Fully CMOS compatible on-LSI capacitive pressure sensor fabricated using standard back-end-of-line processes

A surface micromachined capacitive pressure sensor was fabricated using conventional back-end of line (BEOL) processes in a standard CMOS fabrication line. The combination of standard interlayer dielectric and tungsten was used as sacrificial layers and electrodes, which achieves a large etching selectivity in sacrificial layer removal processes. Measured dependences of capacitance on applied pressure showed a good agreement with simulated results. Although the sensor used metal and amorphous layers in the moving parts (diaphragm), it showed excellent reliability. Sensor characteristics did not change after the deflection test for more than 50M times, temperature cycling test (-55 to 150 deg C, 500 cycles, JEDEC standard) and humidity test (85 deg C, 85% for 100 hr). The process enables us to monolithically integrate MEMS structures with the most advanced CMOS integrated circuits because they use only low temperature processes. Integrating MEMS with high performance digital circuits such as MPU as well as analog circuits enables ultra-tiny one-chip sensor devices.