Research On CMOS Intgrated Two-Dimensional Themal Wind Sensor

Flow sensor is very important in many fields, such as agriculture, industry, and the every life of people. As the improvement of the IC process, people are putting more and more efforts on the silicon flow sensors, which have the virtues of small volume, low power, and high sensitivity. So the study of the silicon flow sensor is becomming more popular. The standard CMOS process makes it possible to realize an intelligent sensor of high performance, which is integrated with circuits. Nowadays the scientists of many countries are working on this field.In this paper a kind of two-dimensional silicon flow sensor based on CMOS process is given, which can measure flow velocity and direction simultaneously. In the structure heater resistors made of polysilicon are on the center of the chip and two orthogonal pairs of integrated thermopiles made of the polysilicon and aluminium are around the heaters. The whole structure is symmetry. The sensor is controled in the constant temperature difference (CTD) mode. The voltage on the heater is adjusted to keep the constant temperature difference between the sensor and the flow. The direction can be gained by the output of the two orthogonal pairs of thermopiles.In this paper the work principles of the flow sensor are also given. The one-dimension and two-dimension structure were simulated by ANSYS separately. The influence of the geometry of the flow sensor on the performance of the sensor was simulated and the optimized results were given. Here the flow range of speed and the sensitivity of the sensor were considered. And the shortcoming of the test method of flow direction is given and another method as GAUSS function is given to measure the flow direction more correctly.The flow sensor has been implemented by standard CMOS process. After the chip was made, the etching of silicon substrate was made at microelectronics center of Southeast University. After etched, the whole structure of the flow sensor is based on the dielectric membrane, which has the high sensitivity, low power and fast response.The flip-chip has been adopted for the package of the flow sensor. The package of Flip-chip makes the sensor contact with the flow while protected against mechanical contact. Meanwhile the package provides a flat plan to for the sensor to contact with the flow. The principle of the packaged sensor was also simulated and some important results have been gained.Finally the silicon flow sensor was measured. Controled in the CTD mode, the maximal velocity measured can reach 25m/s. The minimum sensitivity is about 35mV/(m/s). The direction was also measured, and the maximum error of the direction is no more than 5°.The results of test agree with the target of the design well. Some problems still exist, so more study is necessary for the flow sensor. At the end of the paper a self-packaged thermal flow sensor by CMOS MEMS technology is given.The backside of the sensor chip is used as sensing surface and the thermal interaction is achieved via the rear side of the substrate of the sensor. So conventional IC packaging can be adopted for the sensor. This package way opens new perspectives for the packaging of integrated flow sensors.