Thin ferroelectric interferometer for spatial light modulations.

Thin ferroelectric interferometers (TFI's) for use as light-modulating devices were fabricated entirely with thin-film techniques on sapphire substrates. The ferroelectric layer in the TFI devices was a lead lanthanum zirconated titanate thin-film material, which can be formed from a chemical solution on highly reflective dielectric mirror surfaces. Light intensity modulation in both transmission and reflection modes was demonstrated with the fabricated devices. Experimental data and simulations show that TFI devices possess tremendous potential in spatial light modulators because of their fast-switching, low-driving voltage and readiness for integration with a variety of substrates, including silicon.     

Analysis of self-heating related instability in n-channel polysilicon thin film transistors fabricated on polyimide

In this work, we investigated self-heating related instability in polysilicon thin film transistors (poly-Si TFTs) fabricated on polyimide (PI) substrates. Indeed, when Joule heating becomes relevant, the temperature of the active layer can substantially rise, since the devices are fabricated on thermally insulating substrates. As a result, electrical instability is triggered and attributed to the generation of interface states, due to the Si–H bond breaking, and charge trapping into the gate insulator. In addition, by using 3-dimensional numerical simulations, coupling the thermodynamic and transport models, we analyzed the temperature distribution of the device under operating conditions and found that self-heating is more severe for devices fabricated on plastic substrates.     

Preparation of transparent and conductive cellulose nanocrystals/graphene nanoplatelets films

The manufacture of emerging products such as photovoltaic devices requires combinations of various novel materials to be leveraged into successful, scalable approach. In order to develop new electronic devices, it is necessary to find innovative solutions to the eco-sustainability problem of materials as substrates for circuits. We report on the demonstration of polymer solar cells fabricated on optically transparent and conductive graphene nanoplatelets (GNPs)–cellulose nanocrystals (CNC) film. The solar cells fabricated on the GNPs/CNC films display good rectification in the dark. Such GNPs–CNC functional films are expected to be attractive for eco-friendly electronics.     

Electrowetting on paper for electronic paper display

The use of paper as a material for various device applications (such as microfluidics and energy storage) is very attractive given its flexibility, versatility, and low cost. Here we demonstrate that electrowetting (EW) devices can be readily fabricated on paper substrates. Several categories of paper have been investigated for this purpose, with the surface coating, roughness, thickness, and water uptake, among the most important properties. The critical parameter for EW devices is the water contact angle (CA) change with applied voltage. EW devices on paper exhibit characteristics very close to those of conventional EW devices on glass substrates. This includes a large CA change in oil ambient (90-95°), negligible hysteresis (～2°), and fast switching times of ～20 ms. These results indicate the promise of low-cost paper-based EW devices for video rate flexible e-paper on paper.     

Non-volatile memory properties of metal/SrTiO3/SiO2/Si structures

Non-volatile MIOS-type semiconductor memory elements were fabricated on silicon using electron-beam-evaporated SrTiO₃ as the second insulator. The charge storage properties were characterized for Au/SrTiO₃/SiO₂/Si structures. Our results show that a short-time post-deposition oxygen annealing is essential to anneal out the radiation damage resulting from electron beam deposition. The devices on n-type silicon substrates show fast switching for a positive applied pulse and a much lower switching speed (longer than 20 ms) for a negative pulse, which is believed to be caused by the minority carrier restriction. The devices show a logarithmic decay of the flat-band voltage as a function of time, with a rate of 0.4 V decade^-1 for stored electrons and 0.5 V decade^-1 for stored holes. The devices can survive 10⁴ write-erase cycles of endurance testing. An inversion of the surface silicon layer is found for devices on p-type substrates subjected to high temperature oxygen annealing.     

Perovskite Solar Cells on Corrugated Substrates with Enhanced Efficiency

Organometallic halide perovskites solar cells are fabricated on nano‐scaled corrugated substrates using a sequential deposition method. The corrugated substrates are fabricated using colloidal lithography followed by reactive ion etching. The corrugated structure is found to accelerate the chemical reaction between the sequentially deposited lead iodide (PbI₂) and methyl ammonium iodide layers to form stoichiometric perovskite films, and the corrugated morphology is preserved at the interface of the hole transport layer (HTL) and the perovskite layer. The shunt resistance of the corrugated devices is found to be higher than that of the planar devices, leading to a higher open circuit voltage (V_OC) and fill factor (FF) in the corrugated devices. Finite‐difference time‐domain simulation is carried out on both planar and corrugated devices. The results revealed that light absorption is enhanced in the corrugated devices due to the corrugated HTL/perovskite interface, resulting in a significantly higher short circuit current (J_SC) observed in the corrugated devices. As a result, the average power conversion efficiency increases from 8.7% for the planar devices to 13% for the corrugated devices.     

Integration of carbon nanotubes as hole transport electrode in polymer/fullerene bulk heterojunction solar cells

Transparent and conductive single-walled carbon nanotube (SWNT) thin films were fabricated onto glass substrates and their optical and electrical properties were evaluated. Particular attention was given to the dependence of the conductivity and optical transparency on the thickness of the films. Furthermore, the SWNT thin films were integrated in organic photovoltaic devices as the hole transport electrode. The best photovoltaic performance was observed for the devices utilizing 80 nm SWNT films with a sheet resistance of 362 Ω/sq, and a transmittance of 64% at 520 nm. The experiments reveal that SWNTs films can be used as transparent electrodes for efficient, flexible organic photovoltaic devices.     

A Device-Level Vacuum-Packaging Scheme for Microbolometers on Rigid and Flexible Substrates

This paper reports on the design, fabrication, and characterization of device-level vacuum-packaged microbolometers on rigid Si wafers and flexible polyimide substrates. Semiconducting yttrium barium copper oxide (commonly referred to as YBCO) serves as the bolometric material. Operating micromachined bolometers in vacuum reduces the thermal conductance G_th from the detector to the substrate. If flexibility of the substrate is not to be sacrificed, then the vacuum packaging needs to be done at the device level. Here, the microbolometers are fabricated on a silicon nitride support membrane, isolated from the substrate using surface micromachining. Suitable materials as well as various dimensions in the vacuum cavity are determined using finite-element method (FEM)-based CoventorWARE. A vacuum cavity made of Al₂O₃ has been designed. The thermal conductance G_th of bolometers with the geometry implemented in this work is the same for devices on rigid and flexible substrates. The theoretical value of G_th was calculated to be 4.0 x 10^-6 W/K for devices operating in vacuum and 1.4 x 10^-4 W/K for devices operating at atmospheric pressure. Device-level vacuum-packaged microbolometers on both rigid Si and flexible polyimide substrates have been fabricated and characterized for optical and electrical properties. A low thermal conductance of 1.1 X 10^-6 W/K has been measured six months after fabrication, which implies an intact vacuum cavity.     

Resistance Random Access Memory Based on a Thin Film of CdS Nanocrystals Prepared via Colloidal Synthesis

We demonstrate that resistance random access memory (RRAM) can be fabricated based on CdS-nanocrystal thin films. A simple drop-drying of the CdS-nanocrystal solution leads to the formation of uniform thin films with controlled thickness. RRAMs with a Ag/Al(2) O(3) /CdS/Pt structure show bipolar switching behavior, with average values of the set voltage (V(Set) ) and reset voltage (V(Reset) ) of 0.15 V and -0.19 V, respectively. The RRAM characteristics are critically influenced by the thickness of the Al(2) O(3) barrier layer, which prevents significant migration of Ag into the CdS layer as revealed by Auger electron spectroscopy (AES). Interestingly, RRAM without an Al(2) O(3) layer (i.e., Ag/CdS/Pt structure) also shows bipolar switching behavior, but the polarity is opposite to that of RRAM with the Al(2) O(3) layer (i.e., Ag/Al(2) O(3) /CdS/Pt structure). The operation of both kinds of devices can be explained by the conventional conductive bridging mechanism. Additionally, we fabricated RRAM devices on Kapton film for potential applications in flexible electronics, and the performance of this RRAM device was comparable to that of RRAMs fabricated on hard silicon substrates. Our results show a new possibility of using chalcogenide nanocrystals for RRAM applications.     

Ultrastretchable Conductor Fabricated on Skin‐Like Hydrogel–Elastomer Hybrid Substrates for Skin Electronics

Printing technology can be used for manufacturing stretchable electrodes, which represent essential parts of wearable devices requiring relatively high degrees of stretchability and conductivity. In this work, a strategy for fabricating printable and highly stretchable conductors are proposed by transferring printed Ag ink onto stretchable substrates comprising Ecoflex elastomer and tough hydrogel layers using a water‐soluble tape. The elastic modulus of the produced hybrid film is close to that of the hydrogel layer, since the thickness of Ecoflex elastomer film coated on hydrogel is very thin (30 µm). Moreover, the fabricated conductor on hybrid film is stretched up to 1780% strain. The described transfer method is simpler than other techniques utilizing elastomer stamps or sacrificial layers and enables application of printable electronics to the substrates with low elastic moduli (such as hydrogels). The integration of printed electronics with skin‐like low‐modulus substrates can be applied to make wearable devices more comfortable for human skin.     

Si/a-Si core/shell nanowires as nonvolatile crossbar switches

Radial core/shell nanowires (NWs) represent an important class of nanoscale building blocks with substantial potential for exploring fundamental electronic properties and realizing novel device applications at the nanoscale. Here, we report the synthesis of crystalline silicon/amorphous silicon (Si/a-Si) core/shell NWs and studies of crossed Si/a-Si NW metal NW (Si/a-Si x M) devices and arrays. Room-temperature electrical measurements on single Si/a-Si x Ag NW devices exhibit bistable switching between high (off) and low (on) resistance states with well-defined switching threshold voltages, on/off ratios greater than 10(4), and current rectification in the on state. Temperature-dependent switching experiments suggest that rectification can be attributed to barriers to electric field-driven metal diffusion. Systematic studies of Si/a-Si x Ag NW devices show that (i) the bit size can be at least as small as 20 nm x 20 nm, (ii) the writing time is <100 ns, (iii) the retention time is >2 weeks, and (iv) devices can be switched >10(4) times without degradation in performance. In addition, studies of dense one-dimensional and two-dimensional Si/a-Si x Ag NW devices arrays fabricated on crystalline and plastic substrates show that elements within the arrays can be independently switched and read, and moreover that bends with radii of curvature as small as 0.3 cm cause little change in device characteristics. The Si/a-Si x Ag NW devices represent a highly scalable and promising nanodevice element for assembly and fabrication of dense nonvolatile memory and programmable nanoprocessors.     

Bi2Te3基可穿戴温差发电器件的制备及性能

利用人体体温发电的热电器件因其结构简单、可靠性高,有望为可穿戴电子产品等低功耗设备提供免维护、长期稳定的能源。以高性能无机块体热电材料和低热导环氧树脂/玻璃微珠复合粘结剂作为原料,采用切割粘结法和磁控溅射/电化学镀铜技术,制备了热电臂高度不同的48对温差发电器件。由于该技术不需使用陶瓷覆铜板,在给定的器件厚度条件下,可提高热电臂高度。性能表征结果显示,在实际穿戴条件下,随热电臂高度的增加,器件的输出功率密度持续增加。在相当于一级风的空气对流条件下或正常行走状态下,热电臂高度为3.14mm的器件输出功率密度超过40μW/cm²。     

Direct micro/nano metal patterning based on two-step transfer printing of ionic metal nano-ink

We present a direct metal patterning method by a two-step transfer printing process of non-particle, ionic metal nano-ink solution. This fabrication method allows a simple direct patterning of various micro/nanoscale metallic structures. Complex structures such as multilayer line arrays, patterns along non-flat topologies, and micro/nanoscale hybrid patterns can be achieved by using this process. Also, the low temperature and pressure process conditions are compatible with the fabrication of electronic structures and devices on flexible substrates such as polyimide film and photographic papers. As an application of this process, we fabricated ZnO nanowire-based flexible UV sensors, where metal electrodes were fabricated by two-step transfer printing. In the case of ZnO nanowire sensors, highly sensitive and fast responding performances to UV illumination and good mechanical robustness against repeated bending conditions could be verified.     

Light extraction from organic light emitting diodes using chemically etched glass substrates

We have manufactured highly efficient OLED devices fabricated on chemically etched glass substrates. The external quantum efficiency of the OLED devices with the etched glass substrates was increased by 5-27% in comparison with the reference flat glass substrate. Surface morphology, such as indented patterns, significantly affected the external luminance efficiency. A clean surface and the presence of smooth bent edges of indented patterns were found to be important for improving the external luminous efficacy.     

Harmonic surface acoustic waves on gallium nitride thin films

SAW devices operating at the fundamental frequency and the 5th, 7th, 9th, and 11th harmonics have been designed, fabricated, and measured. Devices were fabricated on GaN thin films on sapphire substrates, which were grown via metal organic vapor phase epitaxy (MOVPE). Operating frequencies of 230, 962, 1338, 1720, and 2100 MHz were achieved with devices that had a fundamental wavelength, /spl lambda/(0) = 20 /spl mu/m. Gigahertz operation is realized with relatively large interdigital transducers that do not require complicated submicrometer fabrication techniques. SAW devices fabricated on the GaN/sapphire bilayer have an anisotropic propagation when the wavelength is longer than the GaN film thickness. It is shown that for GaN thin films, where kh(GaN) > 10 (k = 2/spl pi///spl lambda/ and h(GaN) = GaN film thickness), effects of the substrate on the SAW propagation are eliminated. Bulk mode suppression at harmonic operation is also demonstrated.     

Ru nanostructure fabrication using an anodic aluminum oxide nanotemplate and highly conformal Ru atomic layer deposition

We fabricated metallic nanostructures directly on Si substrates through a hybrid nanoprocess combining atomic layer deposition (ALD) and a self-assembled anodic aluminum oxide (AAO) nanotemplate. ALD Ru films with Ru(DMPD)(EtCp) as a precursor and O(2) as a reactant exhibited high purity and low resistivity with negligible nucleation delay and low roughness. These good growth characteristics resulted in the excellent conformality for nanometer-scale vias and trenches. Additionally, AAO nanotemplates were fabricated directly on Si and Ti/Si substrates through a multiple anodization process. AAO nanotemplates with various hole sizes (30-100?nm) and aspect ratios (2:1-20:1) were fabricated by controlling the anodizing process parameters. The barrier layers between AAO nanotemplates and Si substrates were completely removed by reactive ion etching (RIE) using BCl(3) plasma. By combining the ALD Ru and the AAO nanotemplate, Ru nanostructures with controllable sizes and shapes were prepared on Si and Ti/Si substrates. The Ru nanowire array devices as a platform for sensor devices exhibited befitting properties of good ohmic contact and high surface/volume ratio.     

Ordered Arrays of Nanostructures and Applications in High‐Efficient Nano‐Generators

Large‐scale ordered nanostructure arrays on substrates, including nanowires, nanotubes, nanodots, and nano‐holes, can be fabricated using template fabrication processes. The controllable structural parameters and properties of the ordered nanostructure arrays make them quite suitable to be used in many device‐related application areas. It is shown that large‐scale nanowire arrays are good candidates for the realization of a nano‐generator based on the piezoelectric effect of ZnO nanowires. The mechanism of a proposed high‐efficient nano‐generator based on an assembled nanowire/nanohole embedded structure shows high application potentials for biological and nanometer‐sized devices.     

Direct fabrication of metavanadate phosphor films on organic substrates for white-light-emitting devices

White-light-emitting materials have attracted considerable attention because of their applications, such as large-surface emitting devices. Inorganic phosphor films are expected to be applied to these devices because of good chemical stability; however, a substantial reduction of fabrication temperature is required for future industrial uses such as lighting materials fabricated onto flexible organic substrates. Here we show the optical properties of white-light-emitting metavanadate phosphors, AVO3 (A: K, Rb and Cs), and we report a new direct fabrication process for RbVO3 films onto flexible polyethylene terephthalate (PET) substrates by means of a vacuum ultraviolet irradiation using an excimer lamp. In addition, the (Ca,Sr,Pr)TiO3/a-Al2O3/RbVO3/PET heterostructure prepared by an excimer-laser-assisted metal-organic deposition process has demonstrated the possibility of colour modification for RbVO3 films on PET. Our findings suggest new possibilities for further development of large-surface emitting lighting devices.     

Fabrication of oxide-gate thin-film transistors using PECVD/PLD multichamber system

We developed a new multichamber system which combines a pulsed-laser deposition (PLD) and a plasma-enhanced chemical vapor deposition (PECVD) with shadow masks installed to define the film deposition area on a substrate. In order to verify thecapability of this PLD/PECVD multichamber system, hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) using MgO and Al2O₃ gate dielectrics have been fabricated on glass/indium-tin-oxide (ITO) substrates. The MgO and Al2O₃ films fabricated on fused silica substrates by PLD exhibited transparency higher than 90% and a low leakage current (1 nA/cm² at 1 MV/cm). After depositions of the MgO or Al2O₃ film on the glass/ITO, thesample was transferred to the PECVD chamber for a-Si:H deposition without exposing them to the air. TFTs thus fabricated exhibited such high characteristics as the threshold voltage (VTH) as low as 0.35 V and gate bias dependence of source±drain current exceeding five orders of magnitude. Theresults indicate a high quality a-Si:H/oxide interface and that heterojunction devices can be produced by using the PLD/PECVD multichamber system.     

化学气相催化法生长碳纳米管及其器件的原位制备

本文系统地讨论了化学气相催化法制备碳纳米管的工艺过程。讨论了化学气相催化法原位制备碳纳米管器件的技术 ,即先制备电极和催化剂结构 ,然后在电极上原位生长碳纳米管。与目前通常采用的先制备碳纳米管 ,然后超声分离、沉积 ,再光刻、蒸发制备电极的方法相比 ,该方法可以减少后处理工艺对碳纳米管结构带来的损伤 ,具有潜在的优势