Study of bias voltage effect on the performance of ta-C coating prepared by high power impulse magnetron sputtering

The mechanical and frictional properties of ta-C coatings deposited on the substrate surface affect applications in the field of cutting tools and wear-resistant components.In this paper,the effect of bias parameters on the performance of ta-C coatings was investigated based on high power impulse magnetron sputtering(HiPIMS)technology.The results show that bias voltage has a significant effect on the deposition rate,structure,and wear resistance of the coating.In the range of bias voltage−50 V to−200 V,the ta-C coating performance was the best under bias voltage−150 V.The thickness reached 530.4 nm,the hardness value reached 35.996 GPa,and the bonding force in-creased to 14.2 N.The maximum sp3 bond content was 59.53% at this condition.

EFFECT OF GRID BIAS ON DEPOSITION OF NANOCRYSTALLINE DIAMOND FILMS

A positive grid bias and a negative substrate bias voltages are applied to the self-made hot filament chemical vapor deposited （HFCVD） system. The high quality nanocrystalline diamond （NCD） film is successfully deposited by double bias voltage nucleation and grid bias voltage growth. The Micro-Raman XRD SEM and AFM are used to investigate the diamond grain size, microstructure, surface morphology, and nucleation density. Results show that the obtained NCD has grain size of about 20 nm. The effect of grid bias voltage on the nucleation and the diamond growth is studied. Experimental results and theoretical analysis show that the positive grid bias increases the plasma density near the hot filaments, enhances the diamond nucleation, keeps the nanometer size of the diamond grains, and improves the quality of diamond film.

Effect of bias voltage on microstructure and nanomechanical properties of Ti films

In order to investigate nanomechanical properties of nanostructured Ti metallic material, pure Ti films were prepared by magnetron sputtering at the bias voltage of 0-140 V. The microstructure of Ti films was characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and high-resolution transmission electron microscopy（HRTEM）. It is interesting to find that the microstructure of pure Ti films was characterized by the composite structure of amorphous-like matrix embodied with nanocrystallines, and the crystallization was improved with the increase of bias voltage. The hardness of Ti films measured by nanoindentation tests shows a linear relationship with grain sizes in the scale of 6-15 nm. However, the pure Ti films exhibit a soft tendency characterized by a smaller slope of Hall-Petch relationship. In addition, the effect of bias voltage on the growth orientation of Ti films was discussed.

Self-Aligned InGaP/GaAs Power HBTswith a Low Bias Voltage

A self aligned InGaP/GaAs power HBTs for L band power amplifier with low bias voltage are described.Base emitter metal self aligning,air bridge,and wafer thinning are used to improve microwave power performance.A power HBT with double size of emitter of (3μm×15μm)×12 is fabricated.When the packaged HBT operates in class AB at a collector bias of 3V,a maximum 23dBm output power with 45% power added efficiency is achieved at 2GHz.The results show that the InGaP/GaAs power HBTs have great potential in mobile communication systems operating at low bias voltage.

THE EFFECTS OF PULSE BIAS VOLTAGE AND N_2 PARTIAL PRESSURE ON TiAlN FILMS OF ARC ION PLATING (AIP)

Owing to the characteristics of arc ion plating(AIP) technique, the structure and composition of TiAlN films can be tailored by controlling of various parameters such as compositions of target materials, N2 partial pressure, substrate bias and so on. In this study, several titanium aluminum nitride films were deposited on 1Cr11Ni2W2MoV steel for compressor blade of areo-engine under different d.c pulse bias voltage and nitrogen partial pressure. The effects of substrate pulse bias and nitrogen partial pressure on the deposition rate, droplet formation, microstruture and elemental component of the films were investigated.

Effects of Bias Voltage on the Structure and Mechanical Properties of Thick CrN Coatings Deposited by Mid-Frequency Magnetron Sputtering

Thick CrN coatings were deposited on Si （111） substrates by electron source assisted mid-frequency magnetron sputtering working at 40 kHz. The deposition rate, structure, and microhardness of the coatings were strongly influenced by the negative bias voltage （Vb）. The deposition rate reached 8.96 μm/h at a Vb of -150 V. X-ray diffraction measurement revealed strong CrN （200） orientation for films prepared at low bias voltages. At a high bias voltage of Vb less than -25 V both CrN （200） and （111） were observed. Large and homogeneous grains were observed by both atomic force microscopy and scanning electron microscopy in samples prepared under optimal conditions. The samples exhibited a fibrous microstructure for a low bias voltage and a columnar structure for VD less than -150 V.

Adhesion of NiCu Films DC Biased Plasma-Sputter-Deposited on MgO (001)

NiCu films about 60nm thick were deposited on MgO (001) substrates at 230℃ by DC plasma-sputtering at 2.7kV and 8mA in pure Ar gas using a Ni90Cu10 target. A DC bias voltage of 0, 60, 110 or 140V was applied to the substrate during deposition. The adhesion of the film to the substrate was studied using a scratch test as a function of . The application of is very effective in increasing the adhesion of the film to the substrate. In conclusion, the adhesion increases with cleaning the substrate surface by sputtering off impurity admolecules during the film initial formation due to the energetic Ar ion particle bombardment.

Influence of Negative Bias Voltage on the Mechanical and Tribological Properties of MoS_2/Zr Composite Films

MoS2/Zr composite films were deposited on the cemented carbide YT14 （WC＋14%TiC＋6%Co） by medium-frequency magnetron sputtered and coupled with multi-arc ion plated techniques.The influence of negative bias voltage on the composite film properties,including adhesion strength,micro-hardness,thickness and tribological properties were investigated.The results showed that proper negative bias voltage could significantly improve the mechanical and tribological properties of composite films.The effects of negative bias voltage on film properties were also put forward.The optimal negative bias voltage was -200 V under this experiment conditions.The obtained composite films were dense,the adhesion strength was about 60 N,the thickness was about 2.4 μm,and the micro-hardness was about 9.0 GPa.The friction coefficient and wear rate was 0.12 and 2.1×10-7 cm3/N·m respectively after 60 m sliding operation against hardened steel under a load of 20 N and a sliding speed of 200 rev·min-1.

Effect of bias voltage on microstructure,mechanical and tribological properties of TiAlN coatings

TiAlN multilayer coatings composed of TiAl and TiAlN layers were deposited on ZL109 alloys using filtered cathodic vacuum arc(FCVA)technology.The effect of bias voltage on the microstructure and properties of the coating was systematically studied.The results show that the coating exhibits a multi-phase structure dominated by TiAlN phase.As the bias voltage increases,the orientation of TiAlN changes from(200)plane to(111)plane due to the increase of atomic mobility and lattice distortion.The hardness,elastic modulus and adhesion of the coating show the same trend of change,that is,first increase and then decrease.When the bias voltage is 75 V,the coating exhibits the highest hardness(~30.3 GPa),elastic modulus(~229.1 GPa),adhesion(HF 2)and the lowest wear rate(~4.44×10^(−5)mm^(3)/(N·m)).Compared with bare ZL109 alloy,the mechanical and tribological properties of TiAlN coated alloy surface can effectively be improved.

Relationship between bias voltage and microstructure as well as properties of CrAlYN films

In this work, a series of CrA1YN films doped with 1 at.% yttrium were deposited by unbalanced reactive magnetron sputtering under different bias voltages, The effects of bias voltage on microstrncture and properties of the CrA1YN films were subsequently investigated. It is found that all the as-deposited films have similar chemical composition and crystalline structure. However, the bias voltage has significant impact on the mechanical properties and oxidation resistance of the resulting films. Namely, the film deposited at 100 V has the highest hardness and best oxidation resistance, which are mainly attributed to its denser structure and higher A1 content than others. In addition, the film obtained at 100 V exhibits superior oxidation resistance even at 1000℃, and good friction and wear properties at 600 and 800 ℃, and the latter two are mainly ascribed to the formation of compact transfer layer on the worn surfaces. However, this film experienced obvious wear loss at low testing temperatures （i.e., 200 and 400 ℃） due to the serious abrasive wear.

Influence of substrate bias voltage on the microstructure of nc-SiO_x:H film

Amorphous silicon oxide containing nanocrystalline silicon grain（nc-SiOx：H） films are prepared by a plasmaenhanced chemical vapor deposition technique at different negative substrate bias voltages.The influence of the bias voltage applied to the substrate on the microstructure is investigated.The analysis of x-ray diffraction spectra evidences the in situ growth of nanocrystalline Si.The grain size can be well controlled by varying the substrate bias voltage,and the largest size is obtained at 60 V.Fourier transform infrared spectra studies on the microstructure evolutions of the nc-SiOx：H films suggest that the absorption peak intensities,which are related to the defect densities,can be well controlled.It can be attributed to the fact that the negative bias voltage provides a useful way to change the energies of the particles in the deposition process,which can provide sufficient driving force for the diffusion and movement for the species on the growing surface and effectively passivate the dangling bonds.Also the larger grain size and lower band gap,which will result in better photosensitivity,can also be obtained with a moderate substrate bias voltage of 60 V.

Effect of applied dc bias voltage on composition, chemical bonding and mechanical properties of carbon nitride films prepared by PECVD

Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and chemical bonding of the resulting films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The mechanical properties such as hardness and elastic modulus of the films were evaluated using nano-indentation. As the results, the Raman spectra, showing the G and D bands, indicate the amorphous structure of the films. XPS and FTIR measurements demonstrate the existence of various carbon-nitride bonds in the films and the hydrogenation of carbon nitride phase. The composition ratio of N to C, the nano-hardness and the elastic modulus of the carbon nitride films increase with increasing dc bias voltage and reach the maximums at a dc bias voltage of 300 V, then they decrease with further increase of the dc bias voltage. Moreover, the XRD analyses indicate that the carbon nitride film contains some polycrystalline C3N4 phase embedded in the amorphous matrix at optimized deposition condition of dc bias voltage of 300 V.

Discrimination Voltage and Overdrive Bias Dependent Performance Evaluation of Passively Quenched SiC Single-Photon-Counting Avalanche Photodiodes

In many critical civil and emerging military applications, low-level UV detection, sometimes at single photon level, is highly desired. In this work, a mesa-type 4H-SiC UV avalanche photodiode （APD） is designed and fabricated, which exhibits low leakage current and high avalanche gain. When studied by using a passive quenching circuit, the APD exhibits self-quenching characteristics due to its high differential resistance in the avalanche region. The single photon detection efficiency and dark count rate of the APD are evaluated as functions of discrimination voltage and over-drive voltage. The optimized operation conditions of the single photon counting APD are discussed.

Capacitive micromachined ultrasonic transducer as a resonant temperature sensor

Resonant temperature sensors have drawn considerable attention for their advantages such as high sensitivity,digitized signal output and high precision.This paper presents a new type of resonant temperature sensor,which uses capacitive micromachined ultrasonic transducer(CMUT)as the sensing element.A lumped electro-mechanical-thermal model was established to show its working principle for temperature measurement.The theoretical model explicitly explains the thermally induced changes in the resonant frequency of the CMUT.Then,the finite element method was used to further investigate the sensing performance.The numerical results agree well with the established analytical model qualitatively.The numerical results show that the resonant frequency varies linearly with the temperature over the range of 20℃to 140℃ at the first four vibrating modes.However,the first order vibrating mode shows a higher sensitivity than the other three higher modes.When working at the first order vibrating mode,the temperature coefficient of the resonance frequency(TCf)can reach as high as-1114.3 ppm/℃ at a bias voltage equal to 90%of the collapse voltage of the MCUT.The corresponding nonlinear error was as low as 1.18%.It is discovered that the sensing sensitivity is dependent on the applied bias voltages.A higher sensitivity can be achieved by increasing the bias voltages.

Microstructure and residual stress of TiN films deposited at low temperature by arc ion plating

The TiN films were deposited on 316 L stainless steel substrates at low temperature by arc ion plating. The influences of substrate bias voltage and temperature on microstructure, residual stress and mechanical properties of the films were investigated by EDS, SEM, XRD and nanoindenter tester, respectively. The results showed that the TiN films were highly oriented in（111） orientation with a face-centered cubic structure. With the increase of substrate bias voltage and temperature, the diffraction peak intensity increased sharply with simultaneous peak narrowing, and the small grain sizes increased from 6.2 to 13.8 nm. As the substrate temperature increased from 10 to 300℃, the residual compressive stress decreased sharply from 10.2 to 7.7 GPa, which caused the hardness to decrease from 33.1 to 30.6 GPa, while the adhesion strength increased sharply from 9.6 to 21 N.

Pure spin polarized transport based on Rashba spin orbit interaction through the Aharonov Bohm interferometer embodied four-quantum-dot ring

The spin-polarized linear conductance spectrum and current–voltage characteristics in a four-quantum-dot ring embodied into Aharonov–Bohm （AB） interferometer are investigated theoretically by considering a local Rashba spin–orbit interaction. It shows that the spin-polarized linear conductance and the corresponding spin polarization are each a function of magnetic flux phase at zero bias voltage with a period of 2π, and that Hubbard U cannot influence the electron transport properties in this case. When adjusting appropriately the structural parameter of inter-dot coupling and dot-lead coupling strength, the electronic spin polarization can reach a maximum value. Furthermore, by adjusting the bias voltages applied to the leads, the spin-up and spin-down currents move in opposite directions and pure spin current exists in the configuration space in appropriate situations. Based on the numerical results, such a model can be applied to the design of a spin filter device.

Structural and mechanical properties of amorphous carbon films deposited by the dual plasma technique

Direct current metal filtered cathodic vacuum arc （FCVA） and acetylene gas （C2H2） were wielded to synthesize Ti-containing amorphous carbon films on Si （100）. The influence of substrate bias voltage and acetylene gas on the microstructure and mechanical properties of the films were investigated. The results show that the phase of TiC in the （111） preferential crystallographic orientation exists in the film,and the main existing pattern of carbon is sp2. With increasing the acetylene flow rate,the contents of Ti and TiC phase of the film gradually reduce; however,the thickness of the film increases. When the substrate bias voltage reaches -600 V,the internal stress of the film reaches 1.6 GPa. The micro-hardness and elastic modulus of the film can reach 33.9 and 237.6 GPa,respectively,and the friction coefficient of the film is 0.25.

Spin-dependent Transport Properties of CrO_2 Micro Rod

The Cr O2 micro rod powder was synthesized by decomposing the Cr O3 flakes at a specific temperature to yield precursor and annealing such a precursor in a sealed glass tube. The magneto-transport properties have been measured by a direct current four-probe method using a Cu/Cr O2rods/colloidal silver liquid electrode sandwich device. The largest magnetoresistance(MR) around *72 % was observed at 77 K with applied current of 0.05 l A. The non-linear I–V curve indicates a tunneling type transport properties and the tunneling barrier height is around 2.2 ± 0.04 e V at 77 K, which is obtained with fitting the non-linear I–V curves using Simmons' equation. A mixing of Cr oxides on the surface of Cr O2 rod observed by X-ray photoemission spectroscopy provides a tunneling barrier rather than a single phase of Cr2O3 insulating barrier. The MR shows strong bias voltage dependence and is ascribed to the two-step tunneling process.

Discharge Characteristics of Bubbles at Interface Between AIN Ceramic and FC-72 Liquid

In order to evaluate the insulation of two-phase immersion cooling in the HV power electronic package,the insulation degradation of the dielectric interface induced by bubbles is investigated.In this paper,a test strategy with 50 Hz unipolar DC and AC combined voltage for partial discharge(PD)at boiling interface of AlN ceramic is proposed.The insulation threshold of an AlN ceramic surface is acquired in several dielectric environments,such as air,FC-72 liquid(FC-72,a Fluorinert^(TM) from 3^(TM)),FC-72 vapor,and boiling state of FC72.This reveals the deterioration of boiling on the insulation of the surface immersed in the dielectric refrigerant.To investigate the mechanism of the PD feature at the boiling interface,the PD patterns of the unrestricted bubble and the accumulated bubble are acquired and contrastively analyzed.Combined with the feature of the back discharge and the bubble behavior,the charged vapor-ceramic interface is relatively stable due to the accumulated vapor layer.This stability of the charged vaporceramic interface is broken if the bubble is unrestricted.Besides,it is discovered that the vapor-liquid interface inside the bubble may be another charged interface,which can also trigger a back discharge.

Electrically Driven Nonresonant Single Molecular Switches

Electrical switching of a single-molecule junction provides a practical module to perform sophisticated operations in electronic devices.However,designing an all-electrically-driven molecular switch is a great challenge.Here,we experimentally and theoretically investigated the charge transport characteristics of isoindigo(ISO)-molecules at the single-molecule level using the scanning tunneling microscope break junction technique.We find that the single-molecule junctions of ISO-molecules display bias voltage-driven switching characteristics.These switches are realtime,reversible,and nondestructive under low-bias voltages.Experimental results show that the mechanism of the switch is not the transition from nonresonant charge transport to resonant charge transport,but it is the shift of the frontier orbital energy levels of ISO-molecules and the change of the interfacial electronic coupling with bias voltage.Our results will advance the design of high-performance bias voltage-driven molecular switches.