Rodrigo Martins

Solution-processed metal-oxide thin films with high dielectric constants (k) have been extensively studied for low-cost and high-performance thin-film transistors (TFTs). In this report, MgO dielectric films were fabricated using the spin-coating method. The MgO dielectric films annealed at various temperatures (300, 400, 500, and 600 °C) were characterized by using thermogravimetric analysis, optical spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic-force microscopy. The electrical measurements indicate that the insulating properties of MgO thin films are improved with an increase in annealing temperature. In order to clarify the potential application of MgO thin films as gate dielectrics in TFTs, solution-derived In2O3 channel layers were separately fabricated on various MgO dielectric layers. The optimized In2O3/MgO TFT exhibited an electron mobility of 5.48 cm2/V s, an on/off current ratio of 107, and a subthreshold swing of 0.33 V/dec at a low operation voltage of 6 V. This work represents a great step toward the development of portable and low-power consumption electronics. © 2016 Author(s).

Oxide semiconductor thin-film transistors can show anomalous behavior under bias stress. Two types of anomalies are discussed in this paper. The first is the shift in threshold voltage (VTH) in a direction opposite to the applied bias stress, and highly dependent on gate dielectric material. We attribute this to charge trapping/detrapping and charge migration within the gate dielectric. We emphasize the fundamental difference between trapping/detrapping events occurring at the semiconductor/dielectric interface and those occurring at gate/dielectric interface, and show that charge migration is essential to explain the first anomaly. We model charge migration in terms of the non-instantaneous polarization density. The second type of anomaly is negative VTH shift under high positive bias stress, with logarithmic evolution in time. This can be argued as electron-donating reactions involving H2O molecules or derived species, with a reaction rate exponentially accelerated by positive gate bias and exponentially decreased by the number of reactions already occurred. © 2016 Author(s).

It is shown that the electronic properties of amorphous germanium (a-Ge) prepared by the glow-discharge decomposition of germane can be controlled systematically by substitutional phosphorus doping from the gas phase. Specimens with different doping levels have' been investigated by conductivity, thermoelectric power and Hall effect measurements in a temperature range between 160 and 450 K. The dependence of conductivity on doping level is qualitatively similar to that in a-Si, but the range of control is limited in a-Ge by the smaller mobility gap. Also the larger overall density of gap states in this material reduces the doping sensitivity. The above transport measurements and their temperature dependence can be interpreted in a quantitatively consistent manner- by a two-path model in which conduction takes place in the extended states and in another path through the localized states. As 111 a-Si, the photoconductivity of glow-discharge Ge can be appreciably sensitized by phosphorus doping. The μτ product deduced from such experiments on a-Ge and a-Si are compared for different preparation techniques. The data show that irrespective of the presence of hydrogen the method of deposition remains an important factor in determining the density of gap states. © 1979 Taylor & Francis Ltd.