Temperature Change Leverage on Performance of MEMS Rotational Motion Sensors

This paper presents and analyze results of simulations of two types MEMS vibratory gyroscopes under the influence of temperature changes. This topic has enormous meaning because temperature variation influences on material properties and geometry of device and thus also on its response. Modelling of MEMS device (which includes solid material)and performing simulations in such environment become more complicated. Moreover, because vibratory microgyroscopes are systems of two forced oscillators (for drive and sense directions)with damping, temperature variation influence also on two important quantities characterizes the device: eigenfrequency and Q-factor. Variation of these values under temperature and graphs are presented in paper for different geometries of gyroscopes. Two geometries (structures)are considered here: with one inertial mass only (common for both drive and sense directions)and with central mass and inertial frame. Both geometries were simulated with two different springs configurations. The material used for gyroscope was Polycrystalline Silicon (known also as Polysilicon), with isotropic properties. Mathematical and Finite Element Models in COMSOL, SIMULINK and Coventor MEMS+ are presented as well as results obtained from simulations. These response results (obtained from simulations for one cycle of temperature range 300-400K)show, that MEMS vibrating gyroscopes material and geometrical parameters are sensitive to change of temperature. The main purpose of this paper is to bring up problem of temperature influence on microgyroscope operation. Obviously, this topic is very complex and here some simplifications are assumed. However, results in such simple model clearly indicate the seriousness of the problem and finding additional devise areas influenced by temperature can cause only further performance degradation. The importance of problem of temperature variation influence is particularly seen at the design stage where shape, details of structure, their location are must be taken into consideration. Results presented here show that each detail of structure can meaningfully degrade performance and should be accurately modeled. Unfortunately, imperfections of structure fabricated device cause that precise accuracy of frequency mode-matching cannot be achieved and temperature fluctuations enhance mode-matching inaccuracies.