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

A stainless-steel (SS) chip of capacitive pressure sensor and its integration method are developed with a focus on smart implant applications. The sensors are entirely microfabricated with biocompatible materials, through thermal bonding of gold-polyimide diaphragm film to the chip dies made of medical-grade SS. The reference cavity design with dead-end holes created in the SS die is both theoretically and experimentally verified to enhance pressure sensitivity. Laser microwelding is investigated as an alternative integration path for this type of SS-based sensors to establish permanent and reliable bond onto SS-based platform devices. The microwelded bond is revealed to provide twice the mechanical strength and ∼6 × electrical conductance compared with a conventional conductive epoxy case. The microwelded sensors exhibit an average sensitivity of 110 ppm/mmHg close to its pre-welding level. The microwelding integrations of fabricated chips with the SS antenna stent and hypodermic needle are demonstrated. The results suggest not only that the developed pressure sensor is compatible with laser microwelding, but also that micowelding is a promising packaging technique for SS-based biomedical and implant microdevices that require long-term bond reliability.