Semiconductor acceleration sensor and vehicle control system using the same

• US 5,417,312 A
• Filed: 11/03/1993
• Issued: 05/23/1995
• Est. Priority Date: 05/30/1990
• Status: Expired due to Term

• Current Assignee: Hitachi Automotive Engineering Incorporated (Hitachi, Ltd.), Hitachi, Ltd.
• Original Assignee: Hitachi Automotive Engineering Incorporated (Hitachi, Ltd.), Hitachi, Ltd.
• Inventors: Asano, Yasuhiro, Ebine, Hiromichi, Sugisawa, Yukiko, Matsumoto, Masahiro, Miki, Masayuki, Suzuki, Masayoshi, Tanaka, Tomoyuki, Kubota, Masanori, Ichikawa, Norio, Ueno, Sadayasu, Suzuki, Seiko, Tsuchitani, Shigeki, Sato, Kanemasa
• Primary Examiner(s): Oberleitner, Robert J.
• Assistant Examiner(s): Poon, Peter M.
• Application Number:
  US08/147,083
• Time in Patent Office: 566 Days
• Field of Search: 303/100, 303/105, 188/267, 188/290, 188/181 R, 188/181 A, 73/517 AV, 280/707
• US Class Current: 188/181.00A
• CPC Class Codes: G01P 1/003 used for damping
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A semiconductor acceleration sensor is formed by a cantilever having a conductive movable electrode of predetermined mass at one end, at least one pair of fixed conductive electrodes which are stationary with respect to the movable electrode located on opposing sides of the movable electrode, and gaps provided between the movable electrode and the fixed electrodes. To prevent the movable electrode becoming fused to the contacted fixed electrode, in a first aspect of this invention, an insulating layer is provided between the movable electrode and fixed electrodes, the layer being either on the movable electrode or on the fixed electrodes and in a second aspect the movable electrode or, preferably, the fixed electrodes, are formed of a high melting point material. In such a second aspect, to improve adhesion between the high melting point material and a substrate to which the fixed electrodes are mounted, a lower melting point material is firstly coated on the substrates. A sensor detector unit processing circuit has the output characteristic of the circuit digitally adjusted by suitable switching of a plurality of resistors, and the sensor chip and the detector unit integrated circuit may be located on a common base and mounted in a hermetically sealed chamber to prevent adverse environmental effects affecting operation of the sensor and detector unit assembly. A gas having a dew point of -40° C. or lower is, advantageously, charged into the hermetically sealed chamber.

Claims

1. A semiconductor acceleration sensor comprising a cantilever having a conductive, movable electrode of predetermined mass at one end thereof, said cantilever being made of a material of silicon type, at least one fixed conductive electrode which is stationary with respect to said movable electrode and located on a side of said movable electrode, said fixed electrode being separated from said movable electrode by a predetermined gap, and insulation means located between the movable electrode and the fixed electrode for preventing a short-circuit therebetween, wherein

(a) said sensor is in combination with a detector unit therefor and said sensor and said detector unit are both located in a hermetically sealed chamber,

(b) said detector unit being an integrated circuit and said sensor being an integrated chip device,

(c) said integrated circuit and said chip device being both mounted on a base, and

(d) a cap is hermetically sealed to said base.

2. A sensor as claimed in claim 1 wherein an inert gas having a dew point of -40°

C. or less is charged into the hermetically sealed chamber.

3. A sensor as claimed in claim 1 wherein signals to and from the sensor and detector unit are supplied via lead pins which are hermetically sealed by glass in the base and said lead pins extend through said base into a sealed volume, said sealed volume being formed by a molding to which the hermetically sealed chamber is attached and a cover plate.

4. A sensor as claimed in claim 3 wherein output connectors are connected to said lead pins by metallic wires made from one of Ni, Al, or Au, and wherein said connectors provide external signals indicative of sensor output to control means.

5. A sensor as claimed in claim 3 wherein through-type capacitors are incorporated in said lead pins for reducing broad band noise from the lead wires.

6. A sensor as claimed in claim 1 wherein the detector unit integrated circuit is secured to the base via a bonding layer which is not more than 0.1 mm in thickness.

7. A sensor as claimed in claim 6 wherein said bonding layer is made of silicone resin.

8. A sensor as claimed in claim 1 wherein the integrated circuit and said chip device are mounted on a thick film alumina substrate adapted to provide a ground pattern whereby effect of external radio waves and noise is minimized.

9. A sensor as claimed in claim 1 wherein the distance between the integrated circuit and the chip device is not more than 1 mm.

10. A semiconductor acceleration sensor in combination with an acceleration detector unit, said sensor comprising a cantilever having a conductive, movable electrode of predetermined mass at one end thereof, said cantilever being made of a material of silicon type, at least one pair of fixed conductive electrodes which are stationary with respect to said movable electrode and located on opposing sides of said movable electrode, said fixed electrodes being separated from said movable electrode by a predetermined gap, and insulation means located between the movable electrode and the fixed electrode for preventing a short-circuit therebetween, said detector unit comprising a processing circuit for processing signals from the sensor wherein said processing circuit comprises a first capacitor and a first switching means as a feedback element of an operational amplifier, a negative input terminal of said operational amplifier being connected to said movable electrode and a positive input terminal of said operational amplifier being connected to a predetermined reference voltage, a sample hold circuit comprising a second switching means and a second capacitor for detecting electrostatic capacitance difference between the movable electrode and each of the fixed electrodes as a voltage at the terminal of the operational amplifier, an amplification means for amplifying the output of the second switching means and second capacitor, means for generating a waveform train with a period the pulse width of which is modulated by the amplified signal, means for supplying the voltage waveform train to each of the fixed electrodes, means for turning the said first and second switching means ON or OFF for a predetermined period of time in synchronization with the voltage waveform train, means for converting the voltage waveform train to an analogue voltage, and an output adjustment means for adjusting the analogue voltage to a predetermined characteristic, wherein the sensor and detector unit are both located in a hermetically sealed chamber, the detector unit being an integrated circuit and the sensor being an integrated chip device, said integrated circuit and said chip device being both mounted on a base, and a cap is hermetically sealed to said base.

11. A combination as claimed in claim 10 wherein said processing circuit is arranged such that when said first switching means is OFF the second switching means is ON.

12. A combination as claimed in claim 11 wherein said voltage waveform train is applied to one of said fixed electrodes and the waveform train which reverses the voltage waveform train is applied to the other fixed electrode.

13. A combination as claimed in claim 10 wherein said predetermined reference voltage is the same level as the peak value of said voltage waveform train.

14. A combination as claimed in claim 10 wherein said adjustment means includes at least a plurality of resistors and further switching means is provided for digitally combining said resistors in a desired combination to provide a required output characteristic.

15. A combination as claimed in claim 10 wherein an inert gas having a dew point of -40°

C. or less is charged into the hermetically sealed chamber.

16. A combination as claimed in claim 10 wherein signals to and from the sensor and detector unit are supplied via lead pins which are hermetically sealed by glass in the base and said lead pins extend through said base into a sealed volume, said sealed volume being formed by a molding to which the hermetically sealed chamber is attached and a cover plate.

17. A combination as claimed in claim 16 wherein output connectors are connected to said lead pins by metallic wires made from one of Ni, Al, or Au, and wherein said connectors provide external signals indicative of sensor output to control means.

18. A combination as claimed in claim 17 wherein through-type capacitors are incorporated in said lead pins for reducing broad band noise from the lead wires.

19. A combination as claimed in claim 10 wherein the integrated circuit and said chip device are mounted on a thick film alumina substrate adapted to provide a ground pattern whereby effect of external radio waves and noise is minimized.

20. A combination as claimed in claim 10 wherein the detector unit integrated circuit is secured to the base via a bonding layer which is not more than 0.1 mm in thickness.

21. A combination as claimed in claim 20 wherein said bonding layer is made of silicone resin.

22. A combination as claimed in claim 10 wherein the distance between the integrated circuit and the chip device is not more than 1 mm.

23. A semiconductor acceleration sensor comprising:

a cantilever having a cantilever-movable silicon electrode of predetermined mass at one end thereof;

at least one fixed electrode which is stationary with respect to said movable electrode and located at a cantilever-movable side of said movable electrode, said fixed electrode being separated from said side of said movable electrode by a predetermined gap;

insulation means located directly on at least one of said movable and fixed electrodes at said gap for preventing a short circuit therebetween; and

damping means comprising an inert gas in said gap and said insulation means being in a defined pattern which does not cover the entire surface of said at least one of said movable and fixed electrodes for providing a roughened surface on said at least one of said movable and fixed electrodes, preventing said gas from freely moving over said roughened surface and damping cantilever movement of said movable electrode,

wherein said sensor is in combination with a detector unit therefor and said sensor and said detector unit are both located in a hermetically sealed chamber.

24. A semiconductor acceleration sensor comprising:

a cantilever having a cantilever-movable silicon electrode of predetermined mass at one end thereof;

at least one fixed electrode which is stationary with respect to said movable electrode and located at a cantilever-movable side of said movable electrode, said fixed electrode being separated from said side of said movable electrode by a predetermined gap;

insulation means located directly on at least one of said movable and fixed electrodes at said gap for preventing a short circuit therebetween; and

damping means comprising an inert gas in said gap and said insulation means being in a defined pattern which does not cover the entire surface of said at least one of said movable and fixed electrodes for providing a roughened surface on said at least one of said movable and fixed electrodes, preventing said gas from freely moving over said roughened surface and damping cantilever movement of said movable electrode,

wherein said sensor is in combination with a detector unit therefor and said sensor and said detector unit are both located in a hermetically sealed chamber, and wherein said inert gas has a dew point of -40°

C. or less and said inert gas is charged into the hermetically sealed chamber.

25. A semiconductor acceleration sensor comprising a cantilever having a conductive, movable electrode of predetermined mass at one end thereof, said cantilever being made of a material of silicon type, at least one fixed conductive electrode which is stationary with respect to said movable electrode and located on a side of said movable electrode, said fixed electrode being separated from said movable electrode by a predetermined gap, and insulation means formed in a defined pattern on at least one of the movable electrode and the fixed electrode for preventing a short circuit therebetween, said insulation means providing a roughened surface on said at least one of said movable electrode and the fixed electrode, wherein

(a) said sensor is in combination with a detector unit therefor and said sensor and said detector unit are both located in a hermetically sealed chamber,

(b) said detector unit is an integrated circuit and said sensor is an integrated chip device,

(c) said integrated circuit and said chip device are both mounted on a base,

(d) a cap is hermetically sealed to said base, and

(e) an inert gas is provided in said hermetically sealed chamber in said gap between the movable electrode and said at least one fixed electrode, whereby said insulation means in said defined pattern prevents said gas from freely moving over said roughened surface and damping of said movable electrode is produced.

26. A semiconductor acceleration sensor in combination with an acceleration detector unit, said sensor comprising a cantilever having a conductive, movable electrode of predetermined mass at one end thereof, said cantilever being made of a material of silicon-type, at least one pair of fixed conductive electrodes which are stationary with respect to said movable electrode and located on opposing sides of said movable electrode, said fixed electrodes being separated from said movable electrode by a predetermined gap, insulation means located directly on at least one of said movable electrode and the at least one pair of fixed conductive electrodes, said insulation means being shaped in a defined pattern which does not cover the entire surface of the electrode to which it is applied and said insulation means providing a roughened surface on said electrode to which it is applied, said detector unit comprising a processing circuit for processing signals from the sensor, wherein said processing circuit comprises a first capacitor and a first switching means as a feedback element of an operational amplifier, a negative input terminal of said operational amplifier being connected to said movable electrode and a positive input terminal of said operational amplifier being connected to a predetermined reference voltage, a sample hold circuit comprising a second switching means and a second capacitor for detecting electrostatic capacitance difference between the movable electrode and each of the fixed electrodes as a voltage at the output terminal of the operational amplifier, an amplification means for amplifying the output of the second switching means and second capacitor, means for generating a waveform train with a period the pulsewidth of which is modulated by the amplified signal, means for supplying the voltage waveform train to each of the fixed electrodes, means for turning the said first and second switching means ON or OFF for a predetermined period of time in synchronization with the voltage waveform train, means for converting the voltage waveform train to an analogue voltage, and an output adjustment means for adjusting the analogue voltage to a predetermined characteristic, wherein the sensor and detector unit are both located in a hermetically sealed chamber, the detector unit being an integrated circuit and the sensor being an integrated chip device, said integrated circuit and said chip device being both mounted on a base, a cap hermetically sealed to said base, and an inert gas in said predetermined gap between the movable electrode and said fixed electrodes, whereby said insulation means in said defined pattern prevents said gas from freely moving over said roughened surface and damping of said movable electrode is produced.