Comparison of floating probe transient technique for on-state channel characterization & threshold voltage of an organic thin film transistor for sensing applications

Abstract

For pragmatic utilizations of field-effect transistors (FETs), the control of threshold voltage (Vth) is significant for sensing applications as various sensors and circuits require distinctive electrical characteristics. Moreover, the controllable threshold voltage is essential for creating integrated circuits (IC). The threshold voltage of a TFT is sensitive to numerous factors, which make it alluring for sensing applications. However, its estimation is not simple, particularly when mobility is field-dependent and source/drain resistances are noteworthy. Precise control of the threshold voltage in organic FETs also remains challenging. Conventionally, for an organic transistor threshold voltage is typically an empirical parameter that is obtained by fitting the experimental current–voltage transfer characteristics, which is temperamental as it relies upon the range of the gate bias. However, the turn-on voltage of a transistor is not affected from these downsides and therefore suggests an alternative that can be used for sensing applications. Customary, measurement of on-state voltage requires the estimation of current in the subthreshold region and its extrapolation at the voltage axis, which it is normally not utilized. The present work analyzes the threshold voltage extracted using differential and conventional methods and the turn-on voltage extracted using the floating probe technique which is straightforward and requires the estimation of voltage at the floating terminal as the source voltage is linearly sloped while sustaining gate voltage constant. Two-dimensional numerical simulation results are introduced to support that the floating probe procedure yields reliable parameters than the threshold voltage and subsequently can be suitably used for sensing applications. Experimental results obtained with pentacene based top-contact organic TFT’s (OTFTs) are also shown to delineate the proposed idea.