Optical methods for micromachine monitoring and feedback

Understanding the mechanisms that impact the performance of Microelectromec hanical Systems (MEMS) is essential to the development of optimized designs and fabrication processes, as well as the qualification of devices for com mercial applications. Silicon micromachines include engines that consist of orthogonally oriented linear comb drive actuators mechanically connected t o 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 tra nsient responses needed to optimize designs and manufacturing techniques. O ptical techniques can also be used to provide feedback signals needed for e ngine control and state determination. We describe the development of Micro machine Optical Probe (MOP) technology for the evaluation of micromachine p erformance. The MOP approach is based on the detection of optical signals s cattered by the gear teeth or other physical structures. We present experim ental 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 f or the development of integrated micromachine metrology are detailed. This work is targeted at enabling routine use of optical feedback at the microel ectromechanical device level for MEMS optimal control and lifetime monitori ng. (C) 1999 Elsevier Science S.A. All rights reserved.