Electrothermally actuated polymer microvalves.

Abstract

A new family of thermally activated microactuators that provide both large displacements and forces based on a thin polymer actuating layer are presented. The actuators use the high volumetric expansion of a sealed, surface micromachined patch of paraffin heated near its melting point to deform a sealing diaphragm. The paraffin microactuators have been used as the active elements for microfluidic valves. The paraffin actuated microvalves presented in this work offer good performance for valuing gases and liquids in microchannels with low actuation powers. In addition, many valves can be fabricated on a single die making possible integrated microfluidic systems. The paraffin actuated microvalves are suitable for applications requiring many devices on a single die, low processing temperatures, and simple, non-bonded process technology. Two types of actuators have been fabricated using a simple two mask fabrication process. Two types of microfluidic valves have been fabricated and tested which use a paraffin microactuator as the active element. The normally-open blocking microvalve structure has been used to fabricate a precision flow control system of microvalves consisting of four normally-open, paraffin actuated, blocking valve structures. The control valve is designed to operate over a 0.01--5.0 sccm flow range at a differential pressure of 800 Torr. Flow rates ranging from 0.02 to 4.996 sccm have been measured. Leak rates as low as 5.4 x 10<super>-4</super> sccm have been measured for single valves. System leak rates as low as 3.2 x 10<super> -3</super> sccm have been measured. Finally, a second normally-open, paraffin actuated microvalve structure which uses a piston element is fabricated inside a capillary. The piston element encloses a sealed paraffin actuation layer which can deflect thus stopping flow inside the microchannel. This simple device requires low actuation power, can be batch fabricated and is easily integrated with other fluidic or microelectronic systems. In addition, many valves can be fabricated on a single die permitting the implementation of complex integrated microfluidic systems on the same substrate. Preliminary test results show that the normally-open inline valve stops liquid flow with about 25 mW input electrical power. (Abstract shortened by UMI.)