I. Shih

15.4: Excellent Performance of Indium-Oxide-Based Thin-Film Transistors by DC Sputtering

Results on indium-oxide-based transparent oxide TFTs, which the active layer is prepared by DC sputtering, are presented. The fabricated TOS TFTs show high mobility (37 cm2/V-s), high ON/OFF current ratio and large on-state current. Fabricating oxide TFTs on temperature-sensitive substrates is also attainable owing to the low temperature process of the active layer preparation.

Chemical etching of Y‐Cu‐Ba‐O thin films

Thin films of Y‐Ba‐Cu‐O have been deposited by rf sputtering using a stoichiometric target on alumina, zirconia, and Y2O3 coated silicon substrates. After a brief heat treatment in oxygen, a resistive transition was observed with an onset temperature from 89 to 94.6 K. Etching experiments of the as‐deposited films have been made to determine the etching rates of the compound. It was found that reproducible results can be readily obtained using the following solutions: H3PO4/H2O, HNO3/H2O, and HCl/H2O. Using a positive photoresist technology, 3 μm lines have been successfully produced by etching in these solutions. The present patterning process was found to have no deleterious effect on the superconducting characteristics of the Y‐Ba‐Cu‐O films.

Formation of Tl-Ca-Ba-Cu-O films by diffusion of Tl into rf-sputtered Ca-Ba-Cu-O

Using a rf sputtering method with a single Ca‐Ba‐Cu‐O target (Ca:Ba:Cu=2:2:3), thin films with a thickness of about 1 μm have been deposited on ZrO2 and Si substrates. Diffusion experiments showed that the resistivity can be largely reduced by treating the films in an environment containing O2 and Tl. Treatment experiments at different temperatures further showed that the resistivity was affected by the temperature. By treating at 730u2009°C for about 1 h, a film on ZrO2 with a transition temperature of about 110 K has been obtained. Zero resistance was achieved at 75 K.

Multilayer deposition of Tl‐Ba‐Ca‐Cu‐O films

Thin films of Tl‐Ba‐Ca‐Cu‐O with different atomic ratios and a thickness of about 2 μm have been prepared by a sequential thermal evaporation method on alumina substrates followed by a heat treatment in an environment containing O2 and Tl. The results showed that films with a superconducting onset temperature of about 120 K and a zero resistance temperature of 85 K can be obtained with the following Tl:Ca:Ba:Cu ratios: 2:2:2:3 or 2:2:2:4. Films with a superconducting transition onset at 115 K and a zero resistance temperature of 74 K were also obtained by heating Tl‐free multilayer films in the environment containing O2 and Tl. It was also found that this new material was more resistant to water.

Air heat treatment of In-doped ZnO thin films

Transparent ZnO thin films with a resistivity of about 1−3 × 10−3 ω cm have been prepared on glass substrates held in a horizontal position by an rf sputtering technique. The deposition experiments were made using a ZnO target containing 2 wt.% In2O3. For the films deposited on glass substrates held in a vertical position, a resistivity of 3 × 10−4 ω cm has been obtained. Air heat treatment experiments have been performed on the indium-doped ZnO films at temperatures between 200 and 350 °C. It was found that electrical resistance of the films deposited on horizontal substrates was stable for the treatment at temperatures below 250 °C. For treatment experiments at 350 °C, an increase in resistance by about 2 orders of magnitude has been observed after a period of 2 h. Experiments further showed that the low resistivity films deposited on vertical substrates were relatively unstable in air even at 200 °C.

Effects of FeCl3 doping on polymer-based thin film transistors

Polymer-based thin film transistors (PTFTs) were fabricated on glass substrates with anodized Al2O3 as gate insulators. RR-P3HT (regioregular poly–3-hexylthiophene) and MEH-PPV [poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene)] were respectively used as semiconducting active layers for the transistors. A two orders of magnitude increase in field effect mobility (from 7.2×10−4u200acm2/Vu200as to 7.4×10−2u200acm2/Vu200as) deduced from electrical data of transistors fabricated using FeCl3 doped RR-P3HT was observed. This increase is believed to be mainly due to a large reduction in contact resistance (from 108u200aΩ to 103u200aΩ) to the source and drain Au contacts. The conductivity of RR-P3HT was found to increase only slightly with the doping. For MEH-PPV, doping with FeCl3 also decreased its contact resistance. However, it (4 GΩ) was still much larger than the channel (polymer) resistance (1 MΩ), leading to a slight improvement in its field effect mobility. Theoretically, contacts between Au and P3HT should have very...

Y‐Ba‐Cu‐O films prepared by a paint‐on method

Polycrystalline films of Y‐Ba‐Cu‐O with a thickness of about 20–40 μm have been prepared on alumina substrates using a paint‐on method. The liquid source used was obtained by mixing powder of Y2O3, BaCO3, and CuO in liquid triethanolamine. Several Y‐Ba‐Cu‐O films with an onset temperature of about 100 K and a zero resistance temperature of 85 K have been obtained after a short heat treatment at 1000u2009°C in flowing O2.

Effect of heat treatment on electrodeposited CuInSe2 films

Thin films of CuInSe2 prepared by an electrodeposition method have been heat treated at temperatures up to about 450°C. The heat treatments were done in an evacuated environment. After the heat treatment, the samples were examined by electron probe microanalysis for composition and by X-ray diffraction for determination of crystalline quality. The results obtained showed that the quality of the films was improved by the heat treatment. From the compositional results, it was found that there was a loss of selenium during the heat treatment.

Al/p‐CuInSe2 metal‐semiconductor contacts

Al/p‐CuInSe2 Schottky contacts have been fabricated by vacuum‐depositing Al onto Bridgman‐grown p‐CuInSe2 single crystals. The barrier heights from the temperature‐dependent forward I‐V characteristics are significantly less than the C−2‐V intercepts. This is evidence of the presence of an interfacial layer and surface states in equilibrium with p‐CuInSe2. The barrier height, electron affinity, effective acceptor density, and relative Fermi potential as well as diffusion potential were estimated. The surface‐state density of the minimum order of 1012 cm−2u2009eV−1 was obtained for the etched CuInSe2 surface. The transverse doping profile was qualitatively determined.

Y-Ba-Cu-O thin films prepared by a multilayer vacuum method

Polycrystalline Y‐Ba‐Cu‐O thin films with a thickness of about 1 μm have been deposited on alumina substrates. The deposition was made by first sequentially evaporating Y/Ba/Cu layers followed by a heat treatment in an environment containing oxygen. The treated films were polycrystalline, and the electrical results showed an onset temperature of about 100 K and a zero‐resistance temperature of 78 K for the films treated at 850u2009°C for 2 h in oxygen.