Piezoelectric materials can produce large forces but only small displacements. Hence they scale favorably when devices are miniaturized to a micron scale. Unfortunately piezoelectric materials require special processing that is not always available or compatible with other processes used to make micromachines. Hence other actuation methods such as electrostatic actuation have received more attention.

Pulse actuation Our approach at the SonicMEMS group has been to use bulk piezoelectric plates mounted at the back of a silicon die to actuate surface micromachines. There is a major advantage in this: no special processing is required and the method is suitable for micromachines from any process. Another advantage is that no valuable die surface area is consumed. The GIF graphics below illustrates the idea. The piezoelectric plate generates a vibrations and/or pulses that travels to the surface of the die. These vibrations and pulses can be used to release stuck micromachines and actuate other micromachines. This work has been patented, and for licensing you can contact the Wisconsin Alumni Research Foundation.


Release of stuck beams Another application is to release stuck micromachines. When devices are scaled down, their surface to volume ratio increases. As a result even working micromachines can get stuck if they come in contact with another micromachine or surface of the substrate. Considerable effort has been put into finding suitable coatings to solve this problem. Unfortunately these coatings can wear and leave micromachines without protection. Using stress pulses we successfully released stuck micromachined beams. This is demonstrated in the animation below. We believe this method can increase the reliability of micromachines.


Actuation of flaps We have successfully raised micromachined flaps using the pulsing technique. Because micromachines have very small mass, gravity has negligible effect on them. Raised beams remain up even after pulsing has ended. This can be compared to balancing a card on its side in the "macro world". Drag force, however, cannot be neglected: in atmospheric pressure the flaps hardly move and the raising must be done in a vacuum. This is one example of how forces scale sometimes unintuitively to the micron scale. 

One possible application is parallel assembly of micromachines. Although micromachine fabrication is typically a parallel process, the assembly requires series processing. The cost associated with this can be prohibitive. A SEM of a fully assembled micromachined flap structures is shown below.

Assembled flap


Microengine simuation We have shown the first ever completely surface micromachined ultrasonic rotor. It operates with a single-phase drive, which is different than the many electrodes needed for traditional ultrasonic motors. Driving voltages as low as 4 Vpp has been demonstrated which makes integration with standard CMOS technology feasible. This voltage is very low compared to electrostatic micromotors that typically need around 100 volts to operate. Thermal actuators work with low voltages but compared to ultrasonic actation they require large currents. A complete microengine with 50:7 gear ratio shown in GIF animation below has been demonstrated suggesting high torque capabilities. The motor was operated continously for four days and no problems were observed. The direction of rotation can be controlled by adjusting the drive frequency.


About this page

This page represents some of the work I did while I was a graduate student at the University of Wisconsin-Madison. My adviser, Prof. Amit Lal, has since moved to Cornell University. If you find this work interesting, you may also want to visit his pages.

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