Research On The Front-Sided Silicon Bulk Micromachined Micro Flow-Sensor Based On Differential Pressure Sensing Principle

The quantity of flow has always been a very important parameter for both industrial production and scientific research. Flow measurement has great significance for the control of fluid system. With the progress of micromachining technology, development of micro flow-sensors has gained a lot of attention due to their mini sizes, low power consumptions and abilities to measure extremely small flow rate (μL/min).Working principles of micro flow-sensor have almost contained all domains of physics. Generally speaking, there are two classifications: thermal principles and non-thermal principles. For micro flow-sensors based on thermal prinples, heating itself will be a big problem, especially in biological and chemical fields, because many reagents are heat sensitive, which imposes restriction on their applications. For those based on non-thermal principles, micro flow-sensors based on differential sensing principle is the most prevalent. They are characterized by easy fabrication, simple signal processing and good linearity, thus adopted by our project.Tradtional micro flow-sensors based on differential sensing principle fabricated by bluk silicon technology are all double-layer structures. Trenchs and cavities are processed on one of the layers and form the complete structure by bonding with another wafer. However, wafer bonding is very complex and costly. What's more, it is easy for bonding process to cause deviation and departure to reduce the yeild. Surface micromachining technology is able to fabricate single wafer structure. But constrained by the thickness of the deposited films, structures are several microns high at the most. Thus they are more suitable to test air rather than fluid.This paper presents a fully front-sided silicon bulk micromahined micro flow-sensor based on differential sensing principle, of which all the machining processes are conducted on the front side. The sensors are packaged with surface mounting techonoly, which has a low cost and good compatibility with signal processing circuit or other testing systmes and thus, a promising future. Working principle, processing method and structures design are introduced in details as well as the processing flow and results of the porformance test. In the end of this paper, the writer analyzes the achievements and shortages of this project and the outlook of micro flow-sensors based on differential sensing principle.