Showing papers on "Substrate (electronics) published in 2011"

Metal-Assisted Chemical Etching of Silicon: A Review

Abstract: This article presents an overview of the essential aspects in the fabrication of silicon and some silicon/germanium nanostructures by metal-assisted chemical etching. First, the basic process and mechanism of metal-assisted chemical etching is introduced. Then, the various influences of the noble metal, the etchant, temperature, illumination, and intrinsic properties of the silicon substrate (e.g., orientation, doping type, doping level) are presented. The anisotropic and the isotropic etching behaviors of silicon under various conditions are presented. Template-based metal-assisted chemical etching methods are introduced, including templates based on nanosphere lithography, anodic aluminum oxide masks, interference lithography, and block-copolymer masks. The metal-assisted chemical etching of other semiconductors is also introduced. A brief introduction to the application of Si nanostructures obtained by metal-assisted chemical etching is given, demonstrating the promising potential applications of metal-assisted chemical etching. Finally, some open questions in the understanding of metal-assisted chemical etching are compiled.

Scanning tunnelling microscopy and spectroscopy of ultra-flat graphene on hexagonal boron nitride

Abstract: Using boron nitride as a substrate for graphene has been suggested as a promising way to reduce the disorder in graphene caused by space fluctuations. It is now shown by scanning tunnelling microscopy that graphene conforms perfectly to boron nitride and the charge fluctuations are minimal compared with the conventionally used substrate, silica. Boron nitride could really be the natural graphene substrate. Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy–momentum dispersion relations which cross at the Dirac point1,2. However, accessing the physics of the low-density region at the Dirac point has been difficult because of disorder that leaves the graphene with local microscopic electron and hole puddles3,4,5. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult6,7. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance8. Here we use scanning tunnelling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moire patterns. However, contrary to predictions9,10, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron–hole charge fluctuations are reduced by two orders of magnitude as compared with those on silicon oxide. This leads to charge fluctuations that are as small as in suspended graphene6, opening up Dirac point physics to more diverse experiments.

Nature of electronic states in atomically thin MoS₂ field-effect transistors.

Abstract: We present low-temperature electrical transport experiments in five field-effect transistor devices consisting of monolayer, bilayer, and trilayer MoS(2) films, mechanically exfoliated onto Si/SiO(2) substrate. Our experiments reveal that the electronic states in all films are localized well up to room temperature over the experimentally accessible range of gate voltage. This manifests in two-dimensional (2D) variable range hopping (VRH) at high temperatures, while below ∼30 K, the conductivity displays oscillatory structures in gate voltage arising from resonant tunneling at the localized sites. From the correlation energy (T(0)) of VRH and gate voltage dependence of conductivity, we suggest that Coulomb potential from trapped charges in the substrate is the dominant source of disorder in MoS(2) field-effect devices, which leads to carrier localization, as well.

Large scale, highly conductive and patterned transparent films of silver nanowires on arbitrary substrates and their application in touch screens

Abstract: The application of silver nanowire films as transparent conductive electrodes has shown promising results recently. In this paper, we demonstrate the application of a simple spray coating technique to obtain large scale, highly uniform and conductive silver nanowire films on arbitrary substrates. We also integrated a polydimethylsiloxane (PDMS)-assisted contact transfer technique with spray coating, which allowed us to obtain large scale high quality patterned films of silver nanowires. The transparency and conductivity of the films was controlled by the volume of the dispersion used in spraying and the substrate area. We note that the optoelectrical property, σDC/σOp, for various films fabricated was in the range 75‐350, which is extremely high for transparent thin film compared to other candidate alternatives to doped metal oxide film. Using this method, we obtain silver nanowire films on a flexible polyethylene terephthalate (PET) substrate with a transparency of 85% and sheet resistance of 33 �/ sq, which is comparable to that of tin-doped indium oxide (ITO) on flexible substrates. In-depth analysis of the film shows a high performance using another commonly used figure-of-merit, � TE. Also, Ag nanowire film/PET shows good mechanical flexibility and the application of such a conductive silver nanowire film as an electrode in a touch panel has been demonstrated. (Some figures in this article are in colour only in the electronic version)

Graphene-Silicon Schottky Diodes

Abstract: We have fabricated graphene-silicon Schottky diodes by depositing mechanically exfoliated graphene on top of silicon substrates. The resulting current–voltage characteristics exhibit rectifying diode behavior with a barrier energy of 0.41 eV on n-type silicon and 0.45 eV on p-type silicon at the room temperature. The I–V characteristics measured at 100, 300, and 400 K indicate that temperature strongly influences the ideality factor of graphene–silicon Schottky diodes. The ideality factor, however, does not depend strongly on the number of graphene layers. The optical transparency of the thin graphene layer allows the underlying silicon substrate to absorb incident laser light and generate a photocurrent. Spatially resolved photocurrent measurements reveal the importance of inhomogeneity and series resistance in the devices.

Direct chemical vapor deposition of graphene on dielectric surfaces

Abstract: A substrate is provided that has a metallic layer on a substrate surface of a substrate. A film made of a two dimensional (2-D) material, such as graphene, is deposited on a metallic surface of the metallic layer. The metallic layer is dewet and/or removed to provide the film on the substrate surface.

Graphene-Silicon Schottky Diodes

Abstract: We have fabricated graphene-silicon Schottky diodes by depositing mechanically exfoliated graphene on top of silicon substrates. The resulting current–voltage characteristics exhibit rectifying diode behavior with a barrier energy of 0.41 eV on n-type silicon and 0.45 eV on p-type silicon at the room temperature. The I–V characteristics measured at 100, 300, and 400 K indicate that temperature strongly influences the ideality factor of graphene–silicon Schottky diodes. The ideality factor, however, does not depend strongly on the number of graphene layers. The optical transparency of the thin graphene layer allows the underlying silicon substrate to absorb incident laser light and generate a photocurrent. Spatially resolved photocurrent measurements reveal the importance of inhomogeneity and series resistance in the devices.

Thermal conductivity of suspended pristine graphene measured by Raman spectroscopy

Abstract: The thermal conductivity of suspended single-layer graphene was measured as a function of temperature using Raman scattering spectroscopy on clean samples prepared directly on a prepatterned substrate by mechanical exfoliation without chemical treatments. The temperature at the laser spot was monitored by the frequency of the Raman 2$D$ band of the Raman scattering spectrum, and the thermal conductivity was deduced by analyzing heat diffusion equations assuming that the substrate is a heat sink at ambient temperature. The obtained thermal conductivity values range from $~$1800 W m${}^{\ensuremath{-}1}$K${}^{\ensuremath{-}1}$ near 325 K to $~$710 W m${}^{\ensuremath{-}1}$K${}^{\ensuremath{-}1}$ at 500 K.

Long-wavelength InAs/GaAs quantum-dot laser diode monolithically grown on Ge substrate

Abstract: Growing a group III–V quantum dot laser directly on a group IV substrate could provide silicon photonics with a convenient new form of laser source for use in optoelectronic circuitry.

Rational design of hybrid graphene films for high-performance transparent electrodes.

Abstract: Transparent, flexible conducting films were fabricated by using a metallic grid and graphene hybrid film. Transparent electrodes using the hybrid film and transparent substrate such as glass or polyethylene terephthalate (PET) films were assembled. The sheet resistance of the fabricated transparent electrodes was as low as 3 Ω/◻ with the transmittance at ∼80%. At 90% transmittance, the sheet resistance was ∼20 Ω/◻. Both values are among the highest for transparent electrode materials to date. The materials used for the new hybrid electrode are earth-abundant stable elements, which increase their potential usefulness for replacement of indium tin oxide (ITO) in many applications.

All-optical control of a single plasmonic nanoantenna-ITO hybrid.

Abstract: We demonstrate experimentally picosecond all-optical control of a single plasmonic nanoantenna embedded in indium tin oxide (ITO). We identify a picosecond response of the antenna–ITO hybrid system, which is distinctly different from transient bleaching observed for gold antennas on a nonconducting SiO2 substrate. Our experimental results can be explained by the large free-carrier nonlinearity of ITO, which is enhanced by plasmon-induced hot-electron injection from the gold nanoantenna into the conductive oxide. The combination of tunable antenna–ITO hybrids with nanoscale plasmonic energy transfer mechanisms, as demonstrated here, opens a path for new ultrafast devices to produce nanoplasmonic switching and control.

Hydrothermally synthesized WO3 nanowire arrays with highly improved electrochromic performance

Abstract: A hexagonal WO3 nanowire array film is obtained using a template-free hydrothermal method by adding ammonium sulfate as a capping agent. The WO3 nanowires grown vertically on a FTO-coated glass substrate are woven together at the surface of the film, forming well-aligned arrays at the bottom part and a porous surface morphology. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that each nanowire is a hexagonal single crystal and their long axes are oriented toward the [0001] direction. Due to the highly porous surface, good contact with the conductive substrate and large tunnels of the hexagonal-structured WO3, a fast switching speed of 7.6 and 4.2 s for coloration and bleaching, respectively, and a high coloration efficiency of 102.8 cm2C−1 are achieved for the WO3 nanowire array film.

Directing substrate morphology via self-assembly: ligand-mediated scission of gallium-indium microspheres to the nanoscale

Abstract: We have developed a facile method for the construction of liquid-phase eutectic gallium–indium (EGaIn) alloy nanoparticles. Particle formation is directed by molecular self-assembly and assisted by sonication. As the bulk liquid alloy is ultrasonically dispersed, fast thiolate self-assembly at the EGaIn interface protects the material against oxidation. The choice of self-assembled monolayer ligand directs the ultimate size reduction in the material; strongly interacting molecules induce surface strain and assist particle cleavage to the nanoscale. Transmission electron microscopy images and diffraction analyses reveal that the nanoscale particles are in an amorphous or liquid phase, with no observed faceting. The particles exhibit strong absorption in the ultraviolet (∼200 nm), consistent with the gallium surface plasmon resonance, but dependent on the nature of the particle ligand shell.

Organic electroluminescent device

Abstract: PROBLEM TO BE SOLVED: To provide a multi-photon organic EL device that has high light-extraction efficiency by increasing a light quantity generated inside the organic EL device, and also to provide a lighting apparatus, a planar light source, and a display apparatus. SOLUTION: An organic EL device 10 is equipped with: a support substrate 15; a positive electrode (a first electrode) 14 provided in contact with the support substrate 15 and having the light permeability; a negative electrode (a second electrode) 16 being the other electrode; first/second light-emitting units 11, 12 provided between both electrodes and respectively including an organic light-emitting layer; and a charge generating layer 13 arranged while being sandwiched by the first/second light-emitting units. The charge generating layer 13 includes one or more kinds selected from the group (A) consisting of metals and compounds of the metals respectively having a work function of ≤3.0 eV, and one or more kinds of compounds (B) respectively having a work function of ≥4.0 eV. Each of the refractive index n1 of the positive electrode 14 and the refractive index n2 of the support substrate 15 satisfis a formula (1). COPYRIGHT: (C)2010,JPO&INPIT

Adhesion and electronic structure of graphene on hexagonal boron nitride substrates

Abstract: We investigate the adsorption of graphene sheets on h-BN substrates by means of first-principles calculations in the framework of adiabatic connection fluctuation-dissipation theory in the random-phase approximation. We obtain adhesion energies for different crystallographic stacking configurations and show that the interlayer bonding is due to long-range van der Waals forces. The interplay of elastic and adhesion energies is shown to lead to stacking disorder and moir\'e structures. Band-structure calculations reveal substrate induced mass terms in graphene, which change their sign with the stacking configuration. The dispersion, absolute band gaps, and the real-space shape of the low-energy electronic states in the moir\'e structures are discussed. We find that the absolute band gaps in the moir\'e structures are at least an order of magnitude smaller than the maximum local values of the mass term. Our results are in agreement with recent scanning tunneling microscopy experiments.

Optical impedance matching using coupled plasmonic nanoparticle arrays

Abstract: Silver nanoparticle arrays placed on top of a high-refractive index substrate enhance the coupling of light into the substrate over a broad spectral range. We perform a systematic numerical and experimental study of the light incoupling by arrays of Ag nanoparticle arrays in order to achieve the best impedance matching between light propagating in air and in the substrate. We identify the parameters that determine the incoupling efficiency, including the effect of Fano resonances in the scattering, interparticle coupling, as well as resonance shifts due to variations in the near-field coupling to the substrate and spacer layer. The optimal configuration studied is a square array of 200 nm wide, 125 nm high spheroidal Ag particles, at a pitch of 450 nm on a 50 nm thick Si(3)N(4) spacer layer on a Si substrate. When integrated over the AM1.5 solar spectral range from 300 to 1100 nm, this particle array shows 50% enhanced incoupling compared to a bare Si wafer, 8% higher than a standard interference antireflection coating. Experimental data show that the enhancement occurs mostly in the spectral range near the Si band gap. This study opens new perspectives for antireflection coating applications in optical devices and for light management in Si solar cells.

Electrochemistry of graphene : not such a beneficial electrode material?

Abstract: We critically evaluate the reported electro-catalysis of graphene using inner-sphere and outer-sphere electrochemical redox probes, namely potassium ferrocyanide (II) and hexaammine-ruthenium(III) chloride, in addition to L-ascorbic acid and β-nicotinamide adenine dinucleotide. Well characterised commercially available graphene is utilised which has not been chemically treated, is free from surfactants, and as a result of its fabrication has an extremely low oxygen content allowing the electronic properties to be properly de-convoluted. Surprisingly we observe that graphene exhibits slow electron transfer towards the electrochemical probes studied, effectively blocking underlying electron transfer of the supporting electrode substrate likely due to its large basal and low edge plane content. Such observations, never reported before, suggest that graphene may not be such a beneficial electrode material as widely reported in the literature. Density Functional Theory is conducted on symmetric graphene flakes of varying sizes indicating that the HOMO and LUMO energies are concentrated around the edge of the graphene sheet, at the edge plane sites, rather than the central basal plane region, consistent with experimental observations. We define differentiating coverage-based working regions for the electrochemical utilisation of graphene: ‘Zone I’, where graphene additions do not result in complete coverage of the underlying electrode and thus increasing basal contribution from graphene modification leads to increasingly reduced electron transfer and electrochemical activity; ‘Zone II’, once complete single-layer coverage is achieved, layered graphenevizgraphite materialises with increased edge plane content and thus an increase in heterogeneous electron transfer is observed with increased layering. We offer insight into the electrochemical properties of these carbon materials, invaluable where electrode design for electrochemical sensing applications is sought.

Origin of the mosaicity in graphene grown on Cu(111)

Abstract: We use low-energy electron microscopy to investigate how graphene grows on Cu(111). Graphene islands first nucleate at substrate defects such as step bunches and impurities. A considerable fraction of these islands can be rotationally misaligned with the substrate, generating grain boundaries upon interisland impingement. New rotational boundaries are also generated as graphene grows across substrate step bunches. Thus, rougher substrates lead to higher degrees of mosaicity than do flatter substrates. Increasing the growth temperature improves crystallographic alignment. We demonstrate that graphene growth on Cu(111) is surface diffusion limited by comparing simulations of the time evolution of island shapes with experiments. Islands are dendritic with distinct lobes, but unlike the polycrystalline, four-lobed islands observed on (100)-textured Cu foils, each island can be a single crystal. Thus, epitaxial graphene on smooth, clean Cu(111) has fewer structural defects than it does on Cu(100).

Systems and methods for thin-film deposition of metal oxides using excited nitrogen-oxygen species

Abstract: The present invention relates to a process and system for depositing a thin film onto a substrate. One aspect of the invention is depositing a thin film metal oxide layer using atomic layer deposition (ALD).

Three-dimensional cavity nanoantenna coupled plasmonic nanodots for ultrahigh and uniform surface-enhanced Raman scattering over large area

Abstract: We propose and demonstrate a new SERS substrate architecture that couples a dense three-dimensional (3-D) cavity nanoantenna array, through nano-gaps, with dense plasmonic nanodots; and a new nanofabrication that combines nanoimprint, guided self-assembly and self-alignment and has fabricated the architecture precisely, simply, inexpensively and over large area (4-inch wafer). We experimentally achieved not only high area-average SERS enhancement (1.2 × 109) but also excellent uniformity (22.4% variation) at the same time over the entire large-area sample by measuring 90 points with a regular mapping distance. The best uniformity achieved is 15% variation over 1.6 mm by 1.6 mm area at slightly lower enhancement factor and is independent of the excitation laser probe size, which had an area varying from ~1 to 10,000 μm2.

Novel method for conformal plasma immersed ion implantation assisted by atomic layer deposition

Abstract: Embodiments of the invention provide a novel apparatus and methods for forming a conformal doped layer on the surface of a substrate. A substrate is provided to a process chamber, and a layer of dopant source material is deposited by plasma deposition, atomic layer deposition, or plasma-assisted atomic layer deposition. The substrate is then subjected to thermal processing to activate and diffuse dopants into the substrate surface.

Defect-reduced green GaInN/GaN light-emitting diode on nanopatterned sapphire

Abstract: Green GaInN/GaN quantum well light-emitting diode (LED) wafers were grown on nanopatterned c-plane sapphire substrate by metal-organic vapor phase epitaxy. Without roughening the chip surface, such LEDs show triple the light output over structures on planar sapphire. By quantitative analysis the enhancement was attributed to both, enhanced generation efficiency and extraction. The spectral interference and emission patterns reveal a 58% enhanced light extraction while photoluminescence reveals a doubling of the internal quantum efficiency. The latter was attributed to a 44% lower threading dislocation density as observed in transmission electron microscopy. The partial light output power measured from the sapphire side of the unencapsulated nanopatterned substrate LED die reaches 5.2 mW at 525 nm at 100 mA compared to 1.8 mW in the reference LED.

Fabrication of sub-5 nm nanochannels in insulating substrates using focused ion beam milling.

Abstract: The use of focused ion beam (FIB) milling to fabricate nanochannels with critical dimensions extending below 5 nm is described. FIB milled lines have narrowing widths as they are milled deeper into a substrate. This focusing characteristic is coupled with a two-layered architecture consisting of a relatively thick (>100 nm) metal film deposited onto a substrate. A channel is milled through the metal layer until it penetrates a prescribed depth into the substrate material. The metal is then removed, leaving a nanochannel with smooth surfaces and lateral dimensions as small as sub-5 nm. These open nanochannels can be sealed with a cover plate and the resulting devices are well-suited for single-molecule DNA transport studies. This methodology is used with quartz, single-crystal silicon, and polydimethylsiloxane substrates to demonstrate its general utility.

Light-emitting diode

Abstract: To provide a light-emitting diode (21), transparent resin (27) is filled in a hole (25) through a fiberglass-reinforced epoxy substrate (22) between the upper surface (26a) and the lower surface (26b). A light-emitting diode element (29) formed of semiconducting nitride gallium on a transparent sapphire glass substrate (30) is fixedly attached to the transparent resin (27) with transparent adhesive (37). Opaque electrodes (33, 34) are provided on the light-emitting diode element (29) so that the light from the light-emitting diode element (29) can pass through the transparent resin (27) to the lower surface (26b) of the fiberglass-reinforced epoxy substrate (22). When mounted on a motherboard (41), the light-emitting diode (21) is let fall, with its resin mold (38) down, into a hole (42) opened in the motherboard (41), thereby reducing the height above the motherboard.

Methods For Atomic Layer Etching

Abstract: Provided are methods of etching a substrate using atomic layer deposition apparatus. Atomic layer deposition apparatus including a gas distribution plate with a thermal element are discussed. The thermal element is capable of locally changing the temperature of a portion of the surface of the substrate to vaporize an etch layer deposited on the substrate.

Nanoscale electronics: digital fabrication by direct femtosecond laser processing of metal nanoparticles.

Abstract: For various applications in the electronics industry, the fabrication of electrically conductive nanoand micropatterns has become important. Conventional vacuum metal deposition and photolithography processes are widely used for high-resolution metal patterning of microelectronics. However, those conventional approaches require expensive vacuum conditions, high processing temperatures, many steps, and toxic chemicals to fabricate one layer of a metal pattern. Furthermore, it is almost impossible to change the design of the expensive photomask once it is fabricated. For these reasons, the development of alternative maskless, direct, high-resolution patterning techniques to fabricate conductive microand nanopatterns at atmospheric pressure and low temperature without using vacuum deposition or photolithography has attracted wide attention in recent years. One of the most promising alternatives is the direct patterning of solution-deposited metal nanoparticles (NPs). The development of metal NP solution ink enabled 1) an inexpensive solution-based metal deposition approach without using expensive vacuum deposition and 2) a low-temperature metal deposition process, which allows using heat-sensitive and inexpensive polymer as the substrate. Examples of NP-inkbased direct metal patterning include screen printing, [ 1 ] direct nanoimprinting, [ 2 , 3 ] microcontact printing, [ 4 , 5 ] inkjet printing, [ 6 , 7 ]

Particles on Surfaces 2: "Detection, Adhesion, And Removal"

Abstract: I. General Papers.- Fine Particles on Semiconductor Surfaces: Sources, Removal and Impact on the Semiconductor Industry.- Cleaning Semiconductor Surfaces: Facts and Foibles.- Effect of Chemical Cleaning Sequencing on Particle Addition/Reduction on Silicon Wafers.- Measuring Aerosol Particle Concentration in Clean Rooms and Particle Areal Density on Silicon Wafer Surfaces.- Particulate Contamination on Wafer Surfaces Resulting From Hexamethyldisilazane/Water Interactions.- Contamination of Chip Surfaces by Particles During Destructive Physical Analysis of Integrated Circuit Devices.- Calculation of Hamaker Coefficients for Metallic Aerosols from Extensive Optical Data.- Soiling Mechanisms and Performance of Anti-Soiling Surface Coatings.- Implications of Particulate Contamination in the Performance of Floppy Disks.- II. Particle-Substrate Interaction and Particle Adhesion.- A Theoretical Review of Particle Adhesion.- The Electrostatic Force on a Dielectric Sphere Resting on a Conducting Substrate.- Electrostatic Charge Generation on Wafer Surfaces and Its Effect on Particulate Deposition.- Toner Adhesion in Electrophotography.- Adhesion and Removal of Particles: Effect of Medium.- Strong Adhesion of Dust Particles.- Prevention of Strong Adhesion of Dust Particles.- Dynamic Adhesion of Particles Impacting a Cylinder.- Crossed Fiber Models of the Particle-Surface Interaction.- Sensitive New Method for the Determination of Adhesion Force Between a Particle and a Substrate.- III. Particle Detection, Analysis and Characterization.- Detection of Particles on Clean Surfaces.- Detection of Particles Down to a "Few" Micrometers on Non-Specular Microelectronic Substrates and Other Surfaces.- Accurate Particle Counting for Bare Substrate Inspection.- Automated SEM/EDS Image Analysis of Particles on Filter Blanks.- Particle Sizing and Counting with the Inspex EX20/20.- IV. Particle Removal.- Methods for Surface Particle Removal: A Comparative Study.- Electrostatic Removal of Particles from Surfaces.- Electric Field Detachment of Charged Particles.- A New Approach to the Removal of Sub-Micron Particles From Solid (Silicon) Substrates.- About the Contributors.

Conformal layers by radical-component cvd

Abstract: Methods, materials, and systems are described for forming conformal dielectric layers containing silicon and nitrogen (e.g., a silicon-nitrogen-hydrogen (Si—N—H) film) from a carbon-free silicon-and-nitrogen precursor and radical-nitrogen precursor. The carbon-free silicon-and-nitrogen precursor is predominantly excited by contact with the radical-nitrogen precursor. Because the silicon-and-nitrogen film is formed without carbon, the conversion of the film into hardened silicon oxide is done with less pore formation and less volume shrinkage. The deposited silicon-and-nitrogen-containing film may be wholly or partially converted to silicon oxide which allows the optical properties of the conformal dielectric layer to be selectable. The deposition of a thin silicon-and-nitrogen-containing film may be performed at low temperature to form a liner layer in a substrate trench. The low temperature liner layer has been found to improve the wetting properties and allows flowable films to more completely fill the trench.