Thin Solid Films 427 (2003) 371–376 0040-6090/03/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0040-6090(02)01242-7 Study of organic thin film transistors based on nickel phthalocyanine: effect of annealing R. Ben Chaabane *, A. Ltaief , C. Dridi , H. Rahmouni , A. Bouazizi , H. Ben Ouada a, a a b a a Laboratoire de Physique et Chimie des Interfaces, Faculte des Sciences de Monastir, Boulevard de l’Environnement 5019, Monastir, Tunisia a ´ Laboratoire d’etudes des Systemes thermiques et energetiques, Ecole Nationale d’Ingenieurs de Monastir, Route de l’environnement 5000, b ´ ` ´ ´ ´ Monastir, Tunisia Received 3 June 2002; received in revised form 3 December 2002; accepted 5 December 2002 Abstract Conducting organic materials offer a unique combination of interesting properties that make them more attractive than inorganic materials currently used in microelectronics. It is advantageous to use organic thin film transistors (OTFT) when large display areas are required. This needs the enhancement of transistor performances by increasing the I yI ratio and the field effect on off mobility. In this report, the effects of annealing on the electrical properties of nickel phthalocyanine (NiPc) OTFTs were studied. Our work is based upon an analysis of different carrier-exchange mechanisms occurring at metalyorganic material interface.  2002 Elsevier Science B.V. All rights reserved. Keywords: Thin film transistors; Phthalocyanine; Electrical properties; Annealing 1. Introduction The introduction of new but well-established organic materials into existing microelectronic technologies often leads to dramatic improvement in functionality and qualityycost ratio w1x. Organic semiconductor thin films are recently w2x used as active elements in all- organic circuits, particularly those based on OTFTs organic light emitting diodes (OLEDs) w3,4x. The con- ductivity of these materials can be tuned by simple chemical manipulation of the material backbone w5x and the nature of the doping material as well as the level of doping. A wide variety of organic materials have been employed as active layers in organic TFTs: thiophene derivates; phenylene vinylene derivatives; pentacene; and metallophthalocyanine w5–8x. They have demon- strated interesting electrical performances rivalling those of amorphous silicon TFTs. Mobilities exceeding 1 cm yVs, I yI ratios of more than 10 and sub- 2 6 on off threshold swings below 1 Vydecade have been reported *Corresponding author. Present address: B405 E-Quad, Olden St, Monastir, Tunisia; Tel.: q216-73-500-276; fax: q216-73-500-278. E-mail address: rafik.benchaabane@fsm.rnu.tn (R. Ben Chaabane). w9x. Since the synthesis of the first metal-free-phtalocy- anine (H Pc), a wide range of different metallophthalo- 2 cyanine (MPc) have been produced and studied w5,10,11x. Fig. 1a shows the molecule structure of metallophthalocyanine. Among these organic materials, nickel phthalocyanine (NiPc) have been extensively studied from the point of view of their chemical sensing properties w10–12x. In order to improve the TFTs per- formances, carrier mobility should be increased by enhancing the film microstructure quality, which include defects passivation. In this paper, NiPc films carried out using thermal evaporation under secondary vacuum and are used as the active layer both in diode and TFT devices. The thermal annealing effect was studied and optimised in order to enhance device performances. 2. Experiment NiPc with 97% purity was purchased from KODAK and purified by successive sublimations under a stream of nitrogen in a temperature gradient purification system. Metal and thin NiPc films were fabricated using thermal evaporation under secondary vacuum system. This tech- nique participates to obtain high homogenous layers