CMOS Integrated Thermal Wind Sensor And Circuit Design

As the improvement of the CMOS MEMS process, people are putting more efforts on the sensors on chip, which have the virtue of small volume, low power, and high sensitivity, cheap, portable. So the study of the flow sensor based on silicon is becoming more popular. The standard CMOS process makes it possible that sensors and their processing circuits can be fabricated on the chip. It is possible to realize the so-called SOC (System On a Chip).In this paper a kind of two-dimensional silicon flow sensor based CMOS process is given, which can measure flow velocity and direction simultaneously. The whole structure is symmetry. The heater resistors made of poly-silicon. Thermopiles made of two pairs Aluminum/poly-silicon. And it can convert the temperature difference to electric signal without extra electric energy. The voltage on the heater responds to flow. The direction can be gained by the output of the two orthogonal pairs of thermopiles.The work principle of the flow sensor is introduced firstly, the constant power and the constant thermal control methods were simulated by ANSYS separately, and detailed analysis is given in the results. The influence of the geometry of the flow sensor on the performance of the sensor was simulated and the optimized geometry was given. Also the shortcoming of the test method of flow direction is pointed out.The process circuit on chip includes a controlling circuit and operational amplifier. This paper introduced the principles of the voltage of band-gap-referenced. The circuit of band-gap-referenced was simulated by H-spice and the optimized results were gained.The flow sensor has been implemented by standard CMOS process. Finally the silicon flow sensor was measured. The results agree with the design well. And the sensor has good performance.