Micromachined silicone rubber membrane valves for fluidic applications

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The goal of this thesis is to develop high flow rate, low power consumption valves for micromachined fluid handling systems. It has been identified that large actuation deflection and force are the key. In this thesis, several technologies have been developed to achieve large deflection in micromechanical structures. First, a surface micromachined multi-layer structure, microbellows, has been successfully developed. With polysilicon as the sacrificial layer, the structure of the microbellows has been optimized to achieve large deflection and high strength. It has been shown that the microbellow can deliver more than three times the deflection of a flat membrane of the same size. Thermopneumatic actuators using the microbellows have been demonstrated. Second, silicone rubber has been explored as the valve membrane material. Several methods for fabricating silicone membranes and integrating them with micromachined components to make actuators and valves have been developed. The silicone has been characterized and has been found to have many desirable properties including high elongation, low modulus, and good sealing. A thermopneumatically actuated valve has been successfully demonstrated. Third, a normally open, low power thermopneumatic MEMS valve utilizing a composite silicone/Parylene membrane has been developed. A novel suspended silicon nitride membrane heater has been developed to reduce heat loss. By using a "soft" membrane with a large gap and thermopneumatic actuation, high flow rates are achievable while still keeping power consumption low. The steady state and transient response of the thermopneumatic action with various working liquids have been studied. Valves with various constructions have been tested extensively with nitrogen and water flow. As low as 35.5 mW of power is sufficient to control a nitrogen flow of 1.04 1pm with an inlet pressure of 32 psi. Also, to prevent particles from clogging the microfluidic system, membrane filters (8 x 8 mm[...]) with various shapes of filtering holes have been developed. By varying hole dimensions from 6 to 12 [...], opening factors from 4% to 45% are achieved. A composite silicon nitride/Parylene membrane technology is developed to enhance filter strength. Fluid dynamic performance of the filters has been studied extensively through experiments and numerical simulations