Research On Wafer Lever MEMS Vacuum Measurement Device

Quite a few MEMS devices need vacuum packaging technology to guarantee the desirable performance. But some key issues such as the vacuum packaging process, vacuum retention, vacuum measurement have never been solved completely, especially the vacuum measurement in wafer level vacuum packaging still have no effective testing methods. Current commercial vacuum gauges cannot be applied in MEMS wafer level vacuum package for their big size. In the present work, a micro vacuum measurement device based on film resistance was investigated. Because of simplified processes and structure, they offer significant practical advantages.A micro vacuum measurement device—Pirani gauge—for real-time measuring the vacuum pressure of wafer lever MEMS vacuum packaging is systematically studied based on numerical analysis and experiments. Based on theory of heat transfer, the relationship between the Pirani gauge structure, pressure and Pirani gauge film resistor has been obtained. The experimental results show that the Pirani gauge is capable of measuring pressures from atmospheric value to 1 Pa and has a very good linearity in the range from1 Pa to 1000 Pa. It is found that the linearity is different under different input voltage, and the result shows that the optimal input voltage is 3 V. It has also been proven that each Pirani gauge has its own calibration curve, but the trend is basically the same.The Au-Si bonding experiments have been conducted for the Pirani gauge after fabrication and the leak rate measurement experiments have been conducted after bonding. Compared with traditional leak rate testing methods, the experiment results show that this Pirani gauge can also be used for leak rate testing.The Pirani gauge which was used to detect gas flow is studied in the last part of this paper. Many experiments have been done with different flow rate, different resistance and different input voltages. The experimental results show that this flow sensor is capable of measuring the flow rate and has a good linearity in the flowmeter capacity from 0.1 to1 m3/h. The output voltage is varied with the resistance and the linearity of the sensor is less influenced by the resistance for a constant voltage. The flow direction is also considered, the results show that the response of the sensor were less influenced according to the flow direction.