Controlling the Threshold Voltage of Organic Thin-Film Transistors by Transition Metal Oxides

Abstract

We demonstrate an effective, noble metal-free method to control the threshold voltages <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(V_{T})$</tex></formula> of organic thin-film transistors (OTFTs). Through covering an Al gate electrode with a high work function (WF) transition metal oxide (TMO) layer of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm WO}_{3}$</tex></formula> or <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MoO}_{3}$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{T}$</tex></formula> is shifted in a positive direction from <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 2.15}~{\rm V}$</tex></formula> to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${-}{\rm 1.40}~{\rm V}$</tex></formula> or <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 0.89}~{\rm V}$</tex> </formula> , respectively, with respect to that of OTFTs with a bare Al gate electrode. Together with a thin dielectric layer of cross-linked Cytop, the reduced magnitude of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$V_{T}$</tex></formula> allows for a low-voltage switching operation with a gate voltage as small as 2 V. The amount of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$V_{T}$</tex></formula> shift is shown to correlate well with the change in the WF of the gate electrode upon TMO deposition.