介面修飾對有機薄膜電晶體元件特性之影響

Abstract

本論文探討五環素(pentacene)與絕緣層間的介面修飾對薄膜電晶體啟動電壓(turn-on voltage,Vto)的影響。我們以PMMA、PVP以及HMDS處理絕緣層(SiNx)表面，分別測量電流電壓曲線與電容電壓曲線，發現啟動電壓(Vto)和平帶電壓(VFB)的點並不一致，推測這可能是由於修飾材料的特性造成了捕捉陷阱密度有差異。為了分析捕捉陷阱的來源，我們分為晶粒內部和晶粒邊界(grain boundary)兩部份來探討，我們發現五環素的排列整齊度是影響元件捕捉陷阱密度的主要因素，而造成啟動電壓位移則是由晶粒邊界數目多寡決定。由實驗結果可知，不同的介面修飾可導致元件的開啟電壓與平帶電壓偏移，如此便可利用簡單的旋塗製程調變啟動電壓。

The effect of surface treatments on the performance of organic thin-film transistors(OTFTs) has been investigated using pentacene as the active material. With poly-methyl-meth-acrylate(PMMA), poly-4-vinylphenol(PVP) or 1,1,1,3,3,3- hexamethyldisilazane(HMDS) on SiNx dielectric layers, the mismatch between the turn-on voltages and the flat-band voltages were observed, which were obtained from current-voltage and capacitance-voltage characteristics, respectively. This is probably due to different trap density in the channel of the devices. The traps probably distribute inside the grains and in the grain boundaries. It is found that the arrangement of the pentacene molecules determines the trap density of devices and the turn-on voltage shift is mainly affected by the density of grain boundaries. Using different polymers can modulate the device turn-on voltage and flatband voltage. As a result, a simple fabrication process of devices with various turn on voltage is achieved.