Flow Measurement And Flow Control Devices Based On MEMS Technology

MEMS technology is currently front focuses in science research. Advantages of the flow measurement and flow control based on MEMS technology become more and more valued. This thesis presents two micromachined transducers. A micromachined thermal shear stress sensor is fabricated based on vacuum anodic bonding and bulk micromachined technology which can be used for the flow measurement. A micromachined actuator is fabricated based on electrostatic principle which can be used for the flow control.The main achievements in this thesis are as follows:1) Vacuum anodic bonding technology is applied to fabricate the adiabatic vacuum chamber. A Ti/Pt alloy strip, 2μm×l00μm, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using vacuum anodic bonding and bulk-si anisotropic wet etching process instead of the sacrificial-layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200μm×200μm×400μm, is placed between the silicon nitride diaphragm and glass(corning 7740).This method totally avoid adhesion problem which is a major issue of the sacrificial-layer technique. It makes the process very easy, not only avoid adhesion problem, but also do not influence the vacuum chamber's adiabatic effect.2) The performance of the thermal isolation for our shear-stress sensors is evaluated. Thermal isolation of three different structures ( Ti/Pt resistor located over a vacuum cavity; Ti/Pt resistor located over an air-filled cavity ;Ti/Pt resistor located directly over on top of the substrate)is compared. It is found that a vacuum cavity improves the thermal isolation about 1.17 times over an air-filled cavity, and about 40 times over just the silicon substrate.3) CC (constant current) model circuit for sensor testing is designed and PCB is fabricated. The mathematical relationship between the circuit output voltage and the velocity of the wind-tunnel is obtained. The time-constant is about 500 microseconds; the frequency response is about 2KHZ,the sensitivity is 9.877mv/(m/s).This is the first one in China in measuring the distribution of shear stress with high spatial and temporal resolution area.4) Design and fabricate a micromachined synthetic jet actuator. Attempts to reduce drag by mitigating the strength of vortices in turbulent flow. The micromachined synthetic jet actuator moves up and down under the strength of the electrostatic. The drag reduction can be achieved when these actuators suppress the interaction between stream-wise vortices and the wall significant.