Optimization of packaging process of piezoresistive engine oil pressure sensor

The piezoresistive pressure sensor is one of the major applications of MEMS (Micro-Electro-Mechanical-System) devices. Nowadays, in the field of automotive electronics, silicon-based pressure sensors are playing a significant role in the control of brake, engine, tire pressure, etc. The piezoresistive based engine oil pressure sensor mentioned in this paper is applied to detect the pressure of lubricant of the automobile engine. We firstly study the influence of silicon oil on the offset of pressure sensor. Results show that the offset tends to be relatively large when the amount of the silicon oil increases. In order to minimize the zero offset, ceramic substrate is introduced to reduce the amount of the silicon oil. We also find that the cleanliness and stability of the silicon oil have a considerable impact on the offset. The fully cleaned silicon oil leads to a smaller offset, and few changes are found when temperature increases. The silicon oil with good stability can result in a stable offset even the packaged sensor stored at a high temperature for a long time. Then, the influence of the welding performance of TO base on the hermeticity of pressure sensor is investigated by experimental tests and finite element method (FEM) analysis. Results show that, compared with the iron, Kovar alloy has a better welding performance and the leakage rate of the sealed chamber is less than 10^-8Pa.m³/s. FEM analysis fits well with the experimental tests.