling automobile body 42 in safety.
• the acceleration received by sensor 41 slightly varies depending on the position where sensor 41 is mounted on automobile body 42. Therefore, sensor 41 is desirably arranged in the center of automobile body 42 with the objective of detecting average acceleration.
• a vibration- type piezoelectric acceleration sensor element and vibration-type piezoelectric acceleration sensor according to the present invention are used for detecting gravity on earth as static acceleration, for such as a safety brake system.
• the sensor can be used for detecting an angle of inclination, by detecting static acceleration. Further, the sensor detects an angle of inclination to be applied to a three-dimensional navigation apparatus including a capability of handling altitude.

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Citations (3)

• 2003
  • 2003-11-04 JP JP2003374125A patent/JP2005140516A/ja not_active Withdrawn
• 2004
  • 2004-10-29 WO PCT/JP2004/016463 patent/WO2005043172A1/en active Application Filing

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