Motorola Corporation

Donald O Myers

Youngkee Ahn

Gregory D Stamm

Ruta J Venclovas

David W Mace

A process for manufacturing a pressure transducer of a pressure sensor is disclosed. Initially, a capacitive pressure transducer is formed by bonding a silicon diaphragm to a glass base such that the transducer produces different capacitances in response to different diaphragm deflections provided in response to sensed pressures. The sensitivity of the capacitive pressure transducer is adjusted by etching the silicon diaphragm while it is bonded to the base substrate in accordance with capacitance values of the transducer which were previously obtained at various predetermined pressures. In this manner, the thickness of the silicon diaphragm is selectively reduced to obtain an accurate desired sensitivity for the transducer and handling of very thin silicon diaphragms prior to their assembly to associated transducer bases is eliminated.

Post seal etching of transducer diaphragm

A pressure sensor assembly (10, 10') is disclosed in which a pressure sensing element (11, 11', 11') is protected from external contaminants in an externally-applied pressure (P) to be sensed. This is accomplished by filling an external cavity (36) of a tubular portion (32) of a cover member (30) which fits over the pressure sensing element that has previously been mounted on a metallized substrate (14). The external cavity (36) is totally filled with an incompressibel liquid (35), such as silicon oil, and a thin diaphragm (40), preferably comprising a polyimide film, seals this external cavity and provides a compliant barrier between the externally-applied pressure (P) and the imcompressible fluid (35) and pressure sensing element (11). Chemical inertness of the diaphragm (40) and incompressible fluid (35) prevents contaminants in the sensed pressure (P) from attacking the pressure sensing element (11, 11', 11'), while transmitting changes in the sensed pressure (P) substantially directly to the pressure sensing element.

Pressure sensor assembly

The undesired temperature variation of a capacitive pressure sensing element (10) having a positive temperature coefficient of capacitance (TCC) is compensated by a series resistor R and compensating capacitor (C.sub.c) connected in parallel to the pressure sensing capacitor (C.sub.x). The compensating capacitor and presssure sensing element have opposite polarity temperature coefficients of capacitance, and the magnitude of the resistor is selected such that its resistive impedance is nonnegligible and is comparable to the magnitude of the capacitive reactance of the pressure sensing capacitor or compensating capacitor at a predetermined operative frequency of an electrical signal applied to and/or determined by the pressure sensing and compensating capacitors.

Capacitive temperature compensation for a pressure sensor

A technique for metallizing a substrate while providing stress relief for the metallization on the substrate is disclosed. Chrome conductive metallization (22) is deposited on a top surface (21) of an insulating glass substrate (20). An interior gold conductive metallization (23) is deposited on the chrome, and metallization (24) having a substantial nickel composition is deposited on the gold. Subsequently, an additional outer gold metallization (25) is provided on the nickel, and solder is provided on the additional gold metallization. Prior to the application of solder to the outer gold layer 25, the metallization layers are subjected to anodic bonding temperatures and voltage potentials. The gold layer between the nickel and chrome layers diffuses along the grain boundaries of the nickel and chrome layers, thus reducing the ability to transmit stress through these metallizations induced by the solder. The present metallization structure prevents solder-induced stress from rupturing either the bond between the chrome layer and glass substrate or the glass substrate. This allows application of a relatively thick layer of chrome to glass sufficient such that chrome can be deposited in feedthrough holes (31, 32) in the glass. Preferably, such a metallization technique is utilized for manufacturing a silicon capacitive pressure sensor (30).

Stress relief substrate metallization

A capacitive pressure transducer 10 with an analog output voltage which varies linearly as a function of sensed pressure is provided. A capacitive pressure sensor C.sub.x provides a pressure variable capacitance that determines the frequency of a sensor oscillator 11. The oscillator frequency is combined with a reference frequency by a pair of D-type flip-flops 18 and 19 to provide a resultant signal having a duty cycle related to the sensed pressure. The resultant signal is integrated to provide a first analog signal as an input to a controllable gain amplifier 24 which receives gain control information from a non-linear gain control circuit 40 that receives an analog control signal as an input. The analog control signal varies as a function of sensed pressure in an opposite manner to said first analog signal. Said non-linear circuit provides for non-linearly varying the gain of amplifier 24 as a function of sensed pressure. Preferably the non-linear circuit 40 includes temperature compensating diodes 47. The output of the amplifier is a temperature compensated output signal which has a substantial linear variation as a function of sensed pressure.

Linearized electronic capacitive pressure transducer

A method of utilizing anodic bonding to bond a conductive semiconductor wafer to a metallized dielectric glass plate so as to form a capacitive pressure sensing element is disclosed. The method includes positioning the semiconductor wafer in contact with the glass plate, heating the wafer and glass plate and applying a substantial positive DC potential to the semiconductor wafer and metallization on the glass plate while applying a negative DC voltage potential to the glass plate. The glass plate metallization forms one capacitor plate of the capacitive pressure sensing element while the semiconductor wafer forms the other capacitor plate. By applying the same voltage potential to the glass plate metallization and the semiconductor wafer during anodic bonding of the wafer to the glass plate, the corona field between the glass plate metallization and the semiconductor wafer is reduced thereby improving the bond between the wafer and the glass plate and reducing the possibility of arcing between the semiconductor wafer and the glass plate metallization. Also sodium ion migration to the glass plate metallization and any metallization connected to this metallization is inhibited wherein the ion migration would impair the subsequent solderability of these metallizations.

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Carpentersville, IL, United States of America

Donald O Myers