Carbon Ion Implantation-Modified Hafnium Oxide to Construct a RELESIS for pH Sensing

The reference-less semiconductor ion sensor (RELESIS) addresses pH sensing by eliminating the need for a reference electrode (RE), offering hope for miniaturized and on-chip integrated ion sensors. The key challenge in large scale preparation of RELESIS lies in fabricating a pair of differential sensitive films that can be formed using CMOS compatible process. In this work, differential sensitive films were fabricated through the transformation of a high sensitivity film into a low sensitivity film via carbon ion implantation. Carbon ion implantation effectively reduced the sensitivity of the HfO2 film, achieving a 89% decrease, from 48.93 mV/pH to 6.7 mV/pH. RELESIS was fabricated with HfO2 and carbon ion-implanted HfO2 films and demonstrated excellent pH performance, exhibiting a high sensitivity of 41.79 mV/pH. Microwave annealing (MWA) further enhanced the sensitivity of RELESIS to 44.71 mV/pH and decreasing the sensitivity degradation rate from 17% to 8.4% over a 20-day period.