Effect of geometry and temperature variations on sensitivity and linearity of junctionless pH sensing FET: An experimental study

Here-in this work, boron doped poly-silicon based dimensional variants of thin film planar junctionless field effect transistors are fabricated through CMOS compatible process for pH detection. The dimensional variants are classified into two sets as set-1 (channel length, L = 100 μm) and set-2 (channel length, L = 120 μm) with widths of 3 μm, 5 μm, 10 μm, and 20 μm. Sensitivity of the fabricated devices is analyzed using phosphate buffer saline solutions of pH 3.1, 5.2, 7, 9 and 11.2 and is computed in terms of relative shift in threshold voltage (VTh) and maximum drain current (IDS). The reference VThand IDSare taken at neutral pH 7. Here we have experimentally analyzed the effect on pH sensitivity by varying the device widths and temperatures from 30 °C to 50 °C. It is observed that varying the device width from 3 μm to 20 μm, VThsensitivity reduces from 19.08% to 9.17% and from 16.03% to 8.5% for set-1 and set-2 devices respectively. Increasing temperature from 30 °C to 50 °C causes reduction of VThsensitivity from 18.68% to 13.52% for device with W/L = 3μm/100 μm and 16.78%–10.99% for device with W/L = 3μm/120 μm. The reduction in width causes average VThsensitivity to roll-off by 0.49%/μm and 0.26%/μm for L = 100 μm and L = 120 μm respectively. Also the increase in operating temperature from 30 °C to 50 °C leads VThsensitivity to roll-off by 0.17%/°C and 0.2%/°C for W/L = 3μm/100 μm and W/L = 3μm/120 μm respectively.