Negative Substrate Bias Research Articles

Study of the Pattern Preparation and Performance of the Resistance Grid of Thin-Film Strain Sensors.

The thin-film strain sensor is a cutting-force sensor that can be integrated with cutting tools. The quality of the alloy film strain layer resistance grid plays an important role in the performance of the sensor. In this paper, the two film patterning processes of photolithography magnetron sputtering and photolithography ion beam etching are compared, and the effects of the geometric size of the thin-film resistance grid on the resistance value and resistance strain coefficient of the thin film are compared and analyzed. Through orthogonal experiments of incident angle, argon flow rate, and substrate negative bias in the ion beam etching process parameters, the effects of the process parameters on photoresist stripping quality, etching rate, surface roughness, and resistivity are discussed. The effects of process parameters on etching rate, surface roughness, and resistivity are analyzed by the range method. The effect of substrate temperature on the preparation of Ni Cr alloy films is observed by scanning electron microscope. The surface morphology of the films before and after ion beam etching is observed by atomic force microscope. The influence of the lithography process on the surface quality of the film is discussed, and the etching process parameters are optimized.

Growth of diamond-like carbon films with significant nanocrystalline phases in a low-pressure high-density CH4 plasma in ICP-CVD: Effect of negative dc substrate bias

Working at relatively low-temperature and low-pressure, the development and optimization of diamond-like carbon (DLC) films with significant nanodiamond components on inexpensive glass substrates, without conventional pre-treatment by diamond powders, is the main objective of the present work. Using the most familiar CH4-precursors diluted by Ar in a high-density plasma triggered at high rf power (900 W) in a planar inductively-coupled plasma chemical vapour deposition (ICP-CVD) system, DLC thin-films are prepared via optimization in the flow rate of the precursor gas at 30 mTorr (∼4 Pa) pressure and 450 °C substrate temperature and, further by applying negative dc-bias to the substrates. The optimized samples obtained with negative substrate-bias possess good crystalline properties. From Raman results, the most crystalline sample is obtained with characteristic minimum ID/IG ratio reduced from 0.75 to 0.61, maximum IDia/ID enhanced from 0.94 to 1.09, and the sp3 hybridized CC bonds increased from 44% to ∼64% at a substrate-bias of –40 V. The residual stress, and the optical band gap were calculated from Raman analysis. The optimized DLC film exhibits a high optical band gap (3.71 eV) as calculated from Tauc’s plot analysis of the UV–Vis data. The well-identified 〈111〉 crystallographic planes in the TEM micrograph demonstrate a significant fraction of nanocrystalline diamond component in the optimum DLC film.

The influence of substrate bias on the surface morphology, microstructure and mechanical behaviour of TiNiN coatings

The application of a negative substrate bias during physical vapor deposition can have important effects on the surface morphology, structure and properties of ceramic-based coatings. In this study, a number of TiNiN coatings were prepared onto AISI M2 steel substrates via cathodic arc deposition method by employing a range of different negative substrate bias voltages. The objective of this work is to study the influence of bias voltage on the surface morphology, microstructure and mechanical characteristics of these thin films. A change from a fine columnar grained structure to highly refined equiaxed grains was noted with increasing bias from 0 to −50 V, associated with the energetic ion bombardment at the higher substrate bias. A very high hardness value of ∼ 34.2 GPa was attained at a −100 V substrate bias, which was attributed to the synergistic effects of a number of factors such as the presence of compressive residual stresses, solid solution hardening effects along with grain refinement. In addition, significant reduction in the density of microparticle-related defects generated in these coatings was achieved at ≥ -100 V, which can presumably be ascribed to the higher repulsive force induced at higher substrate bias values.

Effect of Magnetron Sputtering Deposition Conditions on the Mechanical and Tribological Properties of Wear-Resistant Titanium Carbonitride Coatings

In the present work, the titanium carbonitride coatings were deposited by the reactive magnetron sputtering method at different substrate bias: 0, −70 V, and −100 V. The effect of the substrate bias on the structure, composition, and mechanical and tribological properties of titanium carbonitride coatings was studied. Scanning electron microscopy, nanoindentation, sliding wear test (ball-on-disk method), X-ray phase, and elemental analysis methods were used to evaluate the tribological properties and microstructure of the thin coatings. The dependencies obtained resulted in the determination of the most preferred mode of deposition by magnetron sputtering at a negative substrate bias in an atmosphere of argon–acetylene–nitrogen.

Construction and Characterization of TiN/Si3N4 Composite Insulation Layer in TiN/Si3N4/Ni80Cr20 Thin Film Cutting Force Sensor.

The measurement of cutting force is an effective method for machining condition monitoring in intelligent manufacturing. Titanium nitride films and silicon nitride films were prepared on 304 stainless steel substrates by DC-reactive magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). The effects of substrate negative bias and nitrogen flow on the surface microstructures of TiN film were investigated. The smoothness of the film is optimal when the bias voltage is −60 V. X-ray diffraction (XRD) analysis was performed on the samples with the optimal smoothness, and it was found that when the nitrogen flow rate was higher than 2 sccm, the titanium nitride film had a mixed phase of TiN(111) and (200). It is further revealed that the change of peak intensity of TiN(200) can be enhanced by nitrogen flow. Through atomic force microscopy (AFM), it is found that the stronger the intensity of the TiN (200) peak, the smoother the surface of the film is. Finally, the effect of different film thicknesses on the hardness and toughness of the TiN/Si3N4 film system was studied by nanoindentation experiments. The nanohardness (H) of the TiN/Si3N4 film can reach 39.2 GPa, the elastic modulus (E) is 480.4 GPa, the optimal toughness value (H3/E2) is 0.261 GPa, and the sample has good insulation performance. Linear fitting of the film’s toughness to nanohardness shows that TiN/Si3N4 films with higher hardness usually have a higher H3/E2 ratio.

Gold-tantalum alloy films deposited by high-density-plasma magnetron sputtering

Gold-tantalum alloy films are of interest for biomedical and magnetically-assisted inertial confinement fusion applications. Here, we systematically study the effects of substrate tilt (0°–80°) and negative substrate bias (0–100 V) on properties of ≲3-μm-thick films deposited by high-power impulse magnetron sputtering (HiPIMS) from a Au–Ta alloy target (with 80 at. % of Ta). Results reveal that, for all the substrate bias values studied, an increase in substrate tilt leads to a monotonic decrease in film thickness, density, residual compressive stress, and electrical conductivity. Larger substrate bias favors the formation of a body-centered cubic phase, with films exhibiting lower column tilt and higher density, electrical conductivity, and residual compressive stress. These changes are attributed to metal atom ionization effects, based on the lack of correlation with distributions of landing energies and incident angles of depositing species as calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. By varying substrate tilt and bias in HiPIMS deposition, properties of Au–Ta alloy films can be controlled in a very wide range, including residual stress from −2 to +0.5 GPa, density from 12 to 17 g/cm3, and the electrical resistivity from 50 to 4500 μΩ cm, enabling optimum deposition conditions to be selected for specific applications.

Plasma-enhanced atomic layer deposition of titanium molybdenum nitride: Influence of RF bias and substrate structure

In this work, TiMoN thin films were deposited by plasma-enhanced atomic layer deposition with an equal number of Ti and Mo precursor exposures at a substrate temperature of 250 °C. Tetrakis(dimethylamido) titanium and bis(tert-butylimido)bis(dimethylamido) molybdenum were used as sources for Ti and Mo, respectively. N2 and N2/H2 plasma were used, respectively, for TiN and MoN cycles as a source for N. Negative RF substrate bias voltage of magnitude, |Vbias|, of 0, 31, 62, 125, and 188 V were applied during the plasma half cycle. Nanocrystalline rock salt crystal structures were found by x-ray diffraction for films deposited on single-crystal Si and Si-thermal oxide substrates. Applying |Vbias| generated voids by the bombardment of high-energy ions, lowering the density. Further increase of |Vbias| caused the annihilation of voids and a slight increase in density. Four-point probe measurement showed increased electrical resistivity due to a reduction in grain size caused by continuous renucleation during growth. High-energy ions at high |Vbias| sputtered away the films resulting in low growth rates. Stripe test revealed inferior wear rates and coefficients of friction at higher |Vbias| due to low-density porous films. Epitaxial films deposited on c-plane sapphire had (111) orientation and considerable mosaicity with twinned domains rotated at 60° to each other.

Influence of Metal Substitution and Ion Energy on Microstructure Evolution of High-Entropy Nitride (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) Films

Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr, 0.12 ≤ x ≤ 0.30) films were deposited on Si(100) substrates at 400 °C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from ∼10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 ≤ x ≤ 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1–x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached ∼3.1 GPa in Hf- and Cr-containing films deposited at −130 V. The hardness reached a maximum value of 28.0 ± 1.0 GPa at a negative bias ≥100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1–x films can thus guide the design of protective high-entropy nitride films.

Nanoindentation mechanical properties of CoCrFeNi high entropy alloy films

ABSTRACT CoCrFeNi high-entropy alloy films were deposited under different substrate bias by magnetron sputtering using a simple splicing target. The hardness, elastic modulus and creep properties of the films were measured by nanoindentation. The results showed that with the increase in substrate bias, CoCrFeNi films were always mainly composed of FCC phase and demonstrated smooth and dense surface with uniform distribution of elements, but the preferred orientation of the films changed from FCC (200) to no preferred and then to FCC (111). The hardness and elastic modulus of CoCrFeNi films were not sensitive to the strain rate of nanoindentation (0.05–0.15 s−1). The maximum hardness of the film was about 10.4 GPa under the substrate bias of –50 V, while the maximum elastic modulus of 249.8 GPa appeared under the substrate bias of –200 V. The applied negative substrate bias (−50 V ~ –200 V) could improve the elastic modulus and creep properties of the films.

Effect of substrate bias voltage on the mechanical properties of AlTiN/CrTiSiN multilayer hard coatings

During physical vapor deposition (PVD), bias voltage is usually applied to the substrate for tuning the ion energies and tailoring the coating structure and mechanical properties of a protective hard coating for specific applications. In the present study, AlTiN/CrTiSiN multilayer coatings were deposited by a multisource cathodic arc ion deposition system with negative substrate bias voltages ranging from −20 to −180 V. During the coating process, graded CrN, CrN/AlTiN and CrTiSiN were deposited as interlayers to enhance adhesion strength of the coatings. Multisources of Cr, TiSi and AlTi alloy targets were used. Residual stresses and mechanical properties of AlTiN/CrTiSiN multilayer coatings deposited under various bias voltages were investigated. All the AlTiN/CrTiSiN multilayer coatings possessed higher hardness values (38.2–39.6 GPa) than AlTiN (32.5 GPa). As compared to the monolithic AlTiN, which had high residual stress of −9.8 GPa, the AlTiN/CrTiSiN multilayer coatings showed lower residual stresses of −2.4~ −9.1 GPa. The higher bias voltage was used the higher residual stress was observed. The AlTiN/CrTiSiN multilayer coating deposited at −20 V possessed the lowest residual stress (- 2.4 GPa). A cyclic impact test with high frequency were performed to evaluate the impact fatigue performance. The AlTiN/CrTiSiN multilayer coating deposited at −20 V showed the highest H/E (0.082) and H3/E2 (0.265) values to resist impact fatigue. The design of AlTiN/CrTiSiN multilayer coatings via low bias voltage can decrease residual stress and possessed good impact fatigue performance. Although the AlTiN/CrTiSiN coating deposited at high bias voltage of −180 V had similar hardness value to other AlTiN/CrTiSiN coatings under −20 V and −100 V, worse resistance to impact fatigue were found.

Substrate Bias Enhanced Trap Effects on Time-Dependent Dielectric Breakdown of GaN MIS-HEMTs

In this work, we present the substrate bias enhanced trap effects on time-dependent dielectric breakdown (TDDB) in GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) by experiment. Under different substrate biases, the shape parameter β and scale factor η of the Weibull distribution are extracted from the experimental data. A monotonical decrease in β from intrinsic breakdown to extrinsic breakdown relating to the hole-emission from the acceptor-like buffer traps with increased negative substrate biases has been observed, while η is increased at large positive substrate biases. This unexpected increase in η suggests that the donor-like buffer traps play an important role with a longer lifetime. The trap mechanisms, relating to percolation path establishment, are analyzed based on progressive breakdown (PBD). The capacitance-voltage characteristics are measured during each stress cycle confirming the hole fluence and electron injection in the gate-stack layer with different trap distributions under various substrate biases. Finally, 2-D device simulations are carried out to probe for physical insight into the traps on TDDB failure mechanisms.

Effects of substrate termination on R on increase under stress in 650 V GaN power devices

Buffer related electron trapping and hot electron injection are responsible for R on degradation in devices, but the effects of substrate termination are still uncertain. In this work, both positive and negative substrate bias are applied to investigate the different vertical trapping mechanisms in 650 V gallium nitride (GaN) power devices. R on shows an instant and significant increase under vertical bias stress, and the magnitude of downward buffer electron trapping induced R on increase is relatively larger than that induced by upward trapping. Additionally, the substrate floated and grounded GaN devices are also submitted to both off-state and semi-on-state stresses to investigate the effects of substrate termination on hot electron injection induced R on increase. The intensity of the upward electron trapping increases faster with temperature resulting in a higher R on increase than the downward situation. The hot electron effect is only obvious when the substrate is grounded, suggesting that the main injection destination is not in the buffer. The substrate floated device exhibits a lower R on increase after both off-state and semi-on-state stresses at elevated temperatures. Substrate floated packages are suggested to ensure reliable dynamic performance of device, especially for high voltage application design.

Effects of direct current bias on nucleation density of superhard boron-rich boron carbide films made by microwave plasma chemical vapor deposition

We report bias enhanced nucleation and growth of boron-rich deposits through systematic study of the effect of a negative direct current substrate bias during microwave plasma chemical vapor deposition. The current flowing through a silicon substrate with an applied bias of −250 V was investigated for a feedgas containing fixed hydrogen (H2) flow rate but with varying argon (Ar) flow rates for 1330, 2670, and 4000 Pa chamber pressure. For 1330 and 2670 Pa, the bias current goes through a maximum with increasing Ar flow rate. This maximum current also corresponds to a peak in substrate temperature. However, at 4000 Pa, no maximum in bias current or substrate temperature is observed for the range of argon flow rates tested. Using these results, substrate bias pre-treatment experiments were performed at 1330 Pa in an Ar/H2 plasma, yielding the maximum bias current. Nucleation density of boron deposits were measured after subsequent exposure to B2H6 in H2 plasma and found to be a factor of 200 times higher than when no bias and no Ar was used. Experiments were repeated at 2670 and 4000 Pa (fixed bias voltage and Ar flow rate) in order to test the effect of chamber pressure on the nucleation density. Compared to 4000 Pa, we find nearly 7 times higher boron nucleation densities for both 1330 and 2670 Pa when the substrate was negatively biased in the Ar/H2 plasma. Results are explained by incorporating measurements of plasma optical emission and by use of heterogeneous nucleation theory. The optimal conditions at 1330 Pa for nucleation were used to grow boron-rich amorphous films with measured hardness as high as 58 GPa, well above the 40 GPa threshold for superhardness.

Effect of Voltage Pulse Width and Synchronized Substrate Bias in High-Power Impulse Magnetron Sputtering of Zirconium Films

The Zr film microstructure is highly influenced by the energy of the plasma species during the deposition process. The influences of the discharge pulse width, which is the key factor affecting ionization of sputtered species in the high-power impulse magnetron sputtering (HiPIMS) process, on the obtained microstructure of films is investigated in this research. The films deposited at different argon pressure and substrate biasing are compared. With keeping the same average HiPIMS power and duty cycle, the film growth rate of the Zr film decreases with increasing argon pressure and enhancing substrate biasing. In addition, the film growth rate decreases with the elongating HiPIMS pulse width. For the deposition at 1.2 Pa argon, extending the pulse width not only intensifies the ion flux toward the substrate but also increases the fraction of highly charged ions, which alter the microstructure of films from individual hexagonal prism columns into a tightly connected irregular column. Increasing film density leads to higher hardness. Sufficient synchronized negative substrate biasing and longer pulse width, which supports higher mobility of adatoms, causes the preferred orientation of hexagonal α-phase Zr films from (0 0 0 2) to (1 0 1¯ 1). Unlike the deposition at 1.2 Pa, highly charged ions are also found during the short HiPIMS pulse width at 0.8 Pa argon.

Reactive High-Power Impulse Magnetron Sputtering of Chromium-Carbon Films

Chromium-carbon films were deposited by utilizing reactive high-power impulse magnetron sputtering at different mixture ratios of ethyne and argon atmosphere, and different substrate bias voltages and deposition temperature, with the same pulse frequency, duty cycle, and average power. The microstructure and mechanical properties of the obtained films were compared. The films consist of amorphous or nanocrystalline chromium carbide, hydrogenated amorphous carbon, and minor α-chromium phase. Decreasing the fraction of ethyne increases the content of the α-chromium phase but decreases hydrogenated amorphous carbon phase. The film’s hardness increases by enhancing the negative substrate bias and raising the deposition temperature, which could be attributed to the increase of film density and the Hall–Petch strengthening effect induced by the nanoscale crystallization of the amorphous carbide phase.

The effect of substrate bias on the piezoelectric properties of pulse DC magnetron sputtered AlN thin films

Substrate bias was applied for AlN deposition on rolled Ni sheet during pulse DC reactive sputtering to overcome the difficulty caused by thermal expansion mismatch between Ni substrate and AlN upon substrate heating. It was shown by Piezoresponse Force Microscopy (PFM) that the quality of the deposited AlN layer depends strongly on the negative substrate bias, i.e., the energy transferred via the bombardment of the accelerated positive ions on the sample. As the negative substrate bias becomes larger, the so formed layer shows higher piezoresponse, and better homogeneity. A Z-cut LiNbO3 single crystal was used as a reference to correct the PFM signals. The highest average d33 piezoelectric coefficient value, achieved at − 100 V substrate bias, is 3.4 pm/V indicating the feasibility of AlN deposition on rolled Ni substrate for vibration energy harvesting applications.

Deposition of Low-Resistivity Aluminum Thin Films Via Application of Substrate Bias During Magnetron Sputtering

In this study, the critical role of substrate bias during the sputter deposition of Al thin films is discussed. Two sets of Al thin films having a nominal thickness of 300 nm were deposited at sputtering pressures of 4.1 and 1.5 mTorr, respectively, with an applied negative substrate bias in the range of 0-200 V. It was found that the microstructure, surface roughness, film resistivity and grain size were greatly altered by the combination of bias magnitudes and sputtering pressures. The sputtering pressure of 4.1 mTorr resulted in greater changes in the film properties with the application of substrate bias, and a lesser but still significant degree was observed for the films deposited at 1.5 mTorr. The resistivity values for the films deposited at 1.5 mTorr were found to be significantly lower, with the lowest resistivity value of 3.1 µΩcm achieved at a substrate bias of 50 V. Based on grain size measured by the line intercept method and MayadasShatzkes grain boundary scattering model, the resistivity contribution of grain boundary scattering for the lowest-resistivity film was found to be 0.37 µΩcm, which indicates that the film resistivity in the optimized condition is close to the known bulk resistivity of 2.65 µΩcm.

Monolithic Integrated AlGaN/GaN Power Converter Topologies on High‐Voltage AlN/GaN Superlattice Buffer

A high‐voltage AlN/GaN superlattice (SL) buffer for monolithic AlGaN/GaN power circuits is experimentally compared with a step‐graded AlGaN/GaN buffer. The SL as part of a 5.1 μm epitaxial stack withstands over 1.3 kV. Although the step‐graded buffer is sufficient for low‐side circuits, the operation voltage of monolithic topologies such as a half‐bridge is limited: static negative back gating at −200 V depletes the lateral channel completely. Asymmetrical buffer leakage at a positive substrate voltage of +250 V limits the operation voltage further. The SL buffer mitigates both effects: a negative substrate voltage of −200 V reduced the lateral channel current only by 25%. However, this condition is not required for half‐bridge operation on the SL, because low symmetrical vertical buffer leakage at substrate voltages of ±500 V allows operation of power topologies with positive substrate bias. High‐electron‐mobility transistors (HEMTs) on the graded buffer show excessive threshold voltage shift at negative substrate bias. On the SL buffer, the threshold voltage is shifted only +1 V from negative substrate biases, which allows monolithic high‐voltage power topology operation. 98.8% efficient operation of a 6 × 4 mm2 GaN‐on‐Si power integrated circuit with a monolithic half bridge, freewheeling diodes, and drivers is demonstrated on the SL.

Nanostructured boron-doped diamond electrode for degradation of the simulation wastewater of phenol

The applications of a boron-doped diamond (BDD) used in electrode application for toxic and refractory organic degradation have attracted much attention, and its efficiency is considered to be an important factor for its practical application. In this study, BDD thin films were prepared on Ti plates by double bias-assisted hot filament chemical vapor deposition (HFCVD) technique. A reactive ion etching process was introduced by a positive grid bias and a negative substrate bias which can generate an electric field in HFCVD system. Then a novel structure of BDD electrode with nanocone arrays was successfully etched from a flat diamond thin film by this system. The addition of the bias greatly improved the etching efficiency and promoted the formation of nanocones structures. The cyclic voltammograms (CV) test showed nanostructured BDD (NBDD) electrodes had excellent electrochemical performance almost the same as that of the electrodes with untreated surfaces. It had a large effective electroactive surface area (EASA), which was 31.0% greater than the unetched electrode. As a result, the NBDD electrode exhibited improved electrocatalytic performance as compared with the untreated one, i.e., an about 24.3% increase of chemical oxygen demand (COD) removal efficiency. Among them, the superiority of NBDD electrode was obvious in the initial stage due to its highest concentration in the initial stage. In addition, the NBDD electrode achieved higher average current efficiency (ACE) as compared with the untreated one.

Structural transformations of carboxyl acids networks induced by concentration and oriented external electric field

The effects of concentration and an oriented external electric field on the transformations of hydrogen-bonded structures of trimesic acid (TMA) and terephthalic acid (TPA) have been investigated at a liquid–solid interface by scanning tunneling microscopy (STM). The triangular periodic TMA framework can be transformed into a flower-like structure by changing the STM sample bias sign in situ. Networks of TMA and TPA are porous at a negative substrate bias, but typically change to relatively compact forms when the polarity of the applied bias is reversed. This change is reversible if the applied bias is reversed. The effects have potentials to locally control the capture and release of analytes in host-guest systems and the 2D morphology in multicomponent layers.