CMOS-Integrated Poly-SiGe Piezoresistive Pressure Sensor

An integrated poly-SiGe-based piezoresistive pressure sensor, which is directly fabricated above 0.13
$\mu\hbox{m}$
Cu-back-end CMOS technology, is presented. This represents not only the first integrated poly-SiGe pressure sensor directly fabricated above its readout circuit but also the first time that a poly-SiGe MEMS device is processed on top of Cu-back-end CMOS. Despite the low processing temperature
$(\leq\hbox{455}\ ^{\circ}\hbox{C})$
to allow for above-CMOS integration, the poly-SiGe piezoresistive sensor alone (
$\hbox{250} \times \hbox{250}\ \mu\hbox{m}^{2}$
membrane) showed a sensitivity of around 2.5 mV/V/bar. The same sensor exhibited a sensitivity of 159.5 mV/V/bar after on-chip amplification. The CMOS circuit showed no significant deterioration after the MEMS processing, although a resistance increase for the Cu-filled metal-to-metal and the tungsten-filled CMOS–MEMS vias was observed.