Fabrication and pH-Sensitivity Analysis of MOS-HEMT Dimensional Variants for Bio-Sensing Applications

This work reports the fabrication, characterization and testing for pH sensitivity of dielectric modulated MOS-HEMT(Metal oxide semiconductor- high electron mobility transistor) devices for bio-sensing applications. The primary aim here is to develop high sensing devices for bio-detections. The oxide based gate area is used in ensuring the device performance through pH detection done prior to packaging and metal probing. Device parameters; gate length L-G, gate width W-G, gate spacing from source-drain ends, L-SG and L-GD have been varied to investigate the effect on pH sensitivity. The HEMT stack with AlN spacer has been grown through MOCVD (Metal-Organic Chemical Vapor Deposition) technique with no intentional doping on Si (silicon) substrate. Commercial buffer samples for pH values of 4, 7, 9.2 have been used to test the devices using drop casting technique. Drain current (ID) based sensitivity analysis shows that the device having (L-SG = 4 mu m, L-G = 3 mu m and L-GD = 18 mu m) exhibits a maximum sensitivity of 3.361 mA/pH. The devices exhibit exemplary performance when device dimensions meet the following constraints i.e. L-SG: minimum, L-G: moderate and L-GD > 2*L-SG. Average sensitivities attained is in the range 1.69 mA/pH for a device with L-G = 3 mu m, L-SG = 2 mu m and L-GD = 6 mu m.