An ‘aqueous route’ for the fabrication of low-temperature-processable oxide flexible transparent thin-film transistors on plastic substrates

Abstract

Metal-oxide semiconductors have attracted considerable attention as next-generation circuitry for displays and energy devices because of their unique transparency and high performance. We propose a simple, novel and inexpensive 'aqueous route' for the fabrication of oxide thin-film transistors (TFTs) at low annealing temperatures (that is, o200 1C). These results provide substantial progress toward solution-processed metal-oxide TFTs through naturally formed, unique indium complex and post annealing. The fabricated TFTs exhibited acceptable electrical performance with good large-area uniformity at low temperatures. Additional vacuum annealing facilitated the condensation reaction by effectively removing byproduct water molecules and resulted in the activation of the In 2 O 3 TFT at low annealing temperatures, even temperatures as low as 100 1C. In addition, we have demonstrated that the flexible and transparent oxide TFTs on plastic substrates exhibit good resistance to external gate bias stress. INTRODUCTIONMetal-oxide semiconductors (MOSs) are a unique class of materials that have both transparency and electronic conductivity. 1-3 Increasing demand for transparent semiconducting active materials has resulted in increased attention on the MOSs for next-generation electronics, including electronics for use in high-performance, flexible and transparent applications, because of their favorable field-effect mobility, high optical transparency and good environmental stability. 4,5 In the early studies, these materials were primarily prepared using a vacuum process. 6,7 Although the vacuum-based deposition method has advantages, the high fabrication cost and large-area device uniformity restrict its areas of application. We suggest a simple and novel 'aqueous route' for the fabrication of oxide thin-film transistors (TFTs) at low annealing temperatures (that is, o200 1C). These results provide substantial progress toward solutionprocessed metal-oxide TFTs via a unique indium complex (IC) and post annealing. In addition, we have demonstrated that the flexible and transparent oxide TFTs on plastic substrates exhibit good resistance to external gate bias stress.The solution-based synthesis approach is considered a promising solution to the issues of fabrication cost and device uniformity. This

Metal oxide semiconductor thin-film transistors for flexible electronics

“…Due to their high T G % 360 C, PI substrates with thickness ranging from %3 to 50lm are widely used. 83,145,191,193,[197][198][199][220][221][222][223] Polyarylate (PAR) foils have also been employed, 192,200,224,225 given their good temperature stability (T G % 330 C), combined with a colorless transparency in the visible range. If the semiconductor deposition is performed at lower temperatures ( 150 C), also PES foils (T G around 200 C) can be utilized.…”

“…If the semiconductor deposition is performed at lower temperatures ( 150 C), also PES foils (T G around 200 C) can be utilized. 226 In an attempt to reduce the substrate cost, especially when cost-effective high throughput fabrication processes are targeted, less expensive (but also less thermally resistance) polymer substrates like PEN 190,[195][196][197]227,228 and PET 76,194,229,230 have been employed. Additionally, the use of paper substrates for flexible solution-processed ZnO TFTs has been investigated.…”

“…A few examples include c-PVP layers applied to planarize and smoothen the surface of PES or PI, 191,226 as well as PVP films utilized to reduce the surface roughness of PI foils from 3.6 nm down to 0.3 nm (root mean square). 232 145,197 Nevertheless, for solution-deposited metal oxide semiconductors, it is preferable to solution process also the gate dielectric, in order to further benefit from the lowcost large-area approach offered by solution-deposition processes. Within solution-processed gate dielectrics, polymeric materials are especially suitable due to the moderate annealing temperatures needed, as well as the high bendability that can be achieved.…”

“…The contact materials used in n-type solution-processed metal oxide semiconductor TFTs are generally similar to those employed for their vacuum-processed counterparts. Source/drain and gate electrodes are mostly made of Al and Au, 145,193,231 but also of transparent conducting metal oxides, such as ITO, 76,83,190,196,197 IZO, 220,221 or zinc indium tin oxide (ZITO). 192 In addition to the above mentioned materials, gate contacts are also made of Cr 145 or dual layers of Cr/Au, 220,221 which yield a good adhesion.…”

Hybrid complementary circuits based on p-channel organic and n-channel metal oxide transistors with balanced carrier mobilities of up to 10 cm2/Vs

“…31,32 Although it has been proven difficult to achieve high electron mobilities using these materials when processed at temperatures <200 C, various methods have been developed to overcome this limitation, including combustion synthesis, photonic annealing and chemical doping. 8,[33][34][35][36] In this work, we exploited the recently proposed In 2 O 3 /ZnO heterojunction channel architecture to improve the TFT's electron mobility, while maintaining the processing temperature below 200 C. 7 The main advantage of using such bilayer channels is demonstrated in Figure 2(a), where the transfer characteristics of TFTs based on single layers of ZnO and In 2 O 3 , compared with the transfer characteristics of an In 2 O 3 /ZnO bilayer, are plotted on the same graph. In 2 O 3 / ZnO TFTs exhibit consistently higher channel current (I D ) than In 2 O 3 and ZnO TFTs, indicative of higher electron mobility (l).…”