A self-packaged thermal flow sensor by CMOS MEMS technology

An integrated two-dimensional self-packaged flow sensor made by CMOS technology plus micromachining is presented. Heater resistors formed by diffusion of boron into an n-type Si substrate are located on the center of the chip and four substrate bipolar transistors by CMOS for temperature sensing surround the heaters symmetrically. A trench made by ICP (inductively coupled plasma) technology between the heater and the temperature sensor provides thermal isolation. The back of the sensor chip is used as the sensing surface and the thermal interaction is achieved via the substrate of the sensor. Conventional IC packaging can therefore 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 error of velocity and direction are no more than 0.5 m/s and 6° respectively.