Comparing process flow of monolithic CMOS-MEMS intergration on SOI wafers with monolithic BiMOS-MEMS integration on Silicon wafer

This paper describes the two different integrated fabrication process flows for microelectromechanical systems (MEMS) accelerometer with surface micromachining technology at Analog Devices (ADI). Each method has its own identity with several advantages and disadvantages with respect to each other. CMOS-MEMS are fabricated using silicon-on-insulator (SOI) substrate, which allows the monolithic integration of the mechanical transducer and the control electronics on the device single crystal silicon layer. However, BiMOS-MEMS are fabricated on silicon substrates for building the control electronics and where thick poly-silicon is added to form the mechanical sensor. The integrated circuit (IC) industry evolution in two decades has made great strides and provided a mature infrastructure for surface micromachining by which successful miniaturization and multiplicity of traditional electronics systems have been applied to MEMS devices. . We report the fabrication flow for the two integrated MEMS processes incorporating MEMS with the control electronics and how they compare.