Bistable microactuator with coupled membranes

Details Bistable microactuator with coupled membranes Bistable microactuator with coupled membranes

1998-10-13

2001-01-02

Walberg, Teresa (Department: 3742)

Pumps

Motor driven

Electric or magnetic motor

C251S129010

Utility Patent

active

06168395

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a bistable electrostatic actuator with pneumatic or liquid coupling.
2. Prior Art
From power and safety considerations mechanically bistable acuators are of considerable importance. However, only a few bistable microactuators fabricated in silicon technology have been reported
1,2,3
. Due to the low power consumption electrostatic drives are often preferred to electromagnetic and thermomechanic actuators. A drawback of electrostatics is its low range. High voltages are needed to achieve large deflections. Different concepts have been reported to produce non-planar driving electrodes
4,5,6,7
. These technologies are however rather specific and not for general-purpose use. Further prior art is sensitive, since electrodes are free to the environment, e.g. particles. This can be improved, when enclosed electrodes, separated from the gaseous or liquid medium are formed
4
.
1 B. H{umlaut over (a)}lg, On a micro-electro-mechanical nonvolatile memory cell, IEEE Trans. Electron. Dev. 37 (1990) 2230-2236
2 H. Matoba, T. Ishikawa, C.-J. Kim, R. S. Muller, A bistable snapping microactuator, Proc. MEMS 94, Oiso, 45-50
3 M. A. Huff, A. D. Nikolich, M. A. Schmidt, A threshold pressure switch utilizing plastic deformation of silicon, Proc. Transducers 91, San Francisco, 177-180
4 J. Branebjerg, P. Gravesen, A new electrostatic actuator providing improved stroke length and force, Proc. MEMS 92, 6-11
5 A. Bertz, T. Werner, The formation of very flat silicon sidewalls by dry etching, J. Micromech. Microeng. 4 (1994) 23-27
6 M. Shikida, K. Sato, T. Harada, Fabrication of an electrostatic microactuator with an S-shaped film, Proc. Transducers 95 & Eurosensors IX, Stockholm, 426-429
7 P. Rangsten, L. Smith, L. Rosengren, B. Hök, Electro-statically excited diaphragm driven as loudspeaker, Proc. Transducers 95 & Eurosensors IX, Stockholm, 430-433
4 see footnote 4.
SUMMARY OF THE INVENTION
One of the underlying problems addressed by the invention is the reduction of deflection voltage to make the actuator suitable for a general purpose use.
According to the invention two buckled membranes span over connected cavities with enclosed driving electrodes. The membranes operate in counteraction, if one membrane section is pulled down electrostatically, the other membrane section is pushed up and vice versa.
The coupling may be air (pneumatic) or liquid,
The actuator module is designed to achieve a deflection of ±10 &mgr;m and can be integrated in a microvalve for controlling the flow of fluids. With completed actuator modules the electrostatic driving principle is used in examples for a valve application, e.g. an on/off valve or a multi-way-valve, a switch application, e.g. an on/off-switch or a changeover switch, a micropump application. Grey-tone lithography may be applied to fabricate the curved driving electrodes on the curved cavity bottom Compared to flat electrodes the driving voltage can thus be reduced up to a factor of five. The curved cavity bottom (“dimple”) also improves the pneumatic or liquid coupling since the enclosed air or liquid volume is minimized.
The design and technology of the bistable electrostatic actuator with enclosed electrodes for a microvalve application uses curved shape of the electrodes by employing grey-tone lithography, a method to produce arbitrary relief-type surfaces. To produce a membrane deflection away from the substrate a pneumatic coupling of two cavities is incorporated slightly related to the suggestion
8
of MEMS 92, Travem{umlaut over (u)}nde.
8 K. J. Gabriel, O. Tabata, K. Shimaoka, S. Sugiyama, H. Fujita, Surface-normal electrostatic/pneumatic actuator, Proc. MEMS 92, Travem{umlaut over (u)}nde, 128-132
The two buckling sections of the membrane are oppositely stable (claim
15
) and close to each other in the same wafer.


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