Guoxia Liu

Aging effect and origin of deep-level emission in ZnO thin film deposited by pulsed laser deposition

ZnO thin films were deposited on sapphire substrates at 400°C in the pulsed laser deposition (PLD) system. Those thin films showed two emission peaks. One was near band edge emission at around 379nm; the other was deep-level (DL) emission at around 510nm. The aging effect on photoluminescence (PL) of the thin film was observed. It was found that the DL emission decreased with time. Post-annealing processes were carried out to find the origin of the DL emission. The thin films were annealed at 800°C in N2 or O2 ambient gas in a rapid thermal annealing system. An atomic force microscope was used to investigate the surface morphologies of the thin films. The surface roughness of annealed thin film was much smaller than that of the as-deposited one. The transmittance of the annealed thin film decreased much compared with that of the as-deposited thin film. The DL emission of the thin film annealed in N2 increased, and the DL emission of thin film annealed in O2 decreased. The oxygen vacancies instead of zinc ...

High-performance fully amorphous bilayer metal-oxide thin film transistors using ultra-thin solution-processed ZrOx dielectric

In this study, we report high-performance amorphous In2O3/InZnO bilayer metal-oxide (BMO) thin-film transistor (TFT) using an ultra-thin solution-processed amorphous ZrOx dielectric. A thin layer of In2O3 offers a higher carrier concentration, thereby maximizing the charge accumulation and yielding high carrier mobility. A thick amorphous layer of InZnO controls the charge conductance resulting in low off-state current and suitable threshold voltage. As a consequence, the BMO TFT showed higher filed-effect mobility (37.9 cm2/V s) than single-layer InZnO TFT (7.6 cm2/V s). Apart from that we obtain an on/off current ratio of 109, a subthreshold swing voltage of 120 mV/decade, and a voltage shift ≤ 0.4 V under positive bias stress for 2.5 h, for a gate voltage of 3 V and drain voltage of 1 V. These data demonstrate that the BMO TFT has great potential for a broad range of applications as switching low-power transistors.

Hole mobility modulation of solution-processed nickel oxide thin-film transistor based on high-k dielectric

Solution-processed p-type oxide semiconductors have recently attracted increasing interests for the applications in low-cost optoelectronic devices and low-power consumption complementary metal-oxide-semiconductor circuits. In this work, p-type nickel oxide (NiOx) thin films were prepared using low-temperature solution process and integrated as the channel layer in thin-film transistors (TFTs). The electrical properties of NiOx TFTs, together with the characteristics of NiOx thin films, were systematically investigated as a function of annealing temperature. By introducing aqueous high-k aluminum oxide (Al2O3) gate dielectric, the electrical performance of NiOx TFT was improved significantly compared with those based on SiO2 dielectric. Particularly, the hole mobility was found to be 60 times enhancement, quantitatively from 0.07 to 4.4 cm2/V s, which is mainly beneficial from the high areal capacitance of the Al2O3 dielectric and high-quality NiOx/Al2O3 interface. This simple solution-based method for pr...

Low-temperature fabrication of high performance indium oxide thin film transistors

In this study, indium oxide (In2O3) thin-film transistors (TFTs) were fabricated by a solution-process at low temperature. A single precursor in a single solvent system was used as the In2O3 precursor to minimize the carbon-based impurities. The 300 °C-annealed In2O3 TFT with channel thickness of 12 nm exhibits enhanced performance, which shows saturation mobility (μsat) of 3.08 cm2 V−1 s−1, an on/off current ratio (Ion/Ioff) of 1.04 × 108, a threshold voltage (VT) of 12.7 V, and a subthreshold swing (SS) of 1.49 V per decade. Finally, high-performance In2O3 TFT based on solution-processed zirconium oxide dielectric was realized, which shows distinguished electrical performance (μsat = 13.01 cm2 V−1 s−1, Ion/Ioff = 1.09 × 107, VT = 1.2 V, and SS = 0.1 V per decade). These results suggest that solution-processed In2O3 TFTs could potentially be used for low-cost, low-temperature, and high-performance electronic devices.

Eco-friendly water-induced aluminum oxide dielectrics and their application in a hybrid metal oxide/polymer TFT

Solution-processed oxide semiconductors have been widely studied with the objective of achieving high-performance, sustainable and low-cost electronic devices. In this report a simple and eco-friendly water-inducement method has been developed to fabricate high-k dielectrics and hybrid thin-film transistors (TFTs); introducing metal nitrates and deionized water as the precursor materials. The AlOx dielectric films annealed at temperatures higher than 350 °C result in low leakage current densities and the dielectric constants are nearly 7. Instead of the conventional oxide semiconductors, water-induced (WI) polyvinylprrolidone (PVP) was introduced into the In2O3 solution to form a hybrid metal oxide/polymer channel layer. The 250 °C-annealed WI In2O3 : PVP TFTs based on AlOx dielectric exhibit outstanding electrical performances and high stability. These promising properties were obtained at an ultra-low operating voltage of 2 V. The WI metal oxide/polymer hybrid TFTs are promising alternatives for applications in low-cost, low-consumption and eco-friendly flexible electronics.

Solution-processed p-type copper oxide thin-film transistors fabricated by using a one-step vacuum annealing technique

Copper oxide (CuxO) thin films were fabricated on SiO2/Si substrates by using a solution process. The coated CuxO gel films were treated using a vacuum annealing method at various temperatures (400–700 °C). X-ray diffraction results indicated that the vacuum annealing technique was effective in transforming CuO into Cu2O. Atomic force microscopy images showed that the mean grain size and the surface roughness of the resulting films increased with increasing annealing temperature. To verify the possibility of CuxO thin films as channel layers, the bottom gate structured thin film transistors (TFTs) were integrated. The electrical properties of the as-fabricated CuxO TFTs were improved with increasing processing temperature from 400 to 600 °C. The 600 °C-annealed CuxO TFT exhibited the best electrical performances, including a low threshold voltage of −3.2 V, a large field-effect mobility of 0.29 cm2 V−1 s−1, a small subthreshold swing of 0.8 V dec−1, and an on/off current ratio of 1.6 × 104, respectively. However, with increasing annealing temperature, the electrical properties of the CuxO TFTs were degraded dramatically. These results suggest that solution-processed CuxO TFTs achieved by using a one-step vacuum annealing technique could potentially be used for high-performance p-type electronic devices, which represents a great step towards the further development of low-cost and all-oxide CMOS electronics.

Solution Combustion Synthesis: Low‐Temperature Processing for p‐Type Cu:NiO Thin Films for Transparent Electronics

Low-temperature solution processing opens a new window for the fabrication of oxide semiconductors due to its simple, low cost, and large-area uniformity. Herein, by using solution combustion synthesis (SCS), p-type Cu-doped NiO (Cu:NiO) thin films are fabricated at a temperature lower than 150 °C. The light doping of Cu substitutes the Ni site and disperses the valence band of the NiO matrix, leading to an enhanced p-type conductivity. Their integration into thin-film transistors (TFTs) demonstrates typical p-type semiconducting behavior. The optimized Cu5% NiO TFT exhibits outstanding electrical performance with a hole mobility of 1.5 cm2 V-1 s-1 , a large on/off current ratio of ≈104 , and clear switching characteristics under dynamic measurements. The employment of a high-k ZrO2 gate dielectric enables a low operating voltage (≤2 V) of the TFTs, which is critical for portable and battery-driven devices. The construction of a light-emitting-diode driving circuit demonstrates the high current control capability of the resultant TFTs. The achievement of the low-temperature-processed Cu:NiO thin films via SCS not only provides a feasible approach for low-cost flexible p-type oxide electronics but also represents a significant step toward the development of complementary metal-oxide semiconductor circuits.

Photochemical Activation of Electrospun In2O3 Nanofibers for High-Performance Electronic Devices

Electrospun metal oxide nanofibers have been regarded as promising blocks for large-area, low-cost, and one-dimensional electronic devices. However, the electronic devices based on electrospun nanofibers usually suffer from poor performance and inferior viability. Here, we report an efficient photochemical process using UV light generated by a high-pressure mercury lamp to promote the electrical performance of the nanofiber-based electronic devices. Such UV treatment can lead to strong photochemical activation of electrospun nanofibers, and therefore, a stable adherent nanofiber network and electronic-clean interface were formed. By use of UV treatment, high-performance indium oxide (In2O3) nanofiber based field-effect transistors (FETs) with highly efficient modulation of electrical characteristics have been successfully fabricated. To reduce the operating voltage and further improve the device performance, the In2O3 nanofiber FETs based on solution-processed high-k AlOx dielectrics were integrated and investigated. The as-fabricated In2O3/AlOx FETs exhibit superior electrical performance, including a high mobility of 19.8 cm2 V-1 s-1, a large on/off current ratio of 106, and high stability over time and cycling. The improved performance of the UV-treated FETs was further confirmed by the integration of the electrospun In2O3/AlOx FETs into inverters. This work presents an important advance toward the practical applications of electrospun nanofibers for functional electronic devices.

Low-temperature, nontoxic water-induced high-k zirconium oxide dielectrics for low-voltage, high-performance oxide thin-film transistors

The fabrication of water-induced amorphous high-k zirconium oxide (ZrOx) dielectrics has been proposed with the objective of achieving high performance and reducing costs for next generation displays. In this study, the as-prepared ZrOx thin films were fabricated by a sequential process, including a UV-assisted photochemical treatment and a thermal annealing process at temperatures lower than 300 °C. It is observed that the leakage current density of ZrOx thin films decreases, and the capacitance increases with increasing annealing temperatures. To verify the application possibilities of ZrOx thin films as gate dielectrics in complementary metal-oxide semiconductor (CMOS) electronics, both n-type In2O3 and p-type NiOx channel layers were integrated with ZrOx dielectrics and their corresponding electrical performances were examined. The In2O3/ZrOx thin film transistor (TFT) annealed at 250 °C exhibited a high electron mobility of 10.78 cm2 V−1 s−1, a small subthreshold swing of 75 mV dec−1, and a large on–off current ratio (Ion/Ioff) of around 106, respectively. Moreover, the p-type NiOx/ZrOx TFT exhibited an Ion/Ioff of 105 and a hole mobility of 4.8 cm2 V−1 s−1. It is noted that both n- and p-channel oxide TFTs on ZrOx could be operated at voltages lower than 4 V. The low-temperature fabrication process marks a great step towards the further development of low-cost, all-oxide CMOS electronics on flexible substrates.

High-mobility p-type NiOx thin-film transistors processed at low temperatures with Al2O3 high-k dielectric

Although there are a few research studies on solution-processed p-channel oxide thin-film transistors (TFTs), the strict fabrication conditions and the poor electrical properties have limited their applications in low-power complementary metal oxide semiconductor (CMOS) electronics. Here, the application of the polyol reduction method for processing p-type CuxO and NiOx channel layers and their implementation in TFT devices are reported. The optimized CuxO and NiOx TFTs were achieved at low annealing temperatures (∼300 °C) and exhibited decent electrical properties. Encouraged by the inspiring results obtained on SiO2/Si substrates, the TFT performance was further optimized by device engineering, employing high-k AlOx as the gate dielectric. The fully solution-processed NiOx/AlOx TFT could be operated at a low voltage of 3.5 V and exhibits a high hole mobility of around 25 cm2 V−1 s−1. Our work demonstrates the ability to grow high-quality p-type oxide films and devices via the polyol reduction method over large area substrates while at the same time it provides guidelines for further p-type oxide material and device improvements.