The Design Of MEMS Thermal Wind Sensor With High Performance

The measurement of the wind is not only becoming indispensable in aerospace and scientific research,but also playing an important role in people's life,industrial and agricultural production.At present,the wind cup and the wind vane are the most widely used in the wind speed and direction measurement.Nevertheless,these anemometers have many disadvantages,such as their large volume,easy to wear rotating parts,large starting wind speed and so on.Hence the MEMS thermal wind is coming into being at the right moment.Based on lots of previous studies,a more detailed scheme is proposed to improve the performance of the sensor,and also verifies this structure program through the ANSYS simulation and the experimental tests.The main purpose of this scheme is to solve the problem of the existing sensors' high power consumption,and make the sensor become more perfect in its sensitivity and consistency.Firstly,in order to reduce the transverse heat transfer between the elements,the silicon micro mechanical technology is used to etch trenches with the deep reaction ion etching(DRIE)between the heating and temperature resistances.The structure of the sensor is optimized by simulating the performance in the wind fields with ANSYS-CFX.Then it completes the layout design,the tape-out,the packaging and the measurements in the wind tunnel and make the performance of this sensor be verified.The results show that the speed of wind ranges from Om/s to 33m/s when proved the initial heating power of 256mW under the constant pressure(CV)mode.Also,the sensitivity measured at a wind speed of 3.3m/s is 16.37 mV/(m/s),and improved by about 82%compared to conventional wind sensors.Secondly,the sensitivity and precision of the sensor are improved while the power consumption of the chip is reduced by using the combination of the two Wheatstone full-bridges consisting of eight thermistors with the thermal isolation trough.The results show that the maximum of the wind speed is more than 33m/s when proved the same initial heating power.It is worth noting that the sensitivity measured at a wind speed of 3.3 m/s is 29.37mV/(m/s),and improved sensitivity reaches by about 226%compared to conventional wind sensors.At last,on the basis of etching the insulation trench,a method of sintering ceramic on one side of the silicon wafer using a low temperature co-fired ceramic(LTCC)process to form a ceramic-silicon substrate and making heating and temperature components on the other side is proposed.This method combines the process consistency when silicon acts as a substrate with the low power consumption and self-encapsulation when ceramic acts as a substrate to achieve a two-dimensional wind sensor with a low temperature co-fired ceramic-silicon substrate.Now,the project of the sensor structure has been demonstrated by ANSYS-CFX simulation and its performances are verified initially.In this paper,the thermal insulation trough structure of the sensor is improved by comparing the simulation results with the actual measurement results.The reliable simulation data provide the theoretical basis for the realization of the thermal anemometer with the low temperature co-fired ceramic-silicon substrate.