Yongjun Zhao

Date of Award

Spring 2003

Document Type


Degree Name

Doctor of Philosophy (PhD)


Micro and Nanoscale Systems

First Advisor

Tianhong Cui


The objective of this work is to fabricate a laterally driven comb drive on low-cost poly-methyl-meth-acrylate (PMMA) by hot embossing technology.

An electrostatic comb drive is one of the most important components in Micro-Electro-Mechanical Systems (MEMS). A comb drive can work as both a sensor and an actuator. Varieties of comb drives have been developed on silicon and poly-silicon materials.

Hot embossing of polymers is a promising alternative to traditional silicon processes due to cost-reduction. It fulfills the demand for low-cost methods for high volume production of micro-components and micro-systems. The raw materials of polymer are relatively inexpensive. For the manufacturing, a complex micromachining step for the fabrication of mold insert is only necessary once. The desired microstructures can be batch-replicated using the master mold.

In this work we used Finite Element Analysis software to design the structures. Several new process methods have been developed for achieving micro-mechanical structures with high aspect ratio on PMMA by hot embossing technique, forming mold insert by bonding a silicon-wafer mold onto a stainless steel disk, and releasing movable structures on PMMA material.

The comb drive microstructure, consisting of 80 units of interdigitated parallel capacitors with the finger gap and width of both 10 μm, has been fabricated successfully under a typical condition of molding force of 35000 N at 135°C. The minimum feature size is 5 μm and the thickness of the structure is 60 μm, which makes the aspect ratio 12:1. The comb drive strokes 5 μm under a driven potential of 180 V. The natural frequency for the first mode of this comb drive is about 3 kHz.

The testing results matched the simulation results very well. Several advantages of this technique are observed as follows: (1) the whole process is simple and low cost, (2) all the processes are performed under low temperature, below 140°C, (3) PMMA structure has less stress and higher flexibility compared with the counterpart on silicon or poly-silicon, and (4) the driven voltage is much lower compared with the silicon-based devices.

The disadvantage of PMMA material is that it can not endure high temperature.