A Micro Thermal Expansion Fluidic Gyroscope And Its Key Technology

The micro thermal expansion fluidic gyroscope is a novel micro thermal inertial sensor. It has the advantages of simple structure, easy fabrication, low-cost, high reliability, good anti-vibration and anti-shock ability. To improve its performance, several key technologies have been studied.Currently, none of the fluid numerical analysis software can directly calculate the Coriolis-effect of a fluid. Therefore, based on the fundamental theory of thermal fluid, the theoretical model, which includes the Coriolis acceleration term, of the micro thermal expansion fluidic gyroscope has been built. According to the theoretical model, a simplified two dimensional COMSOL model has been developed, and the velocity and temperature of the gas is numerically solved.Because the sensitivity of the micro thermal expansion fluidic gyroscope is much lower than the sensitivity of the micro mechanical gyroscope, the sensitivity of the micro thermal expansion fluidic gyroscope need to be improved. A series study of how different parameters affect the gyroscope’s sensitivity, such as heat capacity of gas, thermal conductivity of gas, viscosity of gas, gas pressure, temperature sensor’s location, frequency of the heater drive signal, and the heater power, have been carried on. And the parameters are optimized.A fabrication process of the micro thermal expansion fluidic gyroscope, which uses platinum as structure material, has been developed. The studies about fabricating platinum structures and low stress releasing structures are carried on. A bi-layer lift off process has been used to form100nm thickness platinum structure. To prevent the platinum resistance broke after releasing structure, a530nm thickness silicon dioxide layer has been used. By taking the advantages of XeF2etch silicon and silicon dioxide at the same time, we use30nm thickness silicon dioxide as the etching masker, instead of using common photoresist, during XeF2etch silicon cavity. This process not only prevent the XeF2over etch silicon sidewall, but also avoid using wet etch method to get rid of photoresist once the structures are released. Finally, the micro thermal expansion fluidic gyroscopes have been fabricated.The gyroscope testing system is built. The experimental results show that the fabricated thermal gyroscope has best sensitivity when the heater drive frequency is12.50Hz, and the duty cycle is37.5%. Also the gyroscope’s sensitivity is a quadratic function of heater power. When the heater drive signal is12.50Hz,37.5%duty cycle square wave, and heater power is4mW, the scale factor (also known as sensitivity) is0.406mV/°/s, the nonlinearity of scale factor is less than0.3%, the repeatability of the scale factor is better than0.2%. The structure sensitivity of the micro thermal expansion fluidic gyroscope is about47μV/°/s. The bias stability is5.59°/s, and the angle random walk is0.3°/(?)s. The bandwidth of the gyroscope is about18Hz.Due to large linear acceleration effect of the micro thermal expansion fluidic gyroscope, the mechanism of linear acceleration effect is investigated. We propose to lower the frequency of the heater drive signal, so that the gas can work at both transient state and steady state. During transient state, the differential temperature detected by the two temperature sensors contain both rotation and acceleration informations. But during steady state, the differential temperature detected by the two temperature sensors contains only acceleration information. Therefore, by using digital signal process method, the differential temperature signal detected in the steady state can be used to compensate for the differential temperature signal detected in the transient state. The experimental results show that under the same heater drive signal condition, the linear acceleration effect is reduced from3.35rps/g to0.39rps/g by using this method. The linear acceleration effect is reduced by a factor of more than eight. The linear acceleration error signal has been greatly reduced. For the very first time, we achieve self-compensating the linear acceleration effect of the thermal gyroscope without the need of additional accelerometer.