A self-packaged thermal flow sensor by CMOS MEMS technology

An integrated two-dimensional self-packaged flow sensor using CMOS MEMS technology is presented. Heater resistors formed by diffusion of boron into an n-type Si substrate are located in the center of the chip, and four poly/Al thermopiles for temperature sensing surround the heaters symmetrically. A trench by ICP technology between the heater and the temperature sensor was made for thermal isolation. The backside of the sensor chip is used as the sensing surface and the thermal interaction is achieved via the substrate of the sensor. Thus, conventional IC packaging can be adopted for the sensor. The influence of the depth of the trench on the performance of the sensor was simulated by ANSYS. An appropriate trench depth was obtained. The sensor has been fabricated and tested. It can detect flow speed with enough sensitivity and flow direction in the full range of 360°. The maximum errors of velocity and direction are no more than 0.5 m/s and 6°, respectively.