Spray‐Deposited Li‐Doped ZnO Transistors with Electron Mobility Exceeding 50 cm²/Vs

Abstract

The ever increasing demand for high performance electronic devices that can be fabricated onto large-area substrates employing low manufacturing cost techniques has given a boost to the development of alternative types of semiconductor materials, such as organics and metal oxides, with desirable physical characteristics that are absent in their traditional inorganic counterparts. Metal oxide semiconductors, in particular, are very attractive for implementation into thin-film transistors (TFTs) [1][2] mainly because of their high charge 2 carrier mobility, high optical transparency, excellent chemical stability, mechanical stress tolerance and processing versatility [3][4][5] . Oxide semiconductors are usually grown using vacuum-based techniques such as sputtering [6][7][8] , pulsed laser deposition [9] , chemical vapour deposition [10] , and ion-assisted deposition [11][12] . Based on these methods, the synthesis of a wide range of metal oxide semiconductors with high charge carrier mobilities and low carrier concentration has been demonstrated [7] . Many of these materials have been investigated for applications in thin-film electronics where transistors with electron mobilities up to 140 cm 2 /Vs have been demonstrated [7,[11][12][13][14][15][16] . Despite the great promise however, the application of vacuum-based technologies for the deposition of complex oxide semiconductors suffers from incompatibility with large-area substrates and hence high manufacturing cost. To this end, the development of alternative deposition methods based on solution processing paradigms could provide a breakthrough in both cost and performance by marrying fabrication simplicity with high-throughput manufacturing.In recent years a wide variety of soluble precursors compounds have been examined as potential alternatives for the fabrication of oxide-based TFTs using large area deposition methods including spin casting, dip coating and spray pyrolysis. For example, metal oxides such as zinc oxide (ZnO) [17][18][19][20][21][22] , indium oxide (In 2 O 3 ) [23][24] , indium gallium oxide (InGaO) [25] , indium zinc oxide (InZnO) [18][19][20][21][22][23][24][25][26] and zinc tin oxide (ZnSnO) [27] have been synthesised using soluble precursors and implemented into TFT structures. Despite the process simplicity, excellent charge carrier mobilities have been achieved, clearly demonstrating the significant potential of this alternative processing methodology. Here we show how spray pyrolysis (SP) can be used for the deposition of doped ZnO films and the fabrication of high electron mobility TFTs onto large area substrates under ambient atmosphere. Doping is achieved by simple physical blending of the soluble precursor compounds in water or alcohol based solutions. Among the various dopants studied, transistors fabricated using Li doped ZnO were 3 found to yield the best performance with maximum electron mobility > 50 cm 2 /Vs and on/off current modulation ratio exceeding 10 6 .Preparation of the Li doped precursor solutions is described in th...

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

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“…The high annealing temperature, which is usually 4400 1C, is not compatible with flexible plastic substrates, with conventional glass or with the stacked multi-layer structures because of the mismatch in the coefficient of thermal expansion between the layers during deposition. [10][11][12] A few studies on low-temperatureprocessable MOSs have been reported. [13][14][15][16] However, the authors of these studies used either complex and unstable precursors that required significant effort and multiple steps for synthesis or complicated chemical reactions that are not appropriate for the general fabrication technique.…”

Spray-combustion synthesis: Efficient solution route to high-performance oxide transistors

“…Sol-gel techniques are used extensively for MO film growth, including films for high-performance TFTs (10)(11)(12)(13). However, the required sol-gel condensation, densification, and impurity removal steps typically require >400-500°C processing temperatures, which are incompatible with inexpensive glasses and typical flexible plastic substrates (14).…”

Printed Oxide Thin Film Transistors: A Mini Review

“…Recently, metal oxide TFTs fabricated via solution-based processes have been considerably pursued for their potentials of offering simplicity, low cost, high throughput, and large area deposition. [9][10][11] Among various solution-based approaches, direct printing is a promising low-cost technique in fabricating TFTs. The printing technique offers several advantages in manufacturing electronics such as a direct writing of materials, reduction of chemical waste, and reproducibility with high-resolution scale, which are not affordable from other solution-based approaches.…”