Kazunori Kurishima

Influence of Al2O3 layer insertion on the electrical properties of Ga-In-Zn-O thin-film transistors

To investigate the influence of ionic/covalent interface of Al2O3/SiO2 gate insulator on the electrical properties of thin-film transistors (TFTs) with ionic Ga-In-Zn-O (GIZO) semiconducting channel layers, Al2O3 layers of different thickness were introduced between SiO2 and GIZO using plasma-enhanced atomic layer deposition. The GIZO layers were obtained by DC magnetron sputtering using a GIZO target (Ga:In:Zn = 1:1:1 mol. %). The GIZO TFTs with an Al2O3/SiO2 gate insulator exhibited positive threshold voltage (Vth) shift (about 1.1 V), Vth hysteresis suppression (0.23 V), and electron mobility degradation (about 13%) compared with those of a GIZO TFT with SiO2 gate insulator by the influence of ionic/ionic and ionic/covalent interface at Al2O3/GIZO and Al2O3/SiO2, respectively. To clarify the origin of the positive Vth shift, the authors estimated the shifts of flatband voltage (0.4 V) due to the dipole and the fixed charge (−1.1 × 1011/cm2) at Al2O3/SiO2 interface, from capacitance–voltage data for Pt/...

Improvement of smooth surface of RuO2 bottom electrode on Al2O3 buffer layer and characteristics of RuO2/TiO2/Al2O3/TiO2/RuO2 capacitors

Ruthenium oxide (RuO2) thin films, which are deposited by plasma-enhanced atomic layer deposition (PE-ALD) with a Ru(EtCp)2 precursor and oxygen plasma, exhibit a smoother surface [root mean square (RMS) roughness <1 nm] on ionic Al2O3 and TiO2 buffer layers than on a covalent SiO2 buffer layer (RMS roughness of RuO2: 2.5 nm). The Al2O3 and TiO2 buffer layers which have some charges enable us to prolong the duration time of the Ru(EtCp)2 precursor on the buffer layer and cause the nucleation of RuO2 to occur uniformly. The RuO2 film deposited on the Al2O3 buffer layer by PE-ALD (hereafter “PE-ALD-RuO2”) was used as the bottom electrode for a metal-insulator-metal with a TiO2/Al2O3/TiO2 (TAT) insulator. RuO2/TAT/RuO2 capacitors on the Al2O3 and TiO2 buffer layers had a low enough leakage current density (J) (on the order of ∼10−8 A/cm2), unlike RuO2/TAT/RuO2 capacitors on the SiO2 buffer layer and TiN/TAT/TiN capacitors. These results suggest that the different J properties must be related to the surface r...

Effect of carbon doping on threshold voltage and mobility of In-Si-O thin-film transistors

In this study, a co-sputtering method with In2O3 and SiC targets was used to fabricate carbon-doped In-Si-O (In1-xSixO1-yCy) as the channel material for oxide thin-film transistors (TFTs). Three types of In1-xSixO1-yCy channels, namely, In0.88Si0.12O0.99C0.01 (Si0.12C0.01), In0.76Si0.24O0.99C0.01 (Si0.24C0.01), and In0.60Si0.40O0.98C0.02 (Si0.40C0.02), were prepared. After annealing at 300 °C, the Si0.24C0.01 and Si0.40C0.02 films retained an amorphous structure, while the Si0.12C0.01 films exhibited a body-centered-cubic structure. However, all the In1-xSixO1-yCy films maintained a smooth surface with a root-mean-square roughness of approximately 0.28 nm, despite structural differences. Results showed that the conductivities of all the In1-xSixO1-yCy films were not sensitive to the O2 partial pressure during sputtering, indicating that In1-xSixO1-yCy films exhibit more stable electrical conductivity than other InOx-based oxides. The field-effect mobility (μFE) with respect to the Si concentration of In1-xSixO1-yCy and In1-xSixO TFTs showed very similar behavior. In contrast, the threshold voltage (Vth) behavior of the two types varied dramatically, with the In1-xSixO TFTs Vth value increasing drastically from −57.7 to 9.7 V with increasing Si concentration, and the Vth of In1-xSixO1-yCy TFTs increasing only gradually from −9.2 to 2.4 V. This indicates that incorporated carbon has a significant effect on Vth at a low Si concentration due to strong C—O bond formation. The highest bond dissociative energy occurs between O and C atoms in the In1-xSixO1-yCy channel. The amount of oxygen vacancy in Si0.12C0.01, Si0.24C0.01, and Si0.40C0.02 was 18.9%, 13.3%, and 12.9%, respectively. As a result, the Si0.12C0.01 TFT exhibited superior transistor properties of Vth = −9.2 V while maintaining a μFE of 32.4 cm2/Vs. Therefore, an In1-xSixO1-yCy film is significantly advantageous as a channel material for oxide TFTs given that it can result in mobility exceeding 30 cm2/Vs.In this study, a co-sputtering method with In2O3 and SiC targets was used to fabricate carbon-doped In-Si-O (In1-xSixO1-yCy) as the channel material for oxide thin-film transistors (TFTs). Three types of In1-xSixO1-yCy channels, namely, In0.88Si0.12O0.99C0.01 (Si0.12C0.01), In0.76Si0.24O0.99C0.01 (Si0.24C0.01), and In0.60Si0.40O0.98C0.02 (Si0.40C0.02), were prepared. After annealing at 300 °C, the Si0.24C0.01 and Si0.40C0.02 films retained an amorphous structure, while the Si0.12C0.01 films exhibited a body-centered-cubic structure. However, all the In1-xSixO1-yCy films maintained a smooth surface with a root-mean-square roughness of approximately 0.28 nm, despite structural differences. Results showed that the conductivities of all the In1-xSixO1-yCy films were not sensitive to the O2 partial pressure during sputtering, indicating that In1-xSixO1-yCy films exhibit more stable electrical conductivity than other InOx-based oxides. The field-effect mobility (μFE) with respect to the Si concentration of In1-...