Direct acting vertical thermal actuator

Details Direct acting vertical thermal actuator Direct acting vertical thermal actuator

2000-09-12

2004-03-23

Nguyen, Hoang (Department: 3748)

Power plants

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

Mass is a solid

C060S528000

Reexamination Certificate

active

06708491

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to micro-mechanical devices, and more particularly, to a micrometer sized, single-stage, vertical thermal actuator capable of repeatable and rapid movement of a micrometer-sized device off the surface of a substrate.
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. 137-46 (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, at 273-278; Harsh et al., “The Realization and Design Considerations of a Flip-Chip Integrated MEMS Tunable Capacitor” 80 Sensors and Actuators 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, at 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. 347-50 (1997). These dual stage actuators are typically used for setup or one-time positioning applications.
The dual-stage actuator systems are complex, decreasing reliability and increasing the cost of chips containing MEMS and MOEMS devices. As such, there is a need for a micrometer sized vertical thermal actuator that is capable of repeatable and rapid movement of a micrometer-sized device off the surface of the substrate.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a micrometer sized vertical thermal actuator capable of repeatable and rapid movement of a micrometer-sized optical device off the surface of the substrate.
The vertical thermal actuator is constructed on a surface of a substrate. At least one hot arm has a first end anchored to the surface and a free end located above the surface. A cold arm has a first end anchored to the surface and a free end. The cold arm is located above the hot arm relative to the surface. A member mechanically and electrically couples the free ends of the hot and cold arms such that the member moves away from the substrate when current is applied to the at least one hot arm.
In one embodiment, the hot arm and the cold arm comprise a circuit through which electric current is passed. In another embodiment, a grounding tab electrically couples the hot arm to the substrate. In the embodiment with the grounding tab, the cold arm can optionally be electrically isolated from the hot arm.
One or more of the free ends optionally include a dimple supporting the member above the surface of the substrate. The cold arm can be located directly over the hot arm. The first end of the hot arm can be attached to the substrate adjacent to the first end of the cold arm or offset from the first end of the cold arm. A metal layer optionally extends along the cold arm. In one embodiment, the at least one hot arm comprises two hot arms each having a first end anchored to the surface and free ends located above the surface.
In another embodiment, the vertical thermal actuator has a first beam with a first end anchored to the surface and a free end located above the surface. A second beam has a first end anchored to the surface and a free end located above the surface. A member electrically and mechanically couples the free end of the first beam to the free end of the second beam. A third beam has a first end anchored to the surface and a free end mechanically coupled to the member. The third beam is located above the first and second beams relative to the surface. First and second electrical contacts are electrically coupled to the first ends of the first and second beams, respectively, such that current supplied to the first and second contacts causes the first and second beams to thermally expand and the member to move in an arc away from the substrate.
In one embodiment, the third beam is located generally over the first and second beams. The third beam may optionally include

Affiliated with

Also associated with

Rating

Direct acting vertical thermal actuator does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Direct acting vertical thermal actuator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Direct acting vertical thermal actuator will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3234992