Current‐Induced Joule Heating and Electrical Field Effects in Low Temperature Measurements on TIPS Pentacene Thin Film Transistors

Abstract

The channel temperature (Tch) of solution‐processed 6,13‐bis(triisopropylsilylethynyl)‐pentacene (TIPS pentacene) thin film transistors (TFTs) is closely monitored in real time during current–voltage (I–V) measurements carried out in a He exchange gas cryostat at various base temperatures (Tb) between 300 K and 20 K. This is done using a platinum (Pt) resistance temperature sensor embedded within the transistor channel. Under large gate (Vg) and source‐drain (Vds) voltage biases, an increase inTchis observed, the magnitude of which depends on the thermal conductivity of the substrate. The increase inTchis associated with a simultaneous increase in the transistor drain current (Id) and becomes particularly pronounced at cryogenicTb. These experimental observations are rationalized using a 1D theoretical model and are attributed to current‐induced Joule heating. However, even though the heating of the channel unquestionably plays an important role, the corresponding amount of increase inIdat cryogenicTband large voltage biases cannot be fully accounted for unless at low temperatures μTIPSis enhanced in the presence of strong electrical fields. Therefore it is concluded that theI–Vcharacteristics of TIPS pentacene TFTs at lowTband large voltage biases are a result of a complex interplay between current‐induced Joule heating and electrical field effects.