Tsukasa Fujimori

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 mm2. 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.

Tiny (0.72 mm 2 ) pressure sensor integrating MEMS and CMOS LSI with back-end-of-line MEMS platform

A back-end-of-line (BEOL) MEMS platform for a compact, high-precision pressure sensor was developed. A CMOS-LSI-integrated MEMS pressure-sensor chip (with a size of 0.72 mm2) was fabricated on the platform. The sensor provides both high accuracy and accommodates miniaturization. Its sensitivity offers design flexibility simply by changing the size of its MEMS capacitors. The pressure sensor is thus suitable for various pressure-range applications.

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.

One-dimensional-motion and pressure hybrid sensor fabricated and process-level-packaged with CMOS back-end-of-line processes

One-dimensional movable structures (motion sensors) made from a metal silicide (WSi) core were successfully encapsulated inside a cavity in an interlayer dielectric (SiO2) covered by another metallic layer. The latter half of the fabrication process is the same as to that for the pressure sensor that we previously reported [1]; thus, both sensors can be fabricated simultaneously. As is the case with our previously reported pressure sensor, the fabrication processes are compatible with CMOS back-end-of-lines (BEOL) processes (carried out below 400°C). The motion sensor can thus be fabricated directly above integrated circuits (ICs). The fabricated sensors were electrically tested, and the measured pull-in voltage was in good agreement with the design value.