Focused ion beams and silicon-on-insulator - a novel approach to MEMS

We report. on the fabrication of microaccelerometer structures in bonded silicon-on-insulator material employing a focused ion beam technique to form the readout gap. The silicon-on-insulator starting material allows the simple fabrication of suspended microstructures with the advantages of single-crystal silicon. Focused ion beam machining is essential for this kind of modification without a photolithographic resist mask. In particular, for the milling of narrow trenches at oblique angles an ion beam has advantages over other etching techniques. We show that milling times can be held short enough to consider this process for manufacturing devices. We also demonstrate other novel applications of focused ion beams for prototyping MEMS.