A Porous Silicon P-Type Interdigitated Extended-Gate Field Effect Transistor pH Sensor

Abstract

We report on a porous silicon (PSi) p-type interdigitated extended-gate field effect transistor (IEGFET) pH sensor. Two types of crystalline orientation substrates were utilized, namely, p-type and p-type . PSi was prepared by an electrochemical etching method with an etching current density of 20 mA/cm2 and an etching time of 20 min. The scanning electron microscopy investigation revealed that the pore sizes of the p-type were smaller and deeper than those of the p-type for the same etching conditions. The average pore sizes of the p-type ranged from 0.2 to 1 μm with a depth of 19 μm. The p-type pore size and depth were found to be 1 to 4.5 μm and 14 μm, respectively. The proposed devices were tested in real time in a pH range of 3 to 11 at room temperature. The PSi p-type pH sensor exhibited enhanced pH sensitivity and linearity compared to the PSi p-type sensor. The voltage and current sensitivities of the p-type sensor were found to be approximately 43.75 mV/pH and 104 μA/pH, respectively. The PSi p-type exhibited comparatively weak voltage and current sensitivities of 7.5 mV/pH and 27.5 μA/pH, respectively. The performance enhancement of the PSi p-type sensor was due to a higher surface area to volume ratio. The crystal orientation steered the etching direction. The study produced all solid-state semiconductor efficient PSi p-type IEGFET pH sensors without the need for a bulky, fragile and liquid filled reference electrode.