Design and fabrication of platinum thin-film based temperature sensor

Abstract

This article presents the development of thin-film temperature sensor with two different types of packaging techniques on silicon wafer. Platinum (Pt) thin film sensing element is designed and fabricated by MicroElectro-Mechanical Systems (MEMS) technology, based on photolithography, e-beam evaporation and lift-off techniques on silicon substrate for machine tools applications. SiO2 and Ti are used as insulation and adhesion layers respectively. The thickness of SiO2, Ti and Pt are in nanometers and coated using e-beam evaporation system. The electrical connections were established using Nickel (Ni) coated Copper (Cu) leads. Temperature sensor was extensively characterized using thermal cycling chamber and Fluke calibrator. We have observed 99.975% linearity and ± 0.50C accuracy for temperature range of -25 to 1800C. The temperature coefficient of resistance (TCR) or Alpha (α) was found to be 0.002335 / 0C after repetitive thermal cycling experiment. The sensor is packaged with two different techniques, epoxy packaging and stainless steel (SS) probe package. Two types of epoxies were used, one is electrically and thermally conductive and the other one is ceramic epoxy for isolation and protection. The response time of the sensor with epoxy packaging and SS packaging are 0.4 Sec and 3 Sec respectively. The response time of SS probe can be further reduced by using thin tubes.