Aqueous Solution-Grown Crystalline Phosphorus Doped Indium Oxide for Thin-Film Transistors Applications.

Solution-grown indium oxide (In2O3) based thin-film transistors (TFTs) hold good prospects for emerging advanced electronics due to their excellent mobility, prominent transparency, and possibility of low-cost and scalable manufacturing; however, pristine In2O3 TFTs suffer from poor switching characteristics due to intrinsic oxygen-vacancy-related defects and require external doping. According to Shanmugam's theory, among potential dopants, phosphorus (P) has a large dopant-oxygen bonding strength (EM-O) and high Lewis acid strength (L) that would suppress oxygen-vacancy related defects and mitigate dopant-induced carrier scattering; however, P-doped In2O3 (IPO) TFTs have not yet been demonstrated. Here, we report aqueous solution-grown crystalline IPO TFTs for the first time. It is suggested that the incorporation of P could effectively inhibit oxygen-vacancy-related defects while maintaining high mobility. This work experimentally demonstrates that dopant with high EM-O and L is promising for emerging oxide TFTs.

UV response characteristics of mixed-phase MgZnO thin films with different structure distribution and high Iuv/Idarkratio and fast speed MgZnO UV detector with tunneling breakdown mechanism.

High performance UV detector with both high response and fast speed is hard to made on homogeneous crystal semiconductor materials. Here, the UV response characteristics of mix-phase MgZnO thin films with different internal structure distribution are studied, the mix-phase MgZnO based detector with given crystal composition own high response at both deep UV light (96 A/W at 240nm) and near UV light (80 A/W at 335nm). Meanwhile, because of quasi-tunneling breakdown mechanism within the device, the high response UV detector also show fast response speed (tr= 0.11 µs) and recovery speed (td1=26 µs) at deep UV light, which are much faster than the both low response mix-phase MgZnO based UV detectors with other structure constitution and reported high response UV devices on homogenous crystal materials. The Idarkof the device is just 4.27 pA under a 5 V bias voltage, so the signal to noise ratio of the device reached 23852 at 5.5uW/cm2 235nm UV light. Therefore, new quasi-tunneling breakdown mechanism is observed in some mix-phase MgZnO thin film that contains both c-MgZnO and h-MgZnO parts, which introduced high response, signal to noise ratio and fast speed into mix-phase MgZnO based UV detector at weak deep UV light.

Electric field modulation in the auxetic effect of BP-analog monolayer As and Sb by first-principles calculations.

In this paper, we have introduced the auxetic effect in black phosphorus (BP) analog Sb and achieved auxetic modulations in monolayer As and Sb via first-principles calculations. Compared with monolayer As, the monolayer Sb is phonon unstable. By applying uniaxial strain along each direction, we discovered zigzag-vertical reversibility on out-of-plane auxeticity, and the negative Poisson's ratios for monolayer As and Sb were simulated to be -0.125/-0.172 and -0.036/-0.063, respectively, by applying the strain along zigzag/vertical directions. The negative Poisson's ratio could be significantly manipulated by applying a vertical electric field as it can be increased up to 70.3% for monolayer As and decreased up to 55.6% for monolayer Sb. Such an intrinsic negative Poisson's ratio and electric field modulation could endow these monolayers with potential applications in auxetic optoelectronic devices, electrodes and sensors, leading to novel multi-functionalities.

Fast Response Solar-Blind Photodetector with a Quasi-Zener Tunneling Effect Based on Amorphous In-Doped Ga2O3 Thin Films.

A high-performance solar-blind photodetector with a metal-semiconductor-metal structure was fabricated based on amorphous In-doped Ga2O3 thin films prepared at room temperature by radio frequency magnetron sputtering. The photodetector shows a high responsivity (18.06 A/W) at 235 nm with a fast rise time (4.9 µs) and a rapid decay time (230 µs). The detection range was broadened compared with an individual Ga2O3 photodetector because of In doping. In addition, the uneven In distribution at different areas in the film results in different resistances, which causes a quasi-Zener tunneling internal gain mechanism. The quasi-Zener tunneling internal gain mechanism has a positive impact on the fast response speed and high responsivity.

Universal Way to Enhance Solution-Processed High-κ Oxide Dielectrics Performance by Sulfate Incorporation.

Vacuum-free, solution-processable high-κ-oxide dielectrics are considered to be a key element for emerging low-cost flexible electronics. However, they usually suffer from low breakdown strength and frequency-dependent capacitance, which limit their broader applications. Here, we report a universal way to improve solution-based high-κ oxide dielectric properties (e.g., Al2O3, ZrO2, Ga2O3, Sc2O3, Ho2O3, and Sm2O3) by sulfate incorporation. In-depth characterization shows that sulfate incorporation could reduce hydrogen and oxygen vacancy-related defects in high-κ oxides, thereby improving the dielectric performance. The optimized S-doped high-κ oxides show smooth surface (rms < 0.20 nm), low leakage current (∼10-7 A/cm2@4 MV/cm), excellent dielectric breakdown strength (>10 MV/cm), and stable capacitance-frequency characteristics. Besides, oxide thin-film transistors based on these high-κ dielectrics exhibit excellent performance (e.g., mobility >20 cm2 V-1 s-1, on/off ratio of ∼107, threshold swing of ∼0.14 V dec-1, threshold voltage of ∼0 V, and hysteresis of ∼0.02 V). Thus, this work provides a general approach for the development of high-quality solution-based high-κ oxides for transistor circuitry.

Boronization: A General Strategy for Rare Earth Oxides with Enhanced High-κ Gate Dielectric Performance.

Rare earth oxides (REOs) can be used as high-κ gate dielectrics that are at the core of electronic devices. However, a bottleneck remains with regard to obtaining high-performance REO dielectrics due to the serious hygroscopic issue and high defect states. Here, a general boronization strategy is reported to enhance the high-κ REO gate dielectric performance. Complementary characterization reveals that boronization is capable of reducing oxygen vacancies/hydroxyl defects in REOs and suppressing moisture absorption, leading to the improvement of leakage current, breakdown strength (up to 9 MV/cm), and capacitance-frequency stability. Furthermore, oxide transistors based on boronized REO dielectrics demonstrate state-of-the-art device characteristics with a high mobility of 40 cm2/V s, a current on/off ratio of 108, a subthreshold swing of 82 mV/dec, a hysteresis of 0.05 V, and superior bias stress stability.

Water-Induced Nanometer-Thin Crystalline Indium-Praseodymium Oxide Channel Layers for Thin-Film Transistors.

We report water-induced nanometer-thin crystalline indium praseodymium oxide (In-Pr-O) thin-film transistors (TFTs) for the first time. This aqueous route enables the formation of dense ultrathin (~6 nm) In-Pr-O thin films with near-atomic smoothness (~0.2 nm). The role of Pr doping is investigated by a battery of experimental techniques. It is revealed that as the Pr doping ratio increases from 0 to 10%, the oxygen vacancy-related defects could be greatly suppressed, leading to the improvement of TFT device characteristics and durability. The optimized In-Pr-O TFT demonstrates state-of-the-art electrical performance with mobility of 17.03 ± 1.19 cm2/Vs and on/off current ratio of ~106 based on Si/SiO2 substrate. This achievement is due to the low electronegativity and standard electrode potential of Pr, the high bond strength of Pr-O, same bixbyite structure of Pr2O3 and In2O3, and In-Pr-O channel's nanometer-thin and ultrasmooth nature. Therefore, the designed In-Pr-O channel holds great promise for next-generation transistors.

Water-Processed Ultrathin Crystalline Indium-Boron-Oxide Channel for High-Performance Thin-Film Transistor Applications.

Thin-film transistors (TFTs) made of solution-processable transparent metal oxide semiconductors show great potential for use in emerging large-scale optoelectronics. However, current solution-processed metal oxide TFTs still suffer from relatively poor device performance, hindering their further advancement. In this work, we create a novel ultrathin crystalline indium-boron-oxide (In-B-O) channel layer for high-performance TFTs. We show that high-quality ultrathin (~10 nm) crystalline In-B-O with an atomically smooth nature (RMS: ~0.15 nm) could be grown from an aqueous solution via facile one-step spin-coating. The impacts of B doping on the physical, chemical and electrical properties of the In2O3 film are systematically investigated. The results show that B has large metal-oxide bond dissociation energy and high Lewis acid strength, which can suppress oxygen vacancy-/hydroxyl-related defects and alleviate dopant-induced carrier scattering, resulting in electrical performance improvement. The optimized In-B-O (10% B) TFTs based on SiO2/Si substrate demonstrate a mobility of ~8 cm2/(V s), an on/off current ratio of ~106 and a subthreshold swing of 0.86 V/dec. Furthermore, by introducing the water-processed high-K ZrO2 dielectric, the fully aqueous solution-grown In-B-O/ZrO2 TFTs exhibit excellent device performance, with a mobility of ~11 cm2/(V s), an on/off current of ~105, a subthreshold swing of 0.19 V/dec, a low operating voltage of 5 V and superior bias stress stability. Our research opens up new avenues for low-cost, large-area green oxide electronic devices with superior performance.

Aqueous Solution-Processed Nanometer-Thin Crystalline Indium Ytterbium Oxide Thin-Film Transistors.

We demonstrate the growth of ultra-thin (~5 nm) indium ytterbium oxide (In-Yb-O) thin film using a simple vacuum-free aqueous solution approach for the first time. The influences of Yb addition on the microstructural, chemical, optical, and electrical properties of In2O3 are well investigated. The analyses indicate that Yb dopant could suppress oxygen vacancy defects effectively owing to the lower standard electrode potential, lower electronegativity, and stronger metal-oxide bond strength than that of In. The optimized In-Yb-O thin-film transistors (TFTs) exhibit excellent electrical performance (mobility of 8 cm2/Vs and on/off ratio of ~108) and enhanced stability. The triumph of In-Yb-O TFTs is owing to the high quality In2O3 matrix, the remarkable suppressor of Yb, and the nanometer-thin and atomically smooth nature (RMS: ~0.26 nm) of channel layer. Therefore, the eco-friendly water-induced ultra-thin In-Yb-O channel provides an excellent opportunity for future large-scale and cost-effective electronic applications.

Great Enhancement Effect of 20-40 nm Ag NPs on Solar-Blind UV Response of the Mixed-Phase MgZnO Detector.

High-performance solar-blind UV detector with high response and fast speed is needed in multiple types of areas, which is hard to achieve in one device with a simple structure and device fabrication process. Here, the effects of Ag nanoparticles (NPs) with different sizes on UV response characteristics of the device are studied, the Ag NPs with different sizes that are made from a simple vacuum anneal method. Ag NPs with different sizes could modulate the peak response position of the mixed-phase MgZnO detector from near UV range (350 nm) to deep UV range (235 nm), and the enhancement effect of the Ag NPs on the UV response differs much with the crystal structure and the basic UV response of the MgZnO thin film. When high density 20-40 nm Ag NPs is induced, the deep UV (235 nm) response of the mixed-phase MgZnO detector is increased by 226 times, the I uv/I dark ratio of the modified device is increased by 17.5 times. The slight enhancement in UV light intensity from 20 to 40 nm Ag NPs induces multiple tunnel breakdown phenomena within the mixed-phase MgZnO thin film, which is the main reason for the abnormal great enhancement effect on deep UV response of the device, so the recovery speed of the modified device is not influenced. Therefore, Ag NPs with different sizes could effectively modulate the UV response peak position of mixed-phase MgZnO thin films, and the introduction of Ag NPs with high density and small size is a simple way to greatly increase the sensitivity of the mixed-phase MgZnO detector at deep UV light without decreasing the device speed.

Ecofriendly Solution-Combustion-Processed Thin-Film Transistors for Synaptic Emulation and Neuromorphic Computing.

The ecofriendly combustion synthesis (ECS) and self-combustion synthesis (ESCS) have been successfully utilized to deposit high-k aluminum oxide (AlOx) dielectrics at low temperatures and applied for aqueous In2O3 thin-film transistors (TFTs) accordingly. The ECS and ESCS processes facilitate the formation of high-quality dielectrics at lower temperatures compared to conventional methods based on an ethanol precursor, as confirmed by thermal analysis and chemical composition characterization. The aqueous In2O3 TFTs based on ECS and ESCS-AlOx show enhanced electrical characteristics and counterclockwise transfer-curve hysteresis. The memory-like counterclockwise behavior in the transfer curve modulated by the gate bias voltage is comparable to the signal modulation by the neurotransmitters. ECS and ESCS transistors are employed to perform synaptic emulation; various short-term and long-term memory functions are emulated with low operating voltages and high excitatory postsynaptic current levels. High stability and reproducibility are achieved within 240 pulses of long-term synaptic potentiation and depression. The synaptic emulation functions achieved in this work match the demand for artificial neural networks (ANN), and a multilayer perceptron (MLP) is developed using an ECS-AlOx synaptic transistor for image recognition. A superior recognition rate of over 90% is achieved based on ECS-AlOx synaptic transistors, which facilitates the implementation of the metal-oxide synaptic transistor for future neuromorphic computing via an ecofriendly route.

High Photoresponse Black Phosphorus TFTs Capping with Transparent Hexagonal Boron Nitride.

Black phosphorus (BP), a single elemental two-dimensional (2D) material with a sizable band gap, meets several critical material requirements in the development of future nanoelectronic applications. This work reports the ambipolar characteristics of few-layer BP, induced using 2D transparent hexagonal boron nitride (h-BN) capping. The 2D h-BN capping have several advantages over conventional Al2O3 capping in flexible and transparent 2D device applications. The h-BN capping technique was used to achieve an electron mobility in the BP devices of 73 cm2V-1s-1, thereby demonstrating n-type behavior. The ambipolar BP devices exhibited ultrafast photodetector behavior with a very high photoresponsivity of 1980 mA/W over the ultraviolet (UV), visible, and infrared (IR) spectral ranges. The h-BN capping process offers a feasible approach to fabricating n-type behavior BP semiconductors and high photoresponse BP photodetectors.

Solar-Blind Photodetector with Lower Dark Current and Higher Ilight/Idark Ratio Based on Mg0.38Zn0.62O Film Deposited by Pulsed Laser Deposition Method.

In this study, pulsed laser deposition method (PLD) was employed to grow MgxZn1-xO films on quartz substrates. The optimal deposition temperature of 300 °C for MgxZn1-xO film was decided and Mg0.38Zn0.62O, Mg0.56Zn0.44O and Mg0.69Zn0.31O films were grown respectively using MgxZn1-xO targets with different Mg contents (x = 0.3, 0.5 and 0.7). As-deposited Mg0.38Zn0.62O film possessed the mixed-phase (hexagonal and cubic phase) structure, appropriate band gap of 4.68 eV and smaller surface roughness of 1.72 nm, and the solar-blind photodetector (PD) based on it was fabricated. The key features of our PD are the cutoff wavelength of 265 nm lying in solar-blind band, lower dark current (Idark) of 88 pA, higher peak responsivity of 0.10 A/W and bigger Ilight/Idark ratio of 1688, which provide the new idea for the application of solar-blind PDs based on MgxZn1-xO films.

Advances of RRAM Devices: Resistive Switching Mechanisms, Materials and Bionic Synaptic Application.

Resistive random access memory (RRAM) devices are receiving increasing extensive attention due to their enhanced properties such as fast operation speed, simple device structure, low power consumption, good scalability potential and so on, and are currently considered to be one of the next-generation alternatives to traditional memory. In this review, an overview of RRAM devices is demonstrated in terms of thin film materials investigation on electrode and function layer, switching mechanisms and artificial intelligence applications. Compared with the well-developed application of inorganic thin film materials (oxides, solid electrolyte and two-dimensional (2D) materials) in RRAM devices, organic thin film materials (biological and polymer materials) application is considered to be the candidate with significant potential. The performance of RRAM devices is closely related to the investigation of switching mechanisms in this review, including thermal-chemical mechanism (TCM), valance change mechanism (VCM) and electrochemical metallization (ECM). Finally, the bionic synaptic application of RRAM devices is under intensive consideration, its main characteristics such as potentiation/depression response, short-/long-term plasticity (STP/LTP), transition from short-term memory to long-term memory (STM to LTM) and spike-time-dependent plasticity (STDP) reveal the great potential of RRAM devices in the field of neuromorphic application.

Recent Advances of Solution-Processed Heterojunction Oxide Thin-Film Transistors.

Thin-film transistors (TFTs) made of metal oxide semiconductors are now increasingly used in flat-panel displays. Metal oxides are mainly fabricated via vacuum-based technologies, but solution approaches are of great interest due to the advantages of low-cost and high-throughput manufacturing. Unfortunately, solution-processed oxide TFTs suffer from relatively poor electrical performance, hindering further development. Recent studies suggest that this issue could be solved by introducing a novel heterojunction strategy. This article reviews the recent advances in solution-processed heterojunction oxide TFTs, with a specific focus on the latest developments over the past five years. Two of the most prominent advantages of heterostructure oxide TFTs are discussed, namely electrical-property modulation and mobility enhancement by forming 2D electron gas. It is expected that this review will manifest the strong potential of solution-based heterojunction oxide TFTs towards high performance and large-scale electronics.

Solar-Blind Photodetector with Lower Dark Current and Higher Ilight/Idark Ratio Based on Mg0.38Zn0.62O Film Deposited by Pulsed Laser Deposition Method.

In this study, pulsed laser deposition method (PLD) was employed to grow MgxZn1-xO films on quartz substrates. The optimal deposition temperature of 300 °C for MgxZn1-xO film was decided and Mg0.38Zn0.62O, Mg0.56Zn0.44O and Mg0.69Zn0.31O films were grown respectively using MgxZn1-xO targets with different Mg contents (x = 0.3, 0.5 and 0.7). As-deposited Mg0.38Zn0.62O film possessed the mixed-phase (hexagonal and cubic phase) structure, appropriate band gap of 4.68 eV and smaller surface roughness of 1.72 nm, and the solar-blind photodetector (PD) based on it was fabricated. The key features of our PD are the cutoff wavelength of 265 nm lying in solar-blind band, lower dark current (Idark) of 88 pA, higher peak responsivity of 0.10 A/W and bigger Ilight/Idark ratio of 1688, which provide the new idea for the application of solar-blind PDs based on MgxZn1-xO films.

High Sensitivity NO2 Gas Sensor Based on 3D WO3 Microflowers Assembled by Numerous Nanoplates.

Tungsten oxide microflowers (WO3 MFs) were fabricated by a simple hydrothermal process through adjusting the pH of the solution by HCl. These MFs possess the outer diameters of about 2 µm and are composed of numerous nanoplates with the average pore size of 10.9 nm. Chemiresistive activity of as-fabricated WO3 MFs sensor was attempted towards oxidizing and reducing target gases, revealing a superior selectivity to NO2 with a maximum response of 22.95 (2 ppm NO2) @105 °C compared to other target gases. One of the key features of as-fabricatedWO3 MFs sensor is the lower detection limit of 125 ppb and operating temperature of 105 °C to NO2 with better reproducibility, signifying commercial prospective of the developed sensor materials. Finally, the gas sensing mechanism of WO3 MFs sensor has been proposed.

Polymer-Assisted Deposition of Gallium Oxide for Thin-Film Transistor Applications.

We report the fabrication of gallium oxide (GaOx) thin films by a novel polymer-assisted deposition (PAD) method. The influence and mechanism of postannealing temperature (200-800 °C) on the formation and properties of GaOx thin films are investigated by complementary characterization analyses. The results indicate that solution-deposited GaOx experiences the elimination of organic residuals as well as the transformation of amorphous GaOx to crystalline GaOx with the increase in annealing temperature. High-quality GaOx could be achieved with a smooth surface, wide band gap, and decent dielectric performance. Moreover, the solution-processed In2O3 thin-film transistors based on optimized GaOx dielectrics demonstrate outstanding electrical performance, including a low operating voltage of 5 V, a mobility of 3.09 cm2 V-1 s-1, an on/off current ratio of 1.8 × 105, and a subthreshold swing of 0.18 V dec-1. Our study suggests that GaOx achieved by PAD shows great potential for further low-cost and high-performance optoelectronic applications.

Field Emission Properties of Molybdenum Nanoparticles Decorated ZnO Nanorod Arrays.

Precisely controlled dimensions of heterostructured ZnO nanorod arrays were grown on micropatterned Au films supported by Si substrate using chemical vapor deposition (CVD). The field emission properties were attributed to pointed nanorods, thickness of catalyst, preferential growth, density, morphology of ZnO and Molybdenum (Mo) decorated ZnO nanorod arrays (Mo/ZnO). The selective restrained heterostructure approach resulted in excellent control over periodicity, location and density of ZnO nanorod arrays. Overall, field emission properties of bare ZnO nanorod arrays showed a low turn-on field of ~4.7 V/µm and a high field enhancement factor (ß) ~1686 to 7.3 V/µm and (ß) ~807 for Mo/ZnO. It was also found that the field emission properties were significantly influenced by densely decorated Mo nanoparticles on as-grown ZnO nanorod arrays.

Recent Advances of Solution-Processed Metal Oxide Thin-Film Transistors.

Solution-processed metal oxide thin-film transistors (TFTs) are considered as one of the most promising transistor technologies for future large-area flexible electronics. This work surveys the recent advances in solution-processed metal oxide TFTs, including n-type oxide semiconductors, oxide dielectrics, and p-type oxide semiconductors. We first deliver a review on the history and present status of metal oxide TFTs. Then, we present the recent progress in solution-processed n-type oxide semiconductors, with a special focus on low-temperature and large-area solution-based approaches as well as emerging nondisplay applications. Next, we give a detailed analysis of the state-of-the-art solution-processed oxide dielectrics for low-power electronics. We further discuss the recent advances in solution-based p-type oxide semiconductors, which will enable the highly desirable future low-cost large-area complementary circuits. Finally, we draw conclusions and outline the perspectives over the research field.