Integrated Hybrid Pressure Sensor Using a Piezoresistive Thickfilm Sensor Element

High-performance electronic systems for automotive engine control largely depend on the existence of qualified sensors. Together with actuators they determine the efficiency, reliability and also the costs of the entire system. In addition to the engine speed, the air flow through the intake manifold and the throttle-valve position, the absolute manifold pressure is an important input parameter for engine-control systems. Appropriate pressure transducers have to be made available for several pressure ranges, e. g. 100 kPa and 200 kPa, and packaged in suitable housings, especially as an on-board component for insertion into electronic control units. On the basis of thick-film technology - well established in the production of automotive microcircuits /1 / - we present a new generation of integrated hybrid pressure sensors. A novel thick-film process was developed, to build up self-supporting micromechanical structures of dielectric materials onto a ceramic substrate. A miniature diaphragm of about 5 mm diameter and 0.1 mm thickness can be produced by applying several screen printing and firing sequences. Together with the substrate it forms a hermetically tight, bubble-like cavity of 60µm in height. Piezoresistive thick-film resistors are printed on the center of the diaphragm. With a gauge factor of 15 they transform the mechanical tension, caused by changes of the ambient pressure, into an electrical signal. Both the sensor element and an electronic signal-conditioning circuit are integrated on one ceramic substrate without additional bonding. The housing, in which the hybrid circuit is mounted, consists of two parts. It is made from glass-reinforced thermoplastic material with excellent mechanical strength.