Orientation Effect of n-Type PSi on Integrated Interdigitated Electrode EGFET pH Sensor Performance

The effect of the crystalline orientation of n-type porous silicon (PSi) on an integrated interdigitated extended-gate field-effect-transistor (IEGFET) pH sensor performance was studied. The PSi n-type <100> and n-type <111> are prepared by a Laser-assistant etching method (LAEM) as sensing layer in the same conditions. The scanning electron microscope (SEM) revealed that the PSi pore size and depth of n-type <100> are 1 to 4.5 µm and 1.5 µm, respectively, whereas for n-type <111> sample are 2 to 4 µm and 0.4 µm, respectively. The integrated interdigitated electrode consists of the reference and the extended gate on a single PSi sensing substrate. The n-type <100> PSi and n-type <111> PSi as the sensing layers were compared and contrast in the pH range from 3 to 11. n-type <111> PSi does not exhibit any pH sensitivity. On another hand, The n-type <100> PSi sensing layer shows a better sensitivity as compared to n-type <111> PSi. The voltage and current sensitivities of n-type <100> PSi are found to be 13 mV/pH and 30.94 µA/ pH, respectively. The sensitivity enhancement for n<100> sample is attributed to the larger porosity and pore deepest, as compared to for n-type <111> which that result in a higher surface area/volume ratio which causes better sensitivity. The studied IEGFET based on PSi is a completely solid-state device which opens a new area to investigate of miniaturization pH.