Body effect minimization using single layer structure for pH-ISFET applications

In this study, the hafnium oxide (HfO 2) thin film deposited by using radio frequency (r.f.) sputter was used as the sensing membrane of ion sensitive field-effect transistor (ISFET) for pH detection. For low cost and easy fabrication, the single HfO 2 gate ISFET without SiO 2 as buffer layer have been developed to compare with the conventional ISFETs with HfO 2 or Si 3N 4 on SiO 2 buffer layer in same process. Electrical characteristics including off current, transconductance, subthreshold swing and body effect of metal–insulator–semiconductor field-effect transistor (MISFET) devices and pH sensing properties including sensitivity, linearity, drift coefficient and body effect of ISFET devices were investigated in detail. The single HfO 2 gate MISFET exhibits better electrical performance like higher transconductance, smaller subthreshold swing and lower body effect than the stack HfO 2/SiO 2 gate MISFET and Si 3N 4/SiO 2 gate MISFET. In pH sensing properties, both the single HfO 2 gate ISFET and the stack HfO 2/SiO 2 gate ISFET show better sensing performance than the stack Si 3N 4/SiO 2 gate ISFET. Due to the concern of exact pH detection and high operation speed for commercial product application, the single HfO 2 gate ISFET with lower body effect on pH detection and higher transconductance is a potential candidate to integrate with an analog readout circuit.