Primary Faculty Mentor Name

Randall L. Headrick

Project Collaborators

Yang Li, Jeffrey G. Ulbrandt, Detlef-M. Smilgies, Jonathan Hollin, Adam C. Whalley

Status

Graduate

Student College

College of Arts and Sciences

Program/Major

Materials Science

Primary Research Category

Engineering & Physical Sciences

Presentation Title

Metal-semicoductor contact effects and temperature-dependence of carrier transport in large-grain organic semiconductor thin film transistors

Time

11:40 AM

Location

Frank Livak Ballroom

Abstract

The pen-writer solution deposition method is used to deposit 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor thin films and also polymer dielectric layers. Organic transistors with source/drain contact layers either below or on top of the semiconductor layer and with or without surface treatment are investigated. An “ageing effect” is observed with the top contact bottom gate transistors, which indicates the passivation of shallow traps since the transistor current increases over the course of several days. Further, we measured the temperature dependence of OFETs of this structure and observed that the “band-like” transport depends on the lateral electric field between source and drain, which suggests that de-trapping of charge carrier occurs at higher lateral fields. The ageing effect can be avoided by using a bottom contact geometry. In addition, a Schottky Barrier model is used to simulate the contact resistance, which produces a pronounced non-linearity in the output characteristics at low drain voltage. By treating the Au electrode with pentafluorobenzenethiol (PFBT) in the bottom contact geometry, the contact resistance is greatly reduced. An optimized geometry is obtained by using pen-written CytopTM dielectric in a top-gate/bottom-contact structure, which exhibits a near-intrinsic average mobility, up to 9.0 cm2/V-s for C8-BTBT thin films deposited at high writing speed (25mm/s) and deposition on a heated substrate (60°C). We will report temperature-dependent carrier transport results for individual devices with both a top gate (with cytop dielectric) and bottom gate (with silicon dioxide dielectric) to compare results at both interfaces of the same C8-BTBT thin film.

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Metal-semicoductor contact effects and temperature-dependence of carrier transport in large-grain organic semiconductor thin film transistors

The pen-writer solution deposition method is used to deposit 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic semiconductor thin films and also polymer dielectric layers. Organic transistors with source/drain contact layers either below or on top of the semiconductor layer and with or without surface treatment are investigated. An “ageing effect” is observed with the top contact bottom gate transistors, which indicates the passivation of shallow traps since the transistor current increases over the course of several days. Further, we measured the temperature dependence of OFETs of this structure and observed that the “band-like” transport depends on the lateral electric field between source and drain, which suggests that de-trapping of charge carrier occurs at higher lateral fields. The ageing effect can be avoided by using a bottom contact geometry. In addition, a Schottky Barrier model is used to simulate the contact resistance, which produces a pronounced non-linearity in the output characteristics at low drain voltage. By treating the Au electrode with pentafluorobenzenethiol (PFBT) in the bottom contact geometry, the contact resistance is greatly reduced. An optimized geometry is obtained by using pen-written CytopTM dielectric in a top-gate/bottom-contact structure, which exhibits a near-intrinsic average mobility, up to 9.0 cm2/V-s for C8-BTBT thin films deposited at high writing speed (25mm/s) and deposition on a heated substrate (60°C). We will report temperature-dependent carrier transport results for individual devices with both a top gate (with cytop dielectric) and bottom gate (with silicon dioxide dielectric) to compare results at both interfaces of the same C8-BTBT thin film.