Fabrication technology for a chronic in-vivo pressure sensor

This work addresses the problems of packaging and process compatibility inherent in the fabrication of integrated silicon sensors. A monolithic piezoresistive absolute pressure sensor designed for catheter tip mounting has been developed. The 1mm × 0.6 mm × 5 mm sensor chip includes on-chip circuitry and a novel lead attachment method to improve chronic stability. The simple on-chip circuit (voltage regulator, amplifier, and output driver) provides some improvement in stability allows process de-bugging, and provides a basis for later complex circuits. This circuit is fabricated at the bottom of a 5 µm deep well etched in the silicon surface, and is then hermetically sealed by coverage with an anodically bonded glass plate. The reference chamber for the absolute pressure sensor is sealed by the same bonding process. Diffused cross-unders beneath the glass connect to etched tunnels at the chip edge into which stainless steel wires can be gang-soldered, giving small-area robust lead attachment. The fabrication technology developed for this sensor should be applicable to a variety of sensor types.