A lateral comb drive on PMMA by hot embossing technique

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.