A stainless-steel-based capacitive pressure sensor chip and its microwelding integration

A stainless-steel (SS) chip of capacitive pressure sensor and its new integration method are developed. The sensors are microfabricated through thermal bonding of the chip dies made of medical-grade SS to the Au-polyimide diaphragm film. The capacitive cavity design with dead-end holes is verified to increase the pressure sensitivity. Laser microwelding is applied to permanently bond the sensor chips onto SS substrates. The microwelding is revealed to provide twice the mechanical strength and ~6× electrical conductance in its bond compared with a conductive epoxy case. The microwelded sensor exhibits an average sensitivity of 120 ppm/mmHg close to its pre-welding level. The welding integration with a SS antenna stent is demonstrated. The results suggest that laser microwelding is a promising packaging technique for SS-based biomedical and implant microdevices that require long-term bond reliability.