Synthetic Metals 148 (2005) 75–79 Surface-treatment effects on organic thin-film transistors Sang Chul Lim a,b , Seong Hyun Kim a,∗ , Jung Hun Lee a,c , Mi Kyung Kim a , Do Jin Kim b , Taehyoung Zyung a a ElectronicsandTelecommunicationsResearchInstitute,Gajeong-dong,Yuseong-gu,Daejeon305-350,RepublicofKorea b Department of Materials Science and Engineering, Chungnam National University, Daejeon 305-764, Republic of Korea c InformationDisplayDepartment,KyungHeeUniversity,Hoegi-dong,Dongdaemun-gu,Seoul130-701,RepublicofKorea Received 13 February 2004; received in revised form 18 August 2004; accepted 18 August 2004 Available online 12 October 2004 Abstract We have fabricated organic thin-film transistors (OTFTs) using pentacene as an active layer with chemically modified SiO 2 gate dielectrics. The effects of the surface treatment of SiO 2 on the electric characteristics of OTFTs were investigated. The SiO 2 gate dielectric surfaces were treated by normal wet-cleaning process, O 2 -plasma treatment, hexamethyldisilazane (HMDS), and octadecyltrichlorosilane (OTS) treatment. After the surface treatments, the contact angle and surface free energy were measured in order to analyze the surface state changes. From the electrical measurements, typical I–V characteristics of TFTs were observed. The field effect mobility, µ, was calculated to be 0.29 cm 2 V -1 s -1 for OTS-treated sample, while those of the HMDS, O 2 -plasma treated, and wet-cleaned samples to be 0.16, 0.1, and 0.04 cm 2 V -1 s -1 , respectively. © 2004 Elsevier B.V. All rights reserved. Keywords: Organic thin-film transistors; O 2 -plasma treatment; HMDS treatment; OTS treatment; Semiconductors 1. Introduction Organic thin-film transistors (OTFTs) have been inves- tigated for many years for possible use in low-cost, large- area, flexible electronic applications, such as driving ele- ments of active-matrix emissive or liquid-crystal flat panel displays, large-area sensor arrays, biochemical sensors, and radio-frequency identification tags. Pentacene (C 22 H 14 ) is a semiconducting organic material currently attracting much interest among scientists and engineers because pentacene films can be used as a channel layer of OTFTs with mobility of ≥1 cm 2 V -1 s -1 [1–3]. The mobility is therefore compara- ble with amorphous silicon thin-film transistors (a:Si-TFTs), which are used, in thin-film transistor driven liquid crystal display (TFT-LCD) and hence, in the mobility point of view, pentacene transistors can be used as a switching device for active-matrix display. ∗ Corresponding author. Tel.: +82 42 860 5090; fax: +82 42 860 6836. E-mailaddress: kimsh@etri.re.kr (S.H. Kim). The pentacene films are usually polycrystalline when they are deposited by organic vapor phase deposition [2] and ther- mal evaporation [1–3]. Polycrystalline films are composed of grains and grain boundaries. The grains are single crystal phase with semiconducting character while the grain bound- aries are amorphous with highly leaky insulating character. Therefore, the performance of the OTFTs highly depends on the film state. Since the organic film of OTFTs is fabricated on to the dielectric layer under the influence of the physi- cal and chemical interactions between organic and dielectric layer, the OTFT performance strongly depends on the semi- conductor/dielectric interface [4]. The purpose of this work is to show the improvement of OTFT performance by controlling the surface treatments of dielectric/polymer interface. The surface properties such as frictional or abrasion, permeability, insulating properties, wettability and chemical reactivity are strongly dependent on a molecular aggregation state of the surface [5,6]. Therefore, the control of a molecular aggregation state on the film is important to construct a highly functionalized surface. One 0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.08.034