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

In this study, the hafnium oxide (HfO2) 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 HfO2 gate ISFET without SiO2 as buffer layer have been developed to compare with the conventional ISFETs with HfO2 or Si3N4 on SiO2 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 HfO2 gate MISFET exhibits better electrical performance like higher transconductance, smaller subthreshold swing and lower body effect than the stack HfO2/SiO2 gate MISFET and Si3N4/SiO2 gate MISFET. In pH sensing properties, both the single HfO2 gate ISFET and the stack HfO2/SiO2 gate ISFET show better sensing performance than the stack Si3N4/SiO2 gate ISFET. Due to the concern of exact pH detection and high operation speed for commercial product application, the single HfO2 gate ISFET with lower body effect on pH detection and higher transconductance is a potential candidate to integrate with an analog readout circuit.