Saturation Field-effect Mobility Research Articles

High-mobility InSnZnO Thin Film Transistors via Introducing Water Vapor Sputtering Gas.

There is always a doubt that introducing water during oxide growing has a positive or negative effect on the properties of oxide films and devices. Herein, a comparison experiment on the condition of keeping the same oxygen atom flux in the sputtering chamber is designed to examine the influences of H2O on In-Sn-Zn-O (ITZO) films and their transistors. In comparison to no-water films, numerous unstable hydrogen-related defects are induced on with-water films at the as-deposited state. Paradoxically, this induction triggers an ordered enhancement in the microstructure of the films during conventional annealing, characterized by a reduction in H-related and vacancy (Vo) defects as well as an increase in film packing density and the M-O network ordering. Ultimately, the no-water thin-film transistors (TFTs) exhibit nonswitching behavior, whereas 5 sccm-water TFT demonstrates excellent electrical performance with a remarkable saturation field-effect mobility (μFE) of 122.10 ± 5.00 cm2·V-1·s-1, a low threshold (Vth) of -2.30 ± 0.40 V, a steep sub-threshold swing (SS) of 0.18 V·dec-1, a high output current (Ion) of 1420 μA, and a small threshold voltage shift ΔVth of -0.77 V in the negative bias stability test (3600 s).

Low-voltage solution-processed NaxCu1−xI thin-film transistors for mimicking synaptic plasticity

In this article, NaxCu1−xI thin-film transistors gated by chitosan for low-voltage operation have been created by doping CuI with different Na concentrations (x = 0, 0.05, 0.1). It is found that the devices exhibit optimal performance when x is 0.05: a large current on/off ratio of 1.62 × 105, a steep subthreshold slope of 17.72 mV/dec, a saturation field-effect mobility of 0.51 cm2/V s, and a threshold voltage of 1.10 V. The operating voltage of the devices is reduced to below 2 V due to the electric-double-layer (EDL) effect. At a frequency of 10 Hz, a maximum specific capacitance of 1.36 μF/cm2 can be obtained in the chitosan. The effects of bias stress and laser on Na0.05Cu0.95I thin-film transistors (TFTs) have been examined at the end of the article, and the results revealed that Na0.05Cu0.95I TFTs possess good stability. As the bias stress gets longer and the laser power increases, the transfer curves of TFTs shift positively. Also, artificial synaptic behaviors and functions have been simulated experimentally. It can be divided into single-pulse, double-pulse, and multiple-pulse. According to the experimental results, features such as short-term plasticity, long-term plasticity, paired-pulse facilitation, high-pass filtering, pulse logic, and spatial summation have been achieved. The electrostatic modulation of EDL due to proton transverse migration is vital for this simulation. The realization of low-voltage synaptic Na0.05Cu0.95I TFTs prepared by solution method with pulse logic and spatial summation functions is crucial for application of portable biosensors and neuromorphic systems.

Synaptic plasticity and memory mimicked in solution-processed K-doped CuI thin film transistors

Low-voltage electric double layer p-type thin film transistors (TFTs) were fabricated on glass substrates with copper iodide doped with potassium iodide (Cu0.95K0.05Ix) as the channel and chitosan as the dielectric. Cu0.95K0.05Ix TFTs exhibited Ion/Ioff ratio of 2.5 × 104, subthreshold swing of 30 mV/dec, threshold voltage of 1.34 V, operating voltage of 2 V, and saturation field-effect mobility of 16.6 cm2 V−1 s−1. The relaxation phenomenon induced by ion migration was effectively utilized, enabling Cu0.95K0.05Ix TFTs to simulate various synaptic plasticity functions. When a pulse is applied, the drain current reaches a peak, but it takes more time for the current to return to its equilibrium position after the pulse is removed, demonstrating the short-term memory (STM) characteristics of Cu0.95K0.05Ix TFT. It was observed an increasing trend in excitatory postsynaptic current (EPSC) with enhanced pulse width and amplitude, and when the pulse amplitude increased to −10 V, the TFT transitioned from STM to long-term memory characteristics. Furthermore, the measurement of consecutive EPSC revealed the paired-pulse facilitation (PPF) characteristics, with a gradual decrease in the PPF coefficient as the time interval increased, and a selective stronger response to high-frequency signals. Based on the aforementioned research, by extending the device structure to a dual in-plane-gate structure configuration and applying different pulse voltage sequences on the dual gate, the NOR logic functionality was achieved. The study demonstrates the significant potential of p-type Cu0.95K0.05Ix TFTs in the field of synaptic bionics, simulating human learning and memory, and neural chips.

Inkjet printing high mobility indium-zinc-tin oxide thin film transistor

Metal oxide thin film transistor has been widely used in flat panel display industry because of its low leakage current, high mobility and large area uniformity. Besides with the development of printed display technology, inkjet printing process can fabricate the customizable patterns on diverse substrates without the need for vacuum or lithography, can significantly reduce cost and has received more and more attention. In this paper, we fabricate a bottom gate bottom contact structure thin film transistor (TFT) with indium-zinc-tin-oxide (IZTO) semiconductor using inkjet printing process. The surface morphology of the printed IZTO film is modified by adjusting the solvent composition and solute concentration of the printing precursor ink. The experimental result show that the use of binary solvents can effectively overcome the coffee ring shape caused by the accumulation of solute edge during the volatilization process of a single solvent, and finally show a uniform and flat contour surface. Further increase in solute concentration is in favor of formation of convex surface topology. The reason for the formation of the flat surface of the oxide film is the balance between the inward Marangoni reflux of the solute and the outward capillary flow during volatilization. In addition, using binary solvents printed IZTO thin film transistor exhibit excellent electrical properties. The ratio of width/length=50/30 exhibit a high on-off ratio of 1.21×10<sup>9</sup>,a high saturation field-effect mobility of 16.6 cm<sup>2</sup>·V<sup>-1</sup>·s<sup>-1</sup>,a low threshold voltage of 0.84 V and subthreshold swing of 0.24 V/dec. The uniform and flat active layer thin film pattern can form good contact with the source leakage electrode, and the contact resistance of TFT devices with different width-to-length ratios is less than 1000 Ω, which can achieve the basic conditions of high mobility thin film transistors prepared by inkjet printing. Therefore, using mixture solvents provides a universal and facile way to print oxide films with desired surface topology and provide a visible path for inkjet printing of high-mobility thin film transistors.

Towards sustainable, solution-processed organic field-effect transistors using cashew gum as the gate dielectric

To realize low-cost, environmentally friendly electronic devices and circuits, there is currently a strong trend to explore plant-based dielectric materials because they can be responsibly sourced from agricultural or forest vegetation, are generally water-soluble, and possess good electrical insulator properties. In this contribution, organic field-effect transistors (OFETs) using a biopolymer dielectric obtained from exudates of Anacardium occidentale Linn. trees, namely, cashew gum (CG), are reported. To characterise the physical and dielectric properties of the gum, thin films and metal-insulator-metal (MIM) capacitors were prepared and characterized. To evaluate the material’s performance in OFETs, bottom-gate top-contact (BGTC) p-channel poly [3,6-di(2-thien-5-yl)-2,5-di(2-octyldodecyl)-pyrrolo (3,4-c)pyrrole-1,4-dione) thieno (3,2-b) thiophene]:polymethyl methacrylate (DPPTTT:PMMA) transistors were engineered and studied. The fabricated MIM capacitors display a comparatively high areal capacitance of 260 nF/cm2 at 1 kHz for 130 nm thick films. As a result, the solution-processed DPPTTT:PMMA OFETs favourably operate at 3 V with the average saturation field-effect mobility equal to 0.20 cm2/Vs., threshold voltage around −1.4 V, subthreshold swing in the region of 250 mV/dec, and ON/OFF current ratio well above 103. As such, cashew gum emerges as a promising dielectric for sustainable manufacturing of solution-processed organic FETs.

High-throughput methodology for the realization of high-entropy sub-nm equivalent-oxide-thickness high-dielectric-constant Ba(Ti,Zr,Ta,Hf,Mo)O3 film-based metal-oxide-semiconductor-related devices

This paper reports the use of a high-throughput sputtering technique for the fabrication of high-entropy high-dielectric-constant (high-k) Ba(Ti,Zr,Ta,Hf,Mo)O3 film libraries on Si substrates and sub-nm equivalent-oxide-thickness (EOT) metal−oxide−semiconductor (MOS) devices and metal−oxide−semiconductor field-effect transistors (MOSFETs). The elemental variations and amorphous microstructures are characterized using high-throughput X-ray fluorescence (XRF) and X-ray diffraction, respectively. The film library was patterned into 100 MOS configurations and the films with (Ba + Ti) = 0.41−0.47 at.%, (Mo + Zr) = 0.28−0.34 at.%, and (Ta + Hf) = 0.23−0.3 at.% exhibited favorably high k (325−374) and low tan δ (0.01−0.08) values with an impressive EOT ≈ 0.8−0.94 nm. The resulting MOSFETs after the rapid thermal annealing (RTA) exhibited excellent characteristics: an on/off current ratio of 8 × 106, saturated field-effect mobility of 138.4 cm2 V−1 s−1, a threshold voltage (VT) of 0.03 V, a subthreshold swing of 0.062 V⋅dec−1, and low interfacial defects of approximately 5.6 × 1010 eV cm−2. Small ΔVT and negligible changes in the maximum drain current were observed for the MOSFETs under various positive and negative gate-bias stress conditions before and after the RTA. Our devices outperformed various reported transistors, indicating the potential of the Ba(Ti,Zr,Ta,Hf,Mo)O3 films for use in a gate-first process for advanced gate stack-related devices.

Electronic and Charge Transport Properties in Bridged versus Unbridged Nanohoops: Role of the Nanohoop Size.

In the field of π-conjugated nanohoops, the size of the macrocycle has a strong impact on its structural characteristics, which in turn affect its electronic properties. In this work, we report the first experimental investigations linking the size of a nanohoop to its charge transport properties, a key property in organic electronics. We describe the synthesis and study of the first example of a cyclocarbazole possessing five constituting building units, namely [5]-cyclo-N-butyl-2,7-carbazole, [5]C-Bu-Cbz. By comparison with a shorter analogue, [4]-cyclo-N-butyl-2,7-carbazole, [4]C-Bu-Cbz, we detail the photophysical, electrochemical, morphological and charge transport properties, highlighting the key role played by the hoop size. In particular, we show that the saturated field effect mobility of [5]C-Bu-Cbz is four times higher than that of its smaller analogue [4]C-Bu-Cbz (4.22×10-5 vs 1.04×10-5 cm2 V-1 s-1 ). However, the study of the other organic field-effect transistor characteristics (threshold voltage VTH and subthreshold slope SS) suggest that a small nanohoop is beneficial for good organization of the molecules in thin films, whereas a large one increases the density of structural defects, and hence of traps for the charge carriers. The present findings are of interest for the further development of nanohoops in electronics.

Low-voltage solution-processed P-type Mg-doped CuI thin film transistors with NAND logic function

Low-voltage electric-double-layer (EDL) p-channel Mg-doped CuI thin-film-transistors (TFTs) have been fabricated on glass substrates at low temperatures. Electrical properties of the solution-processed CuI TFTs with different Mg doping concentrations were investigated. It is observed that compared to undoped CuI TFTs and Mg0.1Cu0.9Ix TFTs, Mg0.05Cu0.95Ix TFTs exhibit an excellent current on/off ratio of 1.1 × 105, a steep subthreshold swing of 21.78 mV/dec, a higher saturation field-effect mobility of 0.95 cm2 V−1 s−1, and the threshold voltage of 1.81 V. The high specific capacitance of 4.7 μF/cm2 is obtained in solution-processed chitosan dielectrics; when it was used as the gate dielectric instead of traditional SiO2, the operating voltage of TFTs can be reduced to 2.5 V. It is noteworthy that the NAND logic function has been realized on the dual in-plane-gate structure of such Mg0.05Cu0.95Ix-based TFTs. Finally, the effects of laser (λ = 638 nm) and negative bias stress (NBS) were observed on Mg0.05Cu0.95Ix TFTs. The transfer curves of the TFT drifted positively as the power of the laser progressively increased; the OFF-state current gradually increased as the NBS time became longer. This paper provides an effective way to improve the performance of p-channel CuI TFTs and indicates that Mg0.05Cu0.95Ix as a promising p-type material for next-generation high-performance low-power-consumption logic circuit applications.

Effect of passivation layer on back channel etching InGaZnO thin film transistors

Amorphous indium gallium zinc oxide (IGZO) thin film transistors (TFT) are widely used in active-matrix displays because of their excellent stability, low off-current, high field-effect mobility, and good process compatibility. Among IGZO TFT device structures, back channel etching (BCE) is favorable due to low production cost, short channel length and small SD-to-gate capacitance. In this work, prepared are the BCE IGZO TFTs each with the passivation layer of silicon dioxide (SiO<sub>2</sub>), polyimide (PI) or SiO<sub>2</sub>-PI stacked structure to study their difference in back channel hydrogen impurity and diffusion behavior. Comparing with the conventional SiO<sub>2</sub> passivation BCE TFT, the performance of PI passivation TFT is improved greatly, specifically, the saturation field effect mobility increases from 4.7 to 22.4 cm<sup>2</sup>/(V·s), subthreshold swing decreases from 1.6 to 0.28 V/decade, and the an on-off current ratio rises dramatically from 1.1×10<sup>7</sup> to 1.5×10<sup>10</sup>. After the SiO<sub>2</sub> passivation layer is substituted with PI, the I<sub> off</sub> decreases from 10<sup>–11</sup> A to 10<sup>–14</sup> A, which indicates that there exist less shallow-level donor states of hydrogen impurities, which might be explained by the following three mechanisms: first, in the film formation process of PI, the direct incorporation of hydrogen-related radicals from SiH<sub>4</sub> precursor into the back channel is avoided; second, the hydrogen content in the PI film is lower and harder to diffuse into the back channel; third, the hydrogen impurity of back channel that is introduced by the H<sub>2</sub>O<sub>2</sub>-based etchant in the SD etching process could diffuse more easily toward the PI layer. The TFTs with PI passivation layer also shows the less electrical degradation after the annealing treatment at 380 ℃ and better output performance, which confirms less defects and higher quality of the back channel. The bias stabilities of PI devices are improved comprehensively, especially negative bias illumination stability with the threshold voltage shifting from –4.8 V to –0.7 V, which might be attributed to the disappearance of hydrogen interstitial sites and hydrogen vacancies that are charged positively in the back channel. The PI passivation layer is effective to avoid back channel hydrogen impurities of BCE TFT and promises to have broad applications in the display industry.

High-performance ITO/a-IGZO heterostructure TFTs enabled by thickness-dependent carrier concentration and band alignment manipulation

Utilization of highly conductive metal-oxide (MO) film such as indium-tin-oxide (ITO) in a channel layer has been considered as a promising strategy to realize high-mobility thin-film transistors (TFTs). However, achieving high-mobility is typically restricted by severe negative threshold voltage (Vth) shift and large off-current which are consequences of channel thickness increment. Here, to realize high-mobility MO TFTs with low Vth and off-current level, a heterogeneous ITO/amorphous indium-gallium-zinc-oxide (a-IGZO) channel structure was implemented. In the channel, the ultrathin (4 nm) ITO layer contributes to retain high electron concentration and boost the mobility, while the overlayered a-IGZO layer mitigates Vth shift and off-current increase. The ITO/a-IGZO TFTs optimized via the thickness-dependent carrier concentration of ITO and band alignment manipulation in the bilayer considerably improved the device performance showing saturation field-effect mobility of >61 cm2/V·s (average of 58.2 ± 2 cm2/V·s), subthreshold slope of <120 mV/decade (average of 129 ± 12 mV/decade), and current on/off ratio of >5 × 1010. Various electrical characterization and technological computer-aided design simulation were performed to establish a plausible mechanism explaining enhanced mobility and Vth regulation in the ITO/a-IGZO TFTs. Additionally, systematic stability tests and spectroscopic analysis were carried out to evaluate the operational stability of the device, and it is suggested that Sn ion diffusing from ITO to the heterogeneous interface can be responsible for enhanced stability by reducing the oxygen vacancy defects.

Khaya gum – a natural and eco-friendly biopolymer dielectric for low-cost organic field-effect transistors (OFETs)

Nature provides a wide range of dielectric biopolymers that can be used in electronic devices. In this work, organic field-effect transistors (OFETs) using khaya gum (KG), a natural, biodegradable biopolymer that can be directly collected from khaya senegalensis trees, as the gate dielectric are demonstrated. The fabricated bottom gate/top contact poly (3,6-di (2-thien-5-yl)-2,5-di (2-octyldodecyl)-pyrrolo [3,4-c] pyrrole-1,4-dione) thieno [3,2-b] thiophene) (DPPTTT) –(polymethylmethacrylate) (PMMA) OFETs operate at 3 V with a saturation field-effect mobility (μsat) 0.3 cm2V−1 s−1, threshold voltage (Vth) -1.3 V, subthreshold swing (SS) 450 mV/dec, and current on/off ratios (ION/OFF) larger than 3 × 103. Significantly, the gate leakage current (IG) does not exceed 10–8 A for the gate-source voltage (VGS) $$\le$$ -3 V. UV–Vis spectra analysis shows that the prepared khaya gum films exhibit low absorbance and high transparency (up to 90%) with a calculated optical band gap of about 4.3 eV. Thermal characterization shows two stages of decomposition and a glass transition at around 60 °C. Characterization of metal–insulator-metal (MIM) capacitors using khaya gum reveals that the KG-based MIM capacitors possess a relatively high capacitance per unit area (Ci) of 130 ± 3 nF/cm2 at 1 kHz. As a result, khaya gum emerges as the dielectric of choice for low voltage, transparent OFETs where environmentally friendly device manufacturing is required.

Threshold Voltage Modulation in a Transistor with a Two-Dimensional Electron Gas Channel at the Interface between Al2O3 and Sub-5 nm ZnO Films

Recent reports on the emergence of two-dimensional electron gas at the heterointerface of amorphous and polycrystalline oxide thin films, such as amorphous-Al2O3/polycrystalline-TiO2 (a-AO/TO) and a-AO/polycrystalline-ZnO on a Si wafer, open a venue for oxide-based thin-film-transistor research. Due to the higher Hall mobility of ZnO, the device performance was considerably improved in a-AO/ZnO compared with a-AO/TO. However, an excessively high negative threshold voltage (Vth) issue still remains, resulting in a static power consumption problem in the channel-off state. In this study, the Vth value of the a-AO/ZnO device was shifted positively by decreasing the thickness of the ZnO thin film (tZnO) to less than 10 nm, accompanied by a grain size reduction of the polycrystalline ZnO film. The large density of grain boundaries in the ZnO film with thinner thickness trapped the 2D electrons, leading to a decrease in effective carrier density (ns). As ns decreased by decreasing the tZnO from 11 to 4.6 nm, the Vth increased from −2.6 to −0.63 V. With an optimized tZnO of 5.6 nm, the transistor exhibited a Vth of −0.86 V, a saturated field-effect mobility of ∼4.8 cm2/(V s), and a subthreshold swing of 194 mV/dec.

Atomic Layer Deposition of Ternary Indium/Tin/Aluminum Oxide Thin Films, Their Characterization and Transistor Performance under Illumination.

Multilayered heterostructures comprising of In2O3, SnO2, and Al2O3 were studied for their application in thin‐film transistors (TFT). The compositional influence of tin oxide on the properties of the thin‐film, as well as on the TFT characteristics is investigated. The heterostructures are fabricated by atomic layer deposition (ALD) at 200 °C, employing trimethylindium (TMI), tetrakis(dimethylamino)tin (TDMASn), trimethylaluminum (TMA), and water as precursors. After post‐deposition annealing at 400 °C the thin‐films are found to be amorphous, however, they show a discrete layer structure of the individual oxides of uniform film thickness and high optical transparency in the visible region. Incorporation of only two monolayers of Al2O3 in the active semiconducting layer the formation of oxygen vacancies can be effectively suppressed, resulting in an improved semiconducting and switching behavior. The heterostacks comprising of In2O3/SnO2/Al2O3 are incorporated into TFT devices, exhibiting a saturation field‐effect mobility (μsat) of 2.0 cm2 ⋅ V−1 s−1, a threshold‐voltage (Vth) of 8.6 V, a high current on/off ratio (IOn/IOff) of 1.0×107, and a subthreshold swing (SS) of 485 mV ⋅ dec−1. The stability of the TFT under illumination is also altered to a significant extent. A change in the transfer characteristic towards conductive behavior is evident when illuminated with light of an energy of 3.1 eV (400 nm).

Analysis of low frequency noise in in situ fluorine-doped ZnSnO thin-film transistors

We report on in situ fluorine-doped ZnSnO (ZTO:F) thin-film transistors (TFTs) fabricated by co-sputtering. The low frequency noise (LFN) characteristics of ZTO:F TFTs under different annealing temperatures and FSnO (FTO) deposition powers are comparatively studied for the first time. The results show that ZTO:F TFTs have the best electrical and LFN characteristics under an FTO deposition power of 25 W and an annealing temperature of 350 °C, while the saturated field effect mobility was measured to be 14.0 cm2 V−1 s−1, the switching current ratio is over 109, and the Hooge parameter is about 10−2 without any passivation. ZTO:F TFTs without rare metals have the potential for low-cost and environmentally safe manufacturing.

Effects of Target Quality on Electrical Performance and Stability of In-Sn-Zn-O Thin-Film Transistors

In this work, we study the intrinsic connection between target quality and performance of sputtered In-Sn-Zn-O (ITZO) thin-film transistors. Using a dense target, the ITZO device overall performance can be improved synergistically. The optimized device exhibits a steep subthreshold swing of 0.13 V/decade, a high on/off current ratio of $2.47\times 10^{{8}}$ , a threshold voltage of −0.03 V, a saturation field-effect mobility ( $\mu _{{FE}}$ ) of 36.1 cm2/Vs, and a small threshold voltage shift ( $\Delta ~{V} _{{th}}$ ) of −0.55 V under negative bias stress (−20 V, 3600 s). In contrast, the $\mu _{{FE}}$ shows a reverse trend to $\Delta {V} _{{th}}$ when using a target with a relatively small density and poor crystallinity. In this case, although the amount of oxygen vacancy in the films can be reduced for better stability via increasing the sputtering power, the film density observably drops due to serious preferential sputtering, leading to smaller $\mu _{{FE}}$ .

One-Volt TiO₂ Thin Film Transistors With Low-Temperature Process

We report one-volt TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film transistors (TFTs) with a low-temperature fabrication process. The TFTs with the 300 °C-annealed TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> channel exhibit a high on/off current ratio ( I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ) of 5.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , a low subthreshold swing (SS) of 75 mV/dec and a saturation field effect mobility ( μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> ) of 2.13 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> under an ultra-low voltage of 1 V. In contrast, the TFTs with the 200 °C-annealed TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> channel show no appreciable currents. Such a distinct conductivity difference is attributed to the crystallinity transformation of stoichiometric TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the charge transport of which can be well explained by the multiple-trapping-and-release (MTR) model. The channel/dielectric interfaces of these one-volt TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> TFTs are further investigated by transmission electron microscopy (TEM), multi-frequency ( f) capacitance-voltage (C-V), and conductance-voltage (G-V) measurements. The interface trap density ( D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) values of ~ 5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ·eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> obtained from both C-V and G-V measurements are in good agreement, suggesting a high-quality channel/dielectric interface. These one-volt TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> TFTs show a great potential in emerging applications, such as foldable displays and wearable sensors, where a battery-powered operation is required.

Atomic-layer-deposited SnO film using novel Sn(dmamb)2 precursor for p-channel thin film transistor

Atomic layer deposition of SnO was explored using a novel Sn complex, bis(dimethylamino-2methyl-2butoxy)tin(II) [Sn(dmamb)2], and H2O as the Sn precursor and reactant, respectively. Sn(dmamb)2 showed a facile ligand exchange reaction with H2O at temperatures of 100–200 °C, which resulted in the fabrication of pure SnO thin films. Amorphous SnO films were obtained at all the investigated temperatures, but the pure Sn2+–O2− phase was observed only in the films produced at 100 and 150 °C. The amorphous SnO was crystallized by a rapid thermal annealing post-process in N2 ambient at 450 °C. A bottom-gate thin film transistor was fabricated using a crystallized SnO channel layer, and excellent drain current modulation and p-type behavior were obtained, with an on/off ratio of ~7 × 104 and a saturation field effect mobility of 0.5 cm2/V·s.

Aqueous Solution Derived Amorphous Indium Doped Gallium Oxide Thin-Film Transistors

In this study, we report high-performance amorphous Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> metal-oxide (AMO) thin film transistor (TFT) using an low-temperature solution-process coupling with In alloy engineering. In doping can lower the activation temperature of gallium oxide and increase the oxygen vacancy concentration to further activate the device. The optical bandgap of IGO film can be changed from 5.3 to 4.25 eV with the In doping concentration (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In</sub> ) increasing from 0 % to 50 %. All TFTs with IGO channels exhibit n-type transistor characteristics and the evolution of their key electrical parameters with the In-dopant is well elucidated by the structural and morphological characterization. With the increase of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In</sub> , the performance of the device becomes better. Finally, a saturation field-effect mobility of 3.63 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , a current on/off ratio of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> , and a threshold voltage of 2.5 V are achieved by the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> O (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In</sub> = 50%) based device. The In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> O TFT also demonstrates good bias stress stability. Under the action of 20 V and -20 V gate bias for 3000 s, the ΔV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> TH</sub> is +2.27 V and -1.95 V, respectively.

Environmentally Stable, Solution-Processed Indium Boron Zinc Oxide Thin-Film Transistors

In this work, solution-processed indium-boron-zinc-oxide (IBZO) thin-film transistors (TFT) have been fabricated by spin-coating. Properties such as the dissociation energy, electronegativity, ionic size and Lewis acid strength significantly influence the electrical properties of amorphous oxide active channel layers. Based on this reasoning, boron was chosen as a carrier suppressor to improve mobility and stability of the thin-film transistor. Boron concentration in precursor solution was varied from 0 at.% to 20 at.% while the indium concentration was fixed at 70 at.% and zinc concentration was decreased with respect to boron concentration. The IBZO thin films were deposited using spin-coating and post-annealed at 350°C. X-ray diffraction and high-resolution transmission electron microscopy studies confirmed the amorphous nature of the thin film. All the IBZO films were seen to be highly transparent (∼ 83%) in the visible region. The environmental electrical stability of the indium-zinc-oxide (IZO) and IBZO were studied, which revealed that the IBZO TFT with 10 at.% boron concentration has a saturated field effect mobility of 0.28 cm2 V−1 s−1, threshold voltage of 8 V and ION/IOFF of 8.54 × 105 after 30 days of exposure to ambient atmosphere, with no shift in the turn-on voltage, whereas the IZO TFT exhibited an enormous shift in turn-on voltage from −26 V to −13 V.

Metal oxide heterojunctions for high performance solution grown oxide thin film transistors

With the continuous development of the next generation display technique, solution-processed thin-film transistors based on metal oxide semiconductors attract researchers’ more and more attentions. Both forming oxide alloys and multi-layer heterojunctions are facilitated to further improve the device performances. Here, employing low temperature and solution processed technique, we alternately stacked InZnO oxide alloy and In2O3 high mobility oxide to form heterojunction transistors. Results showed that the heterojunction device performances depend on the individual oxide layer position in the device structure and the layer number of heterojunctions since they were significantly modulated by the interfacial dipole, gate insulator effect of TFT device, and hall carrier concentrations of heterojunction films. In2O3/IZO heterojunction transistors demonstrated the highest saturation field-effect mobility of 31 cm2 V−1·s−1 which was much higher than those of transistors based on individual In2O3, IZO, and ZnO. Apart from that, a 10 V threshold voltage and a 107 on/off current ratio were achieved for the In2O3/IZO heterojunction transistors. These findings provide a powerful strategy on designing high performance metal oxide channel and a scientific basis for the application of solution processed metal oxide semiconductor heterojunctions in the next generation of electronic devices.