Lateral Comb-Drive Mems Structure For Micro-Measuring Probe Application

Electrostatic comb-drive actuators, which consists of two interdigitated finger structures with one fixed and the other connected to a compliant suspension, are the most widely used micro actuators in micro-electro-mechanical systems(MEMS). In the actuator applications, applying a voltage between the interdigitated fingers will generate a relative displacement between the fixed and the movable comb structures. The capacitance of the comb-drive structures will vary according to the variation of the relative displacement. The relationship between displacement and resulting capacitance variation is linear. With this principle, the comb-drive structure is employed as a micro measuring probe in this paper.A main shaft connected with the movable comb structures protrudes out of the MEMS chip to sense the surface topography of a specimen under test. A ruby sphere which is mounted onto the end of the actuator's main shaft is employed as a tip. The displacement of the shaft will vary with the variation of the surface topography of the specimen. Accordingly, the capacitance of the comb-drive structures will change. A capacitance readout circuit is designed to convert the capacitance variation into a voltage variation. The results of the designed electronics will be presented. And a drive and sensing system which consists of the micro measuring probe, the capacitance readout circuit, and computer controlled piezoelectric stages is constructed to measure the surface topography of the specimen. To calibrate the drive and sensing system, a standard step of 68nm is one-line scanned.