Optical methods for micromachine monitoring and feedback

Understanding the mechanisms that impact the performance of Microelectromechanical Systems (MEMS) is essential to the development of optimized designs and fabrication processes, as well as the qualification of devices for commercial applications. Silicon micromachines include engines that consist of orthogonally oriented linear comb drive actuators mechanically connected to a rotating gear. These gears are as small as 50 mu m in diameter and can be driven at rotation rates exceeding 300,000 rpm. Optical techniques offer the potential for measuring long term statistical performance data and transient responses needed to optimize designs and manufacturing techniques. Optical techniques can also be used to provide feedback signals needed for engine control and state determination. We describe the development of Micromachine Optical Probe (MOP) technology for the evaluation of micromachine performance. The MOP approach is based on the detection of optical signals scattered by the gear teeth or other physical structures. We present experimental results for a prototype system designed to measure engine parameters as well as long term performance data. We also present the extension of the MOP technique to LIGA-fabricated milliengines. Concepts and technologies for the development of integrated micromachine metrology are detailed. This work is targeted at enabling routine use of optical feedback at the microelectromechanical device level for MEMS optimal control and lifetime monitoring. (C) 1999 Elsevier Science S.A. All rights reserved.