Research On Calorimetric And Anemometer Integrated Sensor

Micro electromechanical systems (MEMS) technology has matured to the point where practical industrial applications are possible. One particularly active research area is the development of micro sensor systems. This paper is focused on the design and implementation of micro thermal gas flow sensors.For micro thermal gas flow sensors used in conventional industrial measurement, the following attributes are necessary. Firstly, an effective measurement method must be chosen to obtain a large measurement range. Secondly, the structure of the sensor should provide good anti-pressure and anti-impact performance and good thermal isolation. Thirdly, a proper die package should be used to realize good protection while exposing the sensing elements to the gas medium properly. And finally, fabrication processes should be of low cost and high efficiency.Demonstrated below are an improved thermal flow measurement method, the design of a MEMS thermal gas flow sensor prototype and the design of a CMOS compatible thermal gas flow sensor.The improved thermal flow measurement method integrates both the calorimetric method and the anemometer method into a single sensor chip. The calorimetric method is selected for the measurement of a small flow range while the anemometer method is selected when the flow reaches a larger range. With this integration method the flow sensor features a large measurement range and a high sensitivity at zero flow.The MEMS flow sensor prototype consists of a metal sensing/heating array placed over a glass substrate and a polyimide layer for passivation. The sensor die is packaged onto a PCB using the Chip-on-Board technology. Both the anti-pressure and the anti-impact performance are enhanced by using a solid glass substrate instead of a common silicon suspending structure. This structure also has good thermal isolation. These merits widen the application range of micro flow sensors from millimeter- or sub-millimeter-tubes to conventional industrial tubes. It is shown experimentally that the measuring range of the prototype can fulfill the conventional industrial requirement when the sensor works in the improved thermal flow measurement method.