Study On The Mechanical Properties Of Silicon Nitride Film And Its Applications In RF MEMS Switches

With the development of MEMS technology, more and more film material is fabricated as microstructures and applied in MEMS devices. Silicon nitride film is widely applied in MEMS for its excellent mechanical properties. It is necessary to research the mechanical properties of silicon nitride film, such as residual stress, elasticity modulus etc., in order to understand its properties better and exert its applications. Micro-rotating-structures were simulated by the finite element method (FEM) ANSYS, the result of FEM simulation was conducted to optimize the structure design, and micro-rotating-structures were fabricated to measure the residual stress of silicon nitride films. The elasticity modulus and hardness of silicon nitride film were measured by the nanoindentation method. The relationships between the mechanical properties of silicon nitride film and technical parameters of plasma enhanced chemical vapor deposition (PECVD) method were analyzed and discussed. The metal-metal contact series RF MEMS switch was made, whose suspended beam was made of silicon nitride film. The effect of silicon nitride film mechanical properties on the performances of RF MEMS switch device was researched. The results showed that silicon nitride films deposited in different technical conditions had different mechanical properties, and the mechanical properties of silicon nitride film have vital effect on the performances of RF MEMS switch device. At present, elasticity modulus value of silicon nitride film deposited by PECVD reaches about 185.5Gpa, and the absolute value of residual stress is less than 100MPa. And the performances of RF MEMS switch device are that threshold voltage value is 22 to 27V, lifetime of RF MEMS switch device is over 10000 times.