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

The channel temperature ( T ch ) 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 ( T b ) between 300 K and 20 K. This is done using a platinum (Pt) resistance temperature sensor embedded within the transistor channel. Under large gate ( V g ) and source‐drain ( V ds ) voltage biases, an increase in T ch is observed, the magnitude of which depends on the thermal conductivity of the substrate. The increase in T ch is associated with a simultaneous increase in the transistor drain current ( I d ) and becomes particularly pronounced at cryogenic T b . 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 in I d at cryogenic T b and large voltage biases cannot be fully accounted for unless at low temperatures μ TIPS is enhanced in the presence of strong electrical fields. Therefore it is concluded that the I – V characteristics of TIPS pentacene TFTs at low T b and large voltage biases are a result of a complex interplay between current‐induced Joule heating and electrical field effects.