Investigation on Performance and Vacuum Package of MEMS Infrared Focal Plane Arrays

Abstract

A substrate-free microelectromechanical system (MEMS) focal plane array (FPA) has been successfully developed. Since there is no silicon substrate beneath the FPA's pixels, the infrared radiation (IR) loss has been significantly reduced. However, at ambient pressure, it is difficult to obtain a clear visible image due to the sensitivity loss caused by the thermal conductance of air. To improve the packaged FPA's performance, its thermal sensitivity and response time were investigated under varying air pressure. The high-contrast IR thermal images of a human hand were captured at room temperature and under an air pressure of 0.01 Pa, and the noise-equivalent temperature difference of the FPA was also estimated to be about 373 mK compared with the 1.4 K under a pressure of 10 Pa. What is important is that the FPA's response time was increased from 50.1 to 336.6 ms by the decrease in air pressure. In addition, we present an approach to package the MEMS FPA at a low-pressure vacuum with two optical windows, which is an effective way to increase FPA's sensitivity.Index Terms-Focal plane array (FPA), microelectromechanical systems (MEMSs), response time, thermal sensitivity, uncooled, vacuum package.

Overview of the MEMS Pirani Sensors

“…To monitor the vacuum information in these environments, vacuum sensors are demanded. Additionally, many devices require vacuum encapsulation to optimize performance and reliability [14], such as MEMS gyroscope sensors [15], high-end micro-accelerometers [16], uncooled infrared focal plane arrays (UFPA) [17][18][19], etc. These devices need to operate in a vacuum environment either to reduce gas damping of their moving parts or to decrease gas thermal conduction, thus improving their performance.…”