Indium Gallium Zinc Oxide Thin Film Research Articles

Effect of Channel Shape on Performance of Printed Indium Gallium Zinc Oxide Thin-Film Transistors.

Printing technology will improve the complexity and material waste of traditional deposition and lithography processes in device fabrication. In particular, the printing process can effectively control the functional layer stacking and channel shape in thin-film transistor (TFT) devices. We prepared the patterning indium gallium zinc oxide (IGZO) semiconductor layer with Ga, In, and Zn molar ratios of 1:2:7 on Si/SiO2 substrates. And the patterning source and drain electrodes were printed on the surface of semiconductor layers to construct a TFT device with the top contact and bottom gate structures. To overcome the problem of uniform distribution of applied voltages between electrode centers and edges, we investigated whether the circular arc channel could improve the carrier regulation ability under the field effect in printed TFTs compared with a traditional structure of rectangular symmetry and a rectangular groove channel. The drain current value of the IGZO TFT with a circular arc channel pattern was significantly enhanced compared to that of a TFT with rectangular symmetric source/drain electrodes under the corresponding drain-source voltage and gate voltage. The field effect properties of the device were obviously improved by introducing the arc-shaped channel structure.

Extraction Technique for the Conduction Band Minimum Energy in Amorphous Indium–Gallium–Zinc–Oxide Thin Film Transistors

The conduction band minimum energy in amorphous oxide semiconductor-based thin film transistors (AOS TFTs) is a key parameter governing the accurate extraction of energy distribution for the subgap density-of-states (DOSs) and carrier mobility. We report a technique for extraction of the gate voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}{)}$ </tex-math></inline-formula> and corresponding energy ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F},{\text {CBM}}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {C}-{\text {EREF}}}{)}$ </tex-math></inline-formula> for the quasi-Fermi level ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F}}{)}$ </tex-math></inline-formula> equal to the conduction band minimum ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {C}}{)}$ </tex-math></inline-formula> as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {GS}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {C}}{)}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F},{\text {CBM}}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {GS}}$ </tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}{)}$ </tex-math></inline-formula> . In order to confirm this technique through optoelectronic experimental data, amorphous indium–gallium–zinc–oxide (a-IGZO)-based thin film transistor was irradiated with various wavelengths and power, and obtained <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {CBM}}$ </tex-math></inline-formula> = 7.1 V and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{\text {F} {\text {CBM}}}$ </tex-math></inline-formula> = 71 meV in the dark state. This technique is expected to be useful in the accurate characterization of the subgap DOS and the effective mobility in AOS TFTs through a simple and effective extraction process.

Performance of Transparent Indium–Gallium–Zinc Oxide Thin Film Transistor Prepared by All Plasma Enhanced Atomic Layer Deposition

Transparent indium–gallium–zinc oxide thin film transistor (IGZO-TFT) prepared by all plasma enhanced atomic layer deposition (PEALD) has been firstly investigated. As the chemical composition has a considerable impact on the performance of IGZO TFTs, the properties of IGZO film and IGZO-TFT based on different In2O3 cycle ratios are investigated. The IGZO film prepared by PEALD shows amorphous state with excellent conformity and uniformity. Moreover, the a-IGZO films with different In2O3 cycle ratios are applied to TFT fabrication. When the a-IGZO thin film with 35% In2O3 cycle ratios, the transistor presents satisfactory electrical performance with a threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> ) of 1.7 V, a saturation mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{\text {sat}}$ </tex-math></inline-formula> ) of 8.8 cm2/Vs, a subthreshold swing (SS) of 0.2 V/decade and an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{ON}/\text{I}_{OFF}$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.2\times 10^{{8}}$ </tex-math></inline-formula> . This work provides a new way to achieve transparent TFT which better for practical commercial applications.

Quantitative Analysis of Channel Width Effects on Electrical Performance Degradation of Top-gate Self-aligned Coplanar IGZO Thin-film Transistors under Self-heating Stresses

In this study, a quantitative analysis was conducted on the effects of channel width on electrical performance degradation induced by self-heating stress (SHS) in top-gate self-aligned coplanar indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). From the transfer and capacitance-voltage curves obtained before and after SHS, we revealed that the electrical performance of the TFT was nonuniformly degraded along the channel length direction and the degree of this degradation was more significant in TFTs with a wider channel width. The threshold voltage shift (ΔVSUBTH/SUB) under SHS in the fabricated IGZO TFT was mainly attributed to the increase in the density of shallow donor states and acceptor-like deep states in the IGZO active region and electron trapping into the fast and slow traps in the SiOSUBX/SUB gate dielectric. In addition, we conducted a decomposition of the SHS-induced ΔVSUBTH/SUB originated from each degradation mechanism using the subgap density of states-based ΔVSUBTH/SUB decomposition technique for TFTs with different channel widths. Although every ΔVSUBTH/SUB from each degradation mechanism increased as the channel width increased, increased electron trapping into the slow trap in the SiOSUBX/SUB gate dielectric was the dominant reason for the larger ΔVSUBTH/SUB under SHS in IGZO TFTs with a wider channel width.

Modulation of carrier density in indium–gallium–zinc-oxide thin film prepared by high-power impulse magnetron sputtering

Amorphous indium-gallium-zinc-oxide (α-IGZO) thin films were prepared by high-power impulse magnetron sputtering. The film composition and properties were investigated. The films were zinc-rich when compared to the target material due to the highest sputtering yield, least collision scattering and lowest self-sputtering yield of zinc species among the metallic sputtered species. The carrier-density in the thin film was modulated by the process pressure. Increasing process pressure raised more oxygen radicals and enhanced the oxygen binding ability of the Ga additives. Therefore, the oxygen vacancies were passivated thereby the carrier density was inhibited. Specifically, the carrier density markedly decreased from 8.4 × 1018/cm3 to 9.9 × 1016/cm3 as the process pressure increased. Meanwhile, the electron mobility only slightly decreased from 11.9 cm2/V·s to 8.0 cm2/V·s. Inverted staggered IGZO-TFTs were fabricated. The switch characteristic of the TFTs can be effectively modulated by the pressure during the preparation of IGZO channel.

25.2: High Detectivity Perovskite‐IGZO Phototransistor with Tunable Photoconductive Gain

Organic‐inorganic hybrid perovskite is a highly light sensitive photodetector material(1), which has competitive advantages of low cost, wide and adjustable light absorption range. However, due to its solubility in polar solvent, its fabrication is not compatible with conventional photolithography process, which limits its application as pixel element in high‐resolution image sensors. Therefore, the patterning of perovskite turns out to be a key issue for practical application of perovskite photodetectors in the field of image sensor(2). In this study, we report a Ruddlesden‐Popper (RP) quasi‐two‐dimensional (quasi‐2D) perovskite ‐ indium gallium zinc oxide (IGZO) phototransistor, and their patterning techniques. A patterned quasi‐2D perovskite layer is deposited on the channel region of IGZO thin film transistor (TFT), which enables ultralow off‐state dark currents of 10−11 A and a high responsivity of 103.5 A/W under 400 nm light illumination with tunable photoconductive gain.

Investigation on Physical Properties of IGZO Thin Films under the Conditions of Mixing Oxygen and Argon

Amorphous indium gallium zinc oxide (IGZO) is the most suitable material choice for optoelectronic devices such as thin film transistor (TFT). However, usually, the physical properties of IGZO are of concern rather than the preparation process, which will complicate the control of the main properties of the material. To obtain a simple method of controlling IGZO properties, different proportions of mixed gases of oxygen and argon were added in the process of preparing thin films by pulsed laser deposition (PLD) for studying the fluence of atmosphere on the growth of IGZO. The structure and components of the film are characterized by X-ray diffraction (XRD), which confirmed the amorphous structure. A red-shift of the absorption peak in range of 450–850 nm was generated with the increase in argon concentration. Meanwhile, the transmission spectra showed that the transmittance of the material was lower than 80% in the range of 450–850 nm. Then, different target samples have a wide photoluminescence band at 200–800 nm. Oxygen vacancy defects were considered to be closely related to the photoluminescence behavior. The smallest surface roughness of the films prepared under 50% Ar and 50% O2 and the largest in 100% Ar are proved by atom force microstructure (AFM). Importantly, the greater difference in electrical properties reflects the sensitivity of different oxygen and argon concentrations to material effects. The carrier concentration can be adjusted from 1.08 × 1011 to 1.33 × 1016 by this method. Finally, the IGZO achieved in this work was used in a transistor, which reflected good diode characteristics.

Control of Hydrogen Concentration in Ingazno Thin Film Using Cryopumping System

Recently, amorphous metal-oxide semiconductors (AOSs) such as indium gallium zinc oxide (IGZO) have attracted great attention with their lower power consumption and higher mobility than amorphous silicon in the display field. However, the threshold voltage (Vth) shift of IGZO thin film transistor (TFT) caused by their poor reliability leads to the drop panel luminance. Therefore, improvement of IGZO TFT reliability is necessary, which is largely influenced by oxygen vacancy and hydrogen. In particular, hydrogen has shown different roles inside the IGZO active layer by hydrogen concentration. At lower concentration, the hydrogen passivation of oxygen deficiency region induces the improvement of initial electrical characteristics and reliability [2]. Meanwhile, Vth shift and degradation reliability are generated at higher concentration owing to the hydrogen related defect states [3]. Therefore, controlling excess hydrogen is necessary for reliability enhancement.In this work, IGZO thin film was fabricated by cryopumping system instead of a turbo molecular pump (TMP) for radio frequency sputtering to reduce hydrogen concentration. Cryopump is an adsorption type that enables excellent evacuation ability of hydrogen and moisture taking up most of the partial pressure in high vacuum. As a result, deposition of IGZO thin film with lower hydrogen impurity is available. The hydrogen concentration in the IGZO thin film using both cryopump and TMP was quantitatively analyzed by elastic recoil detection (ERD) analysis. Then, electrical characteristics of the self-aligned top-gate structure TFTs fabricated by both pumps were measured with bias stress conditions.To sum up, we showed the improved reliability of IGZO TFT by controlling excess hydrogen using cryopumping system. Fig.1. (a) Schematic of RF magnetron sputtering process with cryopump. (b) TOF-SIMS depth profiles of hydrogen concentration in IGZO film using TMP and cryopump Acknowledgment This work was supported by the Korea Evaluation Institute of Industrial Technology(KEIT) grant funded by the Korea government (MOTIE) (No. 2021-11-1283) References Chung, Ui-Jin, et al. "15‐1: Invited Paper: Manufacturing Technology of LTPO TFT." SID Symposium Digest of Technical Papers. Vol. 51. No. 1. 2020.Hanyu, Yuichiro, et al. "Hydrogen passivation of electron trap in amorphous In-Ga-Zn-O thin-film transistors." Applied Physics Letters 103.20 (2013): 202114.Mativenga, Mallory, et al. "Origin of light instability in amorphous IGZO thin-film transistors and its suppression." Scientific reports 11.1 (2021): 1-12 Figure 1

P‐3: High Temperature Annealing Behavior of IGZO Using Plasma Enhanced Atomic Layer Deposition

In this study, highly oriented crystalline indium‐gallium‐zinc oxide (IGZO) thin films and its thin film transistors (TFTs) were fabricated using plasma enhanced atomic layer deposition (PEALD). The high temperature (400‐700oC) annealing behavior of IGZO manufactured using PEALD was confirmed. As the temperature increases, the crystallization becomes highly oriented in the c‐axis direction. However, due to the occurrence of dehydrogenation, the electrical performances and reliability of the device are gradually degraded. If the process of highly ordered IGZO thin film with moderate hydrogen content is secured, it is possible to manufacture oxide TFTs with excellent electrical performances.

Effects of Postdeposition Annealing Ambience on NO2 Gas Sensing Performance in Si-Based FET-Type Gas Sensor

We investigate the effects of postdeposition annealing (PDA) ambience on the nitrogen dioxide (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) gas sensing performance in the Si-based field-effect transistor (FET)-type gas sensor having an indium–gallium–zinc oxide (IGZO) as a sensing material. After the IGZO thin films are deposited, the sensors are postannealed in vacuum and atmospheric ambiences. The content of oxygen vacancy in IGZO films varies depending on the PDA ambience, which changes the electrical properties and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensing performance of the sensors. The sensor postannealed in a vacuum ambience has more oxygen vacancy, which acts as an electrical donor, than that in an atmospheric ambience. Thus, the former has a larger coupling ratio and transconductance of the FET transducer. Also, the oxygen vacancy produces negatively charged oxygen species, increasing the response to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Due to a larger response to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas and low noise, the sensor postannealed in a vacuum shows excellent signal-to-noise ratio (SNR) and limit-of-detection performances.

Performance Improvement of Self-Aligned Coplanar Amorphous Indium–Gallium–Zinc Oxide Thin-Film Transistors by Boron Implantation

The electrical properties and device stability of a self-aligned (SA) coplanar amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) were investigated by implanting boron (B) into the source/drain (SD) n+ region. To evaluate the effect according to the depth profile of B in the a-IGZO film, various implantation energies were applied. The electrical properties were optimized when the projection range of B was in the central vertical region of the a-IGZO film. B implantation decreased the resistivity of the a-IGZO film from 3.1 × 102 to 2.1 × 10–3 Ω·cm compared to an untreated a-IGZO film, while the field-effect mobility (μfe) improved from 2.96 to 17.22 cm2/(V·s). Moreover, the fabricated SA coplanar a-IGZO TFTs with a B-doped n+ region exhibited excellent stability, with a threshold voltage shift (ΔVth) of <0.2 V during a 3000 s thermal stability test performed at 200 °C and a bias stress test under a gate voltage of ±20 V. During the implantation process, B ions with high kinetic energy collide with IGZO atoms, resulting in the formation of an oxygen vacancy (VO) and an oxygen interstitial (Oi) simultaneously. The implanted B ions and Oi are bonded such that the VO sites are maintained by the B–O reaction and can contribute to an increase in the carrier concentration in a-IGZO films, thereby increasing the conductivity of the n+ region.

Indium-gallium–zinc oxide (IGZO) thin-film gas sensors prepared via post-deposition high-pressure annealing for NO2 detection

Indium–gallium–zinc oxide (IGZO) thin films were prepared in a N2 environment by varying the annealing pressure and then tested for NO2 gas detection. These thin films, whose average thickness ranged between 5 and 100 nm, were deposited via the sputtering on alumina substrates equipped with interdigitated Au electrodes using an IGZO polycrystalline target (ZnO: Ga2O3:In2O3 = 1:1:1 mol%). The effects of annealing pressure and environment were investigated. A superior sensor response (S) was observed when increasing the annealing pressure; the prepared IGZO thin film showed an S of –800 at an operating temperature of 250 °C for 25 ppm NO2 gas. The recovery time decreased with increasing the annealing temperature. The sensor annealed at 400 °C at 3 atm showed superior selectivity to various gases and longtime stability of 60 days was attained. The role of the oxygen vacancies in the sensor performance was also investigated.

Quantitative Analysis of Positive-Bias-Stress-Induced Electron Trapping in the Gate Insulator in the Self-Aligned Top Gate Coplanar Indium–Gallium–Zinc Oxide Thin-Film Transistors

We experimentally extracted the positive bias temperature stress (PBTS)-induced trapped electron distribution within the gate dielectric in self-aligned top-gate (SA-TG) coplanar indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) using the analytical threshold voltage shift model. First, we carefully examined the effects of PBTS on the subgap density of states in IGZO TFTs to exclude the effects of defect creation on the threshold voltage shift due to PBTS. We assumed that the accumulated electrons were injected into the gate dielectric trap states near the interface through trap-assisted tunneling and were consequently moved to the trap states, which were located further away from the interface, through the Poole–Frenkel effect. Accordingly, we quantitatively analyzed the PBTS-induced electron trapping. The experimental results showed that, in the fabricated IGZO TFTs, the electrons were trapped in the shallow and deep trap states simultaneously owing to PBTS. Electrons trapped in the shallow state were easily detrapped after PBTS termination; however, those trapped in the deep state were not. We successfully extracted the PBTS-induced trapped electron data within the gate dielectric in the fabricated SA-TG coplanar IGZO TFTs by using the proposed method.

Enhanced Ultraviolet Photoresponse Characteristics of Indium Gallium Zinc Oxide Photo-Thin-Film Transistors Enabled by Surface Functionalization of Biomaterials for Real-Time Ultraviolet Monitoring.

Indium gallium zinc oxide (IGZO) is one of the most promising materials for diverse optoelectronic applications based on thin-film transistors (TFTs) including ultraviolet (UV) photodetectors. In particular, the monitoring of UV-A (320-400 nm) exposure is very useful for healthcare applications because it can be used to prevent various human skin and eye-related diseases. However, the relatively weak optical absorption in the UV-A range and the persistent photoconductivity (PPC) arising from the oxygen vacancy-related states of IGZO thin films limit efficient UV monitoring. In this paper, we report the enhancement of the UV photoresponse characteristics of IGZO photo-TFTs by the surface functionalization of biomolecules on an IGZO channel. The biomaterial/IGZO interface plays a crucial role in enhancing UV-A absorption and suppressing PPC under negative gate bias, resulting in not only increased photoresponsivity and specific detectivity but also a fast and repeatable UV photoresponse. In addition, turning off the device without external bias completely eliminates PPC due to the internal electric field induced by the surface functionalization of biomaterials. Such a volatile feature of PPC enables the fast and repeatable UV photoresponse. These results suggest the potential of IGZO photo-TFTs combined with biomaterials for real-time UV monitoring.

Comparative Study on the Separate Extraction of Interface and Bulk Trap Densities in Indium Gallium Zinc Oxide Thin-Film Transistors Using Capacitance–Voltage and Current–Voltage Characteristics

The interface and bulk trap densities were separately extracted from self-aligned top-gate (SA-TG) coplanar indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) using the low-frequency capacitance–voltage (C–V) characteristics and space-charge-limited current (SCLC) under the flat-band condition. In the method based on the C–V curve, the energy distribution of the interface trap density was extracted using the low-frequency C–V characteristics, and that of the bulk trap density was obtained by subtracting the density of interface trap states from the total subgap density of states (DOS) at each energy level. In the SCLC-based method, the energy distribution of the bulk trap density was extracted using the SCLC under the flat-band condition at high drain-to-source voltages, and that of the interface trap density was obtained by subtracting the density of bulk trap components from the total subgap DOS at each energy level. In our experiments, the two characterization techniques provided very similar interface and bulk trap densities and showed that approximately 60% of the subgap states originate from the IGZO/SiO2 interface at the conduction band edge in the fabricated IGZO TFTs, although the two characterization techniques are based on different measurement data. The results of this study confirm the validity of the characterization techniques proposed to separately extract the interface and bulk trap densities in IGZO TFTs. Furthermore, these results show that it is important to reduce the density of interface trap states to improve the electrical performance and stability of fabricated SA-TG coplanar IGZO TFTs.

Sensing Properties of Indium-Gallium-Zinc-Oxide Thin Films under the Influence of Thickness and Annealing Ambient

In this study, indium-gallium-zinc-oxide (IGZO) thin films were investigated for detection of Nitrogen Dioxide (NO2) gas. IGZO films with a thickness range of 25–100 nm were deposited using IGZO (ZnO: Ga2O3:In2O3 = 1:1:1 mol.%) polycrystalline target on interdigitated Au electrode alumina substrates and annealed in different annealing atmosphere of Nitrogen (N2) and Oxygen (O2). The effects of the IGZO thickness and different annealing ambient on IGZO were investigated on sensing properties. The N2 ambient showed a superior response (S = Rgas/Rair) compared to O2 annealing by a factor of 2.3 times. In addition, the sensor response increases with film thickness up to 25 nm and decreases with an increase in thickness. The sensor showed a high response for the IGZO thin film (25 nm), which was 519 times that of the other sensors at 200 °C. The sensor recovery and response time improved, and the sensor selectivity was tested under different gases.

Remote Doping Effects of Indium-Gallium-Zinc Oxide Thin-Film Transistors by Silane-Based Self-Assembled Monolayers.

Oxide thin-film transistors (TFTs), including indium–gallium–zinc oxide (IGZO) TFTs, have been widely investigated because of their excellent properties, such as compatibility with flexible substrates, high carrier mobility, and easy-to-fabricate TFT processes. However, to increase the use of oxide semiconductors in electronic products, an effective doping method that can control the electrical characteristics of oxide TFTs is required. Here, we comprehensively investigate the effect of silane-based self-assembled monolayer (SAM) doping on IGZO TFTs. Instead of a complex doping process, the electrical performance can be enhanced by anchoring silane-based SAMs on the IGZO surface. Furthermore, differences in the doping effect based on the structure of SAMs were analyzed; the analysis offers a systematic guideline for effective electrical characteristic control in IGZO TFTs.

Low Subthreshold Swing and High Performance of Ultrathin PEALD InGaZnO Thin-Film Transistors

Amorphous indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) were fabricated by plasma-enhanced atomic layer deposition (PEALD). The thicknesses of the IGZO thin films varied between 3 and 7.5 nm. The device parameters were optimized at 5 nm, at threshold voltage of -0.07 V, effective mobility of 34.16 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, and subthreshold slope of 75 mV/decade and did not further improve with increasing thickness. To understand the origin of the saturated device properties, the accumulation thickness of TFTs was measured and calculated to be 6.4 nm. In addition, to investigate the origin of degraded properties of 3 nm IGZO TFTs, the Hall effect, interface trap density (D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ), and series resistance were measured. The carrier concentrations were nearly constant regardless of the channel thickness, but the resistivity and Hall mobility were degraded considerably in the 3 nm IGZO. In addition, the D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> and series resistance in the 3 nm TFT were 1.49 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> /eVcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 143.9 Ω cm, respectively, which are relatively higher than those of the other TFTs. Finally, the device reliability of IGZO TFTs under bias thermal stress was assessed. The threshold voltage shift was less than 1 V under 125 °C and 1.5 MV/cm stress conditions.

Study on dielectric properties of PVP and Al2O3 thin films and their implementation in low-temperature solution-processed IGZO-based thin-film transistors

In the present work, we investigated the dielectric properties of solution-processed Poly-(4-vinylphenol) (PVP), and atomic layer deposited (ALD) alumina (Al2O3) thin films. Later, we integrate these dielectric materials into a thin-film transistor (TFT) device fabricated on a glass substrate using solution-processed indium gallium zinc oxide (IGZO) as a semiconductor. Both PVP and Al2O3 films show good dielectric behavior with minimum leakage and capacitance densities of 7.0 nF/cm2 and $$1.034 \times {10}^{-7}$$ F/cm2, respectively. A bottom source/drain top-gate transistor based on PVP as gate insulator operates in the linear region and demonstrates highly negative threshold voltage values beyond − 40 V. On the other hand, the bottom-gate top source/drain transistor based on Al2O3 gate dielectric demonstrates good saturation behavior with saturation current and saturation mobility of $$4.16 \times {10}^{-4}$$ A and 2.203 cm2/Vs, respectively. Further, using the photochemical activation method, the processing temperature of IGZO thin films is reduced to 325 °C from 400 °C. Low-temperature processed IGZO TFTs also show good saturation behavior with low positive threshold voltage values. However, it is achieved at the expense of saturation mobility which decreases to 0.557 cm2/Vs. Our study presents the possibility of producing organic–inorganic hybrid low-cost, and high-performance devices for upcoming flexible electronics.

Preparation and Properties of Crystalline IGZO Thin Films.

IGZO thin films can be used as active layers of thin-film transistors and have been widely studied. However, amorphous indium gallium zinc oxide (IGZO) fabricated at room temperature is vulnerable in subsequent manufacturing processes, such as etching and sputtering; this limits IGZO thin film transistors’ (TFTs) use in commercial products. In this paper, we prepared a c-axis crystallized IGZO thin film by Radio Frequency (RF) sputtering at 180 °C, with a 50% O2 ratio and 110 W power. XRD images show that the crystallized film has an obvious diffraction peak near 31°, and the spacing between the crystal surfaces was calculated to be ≈0.29 nm. The HRTEM map confirmed the above results. The stability of IGZO thin films was investigated by etching them with an acid solution. The crystalline IGZO films exhibited better acid corrosion resistance, and their anticorrosion performance was 74% higher than that of amorphous IGZO (a-IGZO) films, indicating the crystalline IGZO film can provide more stable performance in applications.