Above-IC integration of capacitive pressure sensor fabricated with CMOS interconnect processes

A surface-micromachined capacitive pressure sensor fabricated with a standard CMOS back-end of line processes was integrated above a CMOS LSI with a sensor front end circuit, and the output signal was obtained via the integrated circuit. The sensor was fabricated using only low-temperature processes and conventional materials and equipment. The sensor measures capacitance and electrical output of the C-V converter integrated on the same substrate with no degradation in signal quality. The sensor was placed above the IC region and sub-half-micron CMOS processes were applied to the IC, so the effective chip size is smaller than 2 mm
²
. Basic reliability of the sensor was examined. A passivation layer thicker than 150 nm is necessary for suppressing sensitivity change below 1% for the pressure cooker test (120 deg, 100% relative humidity for 100 hr). Our process enables MEMS integrated on any generation CMOS-LSI, enhancing functionality of the sensor chip and minimizing chip size.