Fabrication of thermal-based vacuum gauge

The fabrication and evaluation of a wide-range vacuum gauge for monitoring the pressure level inside an infrared focal plane array and a wafer-level packaging (WLP) are reported. The proposed vacuum gauge has a microbolometer structure produced using the conventional surface micromachining process to achieve thermal isolation and high sensitivity. This structure has other advantages such as fast response time, a wider measurement range and easier integration to a Si substrate compared with other pressure sensors. The evaluation results show that the fabricated vacuum gauge has a linear dynamic range and a sensitivity of 10^-3 to 10⁵ K/W/torr for vacuum pressures ranging from 10^-6 to 760 torr. Also, the response time to vacuum change is reduced from 0.11 s at 10^-5 torr to 15 ms at 100 torr. Therefore, the microbolometer-based vacuum gauge has good potential for application in WLP, and it is possible to hermetically seal it with various read-out integrated circuit substrates.