A Study Of Radiation Effects On The Resistance Of Polycrystalline Silicon Film In MEMS Devices

MEMS (Micro-electro-mechanical-system) is evolved from the integrated circuit industry. Many kinds of micro sensors and actuators were fabricated based on single crystalline silicon substrate, polycrystalline silicon thin film and other materials. MEMS technology has been widely used in many fields such as commercial, aerospace and military applications. There are several distinct merits for MEMS devices such as miniaturization, microelectronics integration, parallel fabrication with high precision and high Reliability, which makes it perfectly fit in with the mini-satellites which usually has very limited shielding to the space radiation environment. Tthere are few studies on the MEMS device radiation reliability until now. Test performed on MEMS devices has shown the decrease of performances or failure of devices under certain dose of irradiation. Surface micro-machined polycrystalline silicon is a very important structural material widely used in MEMS devices. The study of polycrystalline silicon film radiation reliability has a great significance because it will be widely used in aerospace field which has the extreme demands for reliability.First of all, the concept of MEMS and the basic research methods of MEMS reliability were introduced. Applications of MEMS in space applications were summarized. Then the published data on MEMS radiation reliability was reviewed. The basic damage mechanisms and degradation effects were introduced. The main topic of this paper-study of radiation effects on the resistance of polycrystalline silicon film was introduced.Secondly, the structure and electrical model of polycrystalline silicon were introduced. The effects of grain boundary on the electrical properties of a polycrystalline silicon have been explained by the carrier-trapping model and the dopant-segregation model. The conduction model for polycrystalline silicon was introduced based on the diffuse and drifting of carriers, the thermionic field emission of carriers through the space-charge potential barrier and carrier tunneling through the grain boundary rectangular potential barrier. Then we give the computing steps for our specifically polysilicon film in experiment.Thirdly, the experimental schemes for the study of radiation effects on the resistance of polycrystalline silicon film were introduced including the design and fabrication steps of the test structures, the irradiation experiment was performed under the total doze of space radiation. Then the high precision resistance test method using four-wine measurement and the electrical model of grain boundary were introduced.Finally, the experimental data were analyzed and handled after tests. The change of resistance has been presented. The irradiation effects of polycrystalline silicon film have been discussed. A energy band of grain boundary evolution was presented by the TEM images of grain boundary, the experimental data and the conduction model of heavily doped polysilicon in chapter two, which can reasonably explain the decrease of resistance of grain boundary.The radiation reliability of polycrystalline silicon resistance was studied form theoretically and experimentally. The results have some meaningful values for further study of polycrystalline silicon film radiation reliability. In the end, this work have been concluded.