Differential micro-Pirani gauge for monitoring MEMS wafer-level package

The implementation of differential Pirani gauge for accurately measuring wafer-level package pressures was demonstrated. We proposed a multiple-sensor-solution, where two Pirani gauges were constructed under different pressures; one in sealed micro-cavity for measuring pressures and the other one in opened micro-cavity as a reference. Ambient pressure, structural dimension variations, and resistivity differences among wafers/lots, were captured through the differential scheme for error compensations, allowing accurate pressure determinations. Presented Pirani utilized small gaps (∼2µm) between heater and dual heat sinks to obtain wide operation range (0.05∼100 Torr) and high sensitivity (∼10000 ppm/Torr). With 5X error reductions and high stabilities, the proposed device was successfully used in examining reliabilities and monitoring processes of wafer-level packages.