A Versatile Integration Technology of SOI-MEMS/CMOS Devices Using Microbridge Interconnection Structures

In this paper, a versatile integration technology for thick-film silicon-on-insulator microelectromechanical systems (SOI-MEMS) devices with CMOS electronics using novel microbridge interconnections is reported. The microbridge interconnection proposed in this paper solves the problem regarding the electrical isolation and interconnection between CMOS and SOI-MEMS devices. The integration of SOI-MEMS requires only three additional photolithography steps for the CMOS wafers fabricated by a standard process. On the basis of the developed technology, SOI-MEMS devices integrated with CMOS circuits were fabricated using 20-μm-thick SOI wafers. No significant damage was observed in the measured characteristics of the fabricated CMOS after the integration of MEMS devices. In addition, the electrical isolation of SOI-MEMS from the CMOS substrate was successfully realized and confirmed in the experiment, keeping electrical connectivity between CMOS circuit terminals. The measured isolation resistance between MEMS and the CMOS substrate was more than 10
¹²
Ω, and a proof voltage above 60 Vdc was observed. These values guarantee a small leakage current and a sufficient voltage swing for driving electrostatic microactuators. On the other hand, the resistance of the interconnection over a microbridge structure was below 1 Ω, which is sufficiently low for integrating low-noise microsensors. This integration technology can be used in realizing monolithically integrated SOI-MEMS sensor and actuator devices with high-aspect-ratio structures using the most cost-effective and versatile CMOS fabrication technologies.