Dimension and Shape Effects on the ISFET Performance

In this paper, the ion-sensitive field-effect transistor (ISFET) performance in unmodified complementary metal-oxide-semiconductor is thoroughly studied in terms of transconductance, threshold voltage, offset, and drift for the dimension and shape effects. It is shown that by increasing the ISFET sensing area, decoupling capacitors-as a function of the perimeter of the gate extension metal layers-may degrade the coupling efficiency of the ISFET. For a higher area to perimeter ratio, ISFETs with equilateral square and octagonal shape, as well as single-plate and multiplate sensing layers, were compared, and 24 tests of 8 dies each containing 15 devices were done. It is also shown how the drift direction may be predicted through the reference electrode current. In the end, tradeoffs among area, power, and performance besides challenges in scaling down the dimensions are discussed.