Radio-frequency Sputtering System Research Articles

Ultra-low temperature epitaxial growth of lithium ferrite thin films by high-pressure sputtering

LiFe5O8 epitaxial thin films with high crystalline quality have been successfully synthesized on (001) MgAl2O4 substrates even at an ultra-low working temperature of 200 °C by using a high-pressure radio-frequency sputtering system. Better crystalline qualities of the epitaxial LiFe5O8 films can be obtained with an increase of the deposition temperature in the range from 200 °C to 800 °C. Moreover, the growth temperature can significantly affect the magnetic properties of the LiFe5O8 thin films. The strain states, crystalline quality and defect density should be the main causes for the tunable magnetic properties. Overall, the wide-temperature range processing window, especially the low deposition temperature of 200 °C, of the LiFe5O8 films by this method will offer flexibilities for direct integration with semiconductors, organic electronics, flexible electronic materials and other related elements which are sensitive to the processing temperature.

Germanium coated vertically-aligned multiwall carbon nanotubes as lithium-ion battery anodes

The performance of polycrystalline and amorphous germanium (Ge) as anode active materials for lithium-ion batteries was studied systematically. Polycrystalline Ge on vertically-aligned multiwall carbon nanotube (MWCNT) arrays (MWCNT/c-Ge) and amorphous Ge on the arrays (MWCNT/a-Ge) were fabricated using a low pressure chemical vapor deposition system and a radio frequency sputtering system, respectively. The vertically-aligned MWCNT arrays were used as a platform to minimize pulverization problem. The MWCNT/a-Ge had a specific capacity of 1096.1mAhg−1 at the rate of 162.4mAg−1 at the 100th cycle. In comparison, the MWCNT/c-Ge only showed a specific capacity of 730.2mAhg−1 at the rate of 162.4mAg−1 at the 100th cycle. The MWCNT/a-Ge sample showed better performances as the MWCNT/a-Ge skipped the electrochemically-driven solid-state amorphization of crystalline Ge during the first lithiation.

Data Fusion and Fault Diagnosis for Flexible Arrayed pH Sensor Measurement System Based on LabVIEW

This paper concerns the data fusion (DF) and fault diagnosis (FD), which could increase the reliability of measured results when one sensing window was faulty. The flexible arrayed pH sensor was fabricated by radio frequency sputtering system and screen-printed technology, which the ruthenium dioxide was deposited on the polyethylene terephthalate substrate as sensitive membranes and the miniature reference electrodes were fabricated by screen-printed technology. We measured pH buffer solutions for five times and the flexible arrayed pH sensor had a wide sensing range of pH 1-13 solutions. The average sensitivity and linearity were 47.70 mV/pH and 0.839, respectively. We used the Laboratory Virtual Instrumentation Engineering Workbench to do deficient diagnosis which could remove the fault sensing window. The average DF with FD, self-adaptive data fusion with FD and coefficient of variance data fusion with FD could increase sensitivity and linearity ~ 22% and 0.14, respectively.

Characterizations of Nitrogen Doped Cupric Oxide Thin Films Deposited on Different Substrates for Solar Cell Applications

In this work, structural, optical and electrical properties of nitrogen doped (N-doped) cupric oxide (CuO) thin films deposited on <100> orientated n-type silicon, glass and polyethylene terephthalate substrates using reactive radio frequency sputtering system were investigated. X-ray diffraction results revealed that all films exhibited monoclinic CuO(-111) and have only slightly different structural properties for various substrates. Field effect scanning electron microscopy shown N-doped CuO on Si and glass are denser than on PET substrates and all have nanotriangle-like structure morphologies. The N-doped CuO thin films have an indirect band gap of around 1.30 eV. The resistively, carrier concentration and hall mobility of the N-doped CuO thin film on glass were 1.05 kΩ.cm, 6.70 x 1014 cm-3 and 8.86 cm2/V-s respectively. Furthermore, palladium formed ohmic contact characteristics for N-doped CuO on glass and PET but exhibited schottky contact characteristics for N-doped CuO on Si.

The Effects of Radio Frequency Sputtering of TiO<SUB>2</SUB> on Li[Li<SUB>0.07</SUB>Ni<SUB>0.38</SUB>Co<SUB>0.15</SUB>Mn<SUB>0.4</SUB>]O<SUB>2</SUB> Cathode for Lithium Ion Batteries

A radio frequency (RF) sputtering system is used to coat nano-thick TiO2 layer on the overlithiated layered metal oxide (OLO) electrode. The X-ray diffraction (XRD) and the field emission-scanning electron microscope (FE-SEM) images indicate amorphous TiO2 is coated on the top surface of the electrode with a thickness of approximately 20 nm for the 40 min sputtered sample. The sample sputtered for 40 minutes cycled at 90 mA g(-1) between 2 and 4.8 V versus Li+/Li has 15 mA h g(-1) more specific capacity at 100th cycle than that of the uncoated sample. In the voltage profiles, additional overpotential is unobservable upon sputtering TiO2 in comparison to that of the reference sample. Further analyses by the electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) demonstrate the sputtered sample has less electrolyte decomposition products on the surface than that of the reference sample. Moreover, in the case of sputtering, reduced amount of transition metal and Li2O are deposited on the surface of the counter electrode, Li. In summary, the sputtered TiO2 acts as nano-sized artificial solid electrolyte interface (SEI) layer, which protects the surface of the electrode and improves kinetic properties, leading to improved performance.

Fabrication and Investigation of Arrayed Glucose Biosensor Based on Microfluidic Framework

In this paper, an arrayed glucose biosensor is integrated to the poly-dimethylsiloxane microchannel as the microfluidic device for measuring the characteristics of the arrayed glucose biosensor at dynamical conditions. The radio frequency sputtering system and screen printed technology are used to fabricate the arrayed glucose biosensor. Furthermore, the computer numerical control technique is used to fabricate the microchannel mold. The polypyrrole differential reference electrode has good stable characteristics and provides a stable potential for the arrayed pH sensor. At static conditions, the average sensitivity and linearity of the arrayed pH sensor are 57.85 mV/pH and 0.977, respectively. And at dynamical conditions with 20 mL/min flow rate, the average sensitivity and linearity of the arrayed pH sensor are 66.73 mV/pH and 0.993, respectively. The arrayed pH sensor is dropped glucose sensing membranes as an arrayed glucose biosensor. The arrayed glucose biosensor is measured in different glucose concentrations at static conditions, and the average sensitivity and linearity of the arrayed glucose biosensor are 11.84 mV(100 mg/dl)-1 and 0.995, respectively. At dynamical conditions with 25 mL/min flow rate, the average sensitivity and linearity of the arrayed glucose biosensor are 30.41 mV(100 mg/dl)-1 and 0.975, respectively.

Fabrication of Vertical Standing Carbon Nanosheets for Heat Dissipation in a High-Power Light Emitting Diode

We fabricated vertical standing carbon nanosheets (CNSs) on various substrates by a radio-frequency sputter system. This 3D nanomaterial demonstrated the benefits of a large surface area and laminated nanostructure for heat dissipation in high-power light emitting diodes (LEDs). Experimental measurements of thermal resistance from the CNS assembly confirmed the enhancement of heat transfer. The efficiency of heat transfer depends on the spacing density per unit area of the CNS array and the ambient pressure. Optimizing in the CNS density gives a large surface area with good porosity that enhances the air molecules exchanging heat in high efficiency. In addition, an extra coating on the CNS can further improve the efficiency of thermal conductivity and the best performance discovered in this work was a decrease in thermal resistance of over 18%. A model based on one-dimensional heat conduction was proposed which solving the system's heat conductivity and heat transfer coefficient. Such model explains the reasons for thermal resistance deduction of different CNS densities and coatings. We therefore tested the use of CNSs as heat sinks for high-power LEDs, which suffer from declining light power output and shifts in the output wavelength when temperatures rise. When assisted by cooling from the CNS, the enhancement of light output and a 3.7 nm wavelength shift were achieved.

Optical and thermal properties of V2O5 thin films with crystallization

In order to show the crystallization behavior for various substrate temperatures we grew V2O5 films at different temperatures using a radio frequency sputtering system. Spectroscopic ellipsometry and a thermo-reflectance method were used to investigate the optical and the thermal properties of V2O5 films with different crystallization structures. The transmission spectra and the n and the k spectra revealed changes over the entire measurement range. The optical properties of the V2O5 films were affected by variations in the crystalline structure. The thermal conductivities of the V2O5 films with amorphous and crystalline structures were 0.838 Wm−1K−1 and 1.749 Wm−1K−1, respectively, and the thermal conductivity depended on the crystallization of the film. Furthermore, the variation of the crystalline structure led to changes in the optical and the thermal properties.

Effective conversion efficiency enhancement of solar cell using ZnO/PS antireflection coating layers

Abstract Zinc oxide (ZnO) film was deposited on a porous silicon (PS) layer using a radio frequency sputtering system while the PS layer was prepared by a photoelectrochemical etching method. The ZnO/PS layers were found to be an excellent antireflection coating (ARC), exhibiting exceptional light trapping at wavelengths ranging from 400 to 1000 nm because of their lowest effective reflectance. This, in turn, leads to increase the efficiency of solar cell to 18.15%. The ZnO film was highly oriented with the c -axis perpendicular to the PS layer. The average crystallite size of the PS and ZnO/PS layers were 17.06 and 17.94 nm, respectively. Photoluminescence emission peaks proved the nanocrystalline characteristic of the PS layer and the ZnO film. Raman measurements of the ZnO/PS layers were determined at room temperature and indicate that a high-quality ZnO nanocrystalline film was formed. In the current paper, ZnO/PS ARC layers are attractive and offer a promising technique to produce high-efficiency, low-cost solar cells.

The Effect on Physical, Electrical and Structural Parameters of RF Sputtered Molybdenum Thin Film

In this study, the physical, electrical, and structural parameter on radio frequency (RF) sputtered molybdenum thin film is investigated as a function of two deposition parameters: rf power, and argon (Ar) pressure. Films are sputtered onto the substrates nominally held in room temperature in a RF sputtering system at partial argon (Ar) pressure. A number of 10 films are deposited at 8 sccm of Ar pressure while varying the rf power from 90 to 360 watt. Besides, another set of 7 films are deposited at 240 watt RF power while varying the Ar pressure from 8 to 32 watts. All the films are characterized using FESEM, AFM, XRD, and four points probe. The analysis results substantiate that, to fabricate a low resistive thin layer of molybdenum (Mo) both sputtering power, and deposition time Ar pressure plays significant rules. It is found that, with the increase of the RF power (90 to 280 watt) the deposition rate increase from 1.2 A0/sec to 4.4 A0/sec. But at a RF power higher than 280 watt the deposition rate saturated and it does not increase as linear as before. Also resistivity continuously decreases as the RF power increases from 90 watt up to 270 watt, after that the resistivity remain almost same regardless the RF power increased. Besides, by varying the Ar pressure it is found that with the increase of the Ar pressure the deposition rate increase until 20 sccm (up to 2.4 A0/sec). With further increase of the Ar pressure deposition rate start reducing and reached 2.1 A0/sec at 32 sccm. Based on the above investigation and analysis optimized film is deposited and further analyzed. The surface roughness is analyzed using AFM characterization tool and found 27.4519 nm. The FESEM and XRD analysis along with the resistivity of the film is used to measure the strain of the deposited film and found a strain of less than 0.01% on the optimized film, which is essential for MEMS/NEMS device fabrication and energy harvesting applications.

Nanocrystalline ZnO film grown on porous silicon layer by radio frequency sputtering system

Nanocrystalline zinc oxide (ZnO) film was successfully synthesized on a porous silicon (PS) layer using radio frequency sputtering system. The PS layer was prepared by electrochemical etching method, resulting in 91% porosity with an average pore diameter of 6.2nm. ZnO film was highly oriented along the c-axis perpendicular to the PS layer. The average crystallite size was 17.06nm for the PS layer and 17.94nm for the ZnO film. The low value of the tensile strain 0.36% revealed ZnO nanocrystalline film preferred to grow along the c-axis. The photoluminescence emission spectra of the ZnO/PS layers exhibited three emission peaks: two peaks located at 387.5 and 605nm were due to the ZnO nanocrystalline film, and the third peak at 637.5nm was due to the nanocrystalline PS layer.

Graphitic carbon film formation under Ni templates by radio-frequency sputtering for transparent electrode applications

An alternate approach to the preparation of transfer-free graphitic carbon films is proposed in this paper. Using a standard radio-frequency sputtering system and a high-temperature annealing procedure, graphitic carbon films are prepared under Ni templates. The results demonstrate that carbon precipitation occurs at both Ni template interfaces. With repeated annealing procedures at 1100 °C, a sheet resistance of 1.36 × 104 Ω/□ can be achieved. Selective carbon film deposition has also been developed via pattern formation on the Ni templates. The results indicate the potential application of this method to transparent electrode formation.

Investigations on electrical characteristics and reliability properties of MOS capacitors using HfAlO x on n-GaAs substrates

Radio frequency sputtering system is employed to fabricate metal oxide semiconductor (MOS) capacitors using an ultra-thin layer of HfAlO x dielectric deposited on n-GaAs substrates with and without a Si interface control layer incorporated in between the dielectric and the semiconductor. Measurements are performed to obtain capacitance voltage ( C– V) and current voltage ( I– V) characteristics for GaAs/Si/HfAlO x and GaAs/HfAlO x capacitors under different constant voltage and constant current stress conditions. The variation of different electrical parameters such as change in interface trap density, hysteresis voltage with various values of constant voltage stress and the dependence of flat band voltage, fractional change in gate leakage current density, etc. with stress time are extracted from the C– V and I– V data for capacitors with and without a Si interlayer. Further the trap charge density and the movement of trap centroid are investigated for various injected influences. The dielectric breakdown and reliability properties of the dielectric films are studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t bd ⩾ 1350 s) is observed for HfAlO x gate dielectric with a silicon inter-layer under the high constant voltage stress at 8 V. Compared to capacitors without a Si interlayer, MOS capacitors with a Si interlayer exhibit improved electrical and breakdown characteristics, and excellent interface and reliability properties.

Improved performance of a crystalline silicon solar cell based on ZnO/PS anti-reflection coating layers

A porous silicon (PS) layer was prepared by photoelectrochemical etching (PECE), and a zinc oxide (ZnO) film was deposited on a PS layer using a radio frequency (RF) sputtering system. The surface morphology of the PS and ZnO/PS layers was characterised using scanning electron microscopy (SEM). Nano-pores were produced in the PS layer with an average diameter of 5.7 nm, which increased the porosity to 91%. X-ray diffraction (XRD) of the ZnO/PS layers shows that the ZnO film is highly oriented along the c-axis perpendicular to the PS layer. The average crystallite size of the PS and ZnO/PS layers are 17.06 and 17.94 nm, respectively. The photoluminescence (PL) emission spectra of the ZnO/PS layers present three emission peaks, two peaks located at 387.5 and 605 nm due to the ZnO nanocrystalline film and a third located at 637.5 nm due to nanocrystalline PS. Raman measurements of the ZnO/PS layers were performed at room temperature (RT) and indicate that a high-quality ZnO nanocrystalline film was formed. Optical reflectance for all the layers was obtained using an optical reflectometer. The lowest effective reflectance was obtained for the ZnO/PS layers. The fabrication of crystalline silicon (c-Si) solar cells based on the ZnO/PS anti-reflection coating (ARC) layers was performed. The I– V characteristics of the solar cells were studied under 100 mW/cm 2 illumination conditions. The ZnO/PS layers were found to be an excellent ARC and to exhibit exceptional light-trapping at wavelengths ranging from 400 to 1000 nm, which led to a high efficiency of the c-Si solar cell of 18.15%. The ZnO/PS ARC layers enhance and increase the efficiency of the c-Si solar cell. In this paper, the fabrication processes of the c-Si solar cell with ZnO/PS ARC layers are an attractive and promising technique to produce high-efficiency and low-cost of c-Si solar cells.

Investigation of charge trapping and breakdown characteristics of sputtered-Y 2O 3 on n-GaAs substrates

Metal–oxide–semiconductor (MOS) capacitors fabricated by depositing yttrium oxide (Y 2O 3) using radio frequency sputtering system on top of n-GaAs substrates have been investigated. To study the interface properties, charge trapping behavior and breakdown characteristics of Y 2O 3 gate dielectric, the MOS capacitors were subjected to constant current stress, high pulse voltage stress and high constant voltage stress. The average value of the cross section of generated traps during electrical stress has been determined from our experimental data. Further the trap charge density, its distribution and location have been investigated by measurements on application and subsequent withdrawal of high pulse voltage stress. Additionally, stress induced leakage current density and time dependent dielectric breakdown characteristics have been obtained and time-to-breakdown exceeding 840 s is observed for Y 2O 3 gate dielectrics directly deposited on n-GaAs. Our experimental results have been analyzed with simple analytical formulae available in the literature.

Characteristics of Ultra-Wideband Bandpass YBCO Filter With Impendence Stub

A compact ultra-wideband (UWB) bandpass filter (BPF) is presented for applications to short-range and high-speed wireless communication. Superconducting YBa2Cu3Oy (YBCO) stepped impedance resonators and coupled-line sections as inverter circuits are designed to form the basic filter structure. In the filter design, connected high-low stepped impedance microstrip lines construct the resonators, and open-stub lines are utilized to add return-loss poles in the pass-band and create transmission zeros in the lower/upper stop-band region. Simulation results show that the passband from 3.0 GHz to 8.6 GHz has a 3-dB fractional bandwidth of 99 percent, computed insertion losses better than 0.03 dB, and return losses greater than 15 dB. Rejection levels in the upper/lower stop-bands are better than 20 dB. For fabrication, high-Tc superconducting (HTS) YBCO films were deposited on double-side-polished 0.5-mm-thick MgO (100) substrates by a radio-frequency sputtering system. The filter was made out of patterned double-sided deposited YBCO films integrated with a gold-coated housing. The realized HTS UWB BPF shows a wide passband within 2.9-8.3 GHz with a maximum insertion loss of 0.88 dB. The measured results show good HTS UWB BPF performance. Moreover, the temperature-dependent frequency responses and the insertion loss can be described by the modified two-fluid-model-based formulas, indicating that the frequency shift and the increase in insertion loss for HTS BPF are both dominated by the temperature dependence of the magnetic penetration depth.

Dependence of the Heterojunction Diode Characteristics of ZnO/ZnO/p-Si(111) on the Buffer Layer Thickness

In this study, the effects of an annealed buffer layer with different thickness on heterojunction diodes based on the ZnO/ZnO/p-Si(111) systems were reported. The effects of an annealed buffer layer with different thickness on the structural, optical, and electrical properties of zinc oxide (ZnO) films on p-Si(111) were also studied. Before zinc oxide (ZnO) deposition, different thicknesses of ZnO buffer layer, 10 nm, 30 nm, 50 nm and 70 nm, were grown on p-Si(111) substrates using a radio-frequency sputtering system; samples were subsequently annealed at <TEX>$700^{\circ}C$</TEX> for 10 minutes in <TEX>$N_2$</TEX> in a horizontal thermal furnace. Zinc oxide (ZnO) films with a width of 280nm were also deposited using a radio-frequency sputtering system on the annealed ZnO/p-Si (111) substrates at room temperature; samples were subsequently annealed at <TEX>$700^{\circ}C$</TEX> for 30 minutes in <TEX>$N_2$</TEX>. In this experiment, the structural and optical properties of ZnO thin films were studied by XRD (X-ray diffraction), and room temperature PL (photoluminescence) measurements, respectively. Current-voltage (I-V) characteristics were measured with a semiconductor parameter analyzer. The thermal tensile stress was found to decrease with increasing buffer layer thickness. Among the ZnO/ZnO/p-Si(111) diodes fabricated in this study, the sample that was formed with the condition of a 50 nm thick ZnO buffer layer showed a strong c-axis preferred orientation and I-V characteristics suitable for a heterojunction diode.

Research of Titanium Dioxide Compact Layer Applied to Dye-Sensitized Solar Cell with Different Substrates

In this study, the titanium dioxide (TiO2) powder was annealed to form the colloid and applied to the flexible dye-sensitized solar cell (FDSSC). The structure is that the TiO2 compact layer was fabricated on transparent conducting oxide (TCO) substrate by radio frequency sputtering system (R. F. sputtering system). The compact layer can prevent and suppress the contact and the reverse current created between electrolyte and TCO plastic substrate. So that it can enhance the current density (Jsc) and conversion efficiency (η) of FDSSC with ITO-PET substrate. In accordance with the experimental results, the η were increased from 1.18% to 1.62%. On the other hand, a DSSC with TiO2 compact layers are increased the conversion efficiency from 4.01% to 5.11% with FTO substrate.

Sputtered Indium Tim Oxide Thin Films Deposited on Glass Substrate for Photovoltaic Application

Polycrystalline indium tin oxide (ITO) films were prepared on glass substrates by radio frequency (RF) sputtering system from a high density target (90wt. In2O3 and 10 wt. %SnO2). X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) experiments were performed to study the structure and the surface morphology of these samples. The results show that the as-deposited ITO thin films deposited on glass have a texture, as the film grows the preferred orientation changes from to . The lattice parameters are found to be larger than the bulk value, indicating that the samples are under a tensile stress. The grain size increases with increasing thickness. SEM images show a dense granular structure with grains having different shapes and sizes. After deposition, the samples have been annealed in air at temperature T around 400°C for 1 hour. We found that the texture becomes stronger after the annealing treatment. A large increase in the grain size after annealing is also observed. The lattice constant decreases with T to become closer to the bulk value, i.e. annealing seems to relieve the stress present in the as-deposited films. The optical transmision is greater than 80 % in the visible region.The refractive index n values are found to be in the 1.7-1.9 range. The energy gap values are between 3.58 and 3.88 eV .

Diode Characteristics of n-ZnO/p-Si (111) depend on Si Substrate Doping

We report on the dependence of the diode characteristics of n-ZnO on p-type Si (111) on the dopant concentration in the Si (111) substrate. Silicon substrates were used with a high resistivity (p) (∼1 − 20 Ω·cm) and a low resistivity (p) (∼0.004 − 0.0055 Ω·cm). Zinc-oxide films were deposited using a radio-frequency sputtering system on the p and p-Si (111) substrates at room temperature. The films were subsequently annealed at 800 ◦C in air and in N2 in a horizontal thermal furnace to change the electron carrier concentration. By investigating the current and the voltage characteristics of the diodes, we discovered that the diode characteristics depended on the carrier concentration. We discuss the relationship between the carrier concentration and the emission properties of n-ZnO/p-Si diodes. The devices exhibited excellent rectification behavior and diode characteristics, having a turn-on voltage of about 2.3 − 2.7 V and a series resistance between 215 and 330 Ω. The diode characteristics were modified by thermal annealing in an ambient, and n-ZnO/p-Si (111) heterojunction diodes emitted yellowish light at voltages over 10 V.