Novel Trench Isolation Technology for Suspended MEMS Structures

This study presents a parylene-based trench isolation (PBTI) method using standard silicon wafer to obtain a suspended MEMS structure. The silicon-based suspended structures were electrically isolated using supported parylene beams. The parylene beams provide electrical isolation between the suspended structure and substrate, and prevent anchor movement during actuation and wire-bonding. The proposed process is a simple low-temperature, dry-etching and reliable fabrication method for structure creation and electrical isolation and does not require wet-release, LPCVD, plasma-enhanced chemical vapor deposition (PECVD), ion implantation, sputtering process, or sandwiched oxide/polysilicon/metal isolation. The parylene beams were created by performing multiple steps of parylene deposition and removal inside a silicon mold. The trench etching, polymer deposition for sidewall protection, floor polymer removal, structure release, and polymer stripping steps were completed by modifying the etching or passivation steps of the Bosch process. These steps can be integrated into a single-run ICP process controlled by macro commands; the ICP etcher can automatically complete suspended structure creation in a single run. A test device with a thickness of 50 m and a maximum trench aspect ratio of 10 was created to demonstrate process feasibility. The proposed process can be used for sensors and actuators, requiring a considerable device thickness to enhance sensitivity and performance. The test device is a comb-drive like device used to check the electrical isolation for sensor and actuator. Design, simulation, and fabrication considerations are discussed.