Drift compensation using bulk feedback in a neural recording system based on open-gate FET

The shift from micro-electrode array based neural recording system to an open-gate FET based system, in which direct electrical interaction with a neuron in a nanostructure circuit offers significant advantages. However, the equivalent capacitance (C_eq) of the FET sensor undergoes a slow, monotonic change due to hydration of the insulator layers leading to a threshold voltage drift which ultimately manifest as a drift in the drain current. This paper presents a drift compensation technique for neural recording systems that use open-gate FET sensors by employing feedback to the bulk of the FET. The efficiency of this technique has been validated by simulating a sensor system with practical drift parameters. While the current drift without a feedback was found to be more than 5% of the drain current before hydration, the simulation results show that the current drift is less than 0.042% when there is an active feedback. In general, this technique is applicable to other systems that use open-gate FET based sensors such as the ISFETs.