C-Axis Aligned Composite InZnO via Thermal Atomic Layer Deposition for 3D Nanostructured Semiconductor.

Amorphous oxide semiconductors have been widely studied for various applications, including thin-film transistors (TFTs) for display backplanes and semiconductor memories. However, the inherent instability, limited mobility, and complexity of multicomponent oxide semiconductors for achieving high aspect ratios and conformality of cation distribution remain challenging. Indium-zinc oxide (IZO), known for its high mobility, also faces obstacles in instability resulting from high carrier doping density and low ionization energy. To address these issues and attain a balance between mobility and stability, adopting a highly aligned structure such as a c-axis aligned crystalline IGZO could be advantageous. However, limited studies have reported enhanced electrical performance using crystalline IZO, likely attributed to the high thermal stability of the individual components (In2O3 and ZnO). Here, we first propose a c-axis aligned composite (CAAC) IZO with superior TFT properties, including a remarkable performance of field-effect mobility (µFE) of 55.8 cm2/(V s) and positive-bias-temperature-stress stability of +0.16 V (2 MV/cm, 60 °C, 1 h), as well as a low subthreshold swing of 0.18 V/decade and hysteresis as 0.01 V, which could be obtained through optimization of growth temperature and composition using thermal atomic layer deposition. These results surpass those of TFTs based on nanocrystalline/polycrystalline/amorphous-IZO. We conducted a thorough investigation of CAAC-IZO and revealed that the growth temperature and cation distribution profoundly influence the crystal structure and device properties. Finally, we observed excellent compositional conformality and 97% step coverage of IZO on a high-aspect-ratio (HAR) structure with an aspect ratio reaching 40:1, which is highly promising for future applications. Our results include a detailed investigation of the influence of the crystal structure of IZO on the film and TFT performance and suggest an approach for future applications.

c-Axis Aligned 3 nm Thick In2O3 Crystal Using New Liquid DBADMIn Precursor for Highly Scaled FET Beyond the Mobility-Stability Trade-off.

Oxide semiconductors (OS) are attractive materials for memory and logic device applications owing to their low off-current, high field effect mobility, and superior large-area uniformity. Recently, successful research has reported the high field-effect mobility (µFE) of crystalline OS channel transistors (above 50 cm2 V-1 s-1). However, the memory and logic device application presents challenges in mobility and stability trade-offs. Here, we propose a method for achieving high-mobility and high-stability by lowering the grain boundary effect. A DBADMIn precursor was synthesized to deposit highly c-axis-aligned C(222) crystalline 3 nm thick In2O3 films. In this study, the 250 °C deposited 3 nm thick In2O3 channel transistor exhibited high µFE of 41.12 cm2 V-1 s-1, Vth of -0.50 V, and SS of 150 mV decade-1 with superior stability of 0.16 V positive shift during PBTS at 100 °C, 3 MV cm-1 stress conditions for 3 h.

Thermally Activated Defect Engineering for Highly Stable and Uniform ALD-Amorphous IGZO TFTs with High-Temperature Compatibility.

Highly stable IGZO thin-film transistors derived from atomic layer deposition are crucial for the semiconductor industry. However, unavoidable defect generation during high-temperature annealing results in abnormal positive bias temperature stress (PBTS). Herein, we propose a defect engineering method by controlling the gate insulator (GI) deposition temperature. Applying a GI deposition temperature of 400 °C to the In0.52Ga0.18Zn0.30O active layer effectively suppresses defects even after 600 °C annealing, preserving the amorphous phase of IGZO. The device exhibits a threshold voltage (VTH) of 0.05 V, a field-effect mobility of 27.6 cm2/Vs, a subthreshold swing of 61 mV/decade, and a hysteresis voltage of 0.01 V, demonstrating highly reliable PBTS and negative bias temperature stress. A power-law fit of the PBTS stability under 2 MV/cm of gate field stress and 120 °C of temperature stress predicts a VTH shift of -0.01 V after 10 years. Moreover, the proposed method ensures reliable uniformity over a large 4 in. area.

Electrical conductivity, Seebeck coefficient, and crystal growth of p-type tellurium films through temperature dependent RF sputtering.

Te thin films have recently received considerable attention owing to its superior electrical and thermoelectric properties. During the deposition process, if the temperature of the substrate is raised, high crystallinity and improved electrical properties can be expected. In this study, we used radio frequency sputtering for Te deposition to study the relationship between the deposition temperature, crystal size, and electrical performance. As the deposition temperature is increased from room temperature to 100 °C, we observed an increase in crystal size from the x-ray diffraction patterns and full-width half maximum calculations. With this grain size increment, the Hall mobility and Seebeck coefficient of the Te thin film increased significantly from 16 to 33 cm2V-1s-1and 50 to 138µV K-1, respectively. This study reveals the potential of a facile fabrication method for enhanced Te thin films using temperature control and highlights the importance of the Te crystal structure in determining the electrical/thermoelectrical properties. These findings are particularly significant for the development of semiconductor material systems for various applications, including thermoelectric devices, CMOS, FET, and solar devices.

Selectively Nitrogen Doped ALD-IGZO TFTs with Extremely High Mobility and Reliability.

Achieving high mobility and reliability in atomic layer deposition (ALD)-based IGZO thin-film transistors (TFTs) with an amorphous phase is vital for practical applications in relevant fields. Here, we suggest a method to effectively increase stability while maintaining high mobility by employing the selective application of nitrous oxide plasma reactant during plasma-enhanced ALD (PEALD) at 200 °C process temperature. The nitrogen-doping mechanism is highly dependent on the intrinsic carbon impurities or nature of each cation, as demonstrated by a combination of theoretical and experimental research. The Ga2O3 subgap states are especially dependent on plasma reactants. Based on these insights, we can obtain high-performance indium-rich PEALD-IGZO TFTs (threshold voltage: -0.47 V; field-effect mobility: 106.5 cm2/(V s); subthreshold swing: 113.5 mV/decade; hysteresis: 0.05 V). In addition, the device shows minimal threshold voltage shifts of +0.45 and -0.10 V under harsh positive/negative bias temperature stress environments (field stress: ±2 MV/cm; temperature stress: 95 °C) after 10000 s.

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 100 cm2  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.

Enhanced performance and stability in InGaZnO NIR phototransistors with alumina-infilled quantum dot solid.

The optimized ALD infilling process for depositing Al2O3 in the vertical direction of PbS QDs enhances the photoresponsivity, relaxation rate and the air stability of PbS QDs hybrid IGZO NIR phototransistors. Infilled Al2O3, which is gradually deposited from the top of PbS QDs to the PbS/IGZO interface (1) passivates the trap sites up to the interface of PbS/IGZO without disturbing charge transfer and (2) prevents QDs deterioration caused by outside air. Therefore, an Al2O3 infilled PbS QD/IGZO hybrid phototransistor (AI-PTs) exhibited enhanced photoresponsivity from 96.4 A/W to 1.65 × 102 A/W and a relaxation time decrease from 0.52 to 0.03 s under NIR light (880 nm) compared to hybrid phototransistors without Al2O3 (RF-PTs). In addition, AI-PTs also showed improved shelf stability over 4 months compared to RF-PTs. Finally, all devices we manufactured have the potential to be manufactured in an array, and this ALD technique is a means of fabricating robust QDs/metal oxide hybrids for optoelectronic devices.

Multiple-Actuator Fault Isolation Using a Minimal ℓ1-Norm Solution with Applications in Overactuated Electric Vehicles.

A multiple-actuator fault isolation approach for overactuated electric vehicles (EVs) is designed with a minimal ℓ1-norm solution. As the numbers of driving motors and steering actuators increase beyond the number of controlled variables, an EV becomes an overactuated system, which exhibits actuator redundancy and enables the possibility of fault-tolerant control (FTC). On the other hand, an increase in the number of actuators also increases the possibility of simultaneously occurring multiple faults. To ensure EV reliability while driving, exact and fast fault isolation is required; however, the existing fault isolation methods demand high computational power or complicated procedures because the overactuated systems have many actuators, and the number of simultaneous fault occurrences is increased. The method proposed in this paper exploits the concept of sparsity. The underdetermined linear system is defined from the parity equation, and fault isolation is achieved by obtaining the sparsest nonzero component of the residuals from the minimal ℓ1-norm solution. Therefore, the locations of the faults can be obtained in a sequence, and only a consistently low computational load is required regardless of the isolated number of faults. The experimental results obtained with a scaled-down overactuated EV support the effectiveness of the proposed method, and a quantitative index of the sparsity condition for the target EV is discussed with a CarSim-connected MATLAB/Simulink simulation.

Facile synthesis of an organic/inorganic hybrid 2D structure tincone film by molecular layer deposition.

Organic/inorganic hybrid tincone films were deposited by molecular layer deposition (MLD) using N,N'-tert-butyl-1,1-dimethylethylenediamine stannylene(II) as a precursor and hydroquinone (HQ) as an organic reactant. From previous studies it is known that SnO can be fabricated through a reaction with H2O, which has low oxidizing power. Similarly, when combined with HQ having a bi-functional hydroxyl group, SnO-based 2D hybrid tincones can be produced. In most aromatic ring-based metalcones described in previous studies, graphitization by pyrolysis occurred during post-annealing. In this study of tincones fabricated with a divalent precursor after a vacuum post-annealing process, the structural rearrangement of the SnO and the benzene ring bonds proceeded to form a SnO-based hybrid 2D structure. The rearrangement of the resulting structure occurred through π-π stacking (without pyrolysis) of the benzene ring. To understand the mechanism of fabrication of 2D hybrid tincones by π-π stacking of the benzene ring and the increase of the crystallinity of SnO after the annealing process, the structural rearrangement was observed using X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GIXRD), grazing-incidence wide-angle X-ray scattering (GIWAXS), and Raman spectroscopy. Thereafter, the design of the crystal structure was investigated.

Dry-Etchable Molecular Layer-Deposited Inhibitor Using Annealed Indicone Film for Nanoscale Area-Selective Deposition.

In semiconductor production, the technology node of a device is becoming extremely small below 5 nm. Area selective deposition (ASD) is a promising technique for creating improved overlay or self-alignment, remedying a conventional top-down method. However, the conventional materials and process (self-assembled monolayer, polymer and carbon film fabricated by chemical vapor deposition, and spin coating) for ASD are not suitable for highly conformal deposition. Thus, we investigated a new strategy to deposit conformal films in ASD by molecular layer deposition (MLD). The MLD processes were conducted for an indicone film deposited by INCA-1 (bis(trimethysily)amidodiethyl indium) and hydroquinone (HQ), as well as an alucone film deposited by TMA (trimethylaluminum) and HQ. After thermal heat treatment of the MLD films, variations in thickness, refractive index, and constituent elements of the annealed MLD films were investigated. The indicone film was used as an inhibiting layer for ASD and was etchable with a dry-etching process. The reactive ion etching process on annealed indicone film was optimized according to plasma power, gas concentration, and working pressure. Ruthenium (Ru) ALD was then performed on the annealed MLD films to investigate nucleation delaying cycles and inhibiting properties. A patterned substrate with an MLD/Si line was created via the RIE process, which was allowed to observe the selectivity of the annealed MLD films. In addition, a patterned substrate of SiO2/annealed indicone/Mo was used to investigate the Ru-selective ALD at the nanoscale. The Ru thin film was selectively deposited on the Mo side-wall surface of a 3D trench structure. The growth of the Ru film was inhibited selectively on an annealed indicone surface of approximately 5 nm.

Water vapor and hydrogen gas diffusion barrier characteristics of Al2O3-alucone multi-layer structures for flexible OLED display applications.

Organic light emitting diodes (OLEDs) and amorphous oxide semiconductors (AOSs), which are very important technologies in high performance flexible displays, have issues related to degradation due to diffusion of water and hydrogen, respectively. To solve these issues, gas diffusion barrier properties were evaluated with aluminum oxide deposited by atomic layer deposition (ALD) and alucone deposited by molecular layer deposition (MLD) using trimethylaluminum (TMA) as a metal precursor and H2O and hydroquinone (HQ) as co-reactants, respectively. The water vapor transmission rate (WVTR) and hydrogen gas permeability (HGP) were measured for the fabricated films via electrical calcium tests and vacuum time-lag, respectively. To enhance the diffusion barrier properties, Al2O3/alucone hybrid multi-layer structures were successfully deposited through an in situ ALD/MLD process. The 4.5 dyads of the Al2O3/alucone structure showed improved barrier properties compared to the single Al2O3 film with a WVTR of 8.24 × 10-5 g m-2 day-1 and a HGP of 9.93 × 10-5 barrer, and factors related to gas diffusion in multi-layer structures were discussed. The stability to external stress was also evaluated based on the WVTR change rate after the bending test, and we confirmed that the stability of the multi-layer structures was improved due to the flexibility of inserted alucone layers. All the developed structures had a high optical transmittance of >80% in the 300-800 nm wavelength region based on UV-vis measurements.

Atomic-Layer-Deposited SiOx/SnOx Nanolaminate Structure for Moisture and Hydrogen Gas Diffusion Barriers.

High-density SnOx and SiOx thin films were deposited via atomic layer deposition (ALD) at low temperatures (100 °C) using tetrakis(dimethylamino)tin(IV) (TDMASn) and di-isopropylaminosilane (DIPAS) as precursors and hydrogen peroxide (H2O2) and O2 plasma as reactants, respectively. The thin-film encapsulation (TFE) properties of SnOx and SiOx were demonstrated with thickness dependence measurements of the water vapor transmission rate (WVTR) evaluated at 50 °C and 90% relative humidity, and different TFE performance tendencies were observed between thermal and plasma ALD SnOx. The film density, crystallinity, and pinholes formed in the SnOx film appeared to be closely related to the diffusion barrier properties of the film. Based on the above results, a nanolaminate (NL) structure consisting of SiOx and SnOx deposited using plasma-enhanced ALD was measured using WVTR (H2O molecule diffusion) at 2.43 × 10-5 g/m2 day with a 10/10 nm NL structure and time-lag gas permeation measurement (H2 gas diffusion) for applications as passivation layers in various electronic devices.

Facile rearrangement of molecular layer deposited metalcone thin films by electron beam irradiation for area selective atomic layer deposition.

Area selective atomic layer deposition (AS-ALD) is a promising future technology for the realization of a 5 nm scale Si complementary field effect transistor (FET) and its application in industry. AS-ALD is one of the "bottom-up" technologies, which is a key process that can reduce the cost of fabrication and decrease positional error as an alternative to the conventional "top down" technology. We researched an inhibitor for AS-ALD using molecular layer deposited (MLD) films annealed by electron beam irradiation (EBI). We studied the effect of EBI on an indicone film that was fabricated by using bis(trimethylsilyl)amidodiethyl indium (INCA-1), hydroquinone (HQ), an alucone film fabricated by using trimethylaluminum (TMA) and 4-mercaptophenol (4MP). The EBI effect on MLD films was evaluated by investigating the changes in thickness, composition and structure. In order to observe the selectivity of the annealed indicone film, atomic layer deposition of ZnO was performed on the annealed indicone/silicon line pattern, and it was found that the surface of annealed indicone can inhibit ALD of ZnO for 20 cycles as compared to a Si surface.

Highly Dense and Stable p-Type Thin-Film Transistor Based on Atomic Layer Deposition SnO Fabricated by Two-Step Crystallization.

Over the past several decades, tin monoxide (SnO) has been studied extensively as a p-type thin film transistor (TFT). However, its TFT performance is still insufficient for practical use. Many studies suggested that the instability of the valence state of Sn (Sn2+/Sn4+) is a critical reason for the poor performance such as limited mobility and low on/off ratio. For SnO, the Sn 5s-O 2p hybridized state is a key component for obtaining p-type conduction. Thus, a strategy for stabilizing the SnO phase is essential. In this study, we employ a variety of analytical methods such as X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and Hall measurement to identify the main contributors to the physical properties of SnO. It is revealed that precision control of the process temperature is needed to achieve both the crystallinity and thermal stability of SnO. In other words, it would be ideal to obtain high-quality SnO thin films at low temperature. We find that atomic layer deposition (ALD) is a quite advantageous process for obtaining high-quality SnO thin films by the following two-step process: (i) growth of highly c-axis oriented SnO at the initial stage and (ii) further crystallization along the in-plane direction by a postannealing process. Consequently, we obtained a highly dense SnO thin film (film density: 6.4 g/cm3) with a high Hall mobility of ∼5 cm2/(V·s). The fabricated SnO TFTs exhibit a field-effect mobility of ∼6.0 cm2/(V·s), which is a quite high value among the SnO TFTs reported to date, with long-term stability. We believe that this study demonstrates the validity of the ALD process for SnO TFTs.

Significance of Pairing In/Ga Precursor Structures on PEALD InGaOx Thin-Film Transistor.

Atomic layer deposition (ALD) is a promising deposition method to precisely control the thickness and metal composition of oxide semiconductors, making them attractive materials for use in thin-film transistors because of their high mobility and stability. However, multicomponent deposition using ALD is difficult to control without understanding the growth mechanisms of the precursors and reactants. Thus, the adsorption and surface reactivity of various precursors must be investigated. In this study, InGaO (IGO) semiconductors were deposited by plasma-enhanced atomic layer deposition (PEALD) using two sets of In and Ga precursors. The first set of precursors consisted of In(CH3)3[CH3OCH2CH2NHtBu] (TMION) and Ga(CH3)3[CH3OCH2CH2NHtBu]) (TMGON), denoted as TM-IGO; the other set of precursors was (CH3)2In(CH2)3N(CH3)2 (DADI) and (CH3)3Ga (TMGa), denoted as DT-IGO. We varied the number of InO subcycles between 3 and 19 to control the chemical composition of the ALD-processed films. The indium compositions of TM-IGO and DT-IGO thin films increased as the InO subcycles increased. However, the indium/gallium metal ratios of TM-IGO and DT-IGO were quite different, despite having the same InO subcycles. The steric hindrance of the precursors and different densities of the adsorption sites contributed to the different TM-IGO and DT-IGO metal ratios. The electrical properties of the precursors, such as Hall characteristics and device parameters of the thin-film transistors, were also different, even though the same deposition process was used. These differences might have resulted from the growth behavior, anion/cation ratios, and binding states of the IGO thin films.

Reduction of Persistent Photoconduction with IGZO/ZnON-Tandem-Structure Visible-Near-Infrared Phototransistors.

Indium-gallium-zinc oxide- and zinc oxynitride-based heterojunction phototransistors were successfully demonstrated to control the persistent photoconduction (PPC) effect and be also responded sensitively at the range from visible to near-infrared. ZnON plays a key role in extending the spectral response at various frequencies of operation. The devices show significantly different photoresponse and photorecovery characteristics depending on the number of stacked layers of IGZO and ZnON. After negative bias and illumination stress was applied to the devices for 1 h, tandem-structure-based phototransistors recovered remarkably better than single-component IGZO devices. We suggest that the improvements to photoresponse and photorecovery result from the presence of potential wells between two IGZO layers and the energy band alignment of the tandem structure.

Selective Nonenzymatic Amperometric Detection of Lactic Acid in Human Sweat Utilizing a Multi-Walled Carbon Nanotube (MWCNT)-Polypyrrole Core-Shell Nanowire.

Lactic acid plays an important role as a biochemical indicator for sports medicine and clinical diagnosis. The detection of lactic acid in sweat is a promising technique without any intrusive inconvenience or risk of infection. In this study, we present a selective nonenzymatic amperometric detection method for lactic acid in human sweat utilizing a multi-wall carbon nanotube (MWCNT)-polypyrrole core-shell nanowire. Because polypyrrole is a p-type conducting polymer, onto which anions are exclusively doped, leading to charge transfer, it offers selective detection for lactate anions at a specific potential, while being inert to the neutral and cationic species contained in human sweat. A chronoamperometric study reveals good sensing performance for lactic acid with a high sensitivity of 2.9 µA mM-1 cm-2 and detection limit of 51 µM. Furthermore, the MWCNT-polypyrrole nanowire exhibits excellent selectivity for lactic acid over interfering species, such as sodium chloride, glucose, urea, and riboflavin, which coexist with lactic acid in sweat. Finally, a nonenzymatic amperometric sensor for the selective detection of lactic acid in human sweat is demonstrated on commercial flexible electrodes. The results demonstrate the potential applications of the MWCNT-polypyrrole core-shell nanowire as a nonenzymatic amperometric lactate sensor.

Thermal Annealing of Molecular Layer-Deposited Indicone Toward Area-Selective Atomic Layer Deposition.

Area-selective atomic layer deposition (AS-ALD) is a promising technique for fine nanoscale patterning, which may overcome the drawbacks of conventional top-down approaches for the fabrication of future electronic devices. However, conventional materials and processes often employed for AS-ALD are inadequate for conformal and rapid processing. We introduce a new strategy for AS-ALD based on molecular layer deposition (MLD) that is compatible with large-scale manufacturing. Conformal thin films of "indicone" (indium alkoxide polymer) are fabricated by MLD using INCA-1 (bis(trimethylsily)amidodiethylindium) and HQ (hydroquinone). Then, the MLD indicone films are annealed by a thermal heat treatment under vacuum. The properties of the indicone thin films with different annealing temperatures were measured with multiple optical, physical, and chemical techniques. Interestingly, a nearly complete removal of indium from the film was observed upon annealing to ca. 450 °C and above. The chemical mechanism of the thermal transformation of the indicone film was investigated by density functional theory calculations. Then, the annealed indicone thin films were applied as an inhibiting layer for the subsequent ALD of ZnO, where the deposition of approximately 20 ALD cycles (equivalent to a thickness of approximately 4 nm) of ZnO was successfully inhibited. Finally, patterns of annealed MLD indicone/Si substrates were created on which the area-selective deposition of ZnO was demonstrated.

Plasma-Polymer-Fluorocarbon Thin Film Coated Nanostructured-Polyethylene Terephthalate Surface with Highly Durable Superhydrophobic and Antireflective Properties.

Herein, an antireflection and superhydrophobic film was obtained by uniformly forming nanostructures on the surface of polyethylene terephthalate (PET) substrate using oxygen plasma without a pattern mask and coating plasma-polymer-fluorocarbon (PPFC) on the nanostructured surface by mid-range frequency sputtering. PPFC/nanostructured-PET showed a reflectance of 4.2%, which is 56% lower than that of the PET film. Haze was also improved. Nanostructured-PET exhibited a superhydrophilic surface due to plasma deformation and a superhydrophobic surface could be realized by coating PPFC on the nanostructured surface. The PPFC coating prevented the aging of polymer film nanostructures and showed excellent durability in a high-temperature and high-humidity environment. It exhibited excellent flexibility to maintain the superhydrophobic surface, even at a mechanical bending radius of 1 mm, and could retain its properties even after repeated bending for 10,000 times.

A bow-free freestanding GaN wafer.

For applications as high-brightness light-emitting-diodes, a bow-free freestanding gallium nitride (GaN) wafer 2 inch in diameter and ∼185 µm in thickness was fabricated by process-designing pit and mirror GaN layers grown via hydride-vapor-phase epitaxy, laser lift-off, N-face polishing of the pit GaN layer, and three-step polishing of the mirror GaN layer using 3.0 µm-, 0.5 µm-, and 50 nm-diameter diamond abrasives and by inductively-coupled-plasma reactive-ion etching. The considerably large concave shape of the GaN wafer could be decreased by controlling the removal amount of the Ga-face mirror layer during the first step of the polishing process, which approached a bow-free shape or changed with further polishing; this well correlated with the residual stress of the polished GaN wafer.