A low power, tight seal, polyimide electrostatic microvalve Page: 4 of 10
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A Low Power, Tight Seal, Polyimide Electrostatic Microvalve
Abraham P. Lee, Julie Hamilton, Jimmy Trevino
Lawrence Livermore National Laboratory
7000 East Ave., L-222, Livermore, CA 94550
An electrostatically-actuated polyimide microvalve is developed with sub-micron gaps
between the electrodes to provide high force with low power consumption (<1mW). Built-
in residual stress results in a curled bimorph cantilever which allows for a microactuator
with large displacement. This microactuator is used to open and close a fluid path hole
etched in silicon for a microvalve. The microactuator can be actuated with 25V for a dis-
placement of 200 gm. The cantilever actuator is mainly composed of polyimide, which is
flexible enough to conform over the flow hole, thereby eliminating the need for the design
of a valve seat.
Microvalves provide one of the most important links to a micro total analysis system by
micro electromechanical systems (MEMS) . Applications include fluid injection analy-
sis , chemical processing/analysis stations, drug delivery, atmospheric and temper-
ature control apparatus[5-6], and possibly many more. Among the commercially available
microvalves, each has its strengths and weaknesses and to date no one microvalve can be
applied to all situations. One of the design concerns is the wear to the valve or valve seat
since high pressure is applied to assure tight seals. Many designs of microvalves require a
protruding valve seat for high pressure tight seal [8,9]. Futhermore, since semiconductor
materials such as silicon, silicon dioxide, or silicon nitride are the choice of materials, even
higher pressure is required to minimize leakage. Power consumption of thermally actuated
microvalves typically require higher than 200 mW and high operation temperatures limits
its use in many biomedical applications. In this paper, a polyimide, electrostatically-actu-
ated microvalve is presented which is low power, low temperature, and does not require a
valve seat design since polyimide is flexible enough to easily conform over the much hard-
er silicon substrate on which the flow hole is generated. Polyimide can be spun on sub-
strates to thicknesses less than 0.1 m and the insulation is excellent with large dielectric
constants. This provides the design freedom for small gap, high power density electrostatic
actuators. The one set back of using polyimide is that the hysteresis will be much larger re-
sulting in slower response times than stiffer material valves.
Principle of Operation and Design of Microvalve
The actuation principle is the same as previous electrostatic actuators [5,10-12]. Figure
1 illustrates the actuation principle of the microvalve with the cross-section of the device.
Figure la is the cantilever that is curled upwards by residual stress intentionally built-in us-
ing two polyimide bimorph layers with different coefficients of thermal expansion. As volt-
age is applied bewteen the ground plane and the electrode sandwiched in the polyimide
IMECE 1996 paper
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Lee, A.P.; Hamilton, J. & Trevino, J. A low power, tight seal, polyimide electrostatic microvalve, article, April 17, 1996; California. (https://digital.library.unt.edu/ark:/67531/metadc686540/m1/4/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.