A silicon carbide capacitive pressure sensor for in-cylinder pressure measurement

Abstract

This paper reports a research prototype of a low-cost, miniature, mass-producible sensor for measurement of high-pressure at operating temperatures of 300–600°C, e.g., in-cylinder engine pressure monitoring applications. This all-silicon carbide (SiC) capacitive sensor, i.e., a SiC diaphragm on a SiC substrate, takes advantage of the excellent harsh-environment material properties of SiC and is fabricated by surface micromachining. The sensor is packaged in a high-temperature ceramic package and characterized under static pressures of up to ∼5MPa (700psi) and temperatures of up to 574°C in a custom chamber. An instrumentation amplifier integrated circuit is used to convert capacitance into voltage for measurements up to 300°C; beyond 300°C, the capacitance is measured directly from an array of identical sensor elements using a LCZ meter. After high-temperature soaking and several tens of temperature/pressure cycles, packaged sensors continue to show stable operation. For monitoring the dynamic cylinder pressure in the combustion chamber, the sensor is packaged in a custom probe and inserted into the cylinder head of a research internal combustion engine. The sensor efficacy is verified against the reference probe used for monitoring pressure in the research engine.