Compact model for flexible ion-sensitive field-effect transistor

This paper presents the theoretical modelling, and simulation of bending effects on an ion-sensitive field-effect transistor (ISFET), towards futuristic bendable integrated circuits and microsystems for biomedical applications. Based on variations of threshold voltage and drain current under different bending conditions and orientations of the channel of the device, the bendable ISFET macro-model has been implemented in Verilog-A, and compiled into the Cadence environment. The effects of bending on the behaviour of the device have been simulated over a user-defined range of pH, and sensitivities in a standard 0.18-μm CMOS technology. It has been found that the transfer curves (Id-Vg) of ISFET vary up to 4.46% for tensile and up to 5.15% for compressive bending stress at pH 2, and up to 4.99% for tensile and 5.61% for compressive bending stress at pH 12 with respect to its planar counterpart, while the sensitivity of the device has been found to remain the same irrespectively of the bending stress. The proposed model has been validated by comparing the results with those obtained by other macro-models and experimental results in literature.