High-Performance pH Sensors Using Ion-Sensitive InGaAs-Channel MOSFETs at Sub-100 nm Technology Node

This paper reports unique InGaAs-based ion-sensitive field-effect transistor (ISFET) sensor devices having a sensing gate in addition to the traditional floating gate with different kinds of barrier materials such as no barrier, single barrier (InP) and double barrier (InP and InAlAs), at sub-100 nm technology node. The impact of barrier layers coupled with the modified gate architecture on the sensing performance of the proposed devices has been investigated and compared thoroughly in terms of different performance metrics, e.g., threshold voltage sensitivity, ON-current sensitivity, and ON/OFF-current sensitivity. Interestingly, it has been found that the sensor device with a single barrier exhibits the highest threshold voltage sensitivity of ~ 67 mV/pH and largest I_ON/I_OFF ratio sensitivity of 25/pH, compared to the other devices. Furthermore, it is worth mentioning that the threshold voltage sensitivity of the single-barrier sensor device crosses the conventional Nernst limit of 59 mV/pH at room temperature, by 14%. Critically analyzing the results, it is found that the sensor device with a single barrier has evolved as the most promising device for pH-sensing application, not only from the standpoint of high sensitivity parameters, but also from the fabrication point of view.