This talk reviews the recent progress in the development of transparent electronics based on ZnO.

Wurtzite ZnO is a wide bandgap material (~3.34eV) with an intrinsically high transparency in the visible range and a resistivity that can be tuned from semi-insulating right through to semi-metallic.  Compared with other Transparent Conduction Oxides (TCOs), ZnO has the lowest toxicity, the lowest cost and is the most amenable to chemical etching.  When doped with fluorine, it also has the highest optical transparency and the lowest plasma frequency.  Moreover, ZnO can be readily fabricated in crystalline form at relatively low temperatures using large-area deposition techniques [1]. These properties have led to the adoption of ZnO for a number of TCO applications, such as coatings for UV filtering and contacts for use in flat panel displays, solar cells and LEDs.

Recently, there has been a surge of activity in the development of next-generation Transparent Thin Film Transistors (TTFT) for use in applications such as electronic paper and flexible organic LED panels.  Amongst the TCOs attracting the most interest at present are wurtzite ZnO and amorphous InGaZnO₄ (a-IGZO).  This is due mainly to increases in the carrier mobilities which can be achieved with these materials. Indeed, typical mobilities for TTFTs made with state-of-the-art ZnO and a-IGZO are 250cm²/Vs and 100cm²/Vs, respectively, as compared with values of 100cm²/Vs and 1cm²/Vs for the polycrystalline and amorphous Si TTFTs, used in today's LCD displays.

Currently, there is also a lot of work into the development of p-type ZnO.  If these efforts succeed, we can expect a further generation of transparent electronics which moves on from discrete TTFTs to transparent integrated circuits and completely transparent electronic products [2].

[1] R. G. Gordon, MRS Bulletin, August (2000) 52              

[2] http://techon.nikkeibp.co.jp/article/HONSHI/20071024/141211/

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1. Photoluminescence studies of ZnO nanocolumns and nanocones grown by PLD on various substrates