Multi-directional thermal actuator

Details Multi-directional thermal actuator Multi-directional thermal actuator

2001-04-27

2002-08-27

Nguyen, Hoang (Department: 3748)

Power plants

Motor operated by expansion and/or contraction of a unit of...

Mass is a solid

C310S306000, C310S307000, C310S309000

Reexamination Certificate

active

06438954

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to micro-mechanical devices, and more particularly, to a micrometer sized thermal actuator that is capable of repeatable and rapid movement horizontally across a substrate, vertically off the surface of the substrate, or a combination thereof.
BACKGROUND OF THE INVENTION
Fabricating complex micro-electro-mechanical systems (MEMS) and micro-optical-electro-mechanical systems (MOEMS) devices represents a significant advance in micro-mechanical device technology. Presently, micrometer-sized analogs of many macro-scale devices have been made, such as, for example, hinges, shutters, lenses, mirrors, switches, polarizing devices, and actuators. These devices can be fabricated, for example, using Multi-user MEMS processing (MUMPs) available from Cronos Integrated Microsystems located at Research Triangle Park, N.C. Applications of MEMS and MOEMS devices include, for example, data storage devices, laser scanners, printer heads, magnetic heads, micro-spectrometers, accelerometers, scanning-probe microscopes, near-field optical microscopes, optical scanners, optical modulators, micro-lenses, optical switches, and micro-robotics.
One method of forming a MEMS or MOEMS device involves patterning the device in appropriate locations on a substrate. As patterned, the device lies flat on top of the substrate. For example, the hinge plates of a hinge structure or a reflector device are both formed generally coplanar with the surface of the substrate using the MUMPs process. One challenge to making use of these devices is moving them out of the plane of the substrate.
Coupling actuators with micro-mechanical devices allows for moving these devices out of the plane of the substrate. Various types of actuators, including electrostatic, piezoelectric, thermal and magnetic have been used for this purpose.
One such actuator is described by Cowan et al. in “Vertical Thermal Actuator for Micro-Opto-Electro-Mechanical Systems,” v. 3226, SPIE, pp. 137-146 (1997). The actuator
20
of Cowan et al. illustrated in
FIG. 1
uses resistive heating to induce thermal expansion. The hot arm
22
is higher than the cantilever arm
24
, so that thermal expansion drives the actuator tip
26
toward the surface of the substrate
28
. At sufficiently high current, the downward deflection of the actuator tip
26
is stopped by contact with the substrate
28
and the hot arms
22
bow upward. Upon removal of the drive current, the hot arms
22
rapidly “freeze” in the bowed shape and shrink, pulling the actuator tip
26
upward, as illustrated in FIG.
2
.
The deformation of the hot arm
22
is permanent and the actuator tip
26
remains deflected upward without applied power, forming a backbent actuator
32
. Further application of the drive current causes the backbent actuator
32
to rotate in the direction
30
toward the surface of the substrate
28
. The backbent actuator
32
of
FIG. 2
is typically used for setup or one-time positioning applications. The actuators described in Cowan et al. are limited in that they cannot rotate or lift hinged plates substantially more than forty-five degrees out-of-plane in a single actuation step.
Harsh et al., “Flip Chip Assembly for Si-Based Rf MEMS” Technical Digest of the Twelfth IEEE International Conference on Micro Electro Mechanical Systems, IEEE Microwave Theory and Techniques Society 1999, pp. 273-278; Harsh et al., “The Realization and Design Considerations of a Flip-Chip Integrated MEMS Tunable Capacitor” 80 Sensors and Actuators, pp. 108-118 (2000); and Feng et al., “MEMS-Based Variable Capacitor for Millimeter-Wave Applications” Solid-State Sensor and Actuator Workshop, Hilton Head Island, S.C. 2000, pp. 255-258, disclose various vertical actuators based upon a flip-chip design. During the normal release etching step, the base oxide layer is partially dissolved and the remaining MEMS components are released. A ceramic substrate is then bonded to the exposed surface of the MEMS device and the base polysilicon layer is removed by completing the etch of the base oxide layer (i.e., a flip chip process). The resultant device, which is completely free of the polysilicon substrate, is a capacitor in which the top plate of the capacitor is controllably moved in a downward fashion toward an opposing plate on the ceramic substrate. The device is removed from the polysilicon substrate because stray capacitance effects of a polysilicon layer would at a minimum interfere with the operation of the device.
Lift angles substantially greater than forty-five degrees are achievable with a dual-stage actuator system. A dual-stage actuator system typically consists of a vertical actuator and a motor. The vertical actuator lifts the hinged micro-mechanical device off of the substrate to a maximum angle not substantially greater than forty-five degrees. The motor, which has a drive arm connected to a lift arm of the micro-mechanical device, completes the lift. One such dual-stage assembly system is disclosed by Reid et al. in “Automated Assembly of Flip-Up Micromirrors,” Transducers '97, Int'l Conf. Solid-State Sensors and Actuators, pp. 347-350 (1997). These dual stage actuators are typically used for setup or one-time positioning applications.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a micrometer sized, multi-directional thermal actuator capable of repeatable and rapid displacement in a substantially horizontal direction, a substantially vertical direction, or a combination thereof. In some embodiments, the thermal actuator can be displaced radially in substantially any direction relative to an unactivated position, where radial refers to a direction generally perpendicular to the longitudinal axes of the beam.
In one embodiment, the multi-directional thermal actuator constructed on a surface of a substrate includes first, second, and third beams cantilevered from an anchor at first ends to extend generally parallel to the surface of the substrate in an unactivated configuration. The first, second, and third beams are not coplanar. A member mechanically couples distal ends of the first, second, and third beams. A first circuit comprises at least the first beam, whereby application of current to the first circuit displaces the member in a first radial direction. A second circuit comprises at least the second beam, whereby application of current to the second circuit displaces the member in a second radial direction. A third circuit comprises at least the third beam, whereby application of current to the third circuit displaces the member in a third radial direction.
In one embodiment, a grounding tab electrically couples one or more of the beams to the substrate. A resistance can optionally be located between one or more of the beams and ground. In one embodiment, the first and second beams comprise a first circuit, the second and third beams comprise a second circuit, and the third and first beams comprise a third circuit. In another embodiment, the first beam and a grounding tab comprise a fourth circuit, the second beam and a grounding tab comprise a fifth circuit, and the third beam and a grounding tab comprise a sixth circuit. The same or different levels of current can be applied to one or more of the circuits simultaneously. The first, second, and third beams can be arranged in a symmetrical or an asymmetrical cross-sectional configuration.
Another embodiment includes a fourth beam cantilevered from an anchor at a first end to extend generally parallel to the surface of the substrate in an unactivated configuration. The fourth beam is mechanically coupled to the member.
In the four beam embodiment, the first and fourth beams comprise a seventh circuit, whereby application of current to the seventh circuit displaces the member in a seventh radial direction. The second and fourth beams comprise an eighth circuit, whereby application of current to the eighth circuit displaces the member in a eighth radial direction. The third and fourth beams comprise a ninth circuit, whereby appl

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