The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

Atomic layer deposition: an overview.

Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

We report high-performance ZnO thin-film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19V, a saturation mobility of 27cm2∕Vs, a gate voltage swing of 1.39V∕decade and an on/off ratio of 3×105. The ZnO-TFT presents an average optical transmission (including the glass substrate) of 80% in the visible part of the spectrum. The combination of transparency, high mobility, and room-temperature processing makes the ZnO-TFT a very promising low-cost optoelectronic device for the next generation of invisible and flexible electronics.

Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature

We fabricated ZnO thin-film transistors by rf magnetron sputtering on Si substrates held near room temperature. The best devices had field-effect mobility of more than 2 cm2/V s and an on/off ratio>106. These ZnO films had resistivity ∼105 ohm cm, with high optical transparency (>80% for wavelength >400 nm), and compressive stress <0.5 GPa. The combination of transparency in the visible, excellent transistor characteristics, and low-temperature processing makes ZnO thin-film transistors attractive for flexible electronics on temperature sensitive substrates.

Transparent ZnO thin-film transistor fabricated by rf magnetron sputtering

We prepared by vapor deposition at room temperature thin (500 A) Co/Pt multilayers or layered structures directly onto glass or Si substrates. They show a preferential magnetization perpendicular to the film plane for Co thicknesses below 12 A and a 100% perpendicular remanence for Co thicknesses below 4.5 A. The magnetic anisotropy can be explained by an interface contribution to the anisotropy. We also investigated the magneto‐optical (MO) polar Kerr effect of these multilayers. Because of their excellent magnetic properties and their potentially high oxidation and corrosion resistance, these Co/Pt‐layered structures are very promising candidates for MO recording. The Kerr rotation θk at λ=820 nm for a 35×(4.0 A Co+12.7 A Pt)‐layered structure, which has 100% magnetic remanence, is modest (−0.12°), but the reflectivity R is high (70%), which results in a respectable figure of merit Rθ2k. Furthermore, the Kerr effect increases towards shorter wavelengths and thus favors future higher‐density recording.

Perpendicular magnetic anisotropy and magneto-optical Kerr effect of vapor-deposited Co/Pt-layered structures

Quantitative Ca tests were used to determine the water vapor transmission rate (WVTR) through 25nm thick Al2O3 gas diffusion barriers grown on plastic by atomic layer deposition (ALD). The measured WVTRs were 1.7×10−5g∕m2day at 38°C and 6.5×10−5g∕m2day at 60°C. Based on the apparent activation energy, the WVTR at 23°C is estimated to be only 6×10−6g∕m2day. The WVTR values for the Al2O3 ALD film are very similar to the WVTR value for the glass control. These Ca tests indicate that Al2O3 ALD gas diffusion barriers should enable display and lighting applications of highly moisture sensitive organic light-emitting diodes on plastic.

Ca test of Al2O3 gas diffusion barriers grown by atomic layer deposition on polymers

Thin films of Al2O3 grown by atomic layer deposition (ALD) were investigated as gas diffusion barriers on flexible polyethylene naphthalate and Kapton® polyimide substrates Al2O3 ALD films with thicknesses of 1–26nm were grown at 100–175°C For Al2O3 ALD films with thicknesses ⩾5nm, oxygen transmission rates were below the MOCON instrument test limit of ∼5×10−3cc∕m2∕day Applying a more sensitive radioactive tracer method, H2O-vapor transmission rates of ∼1×10−3g∕m2∕day were measured for single-sided Al2O3 ALD films with thicknesses of 26nm on the polymers Ultrathin gas diffusion barriers grown by Al2O3 ALD may enable organic displays and electronics on permeable, flexible polymer substrates

Gas diffusion barriers on polymers using Al2O3 atomic layer deposition

We fabricated high-performance ZnO thin-film transistors on gate dielectrics of HfO2, HfSiOx, and Al2O3, grown by atomic layer deposition (ALD). Devices on HfO2 had a mobility of 12.2cm2∕Vs with a threshold voltage of 2.6V and subthreshold slope of 0.5V∕decade. Device performance on Al2O3 depended on synthesis temperature. For 100nm thick Al2O3, synthesized at 200°C, ZnO devices had a mobility of 17.6cm2∕Vs with a threshold voltage of 6V and less than ∼0.1nA gate leakage at 20V. The overall trends were that devices on Hf oxides had a lower threshold voltage, while the gate leakage current density was lower on Al2O3. Device characteristics for all ALD dielectrics exhibited negligibly small hysteresis, suggesting a low defect density at the interface of ZnO with the gate dielectric.

P. F. Carcia

Papers

Transparent ZnO thin-film transistor fabricated by rf magnetron sputtering

Perpendicular magnetic anisotropy and magneto-optical Kerr effect of vapor-deposited Co/Pt-layered structures

Ca test of Al2O3 gas diffusion barriers grown by atomic layer deposition on polymers

Gas diffusion barriers on polymers using Al2O3 atomic layer deposition

High-performance ZnO thin-film transistors on gate dielectrics grown by atomic layer deposition