Vacuum Degree Measurement for MEMS Vacuum Package Based on Quartz Crystal Oscillator

摘要

A platform is proposed in this paper for fundamental study of the miniaturized MEMS packaging on its long term performance such as actual vacuum level maintaining inside the packaging cavity, and durability of the packaging shell subjected to cycling thermal loading. In particular, a sensor composed of quartz crystal is introduced for vacuum measurement. The quartz crystal is placed in the internal cavity of the MEMS packaging and is excited by an exciting source which is formed by Direct Digital Synthesizer (DDS). The voltage signal from both ends of the quartz crystal is outputed to comparison circuits to compare the phase and amplitude of the signal. Then it is transmitted to the SCM after AD conversion for measuring and monitoring the vacuum degree of internal cavity of the MEMS package after processing and calibration. It has been found that the actual vacuum level within the cavity is much lower than the applied vacuum level in the packaging chamber. The proposed vacuum packaging shell with double walls has been found to provide perfect structure to help maintain long life when the packaging is subjected to the cycling thermal loading.