Fabrication and Modeling-Based Performance Analysis of Circular GaN MOSHEMT-Based Electrochemical Sensors

C-MOSHEMT (Circular-Metal Oxide Semiconductor High Electron Mobility Transistor) has been modeled, fabricated and sensitivity analysis has been done for pH detection application for the first time. Prototype model of the sensor has been developed considering a ring gate structure. The perimeter of the gate inner ring is taken as the gate length and a gate width of 100 μm has been used to plot normalized device characteristics. Advantage of C-MOSHEMT over L-MOSHEMT (linear MOSHEMT) is that the area available for sensing increases and process cost and complexity involved remains low from the fabrication point of view. The overall fabrication cost and process overheads reduce with elimination of the mesa isolation etch. ALD (Atomic Layer Deposition) deposited Al
₂
O
₃
used as the gate oxide and passivation scheme in the device design ensures higher sensitivities along with current collapse free device operation. Analytical model along with experimental analysis have been done using 3 standard buffer pH samples, pH=4, 7, and 9.2. The devices fabricated showcase a maximum sensitivity of 1.74 mA/pH and 1.86 mA/pH when gate lengths (L
_G
) of 3 μm and 5μm are considered. Further, the model and the physical detection results are compared and contrasted to study the strengths and weaknesses of the model developed. It has been observed that as sensing area is doubled, the sensitivity increases by 41% which can be attributed to the discreteness of charge distribution on the sensing surface.