Large-area Substrates Research Articles

76‐1: Invited Paper: Optimization of Applied Materials PiVotTM Array Coater for Metal Oxide Semiconductor Layers

Applied Materials' static PVD array coater using rotary targets has been developed to provide less in‐film particle, high target utilization performance by novel rotary target technology and uniform layer deposition by unique magnet motion in display industry. It has been optimized to provide highly stable and uniform thin metal oxide layer to reach uniform TFT performance for large area substrate (2500x2200mm glass size).

Fabrication of flexible highly ordered porous alumina templates by combined nanosphere lithography and anodization

In this work, we propose a new method for the large-scale production of flexible, periodic alumina arrays with well-ordered pores. We show the incorporation of pre-patterning based on polystyrene (PS) nanosphere lithography into an aluminium anodization process. We prepared ordered monolayers of PS spheres with average diameters of (510 ± 10) nm and (430 ± 10) nm on a large area (1.5 × 1.5 cm2) of the Si substrate. Next, we deposited a 5 μm aluminium layer on arrays of PS nanospheres using the sputtering technique. After the deposition, we covered the aluminium film with a polymer Scotch adhesive tape, and separated it from the silicon substrate by ultrasonic-assisted lift-off. Finally, we performed the anodization of the aluminium. We compared the pore and cell sizes, and the pore distance for the templates obtained by this technique, with reference to the templates prepared by a two-step anodization process. Using this new approach, we obtained highly ordered hexagonal 2D lattices over a large area of up to 2 cm2 with sparse defects, amounting to not more than four defects per 1000 μm2 on average. Here, we show that the use of indentation techniques is not necessary and can be replaced by a fast, cheap and easy pre-patterning step based on nanosphere lithography.

(Invited) Ultrasonic Spray Coating of Electrochromic Nanomaterials

Ultrasonic spray deposition is a promising and versatile method for both fundamental and industrial researches and applications. It leads to the formation of uniform thin films on large area substrates at atmospheric pressure, with a fine control of the resulting morphology and thickness by adjustment of the practical spray conditions (substrate temperature, nozzle-to-substrate distance, deposition pattern, solution flow rate, carrier gas nature and pressure…). The ultrasonic atomization of the injected precursor solution/suspension is also particularly advantageous as it reduces overspray and energy consumption [1-2]. In our recent works [3-7], we are considering the spray deposition of thin films of electrochromic oxides such as WO3and NiO, which are exploited as nanomaterials for various optical-related devices, notably “smart windows” for energy-efficient fenestration in glass buildings [8-9]. A specific attention is thus paid to the composition of the sprayed solution/suspension (precursor type and concentration, solvent…) as it has a significant influence on film deposition mechanisms and properties. Substrate nature (morphology, crystallinity, conductivity…) is of particular importance too, and different types of transparent conductive oxide (TCO) coated glass are therefore investigated. Incorporation of selected surfactants is also acknowledged for influencing wettability, nucleation and growth processes, and resulting functionality. Consequent characterizations analyze crystallinity, microstructure and porosity, ionic reversibility and diffusion, cycling response, optical modulation, coloration/bleaching kinetics, tint and haze.

(Invited) Bringing III-Vs into CMOS: From Materials to Circuits

High-mobility channel materials such as InGaAs and SiGe alloys are considered to be the leading candidates for replacing strained Si in future low power/high performance logic circuits. However, the integration of InGaAs on Si and the co-integration of InGaAs devices with SiGe devices are extremely challenging. On the one hand, the large lattice mismatch (8 to 10%) and the potential formation of antiphase domains at the polar/non-polar III-V/Si crystalline interface typically hinder the integration of high quality InGaAs crystals on Si. On the other hand, InGaAs and SiGe require very different processing conditions in terms of thermal budgets, dry and wet chemistries, passivation schemes and contacting schemes which complexifies the realization of CMOS circuits. Recently, tremendous progress were achieved as a result of innovation at the material and device levels. Latest technology developments yielded the first demonstration of InGaAs/SiGe CMOS inverters and dense SRAM arrays on Si, fabricated with InGaAs selective epitaxy and standard front end of line processes in a 2D co-planar configuration. This novel and scalable CMOS integration scheme enables InGaAs nFET fabrication in close proximity to SiGe pFETs (down to 25 nm spacing), resulting in 6T-SRAM arrays having a minimum cell size below 0.45 μm2. This scheme can be combined with any bulk Si or SOI-based planar or fin technology, and is compatible with standard large-area Si substrate. Furthermore, progress on 3D Monolithic integration showed that this integration scheme not only an opportunity for further density scaling, but it also offers unique advantages for solving the integration of high mobility materials for 3D CMOS and stacking of functional layers on top of standard CMOS circuitry.

Synthesis of conductive and transparent Nb-doped TiO2 films: Role of the target material and sputtering gas composition

The authors report a comparative study of the electrical and optical properties of Nb:TiO2 thin films (TNO) in relation with their chemical properties. Two types of niobium containing targets, Nb metal and Nb2O5 oxide were employed simultaneously with ceramic TiO2 target for the films growth, in Ar and Ar-O2 discharge. Niobium is found to incorporate easily and substitutionally into titanium lattice site when deposited from oxide targets in oxygen-deficient discharge (Ar plasma). Consequently, the TNO film exhibits lowest resistivity of 1.4×10−3Ωcm with optical transparency of more than 80% in the visible region. On the contrary, doping was not effective in case the TNO films were grown from Nb metal and TiO2 targets in Ar and Ar-O2 plasma, probably due to the growth of niobium sub-oxide phases and lack of oxygen vacancies. The possible reasons of diverse electrical properties are discussed and are link with the growth conditions. Our result indicates that highly conductive and transparent doped-TiO2 film can be obtained by choosing appropriate target material and sputtering gas. The obtained results can significantly contribute to the development of transparent electrodes by RF sputtering, a suitable technique for coating on large area substrates.

Semipolar (202̅1̅) GaN and InGaN Light-Emitting Diodes Grown on Sapphire.

We have demonstrated growing uniform and purely nitrogen polar semipolar (202̅1̅) GaN epilayers on 2 in. patterned sapphire substrates. The as-grown surface of (202̅1̅) GaN is composed of two stable facets: (101̅0) and (101̅1̅). A chemical mechanical polishing process was further used to planarize the surface with a final surface root-mean-square roughness of less than 1.5 nm over an area of 10 × 10 μm2. InGaN light-emitting diodes were grown on a polished (202̅1̅) GaN/sapphire template with an electroluminescence emission at around 490 nm. Our work exhibits the potential to produce high-quality nitrogen-polar semipolar GaN templates and optoelectronic devices on large-area sapphire substrates with economical feasibility.

Achieving Large-Area Planar Perovskite Solar Cells by Introducing an Interfacial Compatibilizer.

Despite the recent unprecedented increase in the power conversion efficiencies (PCEs) of small-area devices (≤0.1 cm2 ), the PCEs deteriorate drastically for PSCs of larger areas because of the incomplete film coverage caused by the dewetting of the hydrophilic perovskite precursor solutions on the hydrophobic organic charge-transport layers (CTLs). Here, an innovative method of fabricating scalable PSCs on all types of organic CTLs is reported. By introducing an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer, fabricating uniform perovskite films on large-area substrates (18.4 cm2 ) and PSCs with the total active area of 6 cm2 (1 cm2 × 6 unit cells) via a single-turn solution process is successfully demonstrated. All of the unit cells exhibit highly uniform PCEs of 16.1 ± 0.9% (best PCE of 17%), which is the highest value for printable PSCs with a total active area larger than 1 cm2 .

Exploring the Leidenfrost Effect for the Deposition of High‐Quality In2O3 Layers via Spray Pyrolysis at Low Temperatures and Their Application in High Electron Mobility Transistors

The growth mechanism of indium oxide (In2O3) layers processed via spray pyrolysis of an aqueous precursor solution in the temperature range of 100–300 °C and the impact on their electron transporting properties are studied. Analysis of the droplet impingement sites on the substrate's surface as a function of its temperature reveals that Leidenfrost effect dominated boiling plays a crucial role in the growth of smooth, continuous, and highly crystalline In2O3 layers via a vapor phase‐like process. By careful optimization of the precursor formulation, deposition conditions, and choice of substrate, this effect is exploited and ultrathin and exceptionally smooth layers of In2O3 are grown over large area substrates at temperatures as low as 252 °C. Thin‐film transistors (TFTs) fabricated using these optimized In2O3 layers exhibit superior electron transport characteristics with the electron mobility reaching up to 40 cm2 V−1 s−1, a value amongst the highest reported to date for solution‐processed In2O3 TFTs. The present work contributes enormously to the basic understanding of spray pyrolysis and highlights its tremendous potential for large‐volume manufacturing of high‐performance metal oxide thin‐film transistor electronics.

Step-and-repeat stamping method for the generation of large-area microscale wrinkle patterns

We proposed a step-and-repeat stamping method for fabricating large-area microscale wrinkles with a Polydimethylsiloxane (PDMS) mold. First, an original wrinkle pattern was created by controlling the thickness of a photocurable resin (NOA-68T), which was exposed to ultraviolet light within a short time and then fully cured at a temperature of 30 °C for approximately 10 h. Microscale wrinkles could be obtained after two successive steps. PDMS was cast in a container with the fabricated wrinkle pattern and then cured at 75 °C for 2 h. A PDMS mold with a wrinkle pattern was then obtained after separating the master wrinkle pattern from the cured PDMS. A Selfassembled monolayer (SAM) was coated onto the surface of the PDMS mold to realize effective wrinkle replication on PDMS. Finally, the wrinkle pattern was stamped directly onto the large-area substrate within a significantly reduced processing time. The contact angles on the wrinkled surfaces of the resin layer and the PDMS mold were 47.8 % and 36.3 % larger than those on the corresponding flat surfaces, respectively. The proposed simple and cost-effective method of generating a large wrinkled area can be applied to surface modification in various engineering applications, including cell culture, microfluidics, biomedical devices, and flexible electronics.

Simulation of thin film thickness distribution for thermal evaporation process using a scanning linear source

Thermal evaporation process is the main process involved in the production of OLED displays and with the trends toward larger substrate size and display resolution, film thickness uniformity must be carefully controlled in order to implement exact pixel data. To secure stable film thickness uniformity on the substrate area, thin films are deposited on large-area glass substrates via thermal evaporation process using a linear source. We designed a linear source and mathematical model was developed to describe the system with a focus on the linear source. Then, system parameters were determined to guarantee uniform thickness using computer-based simulation, replacing wasteful actual experiments, followed by carrying out experiments based on the determined parameters. After the deposition process, data from the mathematical model and experiments was compared and the resulting agreement was good, verifying the validity of the proposed method. Consequently, by applying the proposed method, display manufacturing process related to thermal evaporation can be controlled within a tight tolerance in order to maximize the production yield rate.

Instantaneous Pulsed-Light Cross-Linking of a Polymer Gate Dielectric for Flexible Organic Thin-Film Transistors.

We report the instantaneous pulsed-light cross-linking of polymer gate dielectrics on a flexible substrate by using intensely pulsed white light (IPWL) irradiation. Irradiation with IPWL for only 1.8 s of a poly(4-vinylphenol) (PVP) thin film with the cross-linking agent poly(melamine-co-formaldehyde) (PMF) deposited on a plastic substrate was found to yield fully cross-linked PVP films. It was confirmed that the IPWL-cross-linked PVP films have smooth pinhole-free surfaces and exhibit a low leakage current density, organic solvent resistance, and good compatibility with organic semiconductor, and that they can be used as replacements for typical PVP dielectrics that are cross-linked with time and energy intensive thermal heating processes. The synchronization of the IPWL irradiation with substrate transfer was found to enable the preparation of cross-linked PVP films on large area substrates with a highly uniform capacitance. Flexible OTFT based on IPWL-cross-linked PVP dielectrics were found to exhibit good electrical performance that is comparable to that of devices with thermally cross-linked PVP dielectric, as well as excellent deformation stability even at a bending radius of 3 mm.

Intracellular Delivery Using Nanosecond-Laser Excitation of Large-Area Plasmonic Substrates.

Efficiently delivering functional cargo to millions of cells on the time scale of minutes will revolutionize gene therapy, drug discovery, and high-throughput screening. Recent studies of intracellular delivery with thermoplasmonic structured surfaces show promising results but in most cases require time- or cost-intensive fabrication or lead to unreproducible surfaces. We designed and fabricated large-area (14 × 14 mm), photolithography-based, template-stripped plasmonic substrates that are nanosecond laser-activated to form transient pores in cells for cargo entry. We optimized fabrication to produce plasmonic structures that are ultrasmooth and precisely patterned over large areas. We used flow cytometry to characterize the delivery efficiency of cargos ranging in size from 0.6 to 2000 kDa to cells (up to 95% for the smallest molecule) and viability of cells (up to 98%). This technique offers a throughput of 50000 cells/min, which can be scaled up as necessary. This technique is also cost-effective as each large-area photolithography substrate can be used to deliver cargo to millions of cells, and switching to a nanosecond laser makes the setup cheaper and easier to use. The approach we present offers additional desirable features: spatial selectivity, reproducibility, minimal residual fragments, and cost-effective fabrication. This research supports the development of safer genetic and viral disease therapies as well as research tools for fundamental biological research that rely on effectively delivering molecules to millions of living cells.

Plasma-Enhanced Atomic Layer Deposition of Two-Dimensional WS2 from WF6, H2 Plasma, and H2S

Two-dimensional (2D) transition metal dichalcogenides are potential low dissipative semiconductor materials for nanoelectronic devices. Such applications require the deposition of these materials in their crystalline form and with controlled number of monolayers on large area substrates, preferably using deposition temperatures compatible with temperature sensitive structures. This paper presents a low temperature plasma-enhanced atomic layer deposition (PEALD) process for 2D WS2 based on a ternary reaction cycle consisting of consecutive WF6, H2 plasma, and H2S reactions. Strongly textured, nanocrystalline WS2 is grown at 300 °C. The composition and crystallinity of these layers depends on the PEALD process conditions, as understood by a model for the redox chemistry of this process. The H2 plasma is essential for the deposition of WS2 as it enables the reduction of −W6+Fx surface species. Nevertheless, the impact of subsurface reduction reactions needs to be minimized to obtain WS2 with well-controlled ...

Challenges in the industrial deposition of transparent conductive oxide materials by reactive magnetron sputtering from rotatable targets

Reactive magnetron sputter deposition of transparent conductive oxides (TCOs) is a cost effective deposition technique due to low target costs compared to ceramic processes. Rotatable tube targets are used in industries because of their high material reservoir and a high target utilization (approx. factor 2 compared to planar targets). Another advantage for reactive sputtering is the absence of erosion groves. However, the reactive sputter process is highly complex because nearly any process parameter has strong impact on the properties of the growing film. Thus, the variation of the working point along the tube target may cause serious problems, in particular because conductivity, transparency, and thickness have to be optimized over a large substrate area at the same time. The most commonly sputtered TCO materials are aluminium doped zinc oxide and indium tin oxide. The respective reactive sputter processes are very distinct. This concerns among others the possible process control mechanisms as well as the dependence of the film properties on the reactive working point. The reliable industrial application of the reactive TCO sputter processes is still a big challenge for large area substrates. There are different possibilities to control the sputter process as well as the film properties in situ.

Hierarchical Materials Design by Pattern Transfer Printing of Self-Assembled Binary Nanocrystal Superlattices

We demonstrate the fabrication of hierarchical materials by controlling the structure of highly ordered binary nanocrystal superlattices (BNSLs) on multiple length scales. Combinations of magnetic, plasmonic, semiconducting, and insulating colloidal nanocrystal (NC) building blocks are self-assembled into BNSL membranes via the liquid-interfacial assembly technique. Free-standing BNSL membranes are transferred onto topographically structured poly(dimethylsiloxane) molds via the Langmuir-Schaefer technique and then deposited in patterns onto substrates via transfer printing. BNSLs with different structural motifs are successfully patterned into various meso- and microstructures such as lines, circles, and even three-dimensional grids across large-area substrates. A combination of electron microscopy and grazing incidence small-angle X-ray scattering (GISAXS) measurements confirm the ordering of NC building blocks in meso- and micropatterned BNSLs. This technique demonstrates structural diversity in the design of hierarchical materials by assembling BNSLs from NC building blocks of different composition and size by patterning BNSLs into various size and shape superstructures of interest for a broad range of applications.

Model for large-area monolayer coverage of polystyrene nanospheres by spin coating

Nanosphere lithography, an inexpensive and high throughput technique capable of producing nanostructure (below 100 nm feature size) arrays, relies on the formation of a monolayer of self-assembled nanospheres, followed by custom-etching to produce nanometre size features on large-area substrates. A theoretical model underpinning the self-ordering process by centrifugation is proposed to describe the interplay between the spin speed and solution concentration. The model describes the deposition of a dense and uniform monolayer by the implicit contribution of gravity, centrifugal force and surface tension, which can be accounted for using only the spin speed and the solid/liquid volume ratio. We demonstrate that the spin recipe for the monolayer formation can be represented as a pathway on a 2D phase plane. The model accounts for the ratio of polystyrene nanospheres (300 nm), water, methanol and surfactant in the solution, crucial for large area uniform and periodic monolayer deposition. The monolayer is exploited to create arrays of nanoscale features using ‘short’ or ‘extended’ reactive ion etching to produce 30–60 nm (diameter) nanodots or 100–200 nm (diameter) nanoholes over the entire substrate, respectively. The nanostructures were subsequently utilized to create master stamps for nanoimprint lithography.

Continuous-Wave Optically Pumped 1.55 μm InAs/InAlGaAs Quantum Dot Microdisk Lasers Epitaxially Grown on Silicon

Monolithic integration of high-performance semiconductor lasers on silicon enables wafer-scale optical interconnects within photonic integrated circuits on a silicon manufacturing platform. III–V quantum dot (QD) lasers on silicon stand out for their better device performances and reliability. QD lasers grown on III–V substrates have been integrated by wafer-bonding techniques with high quality. Direct growth of QD lasers on silicon offers an alluring alternative, using widely available large-area silicon substrates. However, to date, notable achievements have been reported only in InAs/GaAs lasers emitting at 1.3 μm, while 1.55 μm InAs/InP QD lasers on silicon remain in uncharted territory. Here we demonstrate the first 1.55 μm band InAs/InAlGaAs quantum dot microdisk lasers epitaxially grown on (001) silicon substrates. The lasing threshold for the seven-layer quantum dot microdisk laser at liquid-helium temperature is 1.6 mW under continuous optical pumping. The observed lasing is attributed to a uniqu...

Continuous fabrication of nanostructure arrays for flexible surface enhanced Raman scattering substrate

Surface-enhanced Raman spectroscopy (SERS) has been a powerful tool for applications including single molecule detection, analytical chemistry, electrochemistry, medical diagnostics and bio-sensing. Especially, flexible SERS substrates are highly desirable for daily-life applications, such as real-time and in situ Raman detection of chemical and biological targets, which can be used onto irregular surfaces. However, it is still a major challenge to fabricate the flexible SERS substrate on large-area substrates using a facile and cost-effective technique. The roll-to-roll ultraviolet nanoimprint lithography (R2R UV-NIL) technique provides a solution for the continuous fabrication of flexible SERS substrate due to its high-speed, large-area, high-resolution and high-throughput. In this paper, we presented a facile and cost-effective method to fabricate flexible SERS substrate including the fabrication of polymer nanostructure arrays and the metallization of the polymer nanostructure arrays. The polymer nanostructure arrays were obtained by using R2R UV-NIL technique and anodic aluminum oxide (AAO) mold. The functional SERS substrates were then obtained with Au sputtering on the surface of the polymer nanostructure arrays. The obtained SERS substrates exhibit excellent SERS and flexibility performance. This research can provide a beneficial direction for the continuous production of the flexible SERS substrates.

Scalable Route to the Fabrication of CH3NH3PbI3 Perovskite Thin Films by Electrodeposition and Vapor Conversion.

Hybrid halide perovskite thin films are applicable in a wide range of devices such as light-emitting diodes, solar cells, and photodetectors. The optoelectronic properties of perovskites together with their simple and inexpensive film deposition methods make these materials a viable alternative to established materials in these devices. However, the potential of perovskite materials is compromised by the limitations of the existing deposition methods, which suffer from trade-off among suitability for large-scale industrial production in a batch or roll-to-roll manner, deposition area, film quality, and costs. We addressed these limitations by developing a deposition method that is inexpensive, applicable to large substrate areas, scalable, and yields high-quality perovskite films. In this study, the low-cost electrodeposition (ED) method and sequential exposure to reagent vapors produce CH3NH3PbI3 perovskite films with thickness nonuniformity below 9% on a centimeter scale. PbO2 films are electrodeposited first and then undergo two vapor conversion steps, with HI vapor in the first step and CH3NH3I vapor in the second step. The second step yields CH3NH3PbI3 films that are continuous and consist of micrometer-sized grains. This process allows the preparation of both α- and β-phase CH3NH3PbI3 films, offers a simple means to control the film thickness, and works over a wide range of film thicknesses. In this work, films with thicknesses ranging from 100 nm to 10 μm were prepared. ED and vapor conversion are inherently scalable techniques and hence the process described herein could benefit application areas in which large device areas and throughput are required, such as the production of solar cells.

Enhanced Self-Organized Dewetting of Ultrathin Polymer Blend Film for Large-Area Fabrication of SERS Substrate.

We study the enhanced dewetting of ultrathin Polystyrene (PS)/Poly (methyl methacrylate) (PMMA) blend films in a mixed solution, and reveal the dewetting can act as a simple and effective method to fabricate large-area surface-enhanced Raman scattering (SERS) substrate. A bilayer structure consisting of under PMMA layer and upper PS layer forms due to vertical phase separation of immiscible PS/PMMA during the spin-coating process. The thicker layer of the bilayer structure dominates the dewetting structures of PS/PMMA blend films. The diameter and diameter distribution of droplets, and the average separation spacing between the droplets can be precisely controlled via the change of blend ratio and film thickness. The dewetting structure of 8 nm PS/PMMA (1:1 wt%) blend film is proved to successfully fabricate large-area (3.5 cm × 3.5 cm) universal SERS substrate via deposited a silver layer on the dewetting structure. The SERS substrate shows good SERS-signal reproducibility (RSD < 7.2%) and high enhancement factor (2.5 × 107). The enhanced dewetting of polymer blend films broadens the application of dewetting of polymer films, especially in the nanotechnology, and may open a new approach for the fabrication of large-area SERS substrate to promote the application of SERS substrate in the rapid sensitive detection of trace molecules.