You Meng

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.

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.

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.

Solution-processed high-k magnesium oxide dielectrics for low-voltage oxide thin-film transistors

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. Thi...

Low-Voltage High-Stability InZnO Thin-Film Transistor Using Ultra-Thin Solution-Processed ZrO

This paper deals with the evaluation of the performances of InZnO thin-film transistor (TFT) using as dielectric an ultra-thin solution-processed ZrOx layer. The ZrOx thin film was formed using ultraviolet (UV) photo-annealing method and shows a low leakage-current density of 4 nA/cm2 at 3.8 MV/cm and a large areal-capacitance of 775 nF/cm2 at 50 Hz. The InZnO TFT incorporating the UV-treated ZrOx dielectric exhibits high stable and enhanced characteristics, an on/off current ratio of 107, a field-effect mobility of 14.7 cm2/V·s, a subthreshold swing voltage of 100 mV/decade and a threshold voltage shift under bias stress, for 2 hours less than 0.1 V. All these performances are obtained at a low operation voltage of 2 V and make it suitable for use as a switching transistor in low-power electronics applications.

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In this paper, high-k strontium oxide (SrO_x) dielectric thin films were fabricated using simple and low-cost solution process. The formation and properties of SrO_x thin films annealed at various temperatures (400 °C, 500 °C, 600 °C, and 700 °C) were investigated using numbers of characterization techniques. The electrical analysis indicates that the insulating properties of SrO_x thin films were improved with increasing annealing temperature. The post-annealing at temperatures higher than 400 °C enables the SrO_x thin film, exhibiting low-leakage current density of ~10⁻⁸ A cm⁻² at 3 V and the areal capacitance larger than 350 nF cm⁻² at 20 Hz. To further explore the possible applications of solution-processed high-k SrO_x thin films for thin-film transistors (TFTs), the indium oxide (In₂O₃) TFTs based on SrO_x thin films were integrated for testing. The optimized In₂O₃/SrO_x TFT exhibits high performance with an average field-effect mobility of 5.61 cm² V⁻¹ s⁻¹, a small subthreshold swing of 110 mV dec⁻¹, and a large on/off current ratio of 10⁷. To demonstrate the potential of In₂O₃/SrO_x TFT toward more complex logic applications, the unipolar inverter was further constructed and exhibited a high gain of 9.7. Importantly, all these device parameters were obtained at an ultralow operating voltage of 3 V, which represents a step toward portable, battery-driven, and low-power consumption electronics and circuits.

Dielectric

In this study, transparent p-type CuCrxOy semiconductor thin films were fabricated using spin coating and integrated as channel layers in thin-film transistors (TFTs). The structural, morphological components, and optical properties of CuCrxOy thin films, together with device performance, were systematically investigated. The phase conversion from a mixture of CuCr2O4 and CuO to pure CuCrO2 was achieved when the annealing temperature (Ta) was higher than 700 °C. The electrical performance of the CuCrxOy TFTs on SiO2 dielectric is improved with increasing Ta from 500 °C to 800 °C. The optimized CuCrO2 TFT exhibits an on/off current ratio of ∼105 and a hole mobility of 0.59 cm2 V−1 s−1, which is much better than those previous works on solution-processed binary CuxO TFTs. To our best knowledge, this work demonstrates the ternary p-type CuCrO2 TFTs fabricated via a low-cost solution process for the first time, which represents an important advancement towards the development of all-oxide, low-cost p–n junctions and CMOS logic circuits.