A Microvalve With Integrated Sensors and Customizable Normal State for Low-Temperature Operation

This paper reports on design, fabrication, and testing of a piezoelectrically actuated microvalve with integrated sensors for flow modulation at low temperatures. One envisioned application is to control the flow of a cryogen for distributed cooling with a high degree of temperature stability and a small thermal gradient. The valve consists of a micromachined die fabricated from a silicon-on-insulator wafer, a glass wafer, a commercially available piezoelectric stack actuator, and Macor ceramic encapsulation that has overall dimensions of 1.5 x 1.5 x 1.1 cm(3). A piezoresistive pressure sensor and a thin-film Pt resistance temperature detector are integrated on the silicon die. The assembly process allows the implementation of normally open, partially open, and normally closed valves. At room temperature, gas flow modulation from 200 to 0 mL/min is achieved from 0-to 40-V actuation. Flow modulation at various temperatures from room temperature to 205 K is also reported. The pressure sensor has sensitivity of 356 ppm/kPa at room temperature, with temperature coefficient of sensitivity of -6507 ppm/K. The temperature sensor has sensitivity of 0.29%/K. The valve and the sensors are tested across a wide range of temperatures, and the effect of temperature on performance is discussed.