Fabrication of Carbon Nanotube Thin Films for Flexible Transistors by Using a Cross-Linked Amine Polymer

Owing to their remarkable properties, single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) are expected to be used in various flexible electronics applications. To fabricate SWCNT channel layers for TFTs, solution-based film formation on a self-assembled monolayer (SAM) covered with amino groups is commonly used. However, this method uses highly oxidized surfaces, which is not suitable for flexible polymeric substrates. In this work, a solution-based SWCNT film fabrication using methoxycarbonyl polyallylamine (Moc-PAA) is reported. The NH₂ -terminated surface of the cross-linked Moc-PAA layer enables the formation of highly dense and uniform SWCNT networks on both rigid and flexible substrates. TFTs that use the fabricated SWCNT thin film exhibited excellent performance with small variations. The presented simple method to access SWCNT thin film accelerates the realization of flexible nanoelectronics.

Wafer-Scale, Conformal, and Low-Temperature Synthesis of Layered Tin Disulfides for Emerging Nonplanar and Flexible Electronics

Two-dimensional (2D) metal dichalcogenides have drawn considerable interest because they offer possibilities for the implementation of emerging electronics. The emerging electronics are moving toward two major directions: vertical expansion of device space and flexibility. However, the development of a synthesis method for 2D metal dichalcogenides that meets all the requirements remains a significant challenge. Here, we propose a promising method for wafer-scale, conformal, and low-temperature (≤240 °C) synthesis of single-phase SnS₂ via the atomic layer deposition technique. There is a trade-off relationship between the crystallinity and orientation preference of SnS₂, which is efficiently eliminated by the two-step growth occurring at different temperatures. Consequently, the van der Waals layers of the highly crystalline SnS₂ are parallel to the substrate. Thin-film transistors (TFTs) comprising the SnS₂ layer show reasonable electrical performances (field-effect mobility: ∼0.8 cm² V^-1 s^-1 and on/off ratio: ∼10⁶), which are comparable to that of a single-crystal SnS₂ flake. Moreover, we demonstrate nonplanar and flexible TFTs to identify the feasibility of the implementation of future electronics. Both the diagonal-structured TFT and flexible TFT fabricated without a transfer process show electrical performances comparable to those of rigid and planar TFTs. Particularly, the flexible TFT does not exhibit substantial degradation even after 2000 bending cycles. Our work would provide decisive opportunities for the implementation of future electronic devices utilizing 2D metal chalcogenides.

Temperature Dependence Of AOS Thin Film Nano Transistors For Medical Applications

Background

A novel temperature dependent amorphous nano oxide semiconductor (AOS) thin-film transistor (TFT) is reported here for the first time, which is vastly different from conventional behavior. In the literature, the threshold voltage of TFTs decreases with increasing temperature. Here, the threshold voltage increased at higher temperatures, which is different from previously reported results and was repeated on different samples.

Methods

Electrical experiments (such as I-V measurements and photoelectron spectrometer experiments) were performed in order to explain such behavior. Double sweeping gate voltage measurements were performed to investigate the mechanism for the temperature dependent behavior.

Results

It was found that there was a change of trap charge under thermal stress, which was released after the stress.

Conclusion

Non-Arrhenius behaviors (including a linear behavior) were obtained for the amorphous nano oxide thin-film transistors within 303~425 K, suggesting their potential to be adjusted by measurement processes and be applied as temperature sensors for numerous medical applications.

Transparent ZnO Thin-Film Deposition by Spray Pyrolysis for High-Performance Metal-Oxide Field-Effect Transistors

Solution-based metal oxide semiconductors (MOSs) have emerged, with their potential for low-cost and low-temperature processability preserving their intrinsic properties of high optical transparency and high carrier mobility. In particular, MOS field-effect transistors (FETs) using the spray pyrolysis technique have drawn huge attention with the electrical performances compatible with those of vacuum-based FETs. However, further intensive investigations are still desirable, associated with the processing optimization and operational instabilities when compared to other methodologies for depositing thin-film semiconductors. Here, we demonstrate high-performing transparent ZnO FETs using the spray pyrolysis technique, exhibiting a field-effect mobility of ~14.7 cm² V⁻¹ s⁻¹, an on/off ratio of ~10⁹, and an SS of ~0.49 V/decade. We examine the optical and electrical characteristics of the prepared ZnO films formed by spray pyrolysis via various analysis techniques. The influence of spray process conditions was also studied for realizing high quality ZnO films. Furthermore, we measure and analyze time dependence of the threshold voltage (V_th) shifts and their recovery behaviors under prolonged positive and negative gate bias, which were expected to be attributed to defect creation and charge trapping at or near the interface between channel and insulator, respectively.

Integration of Electrochemical Microsupercapacitors with Thin Film Electronics for On-Chip Energy Storage

The development of self-powered electronic systems requires integration of on-chip energy-storage units to interface with various types of energy harvesters, which are intermittent by nature. Most studies have involved on-chip electrochemical microsupercapacitors that have been interfaced with energy harvesters through bulky Si-based rectifiers that are difficult to integrate. This study demonstrates transistor-level integration of electrochemical microsupercapacitors and thin film transistor rectifiers. In this approach, the thin film transistors, thin film rectifiers, and electrochemical microsupercapacitors share the same electrode material for all, which allows for a highly integrated electrochemical on-chip storage solution. The thin film rectifiers are shown to be capable of rectifying AC signal input from either triboelectric nanogenerators or standard function generators. In addition, electrochemical microsupercapacitors exhibit exceptionally slow self-discharge rate (≈18.75 mV h^-1 ) and sufficient power to drive various electronic devices. This study opens a new avenue for developing compact on-chip electrochemical micropower units integrated with thin film electronics.

Perovskite and Conjugated Polymer Wrapped Semiconducting Carbon Nanotube Hybrid Films for High-Performance Transistors and Phototransistors

Although organic-inorganic halide perovskites continue to generate considerable interest due to great potentials for various optoelectronic devices, there are some critical obstacles to practical applications, including lead toxicity, relatively low field-effect mobility, and strong hysteresis during operation. This paper proposes a universal approach to significantly improve mobility and operational stability with reduced dual-sweep hysteresis for perovskite-based thin film transistors (TFTs) by coupling low-dimensional lead-free perovskite material (C₆H₅C₂H₄NH₃)₂SnI₄ (hereafter abbreviated as (PEA)₂SnI₄) with embedded conjugated polymer wrapped semiconducting carbon nanotubes (semi-CNTs). In (PEA)₂SnI₄/semi-CNT hybrid TFTs, semi-CNTs can provide highway-like transport paths, enabling smoother carrier transport with less trapping and scattering. We also demonstrate the performance of (PEA)₂SnI₄/semi-CNT hybrid phototransistors with ultrahigh photoresponsivity ( R) of 6.3 × 10⁴ A/W and detectivity ( D*) of 1.12 × 10¹⁷ Jones, which is about 2 or 3 orders of magnitude higher than that of the best devices available to date. The results indicate promising potentials for solution-processed perovskite/semi-CNT hybrid platforms, and the developed strategy can be applied for high-performance perovskite nanomaterial optoelectronics.

Thermopower Modulation Clarification of the Operating Mechanism in Wide Bandgap BaSnO3 -SrSnO3 Solid-Solution Based Thin Film Transistors

The transparent oxide semiconductor (TOS) with large bandgap (E_g ≈ 4 eV) based thin-film transistors (TFTs) showing both high carrier mobility and UV-visible transparency has attracted increasing attention as a promising component for next generation optoelectronics. Among TOSs, BaSnO₃ -SrSnO₃ solid-solutions (E_g = 3.5-4.2 eV) are good candidates because the single crystal shows very high mobility. However, the TFT performance has not been optimized due to the lack of fundamental knowledge especially the effective thickness (t_eff ) and the carrier effective mass (m*). Here, it is demonstrated that the electric field thermopower (S) modulation method addresses this problem by combining with the standard volume carrier concentration (n_3D ) dependence of S measurements. By comparing the electric field accumulated sheet carrier concentration (n_2D ) and n_3D at same S, it is clarified that the t_eff (n_2D /n_3D ) of the conducting channel becomes thicker with increasing Sr concentration, whereas the m* becomes lighter. The former would be due to the increase of E_g and latter would be due to the enhancement of overlap population of neighboring Sn 5s orbitals. The present analyses technique is useful to experimentally clarify the t_eff and m*, and essentially important to realize advanced TOS-based TFTs showing both high optical transparency and high mobility.

Aqueous Solution Processing of Combustible Precursor Compounds into Amorphous Indium Gallium Zinc Oxide (IGZO) Semiconductors for Thin Film Transistor Applications

Combustion synthesis of semiconducting amorphous indium gallium zinc oxide IGZO (In:Ga:Zn, 7:1:1.5) thin films was carried out using urea nitrate precursor compounds of indium(III), gallium(III) and zinc(II). This approach provides further understanding towards the oxide formation process under a moderate temperature regime by employment of well-defined coordination compounds. All precursor compounds were fully characterized by spectroscopic techniques as well as by single crystal structure analysis. Their intrinsic thermal decomposition was studied by a combination of differential scanning calorimetry (DSC) and thermogravimetry coupled with mass spectrometry and infrared spectroscopy (TG-MS/IR). For all precursors a multistep decomposition involving a complex redox-reaction pathway under in situ formation of nitrogen containing molecular species was observed. Controlled thermal conversion of a mixture of the indium, gallium and zinc urea nitrate complexes into ternary amorphous IGZO films could thus be achieved. Thin film transistors (TFTs) were fabricated from a defined compositional mixture of the molecular precursors. The TFT devices exhibited decent charge carrier mobilities of 0.4 and 3.1 cm² /(Vs) after annealing of the deposited films at temperatures as low as 250 and 350 °C, respectively. This approach represents a significant step further towards a low temperature solution processing of semiconducting thin films.

Transparent Electronics Using One Binary Oxide for All Transistor Layers

A novel process is developed in which thin film transistors (TFTs) comprising one binary oxide for all transistor layers (gate, source/drain, semiconductor channel, and dielectric) are fabricated in a single deposition system at low temperature. By simply changing the flow ratio of two chemical precursors, C₈ H₂₄ HfN₄ and (C₂ H₅ )₂ Zn, in an atomic layer deposition system, the electronic properties of the binary oxide (Hf _x Zn_{1- x} O_{2- δ} or HZO) are tuned from conducting, to semiconducting, to insulating. Furthermore, by carefully optimizing the properties of the various transistor HZO layers, all-HZO thin film transistors are achieved with excellent performance on both glass and plastic substrates. Specifically, the optimized all-HZO TFTs show a saturation mobility of ≈17.9 cm² V^-1 s^-1 , low subthreshold swing of ≈480 mV dec^-1 , high I_on /I_off ratio of >10⁹ , and excellent gate bias stability at elevated temperatures. In addition, all-HZO inverters with high DC voltage gain (≈470), and all-HZO ring oscillators with low stage delay (≈408 ns) and high oscillation frequency of 245 kHz are demonstrated. This approach presents a novel, simple, high performance, and cost-effective process for the fabrication of indium-free transparent electronics.

Room-Temperature Fabricated Thin-Film Transistors Based on Compounds with Lanthanum and Main Family Element Boron

For the first time, compounds with lanthanum from the main family element Boron (LaB_x) were investigated as an active layer for thin-film transistors (TFTs). Detailed studies showed that the room-temperature fabricated LaB_x thin film was in the crystalline state with a relatively narrow optical band gap of 2.28 eV. The atom ration of La/B was related to the working pressure during the sputtering process and the atom ration of La/B increased with the increase of the working pressure, which will result in the freer electrons in the LaB_x thin film. LaB_x-TFT without any intentionally annealing steps exhibited a saturation mobility of 0.44 cm²·V⁻¹·s⁻¹, which is a subthreshold swing (SS) of 0.26 V/decade and a I_on/I_off ratio larger than 10⁴. The room-temperature process is attractive for its compatibility with almost all kinds of flexible substrates and the LaB_x semiconductor may be a new choice for the channel materials in TFTs.

Effect of Source/Drain Electrodes on the Electrical Properties of Silicon⁻Tin Oxide Thin-Film Transistors

Ultra-high definition displays have become a trend for the current flat plane displays. In this study, the contact properties of amorphous silicon⁻tin oxide thin-film transistors (a-STO TFTs) employed with source/drain (S/D) electrodes were analyzed. Ohmic contact with a good device performance was achieved when a-STO was matched with indium-tin-oxide (ITO) or Mo electrodes. The acceptor-like densities of trap states (DOS) of a-STO TFTs were further investigated by using low-frequency capacitance⁻voltage (C⁻V) characteristics to understand the impact of the electrode on the device performance. The reason of the distinct electrical performances of the devices with ITO and Mo contacts was attributed to different DOS caused by the generation of local defect states near the electrodes, which distorted the electric field distribution and formed an electrical potential barrier hindering the flow of electrons. It is of significant importance for circuit designers to design reliable integrated circuits with SnO₂-based devices applied in flat panel displays.

Mobility Enhancement in Amorphous In-Ga-Zn-O Thin-Film Transistor by Induced Metallic in Nanoparticles and Cu Electrodes

In this work, we fabricated a high-mobility amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) based on alumina oxide (Al2O3) passivation layer (PVL) and copper (Cu) source/drain electrodes (S/D). The mechanism of the high mobility for a-IGZO TFT was proposed and experimentally demonstrated. The conductivity of the channel layer was significantly improved due to the formation of metallic In nanoparticles on the back channel during Al2O3 PVL sputtering. In addition, Ar atmosphere annealing induced the Schottky contact formation between the Cu S/D and the channel layer caused by Cu diffusion. In conjunction with high conductivity channel and Schottky contact, the a-IGZO TFT based on Cu S/D and Al2O3 PVL exhibited remarkable mobility of 33.5–220.1 cm2/Vs when channel length varies from 60 to 560 μm. This work presents a feasible way to implement high mobility and Cu electrodes in a-IGZO TFT, simultaneously.

Flexible Zinc-Tin Oxide Thin Film Transistors Operating at 1 kV for Integrated Switching of Dielectric Elastomer Actuators Arrays

Flexible high-voltage thin-film transistors (HVTFTs) operating at more than 1 kV are integrated with compliant dielectric elastomer actuators (DEA) to create a flexible array of 16 independent actuators. To allow for high-voltage operation, the HVTFT implements a zinc-tin oxide channel, a thick dielectric stack, and an offset gate. At a source-drain bias of 1 kV, the HVTFT has a 20 µA on-current at a gate voltage bias of 30 V. Their electrical characteristics enable the switching of DEAs which require drive voltages of over 1 kV, making control of an array simpler in comparison to the use of external high-voltage switching. These HVTFTs are integrated in a flexible haptic display consisting of a 4 × 4 matrix of DEAs and HVTFTs. Using a single 1.4 kV supply, each DEA is independently switched by its associated HVTFT, requiring only a 30 V gate voltage for full DEA deflection. The 4 × 4 display operates well even when bent to a 5 mm radius of curvature. By enabling DEA switching at low voltages, flexible metal-oxide HVTFTs enable complex flexible systems with dozens to hundreds of independent DEAs for applications in haptics, Braille displays, and soft robotics.

Modulation-Doped In2 O3 /ZnO Heterojunction Transistors Processed from Solution

This paper reports the controlled growth of atomically sharp In₂ O₃ /ZnO and In₂ O₃ /Li-doped ZnO (In₂ O₃ /Li-ZnO) heterojunctions via spin-coating at 200 °C and assesses their application in n-channel thin-film transistors (TFTs). It is shown that addition of Li in ZnO leads to n-type doping and allows for the accurate tuning of its Fermi energy. In the case of In₂ O₃ /ZnO heterojunctions, presence of the n-doped ZnO layer results in an increased amount of electrons being transferred from its conduction band minimum to that of In₂ O₃ over the interface, in a process similar to modulation doping. Electrical characterization reveals the profound impact of the presence of the n-doped ZnO layer on the charge transport properties of the isotype In₂ O₃ /Li-ZnO heterojunctions as well as on the operating characteristics of the resulting TFTs. By judicious optimization of the In₂ O₃ /Li-ZnO interface microstructure, and Li concentration, significant enhancement in both the electron mobility and TFT bias stability is demonstrated.

A Mixed-Extractor Strategy for Efficient Sorting of Semiconducting Single-Walled Carbon Nanotubes

A general strategy for sorting semiconducting single-walled carbon nanotubes (s-SWNTs) with high efficiency using a mixed-extractor is reported. When the two extractors have a sufficient difference in binding energy with s-SWNTs, and skeleton flexibility, the mixture shows enhanced yield for sorting s-SWNTs. The strategy could be effective when applied to increase the sorting yield of other selective dispersion systems.

Structural and Electrical Characterization of SiO2 Gate Dielectrics Deposited from Solutions at Moderate Temperatures in Air

Silicon dioxide (SiO₂) is the most widely used dielectric for electronic applications. It is usually produced by thermal oxidation of silicon or by using a wide range of vacuum-based techniques. By default, the growth of SiO₂ by thermal oxidation of silicon requires the use of Si substrates whereas the other deposition techniques either produce low quality or poor interface material and mostly require high deposition or annealing temperatures. Recent investigations therefore have focused on the development of alternative deposition paradigms based on solutions. Here, we report the deposition of SiO₂ thin film dielectrics deposited by spray pyrolysis in air at moderate temperatures of ≈350 °C from pentane-2,4-dione solutions of SiCl₄. SiO₂ dielectrics were investigated by means of UV-vis absorption spectroscopy, spectroscopic ellipsometry, XPS, XRD, UFM/AFM, admittance spectroscopy, and field-effect measurements. Data analysis reveals smooth (R_RMS < 1 nm) amorphous films with a dielectric constant of about 3.8, an optical band gap of ≈8.1 eV, leakage current densities in the order of ≈10^-7 A/cm² at 1 MV/cm, and high dielectric strength in excess of 5 MV/cm. XPS measurements confirm the SiO₂ stoichiometry and FTIR spectra reveal features related to SiO₂ only. Thin film transistors implementing spray-coated SiO₂ gate dielectrics and C₆₀ and pentacene semiconducting channels exhibit excellent transport characteristics, i.e., negligible hysteresis, low leakage currents, high on/off current modulation ratio on the order of 10⁶, and high carrier mobility.

Direct Inkjet Printing of Silver Source/Drain Electrodes on an Amorphous InGaZnO Layer for Thin-Film Transistors

Printing technologies for thin-film transistors (TFTs) have recently attracted much interest owing to their eco-friendliness, direct patterning, low cost, and roll-to-roll manufacturing processes. Lower production costs could result if electrodes fabricated by vacuum processes could be replaced by inkjet printing. However, poor interfacial contacts and/or serious diffusion between the active layer and the silver electrodes are still problematic for achieving amorphous indium–gallium–zinc–oxide (a-IGZO) TFTs with good electrical performance. In this paper, silver (Ag) source/drain electrodes were directly inkjet-printed on an amorphous a-IGZO layer to fabricate TFTs that exhibited a mobility of 0.29 cm²·V⁻¹·s⁻¹ and an on/off current ratio of over 10⁵. To the best of our knowledge, this is a major improvement for bottom-gate top-contact a-IGZO TFTs with directly printed silver electrodes on a substrate with no pretreatment. This study presents a promising alternative method of fabricating electrodes of a-IGZO TFTs with desirable device performance.

Significantly Increasing the Ductility of High Performance Polymer Semiconductors through Polymer Blending

Polymer semiconductors based on donor-acceptor monomers have recently resulted in significant gains in field effect mobility in organic thin film transistors (OTFTs). These polymers incorporate fused aromatic rings and have been designed to have stiff planar backbones, resulting in strong intermolecular interactions, which subsequently result in stiff and brittle films. The complex synthesis typically required for these materials may also result in increased production costs. Thus, the development of methods to improve mechanical plasticity while lowering material consumption during fabrication will significantly improve opportunities for adoption in flexible and stretchable electronics. To achieve these goals, we consider blending a brittle donor-acceptor polymer, poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine] (PCDTPT), with ductile poly(3-hexylthiophene). We found that the ductility of the blend films is significantly improved compared to that of neat PCDTPT films, and when the blend film is employed in an OTFT, the performance is largely maintained. The ability to maintain charge transport character is due to vertical segregation within the blend, while the improved ductility is due to intermixing of the polymers throughout the film thickness. Importantly, the application of large strains to the ductile films is shown to orient both polymers, which further increases charge carrier mobility. These results highlight a processing approach to achieve high performance polymer OTFTs that are electrically and mechanically optimized.

Rational Hydrogenation for Enhanced Mobility and High Reliability on ZnO-based Thin Film Transistors: From Simulation to Experiment

Hydrogenation is one of the effective methods for improving the performance of ZnO thin film transistors (TFTs), which originate from the fact that hydrogen (H) acts as a defect passivator and a shallow n-type dopant in ZnO materials. However, passivation accompanied by an excessive H doping of the channel region of a ZnO TFT is undesirable because high carrier density leads to negative threshold voltages. Herein, we report that Mg/H codoping could overcome the trade-off between performance and reliability in the ZnO TFTs. The theoretical calculation suggests that the incorporation of Mg in hydrogenated ZnO decrease the formation energy of interstitial H and increase formation energy of O-vacancy (VO). The experimental results demonstrate that the existence of the diluted Mg in hydrogenated ZnO TFTs could be sufficient to boost up mobility from 10 to 32.2 cm(2)/(V s) at a low carrier density (∼2.0 × 10(18) cm(-3)), which can be attributed to the decreased electron effective mass by surface band bending. The all results verified that the Mg/H codoping can significantly passivate the VO to improve device reliability and enhance mobility. Thus, this finding clearly points the way to realize high-performance metal oxide TFTs for low-cost, large-volume, flexible electronics.

Modulating Cationic Ratios for High-Performance Transparent Solution-Processed Electronics

Amorphous oxide semiconductors such as indium zinc tin oxide (IZTO) are considered favorites to serve as channel materials for thin film transistors (TFTs) because they combine high charge carrier mobility with high optical transmittance, allowing for the development of transparent electronics. Although the influence of relative cationic concentrations in determining the electronic properties have been studied in sputtered and PLD films, the development of printed transparent electronics hinges on such dependencies being explored for solution-processed systems. Here, we study solution-processed indium zinc tin oxide thin film transistors (TFTs) to investigate variation in their electrical properties with change in cationic composition. Charge transport mobility ranging from 0.3 to 20.3 cm(2)/(V s), subthreshold swing ranging from 1.2 to 8.4 V/dec, threshold voltage ranging from -50 to 5 V, and drain current on-off ratio ranging from 3 to 6 orders of magnitude were obtained by examining different compositions of the semiconductor films. Mobility was found to increase with the incorporation of large cations such as In(3+) and Sn(4+) due to the vast s-orbital overlap they can achieve when compared to the intercationic distance. Subthreshold swing decreased with an increase in Zn(2+) concentration due to reduced interfacial state formation between the semiconductor and dielectric. The optimized transistor obtained at a compositional ratio of In/Zn/Sn = 1:1:1, exhibited a high field-effect mobility of 8.62 cm(2)/(V s), subthreshold swing of 1.75 V/dec, and current on-off ratio of 10(6). Such impressive performances reaffirm the promise of amorphous metal oxide semiconductors for printed electronics.

Toward the Limits of Uniformity of Mixed Metallicity SWCNT TFT Arrays with Spark-Synthesized and Surface-Density-Controlled Nanotube Networks

We report the fabrication of thin film transistors (TFTs) from networks of nonbundled single-walled carbon nanotubes with controlled surface densities. Individual nanotubes were synthesized by using a spark generator-based floating catalyst CVD process. High uniformity and the control of SWCNT surface density were realized by mixing of the SWCNT aerosol in a turbulent flow mixer and monitoring the online number concentration with a condensation particle counter at the reactor outlet in real time. The networks consist of predominantly nonbundled SWCNTs with diameters of 1.0-1.3 nm, mean length of 3.97 μm, and metallic to semiconducting tube ratio of 1:2. The ON/OFF ratio and charge carrier mobility of SWCNT TFTs were simultaneously optimized through fabrication of devices with SWCNT surface densities ranging from 0.36 to 1.8 μm(-2) and channel lengths and widths from 5 to 100 μm and from 100 to 500 μm, respectively. The density optimized TFTs exhibited excellent performance figures with charge carrier mobilities up to 100 cm(2) V(-1) s(-1) and ON/OFF current ratios exceeding 1 × 10(6), combined with high uniformity and more than 99% of devices working as theoretically expected.

Performance Enhancement of ZITO Thin-Film Transistors via Graphene Bridge Layer by Sol-Gel Combustion Process

In this article, we reported the stacked structure zinc-indium-tin oxide (ZITO) thin-film transistors (TFTs) with graphene nanosheets (GNSs) prepared by solution process. GNSs were used as bridge layer between dual-ZITO layers. The transmission of stacked ZITO/GNSs/ZITO films are more than 80% in the visible region and the resistivity of ZITO films with GNSs bridge layer decreased from 502.9 to 13.4 Ω cm. The solution-processed TFT devices with GNSs bridge layer exhibited a desirable characteristic with a subthreshold slope of 0.25 V/dec and current on-off ratio of 1 × 10(7), and the saturation filed effect mobility is improved to 45.9 cm(2)V(-1)s(-1), which exceeds the mobility values of the pristine ZITO TFTs by one order. These results demonstrate the solution-processed ZITO/GNSs/ZITO TFTs maybe make a further step to achieve high-performance TFTs and show the potential for next-generation applications.

Stable and High-Performance Flexible ZnO Thin-Film Transistors by Atomic Layer Deposition

Passivation is a challenging issue for the oxide thin-film transistor (TFT) technologies because it requires prolonged high-temperature annealing treatments to remedy defects produced in the process, which greatly limits its manufacturability as well as its compatibility with temperature-sensitive materials such as flexible plastic substrates. This study investigates the defect-formation mechanisms incurred by atomic layer deposition (ALD) passivation processes on ZnO TFTs, based on which we demonstrate for the first time degradation-free passivation of ZnO TFTs by a TiO2/Al2O3 nanolaminated (TAO) film deposited by a low-temperature (110 °C) ALD process. By combining the TAO passivation film with ALD dielectric and channel layers into an integrated low-temperature ALD process, we successfully fabricate flexible ZnO TFTs on plastics. Thanks to the exceptional gas-barrier property of the TAO film (water vapor transmission rate (WVTR)<10(-6) g m(-2) day(-1)) as well as the defect-free nature of the ALD dielectric and ZnO channel layers, the TFTs exhibit excellent device performance with high stability and flexibility: field-effect mobility>20 cm2 V(-1) s(-1), subthreshold swing<0.4 V decade(-1) after extended bias-stressing (>10,000 s), air-storage (>1200 h), and bending (1.3 cm radius for 1000 times).

ZnO-based thin film transistors employing aluminum titanate gate dielectrics deposited by spray pyrolysis at ambient air

The replacement of SiO2 gate dielectrics with metal oxides of higher dielectric constant has led to the investigation of a wide range of materials with superior properties compared with SiO2. Despite their attractive properties, these high-k dielectrics are usually manufactured using costly vacuum-based techniques. To overcome this bottleneck, research has focused on the development of alternative deposition methods based on solution-processable metal oxides. Here we report the application of spray pyrolysis for the deposition and investigation of Al2x-1·TixOy dielectrics as a function of the [Ti(4+)]/[Ti(4+)+2·Al(3+)] ratio and their implementation in thin film transistors (TFTs) employing spray-coated ZnO as the active semiconducting channels. The films are studied by UV-visible absorption spectroscopy, spectroscopic ellipsometry, impedance spectroscopy, atomic force microscopy, X-ray diffraction and field-effect measurements. Analyses reveal amorphous Al2x-1·TixOy dielectrics that exhibit a wide band gap (∼4.5 eV), low roughness (∼0.9 nm), high dielectric constant (k ∼ 13), Schottky pinning factor S of ∼0.44 and very low leakage currents (<5 nA/cm(2)). TFTs employing stoichiometric Al2O3·TiO2 gate dielectrics and ZnO semiconducting channels exhibit excellent electron transport characteristics with low operating voltages (∼10 V), negligible hysteresis, high on/off current modulation ratio of ∼10(6), subthreshold swing (SS) of ∼550 mV/dec and electron mobility of ∼10 cm(2) V(-1) s(-1).

Spatial atmospheric atomic layer deposition of InxGayZnzO for thin film transistors

We have investigated the nucleation and growth of InGaZnO thin films by spatial atmospheric atomic layer deposition. Diethyl zinc (DEZ), trimethyl indium (TMIn), triethyl gallium (TEGa), and water were used as Zn, In, Ga and oxygen precursors, respectively. The vaporized metal precursors have been coinjected in the reactor. The metal composition of InGaZnO has been controlled by varying the TMIn or TEGa flow to the reactor, for a given DEZ flow and exposure time. The morphology of the films changes from polycrystalline, for ZnO and In-doped ZnO, to amorphous for In-rich IZO and InGaZnO. The use of these films as the active channel in TFTs has been demonstrated and the influence of In and Ga cations on the electrical characteristics of the TFTs has been studied.