Fabrication and performance of a fully integrated mu -pirani pressure gauge with digital readout

A thermal absolute pressure sensor of the heated microbridge type has been integrated with an active bias circuit and an 8-bit successive-approximation register (SAR) analog-to-digital (A/D) converter. The chip, which contains about 1000 MOSFETs, measures absolute gas pressure between 10 to 10/sup 4/ Pa, and it is implemented in a 14-mask, 4- mu m NMOS technology merged with the microsensor process. The fabrication process and sensing performance of the mu -pirani gauge are described.<
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