bluuebunny/crossref_metadata_2025 huggingface dataset:
TiN and TiO2:Nb thin film preparation using hollow cathode sputtering with application to solar cells
Authors: Guo S. Y. , Shafarman W. N. , Delahoy A. E.
Published: July 2006

Titanium nitride (TiN) is well known for its excellent conductivity, inertness, and good optical reflectivity at long wavelengths. These properties make it a potential IR-reflective back contact material suitable for ultrathin Cu(In,Ga)Se2 (CIGS) solar cells. Using a pulsed power, 12cm linear hollow cathode source fitted with Ti targets and with N2 as the reactive gas, TiN films were deposited on Mo-coated glass. The static deposition rate was 50nm∕min for a sputtering power of only 500W. The high deposition rate indicates the advantage of the reactive environment, hollow cathode sputtering method, i.e., the reactive gas is excluded from the target. Electrical, optical, and physical properties of the films were measured. Resistivities in the range of 50–60μΩcm were achieved. Reflectance and x-ray diffraction measurements were conducted, and the effects of deposition parameters such as substrate bias and substrate temperature were studied. The optical emission from N and Ti atoms in the plasma was also studied. CIGS solar cells were successfully fabricated on TiN and a conversion efficiency of 12.3% was achieved. Transparent and moderately conductive TiO2 films doped with Nb were also prepared. The electrical and optical properties of these films are reported, and the reflectance of a-Si solar cells was reduced via incorporation of a TiO2:Nb layer.
Surface etching mechanism of Bi4−xLaxTi3O12 thin films using quadrupole mass spectroscopy
Authors: Kim Jong-Gyu , Kim Gwan-Ha , Kim Chang-Il
Published: July 2006

The etching mechanism of (Bi4−xLax)Ti3O12 (BLT) thin films in Ar∕Cl2 inductively coupled plasma (ICP) was investigated as a function of gas mixing ratios, process pressure, and ICP powers at fixed other conditions. Etch rates were measured by using an α-step surface profiler. The maximum etch rate of BLT thin films was 117nm at 0.8 Ar∕(Ar+Cl2) gas mixing ratios with following conditions: process pressure of 15mTorr, gas flow rate of 20sccm, ICP power of 700W, and dc bias of −150V. The etch rate was increased as decreasing the process pressure. For a detailed investigation of etching mechanisms of BLT thin films, the ion energy distributions of each positive species were measured using quadrupole mass spectrometer and analyzed those data. Also the electron energy distribution was measured as a function of Ar∕Cl2 gas mixing ratios.
Effect of Cl2∕Ar gas mixing ratio on (Pb,Sr)TiO3 thin film etching behavior in inductively coupled plasma
Authors: Kim Gwan-Ha , Kim Chang-Il
Published: July 2006

The development of anisotropic etching process for (Pb,Sr)TiO3 (PST) thin films is an important task to provide a small feature size and an accurate pattern transfer. Etching characteristics of PST thin films were investigated using inductively coupled plasma etching system as functions of Cl2∕Ar gas mixing ratio. The PST etch rate increased with the increase of chlorine radical and ion energy intensity. It was found that the increasing of Ar content in gas mixture lead to sufficient increasing of etch rate. The maximum etch rate of PST film is 56.2nm∕min at Cl2∕(Cl2+Ar) of 0.2. It was proposed that the sputter etching is a dominant etching mechanism while the contribution of chemical reaction is relatively low due to low volatility of etching products.
Laser assisted and wet chemical etching of silicon nanostructures
Authors: Kolasinski Kurt W. , Mills David , Nahidi Mona
Published: July 2006

Etching of silicon can be accomplished in a number of ways: in aqueous solutions of fluoride or KOH, or by simultaneous exposure to a gas such as SF6 or HCl and high power laser irradiation. Here we review how laser assisted etching, chemically enhanced laser ablation, and stain etching can be used to create pillars, pores, porosified pillars, and macropores. Pillar dimensions can range from 10μm tall with ∼200nm tips to >100μm high with 10μm tips. Ordered arrays can be produced and sharpening can lead to aspect ratio approaching 104. Porous silicon with a visibly photoluminescent nanocrystalline structure can be made by etching in fluoride solutions. Acidic fluoride+oxidant solutions (stain etchants) allow us to form porous silicon on substrates of arbitrary topology. Moreover, these etchants can be used to control the photoluminescence spectrum of the resulting film, presumably through control of the size distribution of the nanocrystalline structures that are responsible for photoluminescence.
Birefringent films for contrast enhancement of liquid crystal on silicon projection systems
Authors: Hendrix Karen , Tan Kim , Duelli Markus , Shemo David , Tilsch Markus
Published: July 2006

High-performance projection displays based on liquid crystal on silicon (LCoS) panel technology have the potential to deliver very high contrast and performance at an attractive price. These systems use polarization-based light engines that utilize wire grid polarizers (WGP) and vertical-aligned nematic LCoS panels. To achieve high contrast, the linear polarization state created by the WGP must be maintained in the dark state to prevent light leakage to the screen. However, the LCoS panel has a residual retardance, and without compensation, this leakage degrades the system contrast. We describe the design and contrast measurement results of a birefringent contrast enhancing component that compensates this residual retardance and improves the overall system contrast ratio to 6000:1. The component is comprised of birefringent films with individually controllable A-plate and C-plate compensation, accurate retardance targeting, and excellent uniformity for both retardance magnitude and orientation. The component also has good environmental durability and low defects.
Damage-free metal-oxide-semiconductor gate electrode patterning on thin HfSiON film using neutral beam etching
Authors: Noda Shuichi , Ozaki Takuya , Samukawa Seiji
Published: July 2006

The charging damage of metal-oxide-semiconductor (MOS) capacitors and the degradation of HfSiON dielectric films during gate electrode etching were compared with neutral beam etching and conventional plasma etching. Furthermore, residual flux of charged particles (positive/negative ions and electrons) in the neutral beam was analyzed and the relationship between the residual charge flux and the charging damage induced in SiO2 and/or HfSiON gate dielectrics was investigated. Although the residual charge flux and its composition varied depending on the neutral beam acceleration method (dc or rf biasing), the amounts were noticeably lower than that with the plasma etching system. The gate leakage currents of the MOS capacitors etched using the neutral beam were sufficiently lower than those in the plasma etching, which was consistent with the charge flux during the gate electrode etching. On the neutral beam irradiated surface of the HfSiON film, there were no changes in the x-ray photoelectron spectrometry spectra, while large decreases in Hf composition were observed on the plasma-irradiated surface.
Application of the shaped electrode technique to a large area rectangular capacitively coupled plasma reactor to suppress standing wave nonuniformity
Authors: Sansonnens L. , Schmidt H. , Howling A. A. , Hollenstein Ch. , Ellert Ch. , Buechel A.
Published: July 2006

The electromagnetic standing wave effect can become the main source of nonuniformity limiting the use of very high frequency in large area reactors exceeding 1m2 required for industrial applications. Recently, it has been proposed and shown experimentally in a cylindrical reactor that a shaped electrode in place of the conventional flat electrode can be used in order to suppress the electromagnetic standing wave nonuniformity. In this study, we show experimental measurements demonstrating that the shaped electrode technique can also be applied in large area rectangular reactors. We also present results of electromagnetic screening by a conducting substrate which has important consequences for industrial application of the shaped electrode technique.
Controlled gold nanoparticle assembly on DNA molecule as template for nanowire formation
Authors: Kim Hyung Jin , Roh Yonghan , Hong Byungyou
Published: July 2006

A reducer was used to construct Au nanowires (AuNWs) by the conjugation of 2-aminoethanthiol-capped gold nanoparticles (AET-AuNPs) and the immobilized DNA molecules on 3-aminopropyltriethoxysilane-coated Si wafer. The AuNPs coated with AET monolayer seem to be electrostatically assembled along DNA molecules by careful control of the relative molar quantities of AuNPs and AET. A variety of AuNP sizes (2, 5, and 10nm) was used and also the ratio of AET to AuNP solution was varied to control the interparticle spacing and finally to form the nanowire based on DNA template. The formation of long-range AuNWs and the interparticle spacing were observed with atomic force microscopy.
Quantitative assessment of diffusivity and specularity of surface-textured reflectors for light extraction in light-emitting diodes
Authors: Xi Y. , Li X. , Kim J. K. , Mont F. , Gessmann Th. , Luo H. , Schubert E. F.
Published: July 2006

Surface-textured reflectors fabricated by natural lithography and ion beam etching have a specular and a diffusive component of the reflectivity. The diffusely and specularly reflected powers of surface-textured reflectors are measured and analyzed quantitatively in terms of a theoretical model. The diffusive-power-to-total-power ratio is determined and shown to strongly depend on the surface texture. The light extraction efficiency from a waveguide clad by a partially diffuse reflector is analyzed and shown to be enhanced.
Effects of TiOx physical vapor deposition parameters on the preferred orientation and adhesion of Pt films on γ-Al2O3
Authors: Derniaux E. , Kayser P. , Gageant C. , Sanchez C. , Boivin D.
Published: July 2006

Ti O x physical vapor deposition (PVD) films were studied to improve the adhesion of Pt∕AlN∕Pt piezoelectric transducers on γ-Al2O3∕NiCoCrAlY/superalloy components. Thick (1.7–3.8μm) TiOx films deposited by rf reactive cathodic sputtering on α-Al2O3 substrates were analyzed by x-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The influence of substrate temperature (Ts), oxygen mole fraction in the plasma gas and annealing (1050°C, 1h, in air) on structural properties, morphology, and chemical composition of the films was observed. Thin (⩽10nm) TiOx adhesion layers and Pt films were sputtered on α-Al2O3. The effects of TiOx deposition parameters on the adhesion and the orientation of as-deposited and annealed Pt films were examined by tensile pull-off test and XRD, respectively. The results showed a (111) preferred orientation and good adhesion of Pt films. Finally, the selected TiOx deposition parameters were applied on γ-Al2O3∕NiCoCrAlY/superalloy substrates. Adhesion properties of annealed Pt films on γ-Al2O3 and TiOx∕γ-Al2O3 were evaluated. The results showed a drastic improvement of the pull-off force (≈0to≈100MPa) by using the TiOx “glue layer.” The adhesion layer also led to a pronounced (111) preferential orientation of the Pt films.
Effects of various oxidizers on chemical mechanical polishing performance of nickel for microelectromechanical system applications
Authors: Kim Nam-Hoon , Choi Gwon-Woo , Seo Yong-Jin , Lee Woo-Sun
Published: July 2006

Nickel and nickel-based alloys are known candidates to realize movable structures for microelectromechanical system (MEMS) application. Chemical mechanical polishing (CMP) has found extensive application in the fabrication of MEMS. In this study, the CMP of nickel was performed using the commercial slurry with the various ratios of different oxidizers and alumina particle as an abrasive. Moreover, the potentiodynamic polarization behaviors were discussed to evaluate the effects of nickel-CMP performance and electrochemical characteristics between nickel and the various oxidizers. As an experimental result, the removal rate of nickel reached a maximum at 1.0vol% of H2O2 concentration. An addition of 5.0wt% alumina (Al2O3) abrasive could improve the removal rate of nickel; however, many scratches were observed. For the case of Fe(NO3)3 addition as an oxidizer, both the removal rate and the surface topography were insufficient for MEMS applications. The potentiodynamic polarization results indicated that the surface chemistry and electrochemical characteristics of nickel play an important role in controlling the polishing behavior of nickel.
Tribological behavior and thermal stability of TiC∕a-C:H nanocomposite coatings
Authors: Pei Y. T. , Galvan D. , De Hosson J. Th. M.
Published: July 2006

Advanced TiC∕a-C:H nanocomposite coatings have been produced via reactive deposition in a closed-field unbalanced magnetron sputtering system (Hauzer HTC-1200). These wear-resistant coatings are targeted for automotive applications where high load-bearing capacity and thermal stability, low friction, and wear resistance are the primary requirements. In this article the tribological behavior of the nanocomposite coatings is scrutinized by means of ball-on-disk tribotests at elevated temperature or after annealing in the temperature range of 150–400°C. The thermal stability of the coatings in terms of critical temperatures, at which the degradation of wear resistance and friction of the coatings starts, is monitored with depth profiling of oxygen content using Auger spectroscopy in conjunction with detailed examinations of the mechanical properties of the annealed coatings. A striking result is that a coating thermally stable up to 350°C may fail at much lower temperatures during elevated-temperature tribotests. The origin of failure is attributed to the interfacial delamination due to the discontinuity in mechanical properties between the coatings and substrates at elevated temperatures. It indicates a stringent requirement to optimize the interlayer of advanced tribological coatings developed for high temperature applications.
Selective water vapor cryopumping through argon
Authors: Kryukov A. P. , Podcherniaev O. , Hall P. H. , Plumley D. J. , Levashov V. Yu. , Shishkova I. N.
Published: July 2006

A selective cryopumping process for water vapor control takes place in vacuum systems for web coating or plasma operations, such as sputter deposition, etching, etc. Excessive water vapor content will affect the quality of the processes and final products. These vacuum systems typically operate at pressures corresponding to transitional or viscous flow regimes, and water vapor cryopumping is highly limited by diffusion of water vapor molecules through a noncondensable process gas (argon, air). An analytical model was created to describe water vapor condensing process through a noncondensable gas diffusion barrier. The model accounts for the collisions of different molecules by means of Boltzmann kinetic equations for two-component rarefied gas. It was assumed that water vapor content is about three orders of magnitude lower than that of the noncondensable gas (argon). Cryopumping process was analyzed for two simplified cases when water vapor source and cryosurface are parallel plates and coaxial cylinders. The calculations were conducted for different water vapor outgassing rates and argon pressures ranging from 0.5×10−3to20.0×10−3torr. At certain parameters a strongly nonlinear distribution of water vapor pressure and density versus distance between source and cryosurface was obtained. At high argon pressures an increase of water vapor pressure was observed near an outgassing surface. The results were used for calculation of water vapor cryopumping rates.
Improvement of materials surface properties by rf glow discharge treatment
Authors: Huang T. B. , Chen X. , Tian X. Q. , Cha L. Z.
Published: July 2006

Materials surface properties were improved by the application of a rf glow discharge treatment for vacuum and electronic applications. The surface morphology was studied under different glow discharge treatments and it could be shown by experiments that the roughness of materials surface varied due to the glow discharge treating process and that a clean and smooth surface could be obtained after the treatment. The experimental results revealed that the outgassing rates for different gases decreased and the evacuating properties for the materials improved following the application of the glow discharge treatment.
Interface stability between amorphous ferromagnetic layer and Al oxide barrier in tunneling magnetoresistive films at elevated temperatures
Authors: Peng Xilin , Kvitek Dick , Morone Augusto , Axdal Steven H. , Xue Song
Published: July 2006

The interface stability and microstructure between amorphous and crystalline ferromagnetic (FM) layers Fe56Co24B20 and Co70Fe30 (at. %) and oxide barrier layers (AlO) deposited by physical vapor deposition, in both as-deposited and annealed states, have been studied using hysteresis loops for magnetic measurement, x-ray photoelectron spectroscopy for elemental depth profiling, and transmission electron microscopy for atomic-level microstructure. AlO was found to be amorphous on both amorphous Fe56Co24B20 and polycrystalline Fe30Co70 FM layers. Substantial Fe diffusion towards the AlO layer and Al diffusion towards the FM layer are clearly observed for the Fe56Co24B20∕AlO system when annealed above 360°C and will likely cause magnetic tunneling junction devices made from this system to fail.
Thermal conductivity of AlN-diamond particulate composite films on silicon
Authors: Jagannadham K.
Published: July 2006

The thermal conductivity of a particulate composite film of diamond in AlN deposited on silicon was measured using 3ω technique in the temperature range of 205–300K. The experimental results of increase in the temperature of heater line were analyzed using a model of film on semi-infinite substrate. The results of modeling are found to conform to the expected temperature dependence of the thermal conductivity of silicon, AlN, and diamond. Oxygen introduced during the deposition of the AlN-diamond composite film on silicon is found to reduce the thermal conductivity of the film and the substrate. Low cost AlN-diamond particulate composite films are found to offer good heat spreader characteristics for high power semiconductor devices.
Observation of strong red photoluminescence with broadband in indium oxynitride nanoparticles
Authors: Ko T. S. , Chu C. P. , Chen H. G. , Lu T. C. , Kuo H. C. , Wang S. C.
Published: July 2006

Indium oxynitride nanoparticles were synthesized on a silicon substrate in nitrogen atmosphere using the method involving thermal evaporation of pure indium in a two-zone reactor. Nanoscale compositional analysis by energy dispersion spectrum showed the existence of indium oxynitride compound. X-ray diffraction analysis further confirmed high crystallization and nitrogen atom existence within the nanoparticles. Scanning electron microscopy investigations showed shape transformation from amorphous sphere to well-shaped octahedron with an average nanoparticle size ranging from 50nmto1μm when the growth temperature of the substrate was increased from 600to900°C. Photoluminescence study was performed on the indium oxynitride nanoparticle samples grown at different temperatures. It was found that with increasing growth temperatures there was not only the formation of high quality indium oxynitride nanoparticles but also an increase in the intensities of emissions. These nanoparticles grown at 900°C could emit a strong photoluminescence spectrum centered around 700nm with a broad full width at half maximum of about 250nm, spanning the whole red segment.
Modeling of dc magnetron plasma for sputtering: Transport of sputtered copper atoms
Authors: Yagisawa T. , Makabe T.
Published: July 2006

A self-consistent modeling of two-dimensional structures of a dc magnetron plasma with a copper target is performed at 5mTorr in Ar by using a hybrid model consisting of a particle-in-cell/Monte Carlo simulation for electrons and relaxation continuum model for ions. The erosion profile of the copper target is estimated by the flux velocity distribution of ions incident on the target. In the case of a dc magnetron, the discharge is mainly sustained by an E×B drift motion of energetic electrons near the position Bz∼0 with a static doughnutlike magnetic field. Then, a strongly localized profile appears in the plasma structures. The position of a maximum erosion on the copper target exactly coincides with the position where the incident Ar+ ion flux is maximum. Under the system between the light ion and the heavy target atom, the energy of the sputtered Cu atom is low (<10eV) despite the high-energy ion injection (∼200eV) to the target surface. In particular, we have developed a technique to predict the transport of sputtered particles in the gas phase within a reasonable computational time. The spatial distribution of the sputtered particles is divided into two components: “directional” fast-moving particles that do not collide with Ar feed gas in the gas phase and “random” slow-moving particles whose energy is relaxed by collision. The sputtered Cu atoms are widely dispersed from the doughnutlike region on the target. At 5mTorr, the flux of sputtered Cu atoms at the substrate is mainly affected by the random particles with relaxed energy by collision.
Investigation of room temperature electrical resistivities of LaNiO3−δ thin films deposited by rf magnetron sputtering and high oxygen-pressure processing
Authors: Zhang X. D. , Meng X. J. , Sun J. L. , Wang G. S. , Lin T. , Chu J. H.
Published: July 2006

Highly (100)-oriented electrically conductive LaNiO3−δ (LNO) thin film with perovskite-type structure was deposited on Si(100) substrates by rf magnetron sputtering at substrate temperatures of 200, 300, 450, and 600°C with a series of 0%, 20%, 40%, and 60% oxygen partial pressures, respectively. The room temperature (RT) resistivity of LNO films decreases with decreasing substrate temperature at a fixed oxygen partial pressure and with increasing oxygen partial pressure at a fixed substrate temperature. The lowest RT resistivity of as-sputtered LNO thin films was about 5.3×10−4Ωcm. This value could be as low as ∼1.55×10−4Ωcm by postprocessing called high oxygen-pressure processing at 8MPa and is comparable to the lowest one, 1.5×10−4Ωcm, of epitaxial LNO thin film deposited on lattice-matched SrTiO3, LaAlO3, or sapphire single-crystal substrates.
Phase separation of a Ge2Sb2Te5 alloy in the transition from an amorphous structure to crystalline structures
Authors: Kim YoungKuk , Park S. A. , Baeck J. H. , Noh M. K. , Jeong K. , Cho M.-H. , Park H. M. , Lee M. K. , Jeong E. J. , Ko D.-H. , Shin H. J.
Published: July 2006

Changes in the structural and electrical properties of a Ge2Sb2Te5 alloy thin film induced by phase transition were investigated using various analytical techniques. X-ray diffraction and scanning photoelectron microscopy showed that the phase separation occurred in a local area of the film during a phase transition when the amorphous structure was being transformed into crystalline structures. It was found that the heterogeneous distribution of Sb atoms that diffused during the phase transition accompanied the phase separation. Atomic force microscopy was used to examine the changes in surface morphology and roughness. The electrical conductance of the film was dramatically improved after the phase transition from an amorphous structure to crystalline structures as evidenced by the sheet resistance measurements. The sheet resistance changed from ∼109to∼102Ω∕sq. during the phase transition. Differential scanning calorimetry was used to determine the exact phase transition temperature (160–170°C) and the effective activation energy for the phase transition (2.5±0.11eV) on the basis of Kissinger’s equation.
Hysteresis behavior during reactive magnetron sputtering of Al2O3 using a rotating cylindrical magnetron
Authors: Depla D. , Haemers J. , Buyle G. , De Gryse R.
Published: July 2006

Rotating cylindrical magnetrons are used intensively on industrial scale. A rotating cylindrical magnetron on laboratory scale makes it possible to study this deposition technique in detail and under well controlled conditions. Therefore, a small scale rotating cylindrical magnetron was designed and used to study the influence of the rotation speed on the hysteresis behavior during reactive magnetron sputtering of aluminum in Ar∕O2 in dc mode. This study reveals that the hysteresis shifts towards lower oxygen flows when the rotation speed of the target is increased, i.e., target poisoning occurs more readily when the rotation speed is increased. The shift is more pronounced for the lower branch of the hysteresis loop than for the upper branch of the hysteresis. This behavior can be understood qualitatively. The results also show that the oxidation mechanism inside the race track is different from the oxidation mechanism outside the race track. Indeed, outside the race track the oxidation mechanism is only defined by chemisorption while inside the race track reactive ion implantation will also influence the oxidation mechanism.
Effects of pulsing parameters on production and distribution of macroparticles in cathodic vacuum arc deposition
Authors: Hu Yawei , Li Liuhe , Dai Hua , Li Xiaoling , Cai Xun , Chu Paul K.
Published: July 2006

The effects of pulsing parameters such as the duty cycles, frequencies, and arc currents on the production and distribution of macroparticles (MPs) were studied. A tunable pulsed arc power supply that could provide either direct current (dc) or pulsed current plus dc was used in the experiments. Copper and titanium were used as the cathodes, and glasses were used as the substrate. Optical microscopy, scanning electron microscopy, and special image processing were utilized to investigate the MPs deposited onto the substrate. Our results illustrate the general trend that the MP density increases with higher dc but decreases with increasing pulsing frequency. There is no obvious relationship between the MP density and the duty cycle at high dc but the MP density obviously increases with the duty cycle at low dc.
Effect of heat on the pumping performance of cryopump
Authors: Cheng H.-P. , Shen Y.-H.
Published: July 2006

This study used quartz lamp and the small disk heaters as the heating sources to investigate the pumping performance of the two-stage Gifford-McMahon (G-M) closed-loop gaseous helium cryopump with heat transfer effect. In the experiment, the heat was applied by two means, for the first-stage array by thermal radiation and for the second-stage array by applying directly. The test system was constructed in accordance to the single-dome flow-meter pumping measuring apparatus recommended by Welch et al. [J. Vac. Sci. Technol. A 17, 3081 (1999)]. The experiment applied varied levels of electrical power to the heaters, introduced Ar to the test dome, and measured the corresponding dome pressure, gas throughput, and temperatures of the different arrays inside the cryopump. The results showed that the temperature of the introduced gas heated by the heater in the test dome would influence the measured pumping speed of cryopump. When the thermal load is applied primarily on the first-stage array, the temperature of the second-stage array varies significantly as the temperature of the first-stage array changes; when applied directly to the second-stage array, the temperature of the first-stage array varies little as the temperature of the second-stage array changes. The pumping speed of cryopump and temperature of the two-stage arrays increase gradually as gas throughput rises, and sharply when the gas in the test dome is nonmolecular flow. The measured refrigeration capacity of second-stage cooling station is approximate to the data provided by ULVAC.
Working pressure induced structural and mechanical properties of nanoscale ZrN∕W2N multilayered coatings
Authors: Li D. J. , Wang M. X. , Zhang J. J. , Yang J.
Published: July 2006

This article reports the synthesis of ZrN∕W2N multilayered coatings with nanoscale bilayer period using rf magnetron sputtering. X-ray diffraction, Auger electron spectroscopy, scanning electron microscope, nanoindenter, and profiler were employed to investigate the influence of working pressure on microstructural and mechanical properties of the coatings. Well-defined composition modulation and layer structure of the multilayered coating are indicated directly. A mixed polycrystalline of ZrN(111), W2N(111), W2N(200) and W2N(311) textures appeared in the multilayered structures. All multilayered coatings revealed higher nanohardness, elastic modulus, critical load, and lower residual stress than the rule-of-mixture value of monolithic ZrN and W2N coatings, especially for one prepared at 0.8Pa working pressure.
Low-voltage resistive switching of polycrystalline SrZrO3:Cr thin films grown on Si substrates by off-axis rf sputtering
Authors: Park Jae-Wan , Park Jong-Wan , Yang Min Kyu , Jung Kyooho , Kim Dal-Young , Lee Jeon-Kook
Published: July 2006

A polycrystalline Cr-doped SrZrO3∕SrRuO3 layered structure showing a reproducible resistive switching behavior with a resistive switching voltage of ±2.5V was successfully fabricated on commercial Si (100) substrate by off-axis rf sputtering. Typical resistance values of high- and low-resistance states were about 100 and 5kΩ, respectively, so that the ratio of high- to low-resistance value is about 20. These values are appropriate for memory applications, and the resistive switching voltage of ±2.5V is the lowest value among the switching voltages of Cr-doped SrZrO3 films on Si substrates reported in recent literature. We suggest that the low-voltage resistive switching of the polycrystalline Cr-doped SrZrO3 thin film is attributed to the reduction of resputtering effects and the formation of a clean interface between the Cr-doped SrZrO3 thin film and the SrRuO3 bottom electrode layer by the use of 90° off-axis sputtering.
Effect of poly (3-hexylthiophene) film thickness on organic thin film transistor properties
Authors: Jia Huiping , Gowrisanker Srinivas , Pant Gaurang K. , Wallace Robert M. , Gnade Bruce E.
Published: July 2006

We present the effect of poly (3-hexylthiophene) (P3HT) thickness on the performance of organic thin film transistors (OTFTs). The P3HT film thickness varies from 11to186nm. The devices have channel lengths of 5, 10, 20, 40, and 80μm and a channel width of 500μm. The mobility and on/off ratio are up to 0.08cm2∕Vs and 7×103, respectively. The drain current and the mobility increase with thickness. At the same P3HT thickness, the drain current and mobility become higher when the channel length is reduced. The on/off ratio decreases quickly and then saturates for thickness >64nm. Short channel devices have higher on/off ratio than long channel devices. For short channel devices (5μm), the on/off ratio does not change significantly with thickness. The devices with shorter channel length and thicker P3HT films tend to have smaller threshold voltages. The threshold voltage saturates for long channel (20–80μm) devices, for films thicker than 110nm. The gate leakage (ID offset) is higher for thicker film devices. The performance dependence as a function of P3HT film thickness can be explained by the bulk conductance model and the SiO2 surface potential change. Our results suggest that the performance of P3HT OTFTs should be optimized based on the specific application.
Thin oxide-free phosphate films of composition formed on the surface of vanadium metal and characterized by x-ray photoelectron spectroscopy
Authors: Asunskis D. J. , Sherwood P. M. A.
Published: July 2006

This article reports the preparation of thin (less than 100Å) oxide-free phosphate films of various compositions on vanadium metal. These films are interesting because of their potential for corrosion inhibition, adhesion promotion, and biocompatibility. Valence and core-level x-ray photoelectron spectroscopy (XPS) were used to characterize the films. The valence band spectra obtained were compared with spectra generated from band structure calculations for various vanadium phosphates and from previously reported spectra of vanadium phosphates. Vanadium phosphate coatings were created by the reaction of vanadium metal and different phosphorus-oxygen containing acids: H3PO4, H3PO3, H3PO2, and H2P2O7. This article focuses upon the valence band region which shows significant differences between the four vanadium phosphate films formed as well as clear differences between the these phosphates and vanadium oxides. The valence band spectra are effectively interpreted by band structure calculations.
Type of precursor and synthesis of silicon oxycarbide (SiOxCyH) thin films with a surfatron microwave oxygen/argon plasma
Authors: Walkiewicz-Pietrzykowska Agnieszka , Espinós J. P. , González-Elipe Agustin R.
Published: July 2006

Siliconelike thin films (i.e., SiOxCyHz) were prepared in a microwave plasma enhanced chemical vapor deposition reactor from structurally different organosilicon precursors [i.e., hexamethyldisiloxane (HMDSO), dimethylsilane (DMS), and tetramethylsilane (TMS)]. The films were deposited at room temperature by using different oxygen/argon ratios in the plasma gas. By changing the type of precursor and the relative concentration of oxygen in the plasma, thin films with different compositions (i.e., O∕C ratio) and properties are obtained. In general, raising the oxygen concentration in the plasma produces the progressive removal of the organic moieties from the films whose composition and structure then approach those of silicon dioxide. The deposition rate was highly dependent on the type of precursor, following the order HMDSO⪢DMS>TMS. The polarizabilities, optical band gaps, and surface free energy of the films also depended on the thin film composition and structure. It is proposed that the Si–O bonds existing in HMDSO is the main factor controlling the distinct reactivity of this precursor and is also responsible for the different compositions and properties of the SiOxCyHz thin films prepared with very low or no oxygen in the plasma gas.
Copper electroplating to fill blind vias for three-dimensional integration
Authors: Spiesshoefer S. , Patel J. , Lam T. , Cai L. , Polamreddy S. , Figueroa R. F. , Burkett S. L. , Schaper L. , Geil R. , Rogers B.
Published: July 2006

The continued demand for electronic products with decreased size, higher performance, and increased functionality requires improvements in the system level integration of logic, memory, and other functional integrated circuits. The formation of vertical interconnects in silicon may be one approach to provide this integration. This method involves stacking of individual die to form a highly interconnected three-dimensional structure by placing electrically conductive vias through the body of the silicon to bring the connections from top to bottom. Copper is the metal used to fill the through silicon via structure because of its high conductivity and common use in multilevel wiring. A process will be described in this article to electroplate copper into small diameter (5–10μm) vias of aspect ratio >3. The objective of this project is to develop an electroplating process to obtain a void-free copper filled blind via; a via that does not go through the silicon substrate but terminates inside the silicon. Prior to plating, vias are formed by both reactive ion etch (RIE) and deep RIE processes and are then lined with insulation, barrier, and seed films. The insulation layer, SiO2, is deposited by plasma enhanced chemical vapor deposition while the barrier (TaN) and Cu seed layers are deposited by sputtering. A combination of three electroplating techniques is used in this study to fill the vias. They consist of optimized bath composition (additive control), fountain plating, and reverse pulse plating. The goal during electroplating is to achieve a bottom-up fill, also referred to as “a superfill.” This article describes the process that results in void-free electroplating to fill an array of blind vias as well as the related processing issues.
Hot electron transport across manganese silicide layers on the Si(001) surface
Authors: Stollenwerk A. J. , Krause M. R. , Moore R. , LaBella V. P.
Published: July 2006

Ballistic electron emission microscopy (BEEM) has been performed on MnSi∕Si(001) Schottky diodes at 80K to study the hot electron transport properties. The BEEM spectra best fit the thermally broadening 5∕2 power law model with two threshold heights at 0.71 and 0.86eV, indicating a complex interface band structure. In addition, the normalized BEEM current in the MnSi overlayer was found to be approximately seven times less than is observed in Au∕Si(001) samples of similar thicknesses, indicating a larger amount of hot electron scattering in the MnSi∕Si(001) samples.
Understanding ion-milling damage in Hg1−xCdxTe epilayers
Authors: Wang Changzhen , Smith David J. , Tobin Steve , Parodos Themis , Zhao Jun , Chang Yong , Sivananthan Sivalingam
Published: July 2006

Transmission electron microscopy (TEM) is widely used for the characterization of the microstructure of Hg1−xCdxTe epilayers. Traditional TEM sample preparation methods, which usually involve argon ion milling, can easily cause damage to the material, and the size and density of the induced defects depend on the milling conditions. In this work, the structural damage caused by argon ion milling of Hg1−xCdxTe epilayers has been investigated. Multilayer samples with different Hg concentrations, as grown by molecular beam epitaxy, and p-n heterojunctions, as grown by liquid-phase epitaxy, have been examined. It is shown that, in addition to the milling conditions, the extent of the ion-induced damage depends sensitively on the Hg concentration of the Hg1−xCdxTe alloy as well as the epilayer growth conditions (i.e., Hg rich or Te rich). A possible mechanism that explains these results is briefly discussed.
Tunable hydrophilicity on a hydrophobic fluorocarbon polymer coating on silicon
Authors: Kolari K. , Hokkanen A.
Published: July 2006

An efficient, economic, reliable, and repeatable patterning procedure of hydrophobic surfaces was developed. A fluorocarbon polymer derived from the C4F8 gas in an inductively coupled plasma etcher was used as the hydrophobic coating. For a subsequent patterning of hydrophilic apertures on the polymer, a short O2 plasma exposure through a silicon shadow mask was utilized. The overall hydrophilicity of the patterned surface can be tuned by the duration of the O2 plasma exposure, and also by the density and the size of the hydrophilic apertures. The laborious photolithography and tricky lift-off procedures are avoided. Optimization of the whole patterning process is explained thoroughly and supported with experimental data. The hydrophilic adhesion of the patterned polymer was evaluated with aqueous droplets, which were studied on matrices of the hydrophilic apertures of different sizes. The deposition parameters of the fluorocarbon polymer, the size of the droplet required to enable rolling on the patterned surface, and the duration of the O2 plasma exposure were considered as the main parameters. To determine the achievable resolution of the patterning procedure, the subsurface etching beneath the shadow mask was evaluated. The results show that a resolution of less than 10μm can be achieved. The simple hydrophilic patterning procedure described here can be used for the production of on-plane microfluidics, where a controlled adhesion or decohesion of 8–50μl droplets on the surface with a variable hydrophilicity from one location to another can be achieved.
Observations of electrical and luminescence anomalies in InGaN∕GaN blue light-emitting diodes
Authors: Nee Tzer-En , Wang Jen-Cheng , Shen Hui-Tang , Lin Chung-Han , Wu Ya-Fen
Published: July 2006

Unique correlations between the electrical and optical characteristics of InGaN∕(In)GaN multiple quantum-well light-emitting diodes (LEDs) were investigated over a broad range of temperatures. The dependence of nonunity ideality factors extracted from the current-voltage analysis on temperature determines the carrier-transport mechanisms in the heterodevices. The pseudotemperatures To for the LEDs with multiquantum barriers and with GaN barriers were found to be 945 and 1385K, respectively, at temperatures of 180–300K while having values of 1195 and 2720K below about 180K. Correspondingly, the temperature-dependent electroluminescence observations suggest that the To anomaly caused the spectral intensity to deteriorate.
Gallium nitride thin films deposited by radio-frequency magnetron sputtering
Authors: Maruyama Toshiro , Miyake Hidetomo
Published: July 2006

Effects of self-induced negative bias in radio-frequency (rf) sputtering on the structure of the deposited film are discussed on the basis of the measured characteristics of the gallium nitride (GaN) films. A powdered GaN target was sputtered by either argon (Ar) or nitrogen (N2) gas to investigate the effects of the sputtering. When sputtering with Ar gas, the resputtering due to the ion bombardments produces a film deficient in nitrogen with poor crystallinity. The ion bombardment eventually destroys the crystal structure producing a black amorphous film caused by gallium atoms forming clusters. Alternatively, when sputtering with N2 gas, the activated nitrogen atmosphere enhances nitrogen incorporation and prevents the destruction of the crystal structure, making the film stoichiometric. To obtain high crystallinity, the effect of the self-induced negative bias should be minimized by decreasing the rf power and increasing the total pressure.
Physical-vapor deposition flux-distribution calculations for static and rotating substrates: Derivation of the deposition geometry for optimal film-thickness uniformity
Authors: Teeter Glenn
Published: July 2006

Flux-distribution formulas are applied to physical-vapor deposition from open-boat-type sources onto static and rotating substrates. A relation is derived for the dependence of flux variation at the substrate on source-substrate separation for the static-substrate case. For the rotating-substrate case, the deposition geometry that yields optimal film-thickness uniformity for different source-substrate separations is derived empirically. For rotating substrates, both the percentage flux variation and the magnitude of the net deposition flux obey power-law dependences with respect to the source-substrate separation. Finally, a formula is derived for the percentage of source material deposited on the substrate as a function of source position.
Layer structure of ultrathin Ag films on Ni∕Pt(111)
Authors: Ho H. Y. , Chen Y. J. , Su C. W. , Chen R. H. , Shern C. S.
Published: July 2006

The layer structure of Ag on a Ni∕Pt(111) surface after high temperature annealing was studied by Auger electron spectroscopy, depth profile of Ar ion sputtering, and low-energy electron diffraction (LEED). A structural phase p(2×2) LEED pattern was observed in one atomic monolayer (ML) on 1 ML Ni∕Pt(111) surface after annealing at 800K. Based on observations of the change of ion sputtering rates for the Ag overlayers, the LEED pattern, and minimum strain energy, we propose a layer structure of Ag for 1 ML Ag/1 ML Ni∕Pt(111) after the 800K annealing. The compositions in the subsurface region are 0.25 ML Ag in p(2×2) structure on the topmost layer, Ag75Ni25 alloy in the second layer, and Ni–Pt alloy in the remaining layers of the subsurface regions.
Evaluation of the shapes of Auger- and secondary-electron line scans across interfaces with the logistic function
Authors: Wight S. A. , Powell C. J.
Published: July 2006

We report on the use of the extended logistic function for fitting Auger-electron (AE) and secondary-electron (SE) line scans. Such fits provide convenient and objective measures of parameters describing the interface width and possible asymmetry of a line scan. We show examples of fits to AE and SE line scans for three types of samples. Fits to AE and SE data for a gold island on a carbon substrate gave useful measures of the lateral resolution of a scanning Auger microscope and “tails” present in the line scans showed evidence of imperfect alignment of the microscope. Fits to AE spectra obtained as the primary beam was scanned across an edge of Cr∕Cr2O3 lines on an indium tin oxide substrate showed similar tails due to the effect of backscattered electrons on the generation of Auger electrons for primary energies between 15 and 25keV. Fits with the logistic function to SE line scans across a fractured Ni∕Cr multilayer sample and to AE and SE line scans across a sputtered crater of this sample provided useful measures of the interface width.
Structural and electrochromic characterizations of pulsed laser deposited TaxW1−xO3−x∕2 films
Authors: Yang Dongfang
Published: July 2006

Structural and electrochromic property studies of mixed oxide TaxW1−xO3−x∕2 films grown on indium tin oxide coated glass substrates by the reactive pulsed laser deposition in 5.32Pa oxygen atmospheres are presented in this article. The crystallization temperatures of TaxW1−xO3−x∕2 increase with the Ta content in the films: When x=0, TaxW1−xO3−x∕2 (i.e., WO3) films crystallized to a monoclinic phase at substrate temperatures as low as 400°C; when x=0.1, TaxW1−xO3−x∕2 (i.e., Ta0.1W0.9O2.95) films crystallized mainly to a tetragonal phase at substrate temperatures ⩾600°C, and when x=0.3, TaxW1−xO3−x∕2 (i.e., Ta0.3W0.7O2.85) films crystallized to a cubic crystal structure at substrate temperatures ⩾700°C. As the Ta content increases, the degree of symmetry of crystallized TaxW1−xO3−x∕2 films increases resulting in shortening the metal oxygen bond length and forming more rigid structure. Electrochromic properties of amorphous TaxW1−xO3−x∕2 films with different Ta contents were evaluated in 0.1M H3PO4 solution. Under H+ intercalation at negative electrical potentials, WO3 (x=0) film changes its color from light pink to midnight blue, Ta0.1W0.9O2.95 (x=0.1) from light pink to cadet blue, and Ta0.3W0.7O2.85 (x=0.3) from light green to light brown green. The colors of all TaxW1−xO3−x∕2 films at colored state disappeared immediately after the H+ ions were extracted from the film at position electrical potentials showing excellent reversibility. With similar film thickness the change in optical density between colored state and bleached state for the WO3 is about 2 times higher than that of Ta0.1W0.9O2.95 and about 14 times higher than that of Ta0.3W0.7O2.85. The coloration efficiencies at wavelength λ=633nm for WO3, Ta0.1W0.9O2.95, and Ta0.3W0.7O2.85 films are 132, 122, and 65cm2C−1, respectively. The durability of TaxW1−xO3−x∕2 films increases with the increase of the Ta content in the acidic environments: in 0.1M H3PO4 solution the etching rate of WO3 is about 4.6 times higher than that of Ta0.1W0.9O2.95, while Ta0.3W0.7O2.85 has not shown any noticeable degradation after 55 coloring/bleaching cycles (1.5h). The excellent reversibility of ion intercalation/deintercalation, relatively high coloration efficiency, and improved chemical stability and cyclic durability suggest that Ta0.1W0.9O2.95 and Ta0.3W0.7O2.85 are good candidates as the electrochromic cathodic layer for electrochromic devices, especially for proton conducting liquid-gel-type devices. The results have also demonstrated that addition of one metal oxide (e.g., Ta2O5) into another (e.g., WO3) is an effective way to alter the electrochromic properties of the individual constituents and provides a convenient method for tailoring electrochromic properties of materials.