Microvalve

Details Microvalve Microvalve

2001-10-18

2003-07-15

Hirsch, Paul J. (Department: 3754)

Valves and valve actuation

Electrically actuated valve

C251S011000

Reexamination Certificate

active

06592098

ABSTRACT:

TECHNICAL FIELD
The present invention relates, generally, to microvalves, and in particular to an improved microvalve device configured to provide a more robust and durable operation to withstand the demands of various operating environments.
BACKGROUND OF THE INVENTION
Micro Electro Mechanical Systems (MEMS) are an emerging technology used to fabricate working mechanisms on a micro-miniature scale. Typically MEMS devices can be divided between two categories: sensors and actuators. MEMS sensor devices include, for example, the accelerometers used to deploy airbags, pressure sensors, and even chemical sensors. MEMS actuator devices can be configured for applications such as, for example, fluid flow control in microvalves or the control of optical signals utilizing micromirrors and other like devices.
MEMS valves comprise micro-fabricated devices typically having a size of a few &mgr;m to a mm and which are configured to admit, restrict or block the flow of fluid, including air, gas and liquid. Typically, existing microvalve devices suffer from various problems, including a lack of robustness and durability, or quite often from insufficient fluid flow properties, such as flow rate, operating pressure, and limitations on the types of fluid that can be used (e.g., most microvalves only admit air). More recently developed microvalves, including gate valve designs and diaphragm designs, have attempted to address the above problems.
Microvalves using a diaphragm design actuated by the pressure differential across both sides of the diaphragm, for example, valve
100
illustrated in
FIG. 1
, generally comprise a cover plate
101
, a valve plate
102
having a diaphragm
103
, a control gate
104
with a closure plate, and a lower substrate
106
. Diaphragm valve
100
uses a pressure differential across both sides of diaphragm
103
to produce the movement of diaphragm
103
in order to block or free the fluid passage way. The pressure differential is regulated by control gate
104
by activation of the closure plates to regulate the pressure differential through controlling the pressure within a pressure control chamber
108
.
While providing more durability and potentially less power consumption, such pressure balance microvalves usually offer a nonlinear response, provide a poor flow rate performance, require additional wafer bondings, and are more costly to manufacture. For example, because of the structure of diaphragm
103
, a large differential pressure is generally necessary to actuate pressure balanced valve
100
. In addition, due to the structure of diaphragm
103
and the flow passageway, the available flow rate is limited. For example, due to a steeply inclined boss component on diaphragm
103
, fluid flow through the passageway from the inlet orifices to the outlet orifices produces nonlinear flow characteristics, as well as cavitation. Such a steeply inclined boss component is mainly due to current bulk-micromachining techniques currently available, which limit the slope of the boss component to 54.7° angle of inclination. Moreover, in that pressure control chamber
108
is regulated by the small control gate
104
, typically comprising a gate or bimorph-type valve, leaks within control gate
104
often occur, i.e., control gate
104
may not always maintain the pressure (P+&Dgr;P) necessary for regulation and control of diaphragm
103
. Further, in that the mechanisms for actuation for microvalve
100
are configured proximate to, or a part of, the components of microvalve
100
, such as control gate
104
, such a microvalve configuration unfortunately exposes the mechanisms for actuation to any fluids used within the flow passageway, such as to intermix electrical signals with conductive fluids. Still further, in that such pressure balanced microvalves generally require wafer bondings, the manufacture costs are generally high.
Other newly developed microvalves employ a gate valve design which comprise moving gates on the surface of a silicon substrate with orifices. For example, with reference to
FIGS. 2A and 2B
, a gate valve
200
has a gate
202
comprising a nickel flap that is actuated to move horizontally on the surface of a silicon substrate
203
which contains through orifices
204
in order to regulate flows directly. Gate
202
can include a shutter configuration
202
A, or other configurations of openings, which permit regulation of air flow. In addition, gate valve
200
generally provides a greatly increased flow rate, has a faster response, and is more cost effective to fabricate than the pressure balance microvalves.
However, gate valves also have various deficiencies. For example, due to a typical polysilicon thermal actuator design, to actuate gate
202
to open or close valve
200
, a large voltage is necessary, often comprising 30 volts or more. In addition, because of the microelectronic fabrication process of such microvalves, gate valves typically realize leak flow, even despite the application of electrostatic clamping devices. For example, on many occasions, the leak flow can be as high as 10-20% of the overall flow rate, and even worse on other occasions. Further, the appearance of leaks increases as the pressure of the fluid increases. Probably most problematic, due to their unidirectional flow characteristics, these gate valve designs are limited in their capability to withstand back pressures produced during their operation while interfacing with other output devices. For example, any back pressure, for example as little as 10 psi, that may be present in such a device will tend to bend the metal flap and thus fatally and permanently damage it. These back pressure problems result in leaks in the gate valve, even despite the application of electrostatic clamping devices. Still further, gate valves cannot effectively operate with a conductive fluid, e.g., water and the like, because the electronic-based actuation circuit is exposed to the conductive fluid.
Therefore, as one skilled in the art will appreciate, there exists a need for an improved MEMS microvalve device that is more robust and durable to withstand the demands of various operating environments while providing uni-directional and bi-directional fluid flow capabilities, and yet is still cost effective to manufacture.
SUMMARY OF THE INVENTION
A microvalve according to the present invention addresses many of the shortcomings of the prior art. In accordance with various aspects of the present invention, an improved microvalve device is configured to provide a more robust and durable operation to withstand the demands of various operating environments. In accordance with an exemplary embodiment of the present invention, a microvalve may comprise a valve seat and a diaphragm, with the diaphragm operated by an external actuator device through various mechanisms of actuation that are separate from the microvalve. Through use of the various mechanisms of actuation, the actuator device is configured to apply forces on the diaphragm to suitably move the diaphragm to open and close the microvalve. For example, an actuation mechanism may apply force actuated through use of an external actuator device, such as a bladder device, to move the diaphragm as intended.
In accordance with another exemplary embodiment of the present invention, the valve seat and diaphragm can be configured to provide the microvalve with a plurality of openings configured to permit flow thereinbetween. In addition, the microvalve may be configured to facilitate uni-directional or bi-directional flow. Further, in accordance with other exemplary embodiments, a plurality of microvalves can be cascaded together in a parallel and/or series configuration, with each valve having similar or different flow characteristics, and being selectively operated.
In accordance with another aspect of the present invention, the external actuator device can be suitably actuated by various means, including by direct mechanisms such as electrostatic, electromagnetic, piezoelectric, and/or by indirect mechanisms, such as thermal actuati

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