Nano-Crystalline Silicon Thin Film Transistors on PET Substrates Using a Hydrogenation-assisted Metal-induced Crystalliz
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0910-A18-06
Nano-Crystalline Silicon Thin Film Transistors on PET Substrates Using a Hydrogenation-Assisted Metal-Induced Crystallization Technique Ashkan Behnam1, Saber Haji1, Farshid Karbassian1, Shams Mohajerzadeh1, Aida Ebrahimi1, Yaser Abdi1, and Michael D Robertson2 1 Thin Film Laboratory, Department of Electrical and Computer Eng, University of Tehran, Tehran, Tehran, 14395/515, Iran 2 Department of Physics, Acadia University, Wolfville, NS, B4P 2R6, Canada ABSTRACT The effects of RF-Plasma hydrogenation and applied mechanical strain on the crystallization of silicon layers deposited on plastic substrates have been investigated where the maximum temperature remained below 170 °C for the entire process. The structural properties of the samples have been studied by optical, scanning-electron and transmissionelectron microscopies where the nano-crystallinity of the silicon layers has been confirmed. The maximum average diameter of the silicon grains was 4.5 nm and occurred for an applied tensile strain of 4 %. In addition, a thin-film transistor on a plastic substrate has been fabricated and found to possess an electron mobility of 2.4 cm2/Vs. INTRODUCTION Thin film transistors are active switching devices whose performance depends on the quality and crystallinity of the channel material. Although it is essentially possible to achieve poly-crystalline films using high temperature annealing steps, in applications requiring lowcost, flexible substrates such as glass or plastic, low processing temperatures must be maintained in order to avoid thermal degradation of the substrate and crystallization becomes a challenge. Two important applications of polycrystalline silicon are solar cells [1] and thin-film transistor (TFT) drivers in liquid-crystal displays [2]. In these cases, low cost substrates such as glass or Kapton are usually coated by an amorphous silicon layer and crystallization is achieved by means of a subsequent annealing step [3-4]. Several techniques are used for the crystallization of amorphous silicon including solidphase crystallization (SPC), excimer-laser annealing (ELA) and metal-induced crystallization (MIC). SPC requires relatively high temperatures and long processing times, conditions incompatible with many low-cost substrates [5]. Excimer laser annealing is a low temperature approach that is most frequently used at present time, but it requires expensive apparatus to implement. On the other hand, MIC [6] is a promising technique which allows crystallization of the amorphous silicon layer at temperatures conducive to the use of lowcost glass and plastic substrates. In addition, metal-induced lateral crystallization (MILC), stress-assisted reorganization, hydrogenation and several other techniques have been widely studied and characterized during the past two decades[7-8]. We have previously reported the reduction of the annealing temperature for the
crystallization of silicon and germanium films by the application of an external mechanical stress in conjunction with the MIC method [9-11].
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