Early-stage post-surgical infection monitoring is crucial for preserving patients' health and reducing public healthcare costs. Among various parameters and symptoms, local pH shifts can provide valuable insight into the development of infections. An implantable pH sensor can be employed to monitor localised pH changes. The Ion-Sensitive Field-Effect Transistor (ISFET) is a precise pH sensing device that is compact in size and can be integrated with standard CMOS technology. Due to its small size, the ISFET is promising as an implantable sensor for in vivo pH sensing. To avoid a second surgery for sensor removal after its functional lifespan, biodegradable sensors offer an alternative, as they can degrade and be absorbed by the human body after completing their function.

The aim of this project was to design and fabricate the first fully biodegradable ISFET pH sensor, addressing the challenges of accurate real-time monitoring for post-surgical infection, specifically in hip implantation surgery. This project successfully led to the design and fabrication of an 8-mask ISFET/MOSFET device using fully biodegradable materials and incorporating two rounds of ion implantation. Chip thinning via TMAH wet etching was also explored. Several alternatives were studied to overcome challenges with Molybdenum and Mo-Si contact in having suitable interconnections and Ohmic contact between Molybdenum and Silicon.