Indium Gallium Zinc Oxide Layer Research Articles

Floating body effect in indium–gallium–zinc–oxide (IGZO) thin-film transistor (TFT)

In this paper, the floating body effect (FBE) in indium-gallium-zinc-oxide (IGZO) thin-film transistor (TFT) and the mechanism of device failure caused by that are reported for the first time. If the toggle AC pulses are applied to the gate and drain simultaneously for the switching operation, the drain current of IGZO TFT increases dramatically and cannot show the on/off switching characteristics. This phenomenon was not reported before, and our study reveals that the main cause is the formation of a conductive path between the source and drain: short failure. It is attributed in part to the donor creation at the drain region during the high voltage (Vhigh) condition and in part to the donor creation at the source region during the falling edge and low voltage (Vlow) conditions. Donor creation is attributed to the peroxide formation in the IGZO layer induced by the electrons under the high lateral field. Because the donor creation features positive charges, it lowers the threshold voltage of IGZO TFT. In detail, during the Vhigh condition, the donor creation is generated by accumulated electrons with a high lateral field at the drain region. On the other hand, the floating electrons remaining at the short falling edge (i.e., FBE of the IGZO TFT) are affected by the high lateral field at the source region during the Vlow condition. As a result, the donor creation is generated at the source region. Therefore, the short failure occurs because the donor creations are generated and expanded to channel from the drain and source region as the AC stress accumulates. In summary, the FBE in IGZO TFT is reported, and its effect on the electrical characteristics of IGZO TFT (i.e., the short failure) is rigorously analyzed for the first time.

Intense pulsed light annealing of solution-based indium–gallium–zinc–oxide semiconductors with printed Ag source and drain electrodes for bottom gate thin film transistors

In this study, an intense pulsed light (IPL) annealing process for a printed multi-layered indium–gallium–zinc–oxide (IGZO) and silver (Ag) electrode structure was developed for a high performance all-printed inorganic thin film transistor (TFT). Through a solution process using IGZO precursor and Ag ink, the bottom gate structure TFT was fabricated. The spin coating method was used to form the IGZO semiconductor layer on a heavily-doped silicon wafer covered with thermally grown silicon dioxide. The annealing process of the IGZO layer utilized an optimized IPL irradiation process. The Ag inks were printed on the IGZO layer by screen printing to form the source and drain (S/D) pattern. This S/D pattern was dried by near infrared radiation (NIR) and the dried S/D pattern was sintered with intense pulsed light by varying the irradiation energy. The performances of the all-printed TFT such as the field effect mobility and on–off ratio electrical transfer properties were measured by a parameter analyzer. The interfacial analysis including the contact resistance and cross-sectional microstructure analysis is essential because diffusion phenomenon can occur during the annealing and sintering process. Consequently, this TFT device showed noteworthy performance (field effect mobility: 7.96 cm2/V s, on/off ratio: 107). This is similar performance compared to a conventional TFT, which is expected to open a new path in the printed metal oxide-based TFT field.

Design and Simulation of a Triple Absorber Layer Perovskite Solar Cell for High Conversion Efficiency

This paper presents a comprehensive simulation study on the influence of a triple absorber layer configuration in a perovskite-based solar cell using the SCAPS-1D software, under AM1.5 illumination. The simulated structure comprises a Cesium Tin-Germanium Triiodide (CsSn0.5Ge0.5I3) absorber layer sandwiched between Indium gallium zinc oxide (IGZO) and Cu2O layers. The main objective of this study is to enhance the power conversion efficiency (PCE) by optimizing the thicknesses of each layer. To validate our simulation results, we compare them with experimental data obtained from existing literature, and we observe a satisfactory agreement between the two. Our findings reveal that the maximum PCE of 28% can be achieved by utilizing specific thickness values for each layer. Specifically, the optimal thicknesses are determined to be 20 nm for the IGZO layer, 200 nm for the Cu2O layer, and 700 nm for the perovskite layer. These optimized thickness values lead to a significant improvement in the PCE of the solar cell, reaching 29%. This achievement highlights the effectiveness of our proposed triple absorber layer configuration and demonstrates its potential to enhance the overall performance of the perovskite-based solar cell. Overall, this study provides valuable insights into the optimization of the absorber layer configuration in perovskite solar cells, leading to improved power conversion efficiency.

Insight into the evolution of electrical properties for Schottky-barrier IGZO thin-film transistors with Cu-based Schottky contacts

In this work, we performed systematic electrical characterization and analysis of indium–gallium–zinc oxide (IGZO) Schottky-barrier thin-film transistors (SBTFTs) with different Cu-based Schottky contact structures. It was found that the Schottky barrier height (ΦB) between the IGZO layer and the Cu electrode could be modulated notably by changing the thickness of the AlOx tunnel layer, and the variation in ΦB significantly changed the saturation drain current (Idsat) of the IGZO SBTFTs based on the Schottky contacts but only had a minor influence on the saturation voltage (Vdsat) of the devices. Furthermore, Cu/Al stacked source/drain electrodes and silicon nitride (SiNx) passivation were employed to tailor the contact resistance and channel resistance of the IGZO SBTFTs, which led to an increase in Idsat and a variation in Vdsat. A universal resistance–capacitance network model was proposed to explain the observed evolution of Vdsat of the SBTFTs with different device structures. This work provides meaningful insight into developing low-cost metal oxide SBTFTs with tailored device performances.

Approaches for 3D Integration Using Plasma-Enhanced Atomic-Layer-Deposited Atomically-Ordered InGaZnO Transistors with Ultra-High Mobility.

As the scale-down and power-saving of silicon-based channel materials approach the limit, oxide semiconductors are being actively researched for applications in 3D back-end-of-line integration. For these applications, it is necessary to develop stable oxide semiconductors with electrical properties similar to those of Si. Herein, a single-crystal-like indium-gallium-zinc-oxide (IGZO) layer (referred to as a pseudo-single-crystal) is synthesized using plasma-enhanced atomic layer deposition and fabricated stable IGZO transistors with an ultra-high mobility of over 100cm2 Vs-1 . To acquire high-quality atomic layer deposition-processed IGZO layers, the plasma power of the reactant is controlled as an effective processing parameter by evaluating and understanding the effect of the chemical reaction of the precursors on the behavior of the residual hydrogen, carbon, and oxygen in the as-deposited films. Based on these insights, this study found that there is a critical relationship between the optimal plasma reaction energy, superior electrical performance, and device stability.

Field-Effect Mobility Extraction of Solution-Processed InGaZnO Thin-Film Transistors Considering Dielectric Dispersion Behavior of AlOx Gate Insulator

We investigated the effect of the dielectric dispersion behavior of solution-processed aluminum oxide (AlOx) on the field-effect mobility estimation of the solution-processed indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs). In the metal–insulator–metal (MIM) structure, solution-processed AlOx dielectric film annealed at 350 °C showed dielectric dispersion behavior, which was attributed to the electric double layer (EDL) due to the mobile ions, such as a hydrogen ion (H+) or a hydroxyl group (OH–). The annealing process at a higher temperature of 500 °C reduced the number of mobile ions in the AlOx film and removed the dielectric dispersion behavior in the MIM structure. However, solution-processed IGZO TFTs using the AlOx annealed at 500 °C as gate insulator showed dielectric dispersion-related behavior. We found that the chemical reaction to form a solution-processed IGZO layer supplied the mobile ions to the AlOx film, resulting in the EDL and dielectric dispersion phenomenon. Therefore, the dielectric dispersion should be investigated in the metal–insulator–semiconductor–metal structure, although the dispersive behavior does not occur in the MIM structure. Furthermore, the field-effect mobility (μFE) of solution-processed IGZO TFTs was 35.6 and 17.5 cm2/V·s with and without consideration of the dielectric dispersion behavior. The μFE was overestimated by 203% without regard to the dielectric dispersion. Consequently, the dielectric dispersion should be considered to estimate the accurate μFE of solution-processed IGZO TFTs with solution-processed AlOx as the gate insulator layer.

Investigation of persistent photoconductance and related electron mobility in thin IGZO layers with the PDL Hall technique

Indium gallium zinc oxide (IGZO) is a popular material to fabricate thin-film transistors (TFT). The light induced long-term conductance change in the thin IGZO layers (known as persistent photoconductance, PPC) is a significant phenomenon that should be deeply understood and controlled. We used the Parallel dipole line (PDL) AC Hall measurement technique to study the light induced change of the conductance and mobility of charge carriers in IGZO layers and its relaxation in dark. In the PDL systems rotating permanent magnets are applied to realize the AC Hall measurement at large magnetic field with harmonic modulation in a very compact design. Several samples with varying layer thickness, composition, and passivation conditions were prepared to investigate the PPC phenomenon. The magnitude and relaxation of PPC show a very strong dependence on IGZO preparation conditions. In some samples over tenfold conductance increase was observed at room temperature. Relaxations times varied from a few hours up to a few days. An interesting observation was that the mobility (in the range of 1 cm2/Vs-8.9 cm2/Vs) also increases with the conductance as the result of illumination.

Effect of Back-Channel Surface on Reliability of Solution-Processed In0.51Ga0.15Zn0.34O Thin-Film Transistors with Thin Active Layer.

We have investigated the degradation mechanism of solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors. The threshold voltage shift (ΔVth) followed a linear function under negative gate bias stress (NBS), while it showed a stretched-exponential behavior under positive gate bias stress. The slope of ΔVth for stress time was rarely changed with variations below 0.3 mV/s. The thickness of the fabricated IGZO layer (In0.51Ga0.15Zn0.34O) was approximately 10 nm. The Debye length (LD) was larger than IGZO thickness (tIGZO) due to the fully depleted active layer under NBS. Therefore, the degradation phenomenon under NBS was related to the adsorption at back-channel surface. The back-channel surface could be affected by the gate bias under NBS, and the molecules adsorbed at the IGZO layer were positively charged and induced extra electrons by NBS. We verified that the number of positively charged adsorbates had a proportional relationship with the ΔVth based on the two-dimensional technology computer-aided design (TCAD) simulation. Furthermore, we investigated the degradation phenomenon with the ΔVth equation regarding the adsorbates, and the result confirmed that the adsorption process could cause the linear ΔVth. We experimentally confirmed the effect of back-channel surface by comparing the ΔVth between different atmospheric conditions and LD. Consequently, the reaction at the back-channel surface should be considered to develop the metal-oxide semiconductor devices.

Fabrication of Schottky-Barrier-Oxide- Semiconductor Thin-Film Transistors via a Simple Aluminum Reaction Method

In this work, we proposed a simple method for fabricating Schottky-barrier thin-film transistors (TFTs) with tailorable device characteristics. Through a simple post annealing process, an AlOx interlayer was formed between Cu/Al source/drain electrodes and the amorphous indium gallium zinc oxide (IGZO) layer, which induced the formation of a Schottky-barrier between Cu and the IGZO layer at the edge of the electrodes to modulate the carrier injection. Consequently, we found TFTs with different IGZO thicknesses presented notably different operation characteristics. When the thickness of the IGZO layer was 30 nm, the fabricated TFT behaved like a high mobility Ohmic-contact device, with an apparent field effect mobility as high as 82.9 cm2 V−1 s−1. After the thickness of the IGZO layer was reduced to 10 nm, the TFT worked like a Schottky-contact TFT, which exhibited a low saturation voltage of 2.3 V and a high output current of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80~\mu \text{A}$ </tex-math></inline-formula> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{{\mathrm {GS}}} =20$ </tex-math></inline-formula> V.

Non-vacuum room temperature-processed sintering method of molybdenum pattern by intense pulsed light irradiation for high-performance electronic devices

In this study, the molybdenum (Mo) pattern was realized via intense pulsed light (IPL) irradiation process under ambient condition, without vacuum deposition process. The screen printing method was applied to realize a certain pattern using conductive ink composed of Mo nanoparticles. This printed Mo pattern showed low electrical conductivity due to oxide film on the nanoparticles surface. To improve this drawback, the IPL irradiation process was optimized for sintering of Mo pattern, therefore the remarkable electrical conductivity (35 μΩ·cm) was observed after IPL irradiation process. To investigate the microstructure and other reaction effects of Mo pattern, the various analysis was conducted such as scanning electron microscope, X-ray diffraction, focused ion beam analysis. This printed Mo pattern was applied for the source and drain (S/D) electrode of indium gallium zinc oxide (IGZO) based thin film transistor (bottom gate; TFT). The interfacial microstructure between Mo pattern and IGZO layer was investigated by transmittance electron microscope analysis. Consequently, the TFT with IPL-sintered Mo (S/D) pattern showed a noteworthy saturation mobility of 13.5 cm2·(V·s)−1.

The dual-detection mode and improved photoresponse of IGZO-based photodetectors by interfacing with water-soluble biomaterials

The use of conventional fabrication methods rapidly developed the performance and notable enhancements of optoelectronic devices. However, it proved challenging to develop and demonstrate stable optoelectronic devices with biodegradability and biocompatibility properties towards sustainable development and extensive applications. This study incorporates a water-soluble Cr-phycoerythrin (Cr-PE) biomaterial to observe its optical and electronic properties effects on the pristine indium gallium zinc oxide (IGZO)-based photodetector. The fabricated photodetector demonstrates an extended absorption detection region, enhanced optoelectronic performance, and switchable function properties. The resulting photocurrent and responsivity of the IGZO/Cr-PE structure have increased by 5.7 and 7.1 times as compared to the pristine IGZO photodetector. It was also observed that the photodetector could operate in UV and UV–visible with enhanced optical properties by effectively adding the water-soluble Cr-PE. Also, the sensing region of IGZO photodetector becomes changeable. It exhibits switchable dual detection by alternatively dripping and removing the Cr-PE on the IGZO layer. Different measurement parameters such as detectivity, repeatability, and sensitivity are highlighted to effectively prove the advantage of including Cr-PE on the photodetector structure. This study contributes to understanding the potential functions in improving optoelectronic devices through an environmental-friendly method.

Influence of UV/Ozone Treatment on Threshold Voltage Modulation in Sol–Gel IGZO Thin‐Film Transistors

AbstractSol–gel indium–gallium–zinc oxide (IGZO) semiconductors are developed as active components of thin‐film transistors (TFTs) because of their high electron mobility, cost‐effective large‐area fabrication, and applicability for flexible substrates. Controlling oxygen vacancies (Vo) in the IGZO semiconductor channel is always problematic for reliable and long‐term operation. Surplus interfacial charges inside the IGZO channel cause negative shifts in threshold voltages (Vth), resulting in depletion‐mode operation and involuntary high current output. The room temperature and rapid (&lt;3 min) modulation of Vth using a novel ultraviolet ozone (UVO) treatment of IGZO layer (In:Ga:Zn = 7:1:2) are reported. Physicochemical and electrical analysis reveals that UVO treatment enables the reduction of Vo and increases MO bonding with invariant contact resistance, resulting in the normalization of Vth close to 0 V and high operational durability under long‐term bias stress. As a proof of concept, this study demonstrates the depletion‐load n‐type inverters comprising depletion and enhancement modes (without &amp; with UVO) on the same substrate that allow high gain (≈10) with a moderate noise margin. This UVO treatment of the active layer is advantageous for the effective modulation of Vth with stable operation under long‐term bias stress and is superior to logic inverters based on single‐mode sol–gel oxide transistors.

29.5: Reliability Enhancement of an Indium‐Gallium‐Zinc Oxide Thin‐Film Transistor by Pre‐Fluorination Non‐Oxidizing Annealing

Techniques of overcoming issues of device instability and negative turn‐on voltage of an fluorinated indium‐gallium‐zinc oxide (IGZO) thin‐film transistor have been investigated. Such improvement correlates with the annihilation of oxygen‐related defects in the fluorinated channels. However, further extension of the fluorination time has been found to lead to degradation of some device characteristics. An alternative process has been proposed, involving the addition of a non‐oxidizing anneal before the fluorination treatment. Consistenet with the higher fluorine content in the IGZO layer revealed using secondary ion‐mass spectrometry, more positive shift of the turn‐on voltage and improvement in reliability have been obtained, without the TFT suffering from degradation in other device characteristics.

Novel Method for Fabricating Visible-Light Phototransistors Based on a Homojunction-Porous IGZO Thin Film Using Mechano-Chemical Treatment.

A homojunction-structured oxide phototransistor based on a mechano-chemically treated indium-gallium-zinc oxide (IGZO) absorption layer is reported. Through this novel and facile mechano-chemical treatment, mechanical removal of the cellophane adhesive tape induces reactive radicals and organic compounds on the sputtered IGZO film surface. Surface modification, following the mechano-chemical treatment, caused porous sites in the solution-processed IGZO film, which can give rise to a homojunction-porous IGZO (HPI) layer and generate sub-gap states from oxygen-related defects. These intentionally generated sub-gap states played a key role in photoelectron generation under illumination with relatively long-wavelength visible light despite the wide band gap of IGZO (>3.0 eV). Compared with conventional IGZO phototransistors, our HPI phototransistor displayed outstanding optoelectronic characteristics and sensitivity; we measured a threshold voltage (Vth) shift from 3.64 to -6.27 V and an on/off current ratio shift from 4.21 × 1010 to 4.92 × 102 under illumination with a 532 nm green light of 10 mW/mm2 intensity and calculated a photosensitivity of 1.16 × 108. The remarkable optoelectronic characteristics and high optical transparency suggest optical sensor applications.

Performance Enhancement of Transparent Amorphous IGZO Thin-Film Transistor Realized by Sputtered Amorphous AlOx Passivation Layer

We report a high-mobility transparent Indium-Gallium-Zinc-Oxide (IGZO) thin-film transistor (TFT) with sputtered AlOx passivation layer. The interfacial region between the IGZO layer and the AlOx layer played a crucial role in improving the field-effect mobility (the maximum field-effect mobility increased from 6.292 cm2 Vs−1 for the TFT without the AlOx layer to 69.01 cm2 Vs−1 for the TFT with the passivation layer) and the on/off current ratio (from ∼107 without the layer to ∼108 with the layer). The driving current of IGZO TFT was also significantly enhanced. The formation of the interfacial layer has been investigated and verified. The ion bombardment during the AlOx deposition broke the In-O bond in IGZO, generating oxygen ions (O2−). The segregation of the O2− was facilitated by the sputtered amorphous AlOx. A metallic In-rich layer with high oxygen vacancy concentration was formed at the interface, leading to an increase in the carrier concentration in the interfacial layer. Besides the electrical performance, the reliability tests, including long-term exposure in the ambient environment and positive bias illumination stress (PBIS), showed improved results as well.

Analysis of Threshold Voltage Shift for Full VGS/VDS/Oxygen-Content Span under Positive Bias Stress in Bottom-Gate Amorphous InGaZnO Thin-Film Transistors.

In this study, we analyzed the threshold voltage shift characteristics of bottom-gate amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) under a wide range of positive stress voltages. We investigated four mechanisms: electron trapping at the gate insulator layer by a vertical electric field, electron trapping at the drain-side GI layer by hot-carrier injection, hole trapping at the source-side etch-stop layer by impact ionization, and donor-like state creation in the drain-side IGZO layer by a lateral electric field. To accurately analyze each mechanism, the local threshold voltages of the source and drain sides were measured by forward and reverse read-out. By using contour maps of the threshold voltage shift, we investigated which mechanism was dominant in various gate and drain stress voltage pairs. In addition, we investigated the effect of the oxygen content of the IGZO layer on the positive stress-induced threshold voltage shift. For oxygen-rich devices and oxygen-poor devices, the threshold voltage shift as well as the change in the density of states were analyzed.

Structural color switching with a doped indium-gallium-zinc-oxide semiconductor

Structural coloration techniques have improved display science due to their high durability in terms of resistance to bleaching and abrasion, and low energy consumption. Here, we propose and demonstrate an all-solid-state, large-area, lithography-free color filter that can switch structural color based on a doped semiconductor. Particularly, an indium-gallium-zinc-oxide (IGZO) thin film is used as a passive index-changing layer. The refractive index of the IGZO layer is tuned by controlling the charge carrier concentration; a hydrogen plasma treatment is used to control the conductivity of the IGZO layer. In this paper, we verify the color modulation using finite difference time domain simulations and experiments. The IGZO-based color filter technology proposed in this study will pave the way for charge-controlled tunable color filters displaying a wide gamut of colors on demand.

High Photosensitive Indium–Gallium–Zinc Oxide Thin-Film Phototransistor with a Selenium Capping Layer for Visible-Light Detection

Visible light can be detected using an indium-gallium-zinc oxide (IGZO)-based phototransistor, with a selenium capping layer (SCL) that functions as a visible light absorption layer. Selenium (Se) exhibits photoconductive properties as its conductivity increases with illumination. We report an IGZO phototransistor with an SCL (SCL/IGZO phototransistor) that demonstrated optimal photoresponse characteristics when the SCL was 150 nm thick. The SCL/IGZO phototransistor exhibited a photoresponsivity of 1.39 × 103 A/W, photosensitivity of 4.39 × 109, detectivity of 3.44 × 1013 Jones, and external quantum efficiency of 3.52 × 103% when illuminated by green light (532 nm). Ultraviolet-visible spectroscopy and ultraviolet photoelectron spectroscopy analysis showed that Se has a narrow energy band gap, in which visible light is absorbed and forms a p-n junction with IGZO so that photogenerated electron-hole pairs are easily separated, which makes recombination more challenging. We show that electrons generated in the SCL flow through the IGZO layer, which enables the phototransistor to detect visible light. Furthermore, the SCL/IGZO phototransistor exhibited excellent durability and reversibility owing to the constant light and dark current and the time-dependent photoresponse characteristics over 8000 s when a red light (635 nm) source was turned on and off at a frequency of 0.1 Hz.

Remote Gating of Schottky Barrier for Transistors and Their Vertical Integration.

This paper introduces a strategy to modulate a Schottky barrier formed at a graphene-semiconductor heterojunction. The modulation is performed by controlling the work function of graphene from a gate that is placed laterally away from the graphene-semiconductor junction, which we refer to as the remote gating of a Schottky barrier. The remote gating relies on the sensitive work function of graphene, whose local variation induced by locally applied field effect affects the change in the work function of the entire material. Using Kelvin probe force microscopy analysis, we directly visualize how this local variation in the work function propagates through graphene. These properties of graphene are exploited to assemble remote-gated vertical Schottky barrier transistors (v-SBTs) in an unconventional device architecture. Furthermore, a vertical complementary circuit is fabricated by simply stacking two remote-gated v-SBTs (pentacene layer as the p-channel and indium gallium zinc oxide layer as the n-channel) vertically. We consider that the remote gating of graphene and the associated device architecture presented herein facilitate the extendibility of graphene-based v-SBTs in the vertical assembly of logic circuits.

Oxide-Polymer Heterojunction Diodes with a Nanoscopic Phase-Separated Insulating Layer.

Organic semiconductor-insulator blend films are widely explored for high-performance electronic devices enabled by unique phase-separation and self-assembly phenomena at key device interfaces. Here we report the first demonstration of high-performance hybrid diodes based on p- n junctions formed by a p-type poly(3-hexylthiophene) (P3HT)-poly(methyl methacrylate) (PMMA) blend and n-type indium-gallium-zinc oxide (IGZO). The thin film morphology, microstructure, and vertical phase-separation behavior of the P3HT films with varying contents of PMMA are systematically analyzed. Microstructural and charge transport evaluation indicates that the polymer insulator component positively impacts the morphology, molecular orientation, and effective conjugation length of the P3HT films, thereby enhancing the heterojunction performance. Furthermore, the data suggest that PMMA phase segregation creates a continuous nanoscopic interlayer between the P3HT and IGZO layers, playing an important role in enhancing diode performance. Thus, the diode based on an optimal P3HT-PMMA blend exhibits a remarkable 10-fold increase in forward current versus that of a neat P3HT diode, yielding an ideality factor value as low as 2.5, and a moderate effective barrier height with an excellent rectification ratio. These results offer a new approach to simplified manufacturing of low-cost, large-area hybrid inorganic-organic electronics technologies.