Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers1. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H)2,3,4,5 and organic semiconductors2,6,7,8,9,10 have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven organic light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temperature and device performance. Here, we propose to solve this problem by using a novel semiconducting material—namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO)—for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temperature and exhibits Hall effect mobilities exceeding 10 cm2 V-1 s-1, which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit saturation mobilities of 6–9 cm2 V-1 s-1, and device characteristics are stable during repetitive bending of the TTFT sheet.

Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors

We report the fabrication of transparent field-effect transistors using a single-crystalline thin-film transparent oxide semiconductor, InGaO 3 (ZnO) 5 , as an electron channel and amorphous hafnium oxide as a gate insulator. The device exhibits an on-to-off current ratio of ∼10 6 and a field-effect mobility of ∼80 square centimeters per volt per second at room temperature, with operation insensitive to visible light irradiation. The result provides a step toward the realization of transparent electronics for next-generation optoelectronics.

http://science.sciencemag.org/content/sci/300/5623/1269.full.pdf

Thin-Film Transistor Fabricated in Single-Crystalline Transparent Oxide Semiconductor

Recently, we have demonstrated the potential of amorphous oxide semiconductors (AOSs) for developing flexible thin-film transistors (TFTs). A material exploration of AOSs desired as the channel layer in TFTs is most important for developing high-performance devices. Here, we report our concept of material exploration for AOSs in high-performance flexible and transparent TFTs from the viewpoints of chemical bonding and electronic structure in oxide semiconductors. We find that amorphous In–Ga–Zn–O (a-IGZO) exhibits good carrier transport properties such as reasonably high Hall mobilities (>10 cm2V-1s-1) and a good controllability of carrier concentration from <1015 to 1020 cm-3. In addition, a-IGZO films have better chemical stabilities in ambient atmosphere and at temperatures up to 500 °C. The flexible and transparent TFT fabricated using a-IGZO channel layer at room temperature operated with excellent performances, such as normally-off characteristics, on/off current ratios (~106) and field-effect mobilities (~10 cm2V-1s-1), which are higher by an order of magnitude than those of amorphous Si:H and organics TFTs.

https://iopscience.iop.org/article/10.1143/JJAP.45.4303/pdf

Amorphous Oxide Semiconductors for High-Performance Flexible Thin-Film Transistors

https://iopscience.iop.org/article/10.1088/1468-6996/11/4/044305/pdf

Present status of amorphous In–Ga–Zn–O thin-film transistors

An object of the present invention is to provide a new light-emitting device with the use of an amorphous oxide. The light-emitting device has a light-emitting layer existing between first and second electrodes and a field effect transistor, of which the active layer is an amorphous.

Light-emitting device

With the purpose of creating ZnO-based amorphous transparent conductors, a range of amorphous films InGaoO3(ZnO)m (where m ≤ 4) was prepared using a pulsed-laser deposition method. The resulting films exhibited an optical bandgap of 2.8-3.0 eV, and an n-type electric conductivity of 170-400 Scm−1 at room temperature, displaying a slight dependence on the value of m, in which the carrier density was 1019-1020 cm−3 the electron mobili ty was 12-20 cm2 V−1 s−1 showing no p n anomaly between Hall and Seebeck coefficients. The conductivity displayed no significant dependence on the temperature ranging from 10 to 300 K. X-ray diffraction, transmission electron microscopy and extended X-ray absorption fine structure measurements confirmed that the films were amorphous phases. A combined use of bremsstrahlung isochromat spectroscopy and ultraviolet photoelectron spectroscopy revealed that the conduction band tail had a large dispersion and that the Fermi level was located at the conduction band edge. The...

Amorphous transparent conductive oxide InGaO3(ZnO)m (m≤ 4): a Zn4s conductor

Frontier of transparent conductive oxide thin films

Electrical and photoluminescence properties were investigated for epitaxial films of layered oxychalcogenides, LnCuOCh (Ln = La, Pr, and Nd, Ch = S or Se). Epitaxial films of Mg 10 at. % doped LaCuOS1-xSex are the first demonstration of degenerate conduction with high hole concentration >1020 cm-3 in wide gap p-type semiconductors. Ion substitution varied the excitonic emission energy from 3.21 eV to 2.89 eV while lanthanide and chalcogenide ion substitutions displayed the opposite tendency against cell volume. These unique properties are discussed with respect to the electronic structure originating from the layered crystal structure.

Degenerate electrical conductive and excitonic photoluminescence properties of epitaxial films of wide gap p -type layered oxychalcogenides, LnCuOCh (Ln=La, Pr and Nd; Ch=S or Se)

Heteroepitaxial thin films of Cu-based oxychalcogenides, LnCuOCh (Ln = La, Pr and Nd; Ch = mixture of S and Se), were fabricated and their resulting film structures were characterized. A reactive solid-phase epitaxy method successfully yielded heteroepitaxial films on MgO(001) substrates. A high-resolution electron microscopic examination of a LaCuOS film revealed a sharp film-substrate interface. Four-axes high-resolution X-ray diffraction measurements revealed that crystalline lattices in the films are fully relaxed and that the crystallographic orientation is (001)[110] LnCuOCh || (001)[110] MgO. Furthermore, systematic variations in the lattice constant by lanthanide or chalcogen ion substitutions were observed.

M. Hirano

Papers

Amorphous transparent conductive oxide InGaO3(ZnO)m (m≤ 4): a Zn4s conductor

Frontier of transparent conductive oxide thin films

Degenerate electrical conductive and excitonic photoluminescence properties of epitaxial films of wide gap p -type layered oxychalcogenides, LnCuOCh (Ln=La, Pr and Nd; Ch=S or Se)

Heteroepitaxial growth of wide gap p-type semiconductors: LnCuOCh (Lr=La, Pr and Nd; Ch=S or Se) by reactive solid-phase epitaxy