Structure-Dependent Contact Barrier Effects in Bottom-Contact Organic Thin-Film Transistors

Abstract

This paper investigates and compares the structure-dependent contact barrier effects on the electrical performance of two bottom-contact (BC) structure (staggered and inverted coplanar) organic thin-film transistors (OTFTs) by numerical simulations. The drain saturation current ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dsat</sub> ) of the staggered device is found to be more sensitive to the variation of the source/drain (S/D) electrode thickness than that of the inverted coplanar one. The inverted coplanar device shows stronger dependence of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dsat</sub> on the contact barrier than the staggered device, and the dependence is also much more affected by the step coverage profile of the semiconductor layer on top of the S/D electrodes. For the inverted coplanar structure OTFTs, a steeper step coverage profile and a lower contact barrier can help to achieve better tolerance of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dsat</sub> to the variations of the contact barrier and step profile, respectively. The gate structure (self-aligned or fully covered) does not show any influence. The study forms a clear understanding of the device-structure-dependent carrier transport mechanisms in BC OTFTs and could also provide important guidelines for optimal device structure design and related process development for BC OTFTs.