Indium Gallium Oxide Research Articles

P‐2: Investigation of high mobility crystalline IGO TFT with top‐gate structure for LCD display application

The present paper reports the study of electrical characteristics and bias temperature stress (BT) stability of crystalline Indium‐Gallium oxide (IGO) dual‐gate thin film transistor (TFT) with top‐gate structure. TFT with normalized Ion over 100εA and PBTS/NBTIS of 0.35/‐2.85V was successfully fabricated. By adjusting oxygen partial pressure (O2%) and substrate temperature, we can control the wet etching rate (WER) of as‐deposited IGO film. After post annealing, crystalline IGO containing In2O3 phase with preferred orientation of (222) has been formed. The TFT characteristics uniformity and BT stability were found to depend on parameters of gate insulator (GI) deposition and pre‐treatment before GI. Based on experimental results, we propose high GI deposition temperature associated with low N2O plasma treatment power as the optimal condition for industrial production of crystalline IGO TFT.

Strong Immunity to Drain-Induced Barrier Lowering in ALD-Grown Preferentially Oriented Indium Gallium Oxide Transistors.

Drain-induced barrier lowering (DIBL) is one of the most critical obstacles degrading the reliability of integrated circuits based on miniaturized transistors. Here, the effect of a crystallographic structure change in InGaO [indium gallium oxide (IGO)] thin-films on the DIBL was investigated. Preferentially oriented IGO (po-IGO) thin-film transistors (TFTs) have outstanding device performances with a field-effect mobility of 81.9 ± 1.3 cm2/(V s), a threshold voltage (VTH) of 0.07 ± 0.03 V, a subthreshold swing of 127 ± 2.0 mV/dec, and a current modulation ratio of (2.9 ± 0.2) × 1011. They also exhibit highly reliable electrical characteristics with a negligible VTH shift of +0.09 (-0.14) V under +2 (-2) MV/cm and 60 °C for 3600 s. More importantly, they reveal strong immunity to the DIBL of 17.5 ± 1.2 mV/V, while random polycrystalline In2O3 (rp-In2O3) and IGO (rp-IGO) TFTs show DIBL values of 197 ± 5.3 and 46.4 ± 1.2 mV/V, respectively. This is quite interesting because the rp- and po-IGO thin-films have the same cation composition ratio (In/Ga = 8:2). Given that the lateral diffusion of oxygen vacancies from the source/drain junction to the channel region via grain boundaries can reduce the effective length (Leff) of the oxide channel, this improved immunity could be attributed to suppressed lateral diffusion by preferential growth. In practice, the po-IGO TFTs have a longer Leff than the rp-In2O3 and -IGO TFTs even with the same patterned length. The effect of the crystallographic-structure-dependent Leff variation on the DIBL was corroborated by technological computer-aided design simulation. This work suggests that the atomic-layer-deposited po-IGO thin-film can be a promising candidate for next-generation electronic devices composed of the miniaturized oxide transistors.

Double-gate structure enabling remote Coulomb scattering-free transport in atomic-layer-deposited IGO thin-film transistors with HfO2 gate dielectric through insertion of SiO2 interlayer

In this paper, high-performance indium gallium oxide (IGO) thin-film transistor (TFT) with a double-gate (DG) structure was developed using an atomic layer deposition route. The device consisting of 10-nm-thick IGO channel and 2/48-nm-thick SiO2/HfO2 dielectric was designed to be suitable for a display backplane in augmented and virtual reality applications. The fabricated DG TFTs exhibit outstanding device performances with field-effect mobility (μFE) of 65.1 ± 2.3 cm2V−1 s−1, subthreshold swing of 65 ± 1 mVdec−1, and threshold voltage (VTH) of 0.42 ± 0.05 V. Both the (μFE) and SS are considerably improved by more than two-fold in the DG IGO TFTs compared to single-gate (SG) IGO TFTs. Important finding was that the DG mode of IGO TFTs exhibits the nearly temperature independent μFE variations in contrast to the SG mode which suffers from the severe remote Coulomb scattering. The rationale for this disparity is discussed in detail based on the potential distribution along the vertical direction using technology computer-aided design simulation. Furthermore, the DG IGO TFTs exhibit a greatly improved reliability with negligible VTH shift of − 0.22 V under a harsh negative bias thermal and illumination stress condition with an electric field of − 2 MVcm−1 and blue light illumination at 80 °C for 3600 s. It could be attributed to the increased electrostatic potential that results in fast re-trapping of the electrons generated by the light-induced ionization of deep level oxygen vacancy defects.

High Performance Amorphous IGO Thin Film Transistors Grown at Low Temperature

Polycrystalline indium gallium oxide has been widely studied in the domain of oxide thin film transistors (TFTs) due to its high mobility. However, there are few researches focus on amorphous IGO (a‐IGO), which has the advantage of large area display. Herein, high‐performance a‐IGO TFTs are demonstrated by magnetron sputtering method with simple process. The efficiency of a‐IGO TFTs fabricated under various conditions are evaluated, and a‐IGO TFTs prepared by 27 nm thin films grown at 220 °C have the best electrical properties. It exhibits the mobility of 35 cm2 V−1 s−1, threshold voltage of 0.5 V, subthreshold swing of 0.8 V dec−1, and the on/off current ratio over 106. This is due to the precise control of the deposition energy state by temperature during sputtering and the influence of the semiconductor layer thickness on the distribution of the accumulation layer. The results present here demonstrate a simple fabrication method for high‐performance amorphous oxide TFT, providing a new option for display driver circuits.

High mobility of IGO/IGZO double-channel thin-film transistors by atomic layer deposition

In this paper, top-gate thin-film transistors (TFTs) of two stacked double-channel layers derived from atomic layer deposition in combination with the plasma-enhanced chemical vapor deposition (PECVD) process were fabricated. The Hall measurement shows that the Hall mobility of the indium gallium oxide (IGO)/indium gallium zinc oxide (IGZO) active layer is 1.6 times more that of the amorphous In-rich IGZO/IGZO layer due to superior carrier percolation conduction paths from the polycrystalline IGO layer. Furthermore, x-ray photoelectron spectroscopy analysis indicates that the IGO/IGZO film has much less oxygen vacancy concentration, which is advantageous in improving not only mobility but also stability. The optimized IGO/IGZO TFT showed both high mobility (38.0 cm2 V−1 s−1) and high stability (ΔVTH = +0.14 V) of a positive bias stress under post-deposition annealing at 250 °C. This strategy provides a feasible process for realizing high-performance TFTs that is compatible with ALD-derived oxides and commercial PECVD techniques in the industry.

Theoretical study on optoelectronic properties of layered In2O3 and Ga2O3

Composite oxides have been indeed proved to be valuable materials in optoelectronic applications. The combination of indium oxide and gallium oxide and other materials can lead to enhanced optical and electronic properties, making them suitable for a variety of optoelectronic devices. Meticulous analysis of the various optical properties helped to draw conclusions about the heterostructure of Indium and Gallium oxide and its use as a suitable semiconducting material in the medium bandgap range. The density of states and the band structure have been obtained from the density functional theory calculations. Real frequency phonon density of states supports dynamical stability of the crystal structure. A favorable energy band gap is achieved in the visible region of the spectrum, indicating that this mixed oxide is well suited for optoelectronic devices such as LEDs and solar cells.

17.2% Efficient CdSexTe1−x solar cell with (InxGa1−x)2O3 emitter on lightweight and flexible glass

High-efficiency, lightweight, and flexible solar cells are sought for a variety of applications particularly when high power density and flexible form factors are desired. Development of solar cells on flexible substrates may also offer production advantages in roll-to-roll or sheet-to-sheet processes. Here, we report device efficiencies of 17.2% and 14.6%, under AM1.5G and AM0 irradiances, respectively, for a flexible, lightweight, CdTe-based solar cell. To advance the efficiency relative to the highest previously reported AM1.5G value of 16.4%, we used an indium gallium oxide (IGO) emitter layer on a cadmium stannate (CTO) transparent conductor, which was deposited on 100-μm thick Corning® Willow® Glass. A sputtered CdSe layer was employed to incorporate Se into a CdTe absorber that was deposited by close-space sublimation, and CuSCN was used as a hole transport layer between the CdTe and the back metal electrode. The IGO and CTO layers remained intact during the high temperature film processing as seen in cross-sectional imaging and elemental mapping. This device configuration offers great promise for building-integrated photovoltaics, space applications, and higher rate manufacturing.

Achieving High-Performance Self-Powered Visible-Blind Ultraviolet Photodetection Using Alloy Engineering.

The exploration and development of self-powered visible-blind ultraviolet photodetectors (VBUV PDs) with high responsivity and wavelength selectivity have far-reaching significance for versatile applications. Although In2O3 shows potential for UV detection due to good UV absorption and electrical transport properties, the poor wavelength selectivity impedes further application in VBUV PDs. Here, a self-powered photoelectrochemical-type (PEC) VBUV PD is demonstrated by using gallium-indium oxide alloys (Ga-In OAs). The self-powered Ga-In OAs-based PEC VBUV PDs exhibit good VBUV photodetection performance, including a high responsivity of 50.04 mA/W and a high detectivity of 6.03 × 1010 Jones under 254 nm light irradiation, a good wavelength selectivity (UV/visible light rejection ratio of 262.45), and a fast response time (0.45/0.38 s). The good self-powered VBUV detection performance of Ga-In OAs is attributed to the larger band gap and smaller charge-transfer resistance induced by alloy engineering, which not only suppresses the absorption of visible light but also accelerates interfacial charge transfer. Moreover, an underwater optical communication system is demonstrated by using the self-powered Ga-In OAs PEC VBUV PDs. This study demonstrates that alloy engineering is a powerful tool to improve the performance of In2O3-based PEC PDs, and Ga-In OAs have great application potential for underwater optoelectronic devices.

Hydrogen detecting characteristics of a palladium nanoparticle/indium gallium oxide based sensor

An investigation and analysis have been conducted on a newly developed chemiresistive-type sensor to detect hydrogen gas. The studied senor is synthesized with an indium gallium oxide (IGO) thin film formed by RF magnetron sputtering and palladium (Pd) nanoparticles (NPs) deposited by vacuum thermal evaporation. The utilize of Pd NPs can significantly improve the sensing response and sensing speed for hydrogen gas. Energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), high-resolution scanning electron microscopy (HRSEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) are employed for the analyses of the relevant structure, element, and composition properties. The sensing mechanism for hydrogen gas is elucidated in this work. In this experiment, the studied Pd NP/IGO sensor exhibits an ultra high sensing response SR of 1.39×107 under 1% H2/air gas at 300°C.. The studied sensor can be operated at room temperature with a significant SR of 304.3. Besides, the studied sensor shows good repetitive operation performance. Hence, the studied Pd NP/IGO structure offers a great potential for the development of hydrogen sensing applications with outstanding performance.

Short-range positional order in phase separated indium gallium oxide islands deposited in a reducing atmosphere

We report a spontaneous phase separation in indium gallium oxide thin films with a nominal composition of (In0.006Ga0.994)2O3 grown on sapphire (0001) substrates using a powder sputtering method in a reducing atmosphere. The In-rich (In0.24Ga0.76)2O3-x domains are non-stoichiometric and located underneath the surface islands, whereas the In-poor domains are nearly stoichiometric Ga2O3, forming a continuous flat surface, though both domains have a monoclinic crystal structure. Furthermore, the In-rich domains exhibit a short-range positional order with a correlation length of approximately 1 μm because the phase separation occurs along the binodal decomposition accompanying periodic concentration profiling of In atoms. The analysis of X-ray photoelectron spectroscopy confirmed that the non-stoichiometry of the thin films originated from the formation of Ga sub-oxide (Ga2O) and metallic Ga, whereas the chemical state of the In atoms was close to In2O3 rather than metallic In. Our results indicate that the spontaneous phase separation occurs in (InxGa1-x)2O3 thin films even at an In content of 0.6 at%. Also, the non-stoichiometry associated with oxygen vacancies is an important parameter for causing spontaneous phase separation via the segregation of In atoms.

P‐154: Late‐News Poster: High‐Performance Indium‐Gallium Oxide Thin‐Film‐Transistors via Plasma‐Enhanced Atomic‐Layer‐Deposition

We report the fabrication of high‐performance indium‐gallium oxide (IGO) thin‐film transistors (TFTs) via plasma‐enhanced atomic‐layer‐deposition (PE‐ALD) process with cation composition ratio variation. With accurate control of the composition ratio, IGO(12:3) TFTs showed stable characteristics along with high field‐effect mobility (μFET) of 70.69 cm 2 /Vs. Furthermore by increasing the gallium ratio, IGO(6:3) TFTs showed extremely stable characteristics with threshold voltage (VTH) variations lower than 0.1 V in both positive bias stress (PBS) and negative bias stress (NBS) conditions.

Inducement of an Anisotropic One‐dimensional Surface of Solution‐derived Indium Gallium Oxide Film via Imprint Lithography for Liquid Crystal Alignment

AbstractThis study uses imprint lithography to produce an anisotropic unidirectional indium gallium oxide (IGO) film for the uniform liquid crystal (LC) alignment layer. The curing temperature was controlled to 110, 180, and 250 °C during the process, and the 250 °C cured film presented a distinct one‐dimensional pattern transferred from the polydimethylsiloxane (PDMS) mold during scanning electron microscopy (SEM). X‐ray photoelectron spectroscopy (XPS) confirmed an active thermal oxidation effect at a high curing temperature, contributing to the formation of a unidirectional structure. This unidirectional IGO structure functioned as a guide for LCs and induced a uniform alignment state, verified by polarized optical microscopy (POM) and a pre‐tilt angle analysis. The IGO film also revealed improved thermal endurance to the LC alignment state and optical transmittance compared with the conventional rubbed polyimide (PI) layer. Given this performance, the one‐dimensional pattern‐imprinted IGO film can be a promising LC alignment layer for an advanced LC system.

High-Performance Thin-Film Transistor with Atomic Layer Deposition (ALD)-Derived Indium-Gallium Oxide Channel for Back-End-of-Line Compatible Transistor Applications: Cation Combinatorial Approach.

In this paper, the feasibility of an indium-gallium oxide (In2(1-x)Ga2xOy) film through combinatorial atomic layer deposition (ALD) as an alternative channel material for back-end-of-line (BEOL) compatible transistor applications is studied. The microstructure of random polycrystalline In2Oy with a bixbyite structure was converted to the amorphous phase of In2(1-x)Ga2xOy film under thermal annealing at 400 °C when the fraction of Ga is ≥29 at. %. In contrast, the enhancement in the orientation of the (222) face and subsequent grain size was observed for the In1.60Ga0.40Oy film with the intermediate Ga fraction of 20 at. %. The suitability as a channel layer was tested on the 10-nm-thick HfO2 gate oxide where the natural length was designed to meet the requirement of short channel devices with a smaller gate length (<100 nm). The In1.60Ga0.40Oy thin-film transistors (TFTs) exhibited the high field-effect mobility (μFE) of 71.27 ± 0.98 cm2/(V s), low subthreshold gate swing (SS) of 74.4 mV/decade, threshold voltage (VTH) of -0.3 V, and ION/OFF ratio of >108, which would be applicable to the logic devices such as peripheral circuit of heterogeneous DRAM. The in-depth origin for this promising performance was discussed in detail, based on physical, optical, and chemical analysis.

Polycrystalline InGaO Thin-Film Transistors with Coplanar Structure Exhibiting Average Mobility of ≈78 cm2 V-1 s-1 and Excellent Stability for Replacing Current Poly-Si Thin-Film Transistors for Organic Light-Emitting Diode Displays.

Highly ordered polycrystalline indium gallium oxide (PC-IGO) film is obtained by the crystallization of room temperature sputtered amorphous IGO on a hot plate at 350°C for 1 h and then annealed for 1 h in an N2 O environment. A high-density PC-IGO of ≈7.15g cm-3 with reduced oxygen vacancy (≈14.83%) and hydroxyl (OH) related defects (≈10.96%) has been obtained by N2 O annealing. Self-aligned coplanar thin-film transistor (TFT) with the PC-IGO exhibits the average saturation mobility of 78.73 cm2 V-1 s-1 , threshold voltage of -1.07V, subthreshold swing of 0.147V dec-1 , and the on/off current ratio of over 108 . The TFTs show excellent stability under bias-temperature stress with a negligible threshold voltage shift (ΔVTH ) of + 0.1 and -0.1V for the positive and negative bias stresses, respectively. The TFTs exhibit very stable environmental stability when the TFTs are stored under high humidity (85%) and a high temperature (85°C) for 2 days. The ring oscillator and the gate driver mode of the PC-IGO TFTs exhibit the propagation delay of 7.44ns/stage with rising/falling times of less than 0.7 μs, respectively. Therefore, the PC-IGO TFTs are suitable for large area, high-resolution active-matrix organic, and inorganic light-emitting diodes displays.

Indium Gallium Oxide Emitters for High-Efficiency CdTe-Based Solar Cells

Indium Gallium Oxide Emitters for High-Efficiency CdTe-Based Solar Cells

Comparative Study of Atomic Layer Deposited Indium-Based Oxide Transistors with a Fermi Energy Level-Engineered Heterojunction Structure Channel through a Cation Combinatorial Approach.

Amorphous indium-gallium-zinc oxide (a-IGZO) has become a standard channel ingredient of switching/driving transistors in active-matrix organic light-emitting diode (AMOLED) televisions. However, mobile AMOLED displays with a high pixel density (≥500 pixels per inch) and good form factor do not often employ a-IGZO transistors due to their modest mobility (10-20 cm2/(V s)). Hybrid low-temperature polycrystalline silicon and oxide transistor (LTPO) technology is being adapted in high-end mobile AMOLED devices due to its ultralow power consumption and excellent current drivability. The critical issues of LTPO (including a complicated structure and high fabrication costs) require a search for alternative all-oxide thin-film transistors (TFTs) with low-cost processability and simple device architecture. The atomic layer deposition (ALD) method is a promising route for high-performance all-oxide TFTs due to its unique features, such as in situ cation composition tailoring ability, precise nanoscale thickness controllability, and excellent step coverage. Here, we report an in-depth comparative investigation of TFTs with indium-gallium oxide (IGO)/gallium-zinc oxide (GZO) and indium-zinc oxide (IZO)/GZO heterojunction stacks using an ALD method. IGO and IZO layers with different compositions were tested as a confinement layer (CL), whereas the GZO layer was used as a barrier layer (BL). Optimal IGO/GZO and IZO/GZO channels were carefully designed on the basis of their energy band properties, where the formation of a quasi-two-dimensional electron gas (q2DEG) near the CL/BL interface is realized by rational design of the band gaps and work-functions of the IGO, IZO, and GZO thin films. To verify the effect of q2DEG formation, the device performances and stabilities of TFTs with CL/BL oxide heterojunction stacks were examined and compared to those of TFTs with a single CL layer. The optimized device with the In0.75Zn0.25O/Ga0.80Zn0.20O stack showed remarkable electrical performance: μFE of 76.7 ± 0.51 cm2/(V s), VTH of -0.37 ± 0.19 V, SS of 0.13 ± 0.01 V/dec, and ION/OFF of 2.5 × 1010 with low operation voltage range of ≥2 V and excellent stabilities (ΔVTH of +0.35, -0.67, and +0.08 V for PBTS, NBIS, and CCS, respectively). This study suggests the feasibility of using high-performance ALD-derived oxide TFTs (which can compete with the performance of LTPO transistors) for high-end mobile AMOLED displays.

Efficient separation and purification of indium and gallium in spent Copper indium gallium diselenide (CIGS)

Copper indium gallium diselenide (CIGS), is a promising commercial thin-film solar cell, and its disposal after scrapping and recycling critical metals has attracted tremendous attention since CIGS can be considered an important type of urban mining. The main phase of spent CIGS is selenide, which is a hazardous contaminant that may have a potential impact on the environment and human body. In our previous study, selenium and copper in spent CIGS separated efficiently, while more scarce metals: indium and gallium were obtained in the form of mixed indium gallium oxide (IGO). Therefore, in this study, the separation and purification of indium and gallium was investigated in detail. The solution chemical behavior shows that the dissolution of indium gallium oxide (IGO) in an alkaline environment was significantly different. Selective alkali leaching is feasible to separate indium and gallium effectively. The process realized 97.26% gallium leaching out, while that of indium was 3.37%. Moreover, the mechanism of the leaching process and the removal of copper impurities were explored, with further purification, indium and gallium were obtained in the form of relatively pure indium oxide (96.04%) and gallium oxide (99.83%), respectively. This study will provide guidance for the recycling of critical metals from secondary waste.

Improvement in performance of indium gallium oxide thin film transistor via oxygen mediated crystallization at a low temperature of 200 °C

We report the fabrication of high-performance polycrystalline indium gallium oxide (IGO) thin film transistors (TFTs) at a low temperature of 200 °C. Growth of a highly aligned cubic phase with a bixbyite structure was accelerated at a certain proportion of oxygen plasma density during deposition of the IGO thin film, which leads to outstanding electrical characteristics. The resulting polycrystalline IGO TFT exhibited a high field-effect mobility of 56.0 cm2/V, a threshold voltage (VTH) of 0.10 V, a low subthreshold gate swing of 0.10 V/decade, and a current modulation ratio of >108. Moreover, the crystalline IGO TFTs have highly stable behaviors with a small VTH shift of +0.8 and −1.0 V against a positive bias stress (VGS,ST−VTH = 20 V) and negative bias illumination stress (VGS,ST−VTH = −20 V) for 3,600 s, which is attributed to the high quality of the bixbyite crystalline structure.

Energy level regulation to optimize hydrogen sensing performance of porous bimetallic gallium-indium oxide with ultrathin pore walls

Although hydrogen sensors with high-response have been extensively studied and developed, it is still a great challenge to achieve ultra-fast response and recovery, high sensitivity and excellent selectivity towards hydrogen (H2) for a gas sensor. Herein, porous Ga-In bimetallic oxide with atomically thin pore wall was synthesized by electrospinning and followed calcination. The sensor based on this sensing material (Ga1.2In0.8O3) showed ultra-short response and recovery time (≈1 s and 3 s), high response (Ra/Rg≈15–500 ppm H2), good reproducibility, remarkable stability, low detection limit (2 ppm) and excellent selectivity (without cross-response to carbon monoxide). The enhanced hydrogen gas sensing performance of this material can be attributed to its novel atomically thin wall, optimal Fermi level and abundant chemisorbed oxygen.

Enhanced Negative‐Bias Illumination Temperature Stability of Praseodymium‐Doped InGaO Thin‐Film Transistors

The performance of praseodymium‐doped indium gallium oxide (PrIGO) as the channel layer of thin‐film transistors (TFTs) is widely investigated. The TFTs with Pr doping exhibit a remarkable suppression of the light‐induced instability including a negligible photoresponse and significant enhancement in negative gate bias stress under illumination (NBITS). The structure, chemical composition, and oxygen vacancy concentration of PrIGO films are analyzed by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS), respectively. In addition, the low‐frequency noise test is introduced to analyze the variation of trap density with Pr doping. The results indicate that the trap states induced by Pr doping facilitate the capture of free electrons by positively charged oxygen vacancies under illumination, which leads to the suppression of photoinduced carriers in the conduction band.