Search

A facile route to mitigate the Fermi-level pinning between a p-type GaSb semiconductor and an Al 2O3 dielectric is proposed. Combination of the sulphurization of the GaSb surface and the subsequent rapid thermal annealing allowed for high quality GaSb/Al2O3 interfacial characteristics; the interfacial trap density value was ≤2.0 x 1012 cm-2 eV-1 in an energy range of 0.05 ≤ET -- Ev ≤0.45 eV for the PMOS capacitor via rapid thermal annealing at 575 °C. A physical rationale was given on the basis of the thermo-chemical conversion of Ga2O into Ga2O3 and the conformal elimination of Sb related elements and oxides on the GaSb surface. [ABSTRACT FROM AUTHOR]

Transition tantalum induced crystallization of amorphous zinc tin oxide (a-ZTO) was observed at low temperature annealing of 300 °C. Thin-film transistors (TFTs) with an a-ZTO channel layer exhibited a reasonable field-effect mobility of 12.4 cm2/Vs, subthreshold swing (SS) of 0.39V/decade, threshold voltage (VTH) of 1.5 V, and ION/OFF ratio of ~107. A significant improvement in the field-effect mobility (up to ~33.5 cm2/V s) was achieved for crystallized ZTO TFTs: this improvement was accomplished without compromising the SS, VTH, or ION/OFF ratio due to the presence of a highly ordered microstructure. [ABSTRACT FROM AUTHOR]

Thin film transistors (TFTs) were fabricated with a zinc oxide (ZnO) channel deposited by ultralow-pressure sputtering (ULPS) at a pressure less than 1.3x10-3 Pa. The field-effect mobility (μFE) and the subthreshold gate swing (SS) of the ULPS-ZnO TFTs were dramatically improved up to 8.5 cm2 /V s and 0.31 V/decade, respectively, compared to 1.6 cm2 /V s and 1.31 V/decade for the ZnO TFTs fabricated by a conventional sputtering pressure (CSP) of 6.7(10-1 Pa. The improved characteristics of the ULPS-ZnO TFTs compared to the CSP-ZnO one can be attributed to the greater densification of the ZnO semiconductor film at the lower deposition pressure. [ABSTRACT FROM AUTHOR]

Bias temperature instability of metal-oxide-semiconductor field effect transistors (MOSFETs) with various concentrations of La incorporation in Hf-based dielectrics was characterized by varying the magnitude and polarity of the stress biases. Contrasting dependences of charge trapping on the magnitude of the stress biases are shown by changing the bias polarity. A model based on the distortion of asymmetric energy band diagrams and La-induced interface dipoles is suggested to explain this behaviour. Change of gate leakage currents according to La-incorporation, magnitude, and polarity of bias stresses supports the validity of the model. [ABSTRACT FROM AUTHOR]

This study examined the impact of the passivation layer on the light-enhanced bias instability of Al–Sn–Zn–In–O (AT–ZIO) thin film transistors. The suitably passivated device exhibited only a threshold voltage (Vth) shift of 0.72 V under light-illuminated negative-thermal stress conditions, whereas the device without a passivation layer suffered from a huge negative Vth shift of >11.5 V under identical conditions. The photocreated hole trapping model could not itself explain this behavior. Instead, the light-enhanced Vth instability of the unpassivated device would result mainly from the photodesorption of adsorbed oxygen ions after exposing the AT–ZIO back-surface in an ambient atmosphere. [ABSTRACT FROM AUTHOR]

We investigated the impact of photon irradiation on the stability of gallium-indium-zinc oxide (GIZO) thin film transistors. The application of light on the negative bias temperature stress (NBTS) accelerated the negative displacement of the threshold voltage (Vth). This phenomenon can be attributed to the trapping of the photon-induced carriers into the gate dielectric/channel interface or the gate dielectric bulk. Interestingly, the negative Vth shift under photon-enhanced NBTS condition worsened in relatively humid environments. It is suggested that moisture is a significant parameter that induces the degradation of bias-stressed GIZO transistors. [ABSTRACT FROM AUTHOR]

Effects of Gd capping of HfSiON gate dielectric on the characteristics of n metal-oxide-semiconductor field effect transistor (nMOSFET) with TaC gate electrode were investigated. MOSFETs with an in situ deposited Gd/TaC bilayer demonstrated a reduced equivalent oxide thickness, 0.9 nm, and low VTH, 0.25 V, compared with MOSFETs without Gd capping layer. Backside secondary ion mass spectroscopy revealed that Gd atoms were diffused into the high-k gate dielectric and interfacial layer between high-k dielectric and Si substrate. The dipole moment at the high-k/SiO2 interface due to Hf–O and RE–O bonds is used to explain the VTH change. [ABSTRACT FROM AUTHOR]

We compared the effect of the temperature on the device stability of Al–Zn–Sn–O (AZTO) thin film transistors (TFTs) with top gate and bottom gate architectures. While the bottom gate device without any passivation layer on the AZTO channel layer showed a large threshold voltage (Vth) shift of 1.6 V after heating it from 298 to 398 K, the naturally passivated top gate device exhibited a smaller Vth shift of 0.6 V. This different behavior is discussed based on the concept of the thermal activation energy of the subthreshold drain current. It is proposed that the suitable passivation and lower interfacial trap density for the top gate TFT are responsible for its superior temperature stability compared to the bottom gate device. [ABSTRACT FROM AUTHOR]

Thin film transistors with a channel of Zn–In–Sn–O were fabricated via a combinatorial rf sputtering method. It was found that the role of the In atoms is to enhance the mobility and to shift the threshold voltage (Vth) negatively. On the other hand, the Sn fraction is critical for improving the overall trap density including the density-of-states of the bulk channel layer and the interfacial trap density at the ZnInSnO interface. The optimized transistor was obtained at a compositional ratio of Zn:In:Sn=40:20:40, which exhibited an excellent subthreshold gate swing of 0.12 V/decade, Vth of -0.4 V, and high Ion/off ratio of >109 as well as a high field-effect mobility of 24.6 cm2/V s. [ABSTRACT FROM AUTHOR]

The local structures of amorphous In–Ga–Zn–O (InGaZnO4 and In2Ga2ZnO7) films were examined by x-ray absorption spectroscopy and fine structure analysis. The local metal-oxygen coordination in both films indicated bipyramidal GaO5, ZnO5, and trigonal InO6 clusters. Further analyses showed splitting of the Zn–O bond length suggesting distortion of the ZnO5 cluster, which evidenced the existence of localized holes in the Zn atoms. In combination with the abundance of In 5s electrons, this shows that the In–Zn hopping interactions contribute to electrical conduction. [ABSTRACT FROM AUTHOR]

We investigated the effect of the high-k TiOx (k∼40) gate dielectric on the mobility (μFE) of indium-gallium-zinc oxide (IGZO) transistors. As the thickness of the TiOx layer at the interface of the IGZO channel and SiNx gate dielectric layer increased from 2 to 8 nm, the μFE value was monotonously reduced from 9.9 to 1.8 cm2/V s. The degradation of the mobility was attributed to the Coulomb scattering mechanism rather than the phonon scattering mechanism of the high-k TiOx layer based on the behavior of the temperature-dependent mobilities for all of the IGZO transistors. [ABSTRACT FROM AUTHOR]

We proposed a homojunctioned amorphous InGaZnO (a-IGZO) thin film transistor (TFT) and compared its performance to that of a conventional structured TFT. The source/drain regions were formed in the a-IGZO channel layer using Ar and H2 plasma treatments, respectively. Hydrogen itself was found to act as a carrier of donors with H2 plasma treatment, which had effects to a depth of 50 nm. Our TFT had a field-effect mobility of 7.27 cm2/V s, an on/off ratio of 1.2×107, a threshold voltage of 0.96 V, and a subthreshold swing of 0.49 V/decade. [ABSTRACT FROM AUTHOR]

We investigated the impact of the passivation layer on the stability of indium-gallium-zinc oxide (IGZO) thin film transistors. While the device without any passivation layer showed a huge threshold voltage (Vth) shift under positive gate voltage stress, the suitably passivated device did not exhibit any Vth shift. The charge trapping model, which has been believed to be a plausible mechanism, cannot by itself explain this behavior. Instead, the Vth instability was attributed to the interaction between the exposed IGZO backsurface and oxygen and/or water in the ambient atmosphere during the gate voltage stress. [ABSTRACT FROM AUTHOR]

We investigated the feasibility of controlling the threshold voltage (Vth) by adjusting the thickness of the active layer (tactive) rather than by conventional chemical doping in indium-gallium-zinc oxide (IGZO) transistors with an inverted staggered structure. The value of Vth of the IGZO transistor was linearly modulated from -15.3±1.6 to -0.1±0.21 V by reducing tactive without any significant change in the field-effect mobility (μFE), subthreshold gate swing, or Ion/off ratio. The free electron density extracted from the relationship between tactive and Vth was 1.9×1017 cm-3, which was consistent with the value of 1.5×1017 cm-3 obtained from the C-V measurement for the 30-nm-thick IGZO films. The slight increase in the μFE with increasing tactive, which was in contradiction with the behavior of the corresponding amorphous Si transistor, was explained by the anomalous behavior of the source/drain contact resistance. [ABSTRACT FROM AUTHOR]

The effect of water exposure on amorphous indium-gallium-zinc oxide (a-IGZO) semiconductors was reported. It was found that water can diffuse in and out of the a-IGZO film, reversibly affecting the transistor properties. Two competing mechanisms depending on the thickness of the active channel were clarified. The electron donation effect caused by water adsorption dominated for the thicker a-IGZO films (>=100 nm), which was manifested in the large negative shift (>14 V) of the threshold voltage. However, in the case of the thinner a-IGZO films (<=70 nm), the dominance of the water-induced acceptorlike trap behavior was observed. The direct evidence for this behavior was that the subthreshold swing was greatly deteriorated from 0.18 V/decade (before water exposure) to 4.4 V/decade (after water exposure) for the thinnest a-IGZO films (30 nm). These results can be well explained by the screening effect of the intrinsic bulk traps of the a-IGZO semiconductor. [ABSTRACT FROM AUTHOR]

The authors attempted to grow a semi-insulating silicon carbide (SiC) epitaxial layer by in situ iron doping. The homoepitaxial growth of the iron-doped 4H-SiC layer was performed by metal-organic chemical vapor deposition using the organo-silicon precursor bis(trimethylsilylmethane) (C7H20Si2) and the metal-organic precursor t-butylferrocene (C14H17Fe). For the measurement of the resistivity of the iron-doped 4H-SiC epilayers, the authors used the on resistance of Schottky barrier diode. Based on the measurement of the on resistance, it is shown that the free carrier concentration was decreased with increasing partial pressure of t-butylferrocene. The resistivity of the iron-doped 4H-SiC epilayer was about 108 Ω cm. [ABSTRACT FROM AUTHOR]