Influence of Substrate Modification with Dipole Monolayers on the Electrical Characteristics of Short-Channel Polymer Field-Effect Transistors

Takashi Nagase,Akira Otomo,Hiroyoshi Naito,Rieko Ueda,Takashi Kobayashi,Takeshi Hirose

doi:10.3390/app8081274

Takashi Nagase, Akira Otomo + Show 4 more

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https://doi.org/10.3390/app8081274

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Abstract

This study investigates the influence of self-assembled monolayer treatment of gate insulators on the electrical characteristics of bottom-gate/bottom-contact organic field-effect transistors (OFETs) with short channel lengths of 5 μm to 30 nm. The treatment of 3-chloropropyltrichlorosilane (CPTS) with large dipoles produces a high built-in electric field perpendicular to the SiO2 gate insulator surface, which results in a threshold voltage shift and enhanced hole injection compared to the treatment of phenethyltrichlorosilane (PETS) with small dipoles. Pronounced parabolic drain current‒voltage (ID‒VD) characteristics due to a space-charge limited current are observed in short-channel OFETs based on poly(3-hexylthiophene) with CPTS-treated gate insulators. CPTS treatment on short-channel OFETs based on poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) suppresses the nonlinear ID increase in the low VD region caused by the voltage drop at the Au/F8T2 contact. The influence of the increase in the net source-drain electric field associated with the reduced voltage drops on the channel-length dependence of the field-effect mobility of short-channel F8T2 FETs is also discussed.

Highlights

There has been considerable interest in the development of organic field-effect transistors (OFETs) with high electrical performance because of their potential use in various organic devices, such as flexible displays, low-cost radio frequency identification tags, and large-area sensors [1,2,3]
To clarify the difference in effects of the built-in electric field produced by the dipole self-assembled monolayers (SAMs) and increased gate electric field with thinner gate insulators, we investigated the electrical characteristics of short-channel P3HT and F8T2 FETs fabricated on thinner SiO2 insulators (50 nm thick) treated with the PETS SAMs (Figure 5)
We have investigated the electrical characteristics of short-channel OFETs based on polymer

Summary

Introduction

There has been considerable interest in the development of organic field-effect transistors (OFETs) with high electrical performance because of their potential use in various organic devices, such as flexible displays, low-cost radio frequency identification tags, and large-area sensors [1,2,3]. We have previously studied the influence of the source electrode/organic semiconductor contact on the current–voltage characteristics of short-channel OFETs based on p-type organic semiconductors and reported that the parabolic ID –VD characteristics and high off current are suppressed by using organic semiconductors with high ionization potentials [11] This behavior originates in the formation of Schottky barriers for hole injection at the source electrode/organic semiconductor contact, which reduces the SCLC and increases the effectiveness of the gate electric field in the channel because of the decrease in the net source-drain electric field. SAMs on the electrical characteristics of short-channel OFETs with L of 5 μm to 30 nm fabricated using p-type polymer semiconductors with different ionization potentials

Experimental

3.3.Results

Schematic

Conclusions