Motion amplification based sensors

Details Motion amplification based sensors Motion amplification based sensors

1999-07-08

2001-02-06

Sikder, Mohammad Y. (Department: 2872)

Optical: systems and elements

Mirror

With support

C359S872000, C359S874000, C359S223100, C359S225100, C359S226200, C359S291000

Reexamination Certificate

active

06183097

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates in general to micromechanical motion amplifiers and more particularly, to integrated micromechanical structures wherein a small amount of driving force or motion translates through the device to produce a relatively large motion in a direction transverse to the driving motion. In such devices, relatively thin, elongate beams are designed to buckle in response to an applied axial compressive force induced by axial motion. The motion produced by the deformation or buckling is an order of magnitude greater than the applied axial motion which causes it. Thus, micromotion amplifiers may be provided.
Such prior art devices exhibit a limited amount of output and are thereby constrained with respect to a maximum amount of sensitivity with which they may operate. It follows that such devices are necessarily greatly limited in their application as sensors. Accordingly, there has been a long felt need for integrated micromotion amplification apparatus in which the amount of output deflection and hence sensitivity, is not limited or constrained by a single beam. In accordance with the present invention, the need for increased sensitivity in a micromotion device, is fulfilled by a micromotion amplifier wherein the ultimate output deflection or buckling, and hence overall sensitivity, is predetermined by the additive effect of assembling buckling beams in cooperating pairs or stages.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a buckling beam micromotion amplifier in which the ultimate output deflection, and hence sensitivity, is not constrained by the deflection of a single beam.
It is also an object of the present invention to provide a micromotion amplifier in which the sensitivity to an applied axial force is greatly increased over that of the prior art.
It is also an object of the present invention to provide micromotion amplifier stages, in the form of cooperating pairs of buckling beams, which may be cascaded.
It is also an object of the present invention to provide a method and apparatus by which minute amounts of movement may produce greatly increased motion within an integrated device, in orders of magnitude heretofore previously unattained, to form the basis of highly sensitive motion amplification sensors, switches and the like. Other features and advantages will be made apparent from the following description.
In accordance with the present invention, a method and apparatus are provided for amplifying micromechanical or microelectromechanical motion in orders of magnitude unattainable by prior micron-scale mechanical devices. Integrated buckling beams are released from a single crystal silicon substrate in cooperating pairs or stages. Each buckling beam is formed having an asymmetrical cross-section (high aspect ratio), i.e., the height of each beam is much greater than its' width. This asymmetry will effectively bias or predispose each beam to bend or buckle in a predetermined direction when an applied axial force exceeds a critical value. The initial input axial force applied to a first beam can be provided by any desired source. Axial forces acting upon any subsequent beam in a pair or series of beam pairs are provided by the previous beam buckling in response to a lesser axial force. In other words, the beams are arranged in such a manner as to induce a chain reaction of buckling in one or more subsequent beams in response to an input axial force applied to the first beam. Since the amount of transverse deformation of any one beam is greater than the amount of axial motion necessary to cause it, the net deformation or buckling from a final beam in a cascade array of beam pairs or stages is significantly greater in magnitude than the initial input movement applied. Amplification of micromotion may thereby be provided as a function of a number of micromotion amplifier stages and these stages may be cascaded as desired.
In a preferred form of the present invention, a first micromechanical beam has a free first end and a second end fixed to a reference point on the substrate. A second micromechanical beam has a first end connected to a middle or buckling region of the first beam and a second end fixed to another reference point on the substrate. The first and second beams are arranged to be substantially coplanar and perpendicular to each other. The first end of the first beam may be acted upon by an actuator to induce an input axial force or movement upon the first beam and thereby produce an output buckling of the first beam. The output buckling of the first beam provides an input axial force or movement upon the second beam, thereby producing an output buckling of the second beam. Accordingly, the first and second beams arranged to function in this manner comprise a micromotion amplifier stage and any number of such stages may be cascaded.
Suitable actuators for inducing an input axial force may comprise devices having physical properties which are responsive to temperature, pressure, humidity, impact, acceleration or other parameters. Suitable actuators may also comprise active devices such as capacitive comb-drive actuators. Preferably, one or more integrated tunneling tips are provided for detecting, measuring and indicating an amount of buckling produced by any or all beams in a stage or cascade array. In addition, integrated capacitive or resistive sensors or other non-integrated external devices such as atomic force microscopes may be used for detecting the motion of the beams. The preferred form may further include adjunct beams provided at one or more beam ends in one or more stages, for the purpose of prestressing a beam and thereby reducing the amount of axial force necessary to induce buckling. Sensitivity of the device in any one or more stages is thereby greatly enhanced.
An alternate embodiment of the present invention provides micromotion amplifier stages each comprising a first beam having first and second ends fixed to reference points on the substrate; a second beam having a first end connected to the first beam with a second end fixed to another reference point on the substrate; and an actuator. The exact point along the first beam where the first end of the second beam is connected, is chosen so as to influence the direction in which the second beam will buckle. The actuator is provided at this point of connection, acting transverse to the first beam and coaxial to the second beam, so as to induce a buckling force in the second beam in the predetermined direction. In this embodiment, the beams may be made electrically conductive. Two of such stages, electrically isolated, may be disposed in parallel opposing relationship such that one or both of the second beams of each stage will buckle into or out of contact with one another, in response to energization of one or both of the actuators. Beam stages arranged according to this alternate embodiment may thereby function as a micromechanical switch. Such switches may be made highly sensitive by prestressing the first beam in each stage. Sensitivity may be enhanced even further by the addition of one or more micromotion amplifier stages of the preferred embodiment for amplifying buckling forces transmitted by one or more of the actuators.


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