基于非晶锗热电阻的柔性MEMS流速传感器的设计与仿真

Design and Simulation of Flexible MEMS Flow Sensor Based on Amorphous Germanium Thermistors

针对铂等常用金属热敏材料电阻温度系数(TCR)不高,导致热式MEMS流速传感器宽量程测量时功耗高的问题,设计了一种基于非晶锗(a-Ge)薄膜热电阻的低功耗、宽量程柔性MEMS流速传感器。非晶锗热电阻材料具有较高的TCR系数(约为-0.02/K)和室温电阻率(5Ω·m),传感器在较低的工作温差和功耗下可获得宽量程的流速测量。阐述了该柔性MEMS流速传感器的设计结构、工作原理、3D有限元建模和热-流场仿真结果。利用聚酰亚胺衬底空腔膜上的四个非晶锗热电阻同时作为自加热热源和测温元件。四个非晶锗热电阻组成一个惠斯通电桥,同时结合热损失和热温差原理来实现宽量程流速测量和测向。仿真结果表明,惠斯通电桥采用恒电流供电只需120μA,使得非晶锗热阻的工作温度与环境温度之间的温差不高于6K,就可对0~50m/s范围内的流速进行测量,且功耗在1.368mW以内。该柔性流速传感器易于采用MEMS技术批量制造,可贴于曲面应用,非常适于物联网等低功耗流速传感领域。

In order to solve the problem of high power consumption in wide range measurement of flow velocity caused by low temperature coefficient of resistance(TCR)of commonly used metal thermistors materials such as platinum,a flexible MEMS thermal flow sensor with low power consumption and wide range based on amorphous germanium(a-Ge)film thermistors was designed.The a-Ge thermistor material has high TCR coefficient(about-0.02/K)and room temperature resistivity(5Ω·m),which makes the sensor can achieve a wide range of flow velocity measurement under low working temperature difference and power consumption.The design structure,working principle,3 Dfinite element modeling and thermalflow field simulation results of the flexible MEMS flow sensor are described.It uses four a-Ge thermistors in the cavity film of flexible polyimide substrate as self-heating heat source and temperature measuring element at the same time.These four a-Ge thermistors form a Wheatstone bridge,which combines the principles of heat loss and thermal temperature difference to achieve a wide range of flow velocity measurement and direction finding.The simulation shows that the constant current power supply of Wheatstone bridge only needs 120μA,so that the temperature difference between the working temperature of a-Ge thermistors and the ambient temperature is no more than 6 K,the flow velocity in the range of 0~50 m/s can be measured,and the power consumption is within 1.368 mW.This flexible flow sensor is easy to be fabricated in batches by using MEMS technology and can be applied to curved surfaces,which is very suitable for low-power flow sensing fields such as the Internet of Things.