| Studies of MEMS devices in recent years have shown that the performance of the devices is dependent on the basic material quality. Current research and development in surface micromachining are focusing on ways of improving the stability of mechanical properties and increasing the thickness of the polysilicon film. In this work, we have developed a new thick polysilicon surface micromachining technology. A 12μm thick polysilicon film is processed and has a small tensile residual stress of approximately 0.6MPa with no visible stress gradient. Surface roughness is estimated in the range of 3% of the film thickness with a root mean square (rms) value of approximate 30 nm over a 100μm2 area. The consistency of the measurements for the different batches of wafers demonstrates the ultimate success of the thick polysilicon process. This new technology offers more flexibility in the design of MEMS devices. The important design parameters can therefore be independently varied depending on the necessary resolution and sensitivity requirements. In addition, this new technology is compatible with VLSI fabrication, allowing integration with on-chip electronics and use of standard fabrication tools.; Current accelerometers in MEMS market are susceptible to electromagnetic interference or thermal fluctuations. As a result, an accelerometer that is economically feasible and workable in the most severe as well, as typical environments is needed. A miniature thick polysilicon accelerometer, whose motion is detected by optical intensity modulation due to the interaction between a light beam and a moving optical grating has been designed, fabricated and tested.; Testing results are obtained using a vibration table to simulate acceleration for a device that was designed with a sensitivity of mg, an intermediate value among the conventional accelerometers currently available. A linear characteristic between acceleration and output signal is obtained in the acceleration range of 0 to 8g, which is limited by the instrumentation. Sensitivity of 180mV/g is measured and noise analysis shows a 5mV/rt Hz response. As a result, the resolution is in the mg/rt Hz range, as expected.; The accelerometer has the advantages of simplicity, high reliability, low cross talk and low cost. An inexpensive light-emitting diode (LED), white light source, or even an off the shelf light bulb can be used to provide illumination. |
