Decoupling the Bias-Stress-Induced Charge Trapping in Semiconductors and Gate-Dielectrics of Organic Transistors Using a Double Stretched-Exponential Formula

A novel strategy for analyzing bias-stress effects in organic field-effect transistors (OFETs) based on a four-parameter double stretched-exponential formula is reported. The formula is obtained by modifying a traditional single stretched-exponential expression comprising two parameters (a characteristic time and a stretched-exponential factor) that describe the bias-stress effects. The expression yields two characteristic times and two stretched-exponential factors, thereby separating out the contributions due to charge trapping events in the semiconductor layer-side of the interface and the gate-dielectric layer-side of the interface. The validity of this method was tested by designing two model systems in which the physical properties of the semiconductor layer and the gate-dielectric layer were varied systematically. It was found that the gate-dielectric layer, in general, plays a more critical role than the semiconductor layer in the bias-stress effects, possibly due to the wider distribution of the activation energy for charge trapping. Furthermore, the presence of a self-assembled monolayer further widens the distribution of the activation energy for charge trapping in gate-dielectric layer-side of the interface and causes the channel current to decay rapidly in the early stages. The novel analysis method presented here enhances our understanding of charge trapping and provides rational guidelines for developing efficient OFETs with high performance.