Xiao Zou

Top-Gate Low-Threshold Voltage

Copper oxide (Cu<i>x</i>O) thin films were grown on SiO₂/Si substrate by pulsed laser deposition under different substrate temperatures. Top-gate Cu<i>x</i> O semiconductor thin-film transistors (TFTs) were fabricated with high- κ HfON as gate dielectric. The performance of Cu₂O TFTs was improved due to increased Hall mobility resulting from the decreased scattering of both the ionized defects and the grain boundary for Cu₂O channel films. The <i>p</i>-channel pure polycrystalline Cu₂O TFTs (<i>W</i>/<i>L</i> = 500 μm/20 μm) exhibited a low threshold voltage of -0.8 V, an on-off current ratio of 3 x 10⁶, a saturation mobility of 4.3 cm²/ V s, and a subthreshold swing of 0.18 V/decade.

p\hbox{-}\hbox{Cu}_{2} \hbox{O}

We have fabricated and investigated amorphous indium gallium zinc oxide (α-IGZO) thin-film transistors (TFTs) by using HfO_xN_y/HfO₂/HfO_xN_y (NON) as the gate dielectric. The NON tristack dielectric structure can increase the gate capacitance density, effectively improve interface properties of both the gate/dielectric and dielectric/active channels, suppress the charge trap density, and reduce the gate leakage. The α-IGZO TFT (W/L = 200/10 μm) with NON shows superior performance such as a saturation current of 0.33 mA, an ON/OFF-current ratio of 2.2 × 10⁶, a saturation mobility of 10.2 cm²/V · s, a source/contact resistivity of 83 Ω · cm, a subthreshold swing of 0.13 V/dec, and enhanced stressing reliability.

Thin-Film Transistor Grown on

A low-cost Al-doped ZnO (AZO) thin film was deposited by radio-frequency magnetron sputtering with different Ar/O2 flow ratios. The optical and electrical properties of an AZO film were investigated. A highly conductive AZO film was inserted between the amorphous InGaZnO (a-IGZO) channel and the metal Al electrode to form a heterojunction source/drain contact, and bottom-gate amorphous a-IGZO thin-film transistors (TFTs) with a high κ HfON gate dielectric were fabricated. The AZO film reduced the source/drain contact resistivity down to 79 Ω cm. Enhanced device performance of a-IGZO TFT with Al/AZO bi-layer S/D electrodes (W/L = 500/40 µm) was achieved with a saturation mobility of 13.7 cm2 V−1 s−1, a threshold voltage of 0.6 V, an on-off current ratio of 4.7 × 106, and a subthreshold gate voltage swing of 0.25 V dec−1. It demonstrated the potential application of the AZO film as a promising S/D contact material for the fabrication of the high performance TFTs.

\hbox{SiO}_{2}/ \hbox{Si}

p-Type Cu₂O thin films and HfO₂ high-<i>k</i> gate dielectrics are deposited by pulsed laser ablation. p-Type Cu₂O metal-oxide-semiconductor capacitors and thin-film transistors (TFTs) are then fabricated and investigated. Experimental results show that a HfO₂/SiO₂-stacked gate dielectric can effectively improve interface properties and decrease gate-leakage current when compared with a SiO₂ gate dielectric. Thus, increased mobility, a decreased subthreshold swing, and enhanced gate-bias-voltage stressing stability have been achieved for the relevant Cu₂O TFTs. Bottom-gate and top-source/drain-contact p-channel Cu₂O TFTs (<i>W</i>/<i>L</i>= 500/20 μm) with the HfO₂/SiO₂-stacked gate dielectric exhibit superior performance with a saturation-carrier-mobility value of 2.7 cm²/V·s, an on-off current ratio of 1.5×10⁶, a subthreshold swing of 137 mV/dec, and a threshold-voltage shift of 1.4 V after gate-bias stress at 10 V for 3600 s.

Substrate Using a High-

High-κ HfOxNy and HfO2 films are applied to amorphous InGaZnO (a-IGZO) devices as gate dielectric using radio-frequency reactive sputtering. The electrical characteristics and reliability of a-IGZO metal–insulator–semiconductor (MIS) capacitors and thin-film transistors (TFTs) are then investigated. Experimental results indicate that the nitrogen incorporation into HfO2 can effectively improve the interface quality and enhance the reliability of the devices. Electrical properties with an interface-state density of 5.2 × 1011 eV−1 cm−2, capacitance equivalent thickness of 1.65 nm, gate leakage current density of 3.4 × 10−5 A cm−2 at Vfb +1 V, equivalent permittivity of 23.6 and hysteresis voltage of 110 mV are obtained for an Al/HfOxNy/a-IGZO MIS capacitor. Superior performance of HfOxNy/a-IGZO TFTs has also been achieved with a low threshold voltage of 0.33 V, a high saturation mobility of 12.1 cm2 V−1 s−1 and a large on–off current ratio up to 7 × 107 (W/L = 500/20 µm) at 3 V.

\kappa

ZnO nanorod strain driving transistor (SDT) with 107 scale “on”-“off” ratio has been fabricated on Kapton substrate by a single-step hydrothermal reaction. The transistor is driven by strain due to the change in Schottky barrier height caused by piezoelectric effect as well as the change of contact area between ZnO bridging nanorods. Moreover, via utilizing two SDTs on the top and bottom surfaces of the substrate as two complementary metal-oxide-semiconductor transistors, several logic operations such as inverter, NAND, NOR, XOR, MUX, and DEMUX with good rectifying behaviors have been demonstrated.

HfON Gate Dielectric

Highly transparent and amorphous InGaZnO thin films with high mobility were deposited on fused silica by pulsed laser deposition. The films remained amorphous after annealing at 700 °C and had bandgaps in the range 3.50–3.62 eV. The film deposited at 5 Pa and room temperature exhibits a Hall mobility of 54 cm2 V−1 s−1. An α-InGaZnO thin film transistor with high-k Ba0.6Sr0.4TiO3 as a dielectric layer and operating in enhanced mode with a saturation mobility of 5.8 cm2 V−1 s−1 and on/off ratio of 2 × 105 is demonstrated.

High-Performance Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors With

High-quality Mn:ZnO (MZO) film had been prepared on N-GaN coated sapphire substrates followed by postdeposition thermal annealing treatment at 700 °C. For the annealed MZO/GaN heterojunction, a 15 nm cubic structural ZnGa(2)O(4) layer was observed at the MZO/GaN interface through transmission electron microscope analysis. Through electroluminescence (EL) measurement, the formation of the nanointerface results in an EL transition from ultraviolet- to red-dominant mode for n-Mn:ZnO/N-GaN heterojunction light-emitting diodes (LEDs). The heterojunction LED showed a rectification ratio of ∼2.0 × 10(5) at ±2 V, a dark current of 3.5 nA at -2 V and a quite strong red EL with a low turn-on voltage of 3 V. On the basis of the energy band diagram, we think the EL transition from ultraviolet- to red-dominant mode is mainly due to the formation of a thin oxide blocking nanolayer at the MZO/GaN interface during the annealing process.