| Micro-electro-mechanical systems (MEMS) Pirani vacuum gauge is a heat conduction type vacuum pressure measuring device based on micro structures, it measures and monitors vacuum pressure by the Pirani effect and the principle of thermoelectric coupling. Compared with the conventional vacuum pressure gauges, MEMS Pirani gauges have advantages of small size, low energy consumption, low working temperature, also gain fast thermal response and wide range, thus research on micro Pirani gauge has very important scientific value and engineering application value. This dissertation carried out detailed research on MEMS Pirani vacuum pressure measurement operational principle and related theoretical background. After the investigation on domestic and foreign development and application, this essay puts forward an novel structure of a silicon nitride (Si3N4) thin film Pirani vacuum gauge, to carry out the key research to use structures of silicon nitride thin films, aiming at imporving the performance of MEMS Pirani gauge.A silicon nitride thin film structure Pirani vacuum gauge is designed. Based on thin film vacuum gauge functioning principle and the heat conduction model of vacuum gas, a thermo-electric coupling model is developed for the vacuum gauge research, heat conduction model of gas in micro scale is analyzed to obtain the optimized device performance parameters. A fabircation method for MEMS Pirani vacuum pressure gauge is proposed, the sensitive part of the vacuum gauge is carried out on 4 inch silicon wafer, which gets the high-end silicon nitride thin film Pirani vacuum gauge sensor and can measure pressure ranges from 0.107 to 74.12 Pa. According to the difficulties in fabircation process, such as hollowed double sides lithography and silicon nitride etching, a series of research attempts were carried out, summing up the most proper fabricaion process parameters. These works above build a solid fondation for Pirani gauge design.For characterizing the performance of fabricated device, a vacuum test environment is built. The influences of hot plate width change, hot plate gap width change and hollowed diaphgragm structure on the performance of the device are analysed. The experiment results demostrate that device sensibility is imporved by decreasing the hot plate gap width from 20μm to 10μm, the measuring lower limit can’t extends to wider range by decreasing hot plate gap width from 20μm to 10μm, the measuring upper limit extends to wider range when hollowed diaphgragm structure is applied on the device. |
