Low-temperature Sputtering Research Articles

High-quality GeSn Layer with Sn Composition up to 7% Grown by Low-temperature Magnetron Sputtering for Optoelectronic Application.

In this paper, a high-quality sputtered-GeSn layer on Ge (100) with a Sn composition up to 7% was demonstrated. The crystallinity of the GeSn layer was investigated via high-resolution X-ray diffraction (HR-XRD) and the strain relaxation degree of the GeSn layer was evaluated to be approximately 50%. A novel method was also proposed to evaluate the averaged threading dislocation densities (TDDs) in the GeSn layer, which was obtained from the rocking curve of GeSn layer along the (004) plane. The photoluminescence (PL) measurement result shows the significant optical emission (1870 nm) from the deposited high-quality GeSn layer. To verify whether our deposited GeSn can be used for optoelectronic devices, we fabricated the simple vertical p-i-n diode, and the room temperature current–voltage (I–V) characteristic was obtained. Our work paves the way for future sputtered-GeSn optimization, which is critical for optoelectronic applications.

Formation of Wear- and Corrosion-Resistant Ceramic Coatings by Combined Technologies of Spraying and Micro-Arc Oxidation

Technological aspects of the formation of wear- and corrosion-resistant coatings on aluminum alloys and steel via an integrated use of methods of the low-temperature heterophase transfer, microarc oxidation, and magnetron sputtering. The tribological and anticorrosion properties of the coatings developed were estimated.

Large piezoelectricity on Si from highly (001)-oriented PZT thick films via a CMOS-compatible sputtering/RTP process

Integration of lead zirconate titanate (PZT) ferroelectrics into CMOS-Si technology has become a perennial challenge due to the continuously shrinking thermal budget in semiconductor processing. In this work, Pb(Zr0.53Ti0.47)O3 (PZT) thick films (∼1 µm) were prepared on LaNiO3 buffered (111)Pt/Ti/SiO2/(100) Si substrates via a low temperature (350 °C) sputtering deposition followed by a rapid thermal process (RTP). This two-step fabrication process resulted in a highly (001)-oriented perovskite PZT film with a dense, fine-grain morphology and reduced strains, hence an optimal electrical performance intrinsic to the chemical composition was achieved. EDS and XPS analyses verified a desirable evolution of the chemical stoichiometry in the RTP, as well as the expected chemical bonding states of the elements in the annealed films. Moreover, prototypical piezoelectric thin film cantilevers fabricated from the PZT/LaNiO3/Pt/Ti/SiO2/(100)Si heterostructure yielded a large transverse piezoelectric coefficient (e31,f) up to 15.7 C/m2, together with a high coupling coefficient k2∼0.23 for energy conversion efficiency. The PZT films showed high e31,f coefficients (∼10 C/m2) even when the RTP annealing time was reduced down to 2 min. Such a piezoelectric performance is close to the highest ones reported in the literature from epitaxial or highly-oriented PZT films, which require a much higher thermal budget for processing. These high quality PZT films open up many possibilities for the integration of piezoelectricity into Si-based micro-electro-mechanical systems (MEMS).

Ion-flux characteristics during low-temperature (300 °C) deposition of thermochromic VO2 films using controlled reactive HiPIMS

The ion-flux characteristics at a substrate position and the corresponding discharge characteristics were investigated during controlled low-temperature (300 °C) reactive high-power impulse magnetron sputtering (HiPIMS) depositions of thermochromic VO2 films onto conventional soda-lime glass substrates without any substrate bias voltage and without any interlayer. It was shown that the phase composition of the films correlates with the (V+ + V2+) ion fraction and the (V+ + V2+):() ion ratio in the total ion flux onto the substrate. Setting the amount of oxygen in the gas mixture allowed us to control not only the phase composition of the films but also their crystallinity. It was found that an appropriate composition of the total ion flux and high ion energies (up to 50 eV relative to ground potential) support the crystallization of the thermochromic phase in the VO2 films. We achieved a high modulation of the transmittance at 2500 nm (between 51% and 8%) and of the electrical resistivity (changed 350 times) for a 88 nm thick VO2 film.

Improved performance of thermochromic VO2/SiO2 coatings prepared by low-temperature pulsed reactive magnetron sputtering: Prediction and experimental verification

The paper deals with thermochromic VO2/SiO2 coatings prepared by low-temperature pulsed reactive magnetron sputtering on conventional soda-lime glass substrates without any substrate bias and without any interlayer. Thermochromic VO2 layers were deposited using reactive high-power impulse magnetron sputtering with a pulsed O2 flow control at a substrate surface temperature of 300 °C. Antireflection SiO2 layers were deposited using mid-frequency bipolar dual magnetron sputtering onto the top of VO2 layers at a surface temperature below 35 °C in order to improve the optical and mechanical performance. We focus on the dependence of the luminous transmittance (Tlum) and the modulation of the solar transmittance (ΔTsol) on the SiO2 layer thickness. The measured dependencies are in good agreement with those predicted using properties of pure VO2 layers measured by spectroscopic ellipsometry. Two different VO2 layer thicknesses (30 and 88 nm) have been used to demonstrate the tradeoff between Tlum and ΔTsol. We show an improvement due to the SiO2 overlayer of up to 16% (from 40.3% to 56.3%) for Tlum measured at 25 °C and up to 2.6% (from 7.7% to 10.3%) for ΔTsol. The results are important for the design and low-temperature fabrication of high-performance durable thermochromic VO2-based coatings for smart window applications.

Enhanced process stability for the low temperature sputter deposition of aluminium nitride thin films

MEMS (micro electro-mechanical systems) operated in resonance and excited piezoelectrically are nowadays used for a broad range of different application scenarios. To enhance the process stability and hence, the reproducibility of key film parameters of sputter-deposited aluminium nitride such as the film stress, the piezoelectric coefficient d33 and low leakage current levels, a novel aluminium clamped substrate holder is reported. Compared to the standard molybdenum based solution, where the thermal contact between the wafer and substrate holder varies during deposition, as the wafer can move freely, the substrate temperature variations are substantially reduced due to clamped configuration. Independent of AlN film thickness ranging between 0.5 μm and 2.0 μm the scatter in piezoelectric constant d33 and leakage current characteristics represented by the barrier height and the activation energy is reduced up to a factor of 3. These results demonstrate the importance to control carefully the temperature conditions during low-temperature AlN deposition to ensure a high reproducibility in film properties.

RF sputtered CdS films as independent or buffered electron transport layer for efficient planar perovskite solar cell

Metal sulfide has the potential to take the place of high temperature sintered TiO2 as electron transportation layer for perovskite solar cell (PSC) with improved light stability and suppressed hysteresis. In this work, CdS films were used as independent or buffered electron transport layer for planar perovskite solar cell by a low-temperature RF sputtering method for the first time. The effects of surface roughness and optical absorption of CdS films on the photovoltaic performance of PSCs were discussed. The PSC with sputtered CdS film shows a higher open-circuit voltage (Voc) and efficiency of 13.17% than high temperature sintered TiO2 ETL (12.71%). Moreover, a RF sputtered CdS buffer layer between TiO2 and perovskite could tune the conduction band edge of TiO2 and perovskite and passivating the surface defects. Time resolved photoluminescence results indicate the RF sputtered CdS film buffer layer could accelerate charge transportation and a higher conversion efficiency over 16% has thus been achieved, with enhanced air stability and minimized hysteresis. These findings offer new research directions for low-temperature sputtered metal sulfide film as a promising electron transport material for stable and high efficient planar perovskite solar cell.

Development of extremely low temperature processed oxide thin film transistors via atmospheric steam reforming treatment: Interface, surface, film curing

We have developed an “atmospheric steam reforming treatment” technique to obtain high-performance flexible amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) for applications in wearable/imperceptible electronics. The oxide TFTs, using as-grown a-IGZO with low-temperature sputtering and atomic layer deposition of Al2O3, showed unstable electrical behavior and poor transfer characteristics, which originated from a highly defective channel, gate insulator, and channel/gate insulator interface. Surprisingly, stable a-IGZO TFTs were obtained by atmospheric steam reforming treatment at an extremely low temperature (∼90 °C), and they exhibited good TFT performance with high field-effect mobility (13.3 cm2/V·s), high on/off ratio (4.5 × 108), and small SS value (0.23 V/dec). Despite the extremely low thermal budget, this steam treatment has a positive effect on the TFT characteristics because of an effective oxygen diffusion source, thereby resulting in successful healing of oxygen-related defects in the bulk oxide channel, channel/gate insulator interface, and gate insulator. Finally, by carrying out the atmospheric steam treatment at an extremely low temperature, we successfully fabricated ultrathin flexible a-IGZO TFTs with good electrical performance from a vacuum deposition system at the maximum process temperatures of 100–150 °C.

Structural study of NiOx thin films fabricated by radio frequency sputtering at low temperature

Structure and crystal growth of nickel oxide thin films (10–300nm) prepared by low-temperature sputtering have been investigated by scanning electron microscopy (SEM), X-ray diffraction, and spectroscopic ellipsometry. Very thin films are compact and homogeneous and are made of almost randomly oriented crystals. A preferential growth direction is then observed following the (111), (220) and (311) planes to the detriment of the (222) and (200) planes, inducing a growth of the materials in columns perpendicularly to the substrate. An optical model able to account for this particular structure has been created from the spectroscopic ellipsometry measurements, and correlates well with the structure observed by SEM. Moreover, it enables an accurate estimation of the thickness without damage to the substrate.

Highly conductive Ge-doped GaN epitaxial layers prepared by pulsed sputtering

Highly conductive Ge-doped GaN epitaxial layers were grown by low-temperature pulsed sputtering, and their fundamental structural and electrical properties were investigated. The room-temperature (RT) electron concentration was increased to 5.1 × 1020 cm−3 by the Ge doping, and the atomically flat stepped and terraced surface and the crystalline quality of the layers were maintained. Consequently, the RT resistivity was reduced to 0.20 mΩ·cm, which is comparable to that for typical transparent conductive oxides such as indium tin oxide. The contact resistance of Ge-doped GaN with a Ti/Al/Ti/Au metal stack prepared without annealing was as low as 0.087 Ω·mm. Furthermore, the selective formation of a Ge-doped region using an SiO2 mask was demonstrated. The results clearly indicate the strong potential of pulsed sputtering Ge-doped GaN growth for forming low-parasitic-resistance contact layers of various electrical and optical devices.

Improve matching ability of stent and balloon via preparing nano-structure by low-temperature plasma treatment

ABSTRACTThe matching ability between stent and balloon is an important property to the trackability and crossibility of delivering system; it's also influence the flexibility of operation in clinic. In this work, the low-temperature plasma sputtering method was employed to prepare nano-structure on balloon surface, the matching properties were investigated via the removing force, compliance and aging test; the micro-morphous was also characterized by scanning electron microscope. The result indicates that the removing force of the sputtered balloon is obviously increased comparing to un-treated that, and the compliance of both balloon catheters is similar, but the lower-temperature plasma treated balloon is more preferable than that of untreated that through aging test results. The distribution of stent struts on balloon surface is more uniform than untreated surface, and the deformation and fold of treated surface wasn't found, which indicates that the matching ability between stent and balloon would be enhance via low-temperature plasma sputtering.

Low-temperature pulsed sputtering growth of InGaN multiple quantum wells for photovoltaic devices

We investigated the potential of low-temperature pulsed sputtering deposition (PSD) for the fabrication of high-In-composition thick InGaN multiple quantum wells (MQWs). Low-temperature PSD growth allowed the growth of a 100-period 1.2-nm-thick In0.3Ga0.7N MQW on GaN bulk crystals without apparent lattice relaxation. We fabricated a nitride-based photovoltaic device using 100-period In0.3Ga0.7N MQW absorption layers and obtained a clear photovoltaic response with an open-circuit voltage of 1.24 V, a short-circuit current density of 1.76 mA·cm−2, and a maximum output power density of 1.10 mW·cm−2 under 1 sun with air mass 1.5 illumination.

Electrical properties of Si-doped GaN prepared using pulsed sputtering

In this study, we investigated the basic electrical properties of Si-doped wurtzite GaN films prepared using a low-temperature pulsed sputtering deposition (PSD) process. We found that the electron concentration can be controlled in the range between 1.5 × 1016 and 2.0 × 1020 cm−3. For lightly Si-doped GaN ([Si] = 2.1 × 1016 cm−3), the room temperature (RT) electron mobility was as high as 1008 cm2 V−1 s−1, which was dominantly limited by polar optical phonon scattering. Moreover, we found that heavily Si-doped GaN prepared using PSD exhibited an RT mobility as high as 110 cm2 V−1 s−1 at an electron concentration of 2 × 1020 cm−3, which indicated that the resistivity of this film was almost as small as those of typical transparent conductive oxides such as indium tin oxide. At lower temperatures, the electron mobility increased to 1920 cm2 V−1 s−1 at 136 K, and the temperature dependence was well explained by conventional scattering models. These results indicate that Si-doped GaN prepared using PSD is promising not only for the fabrication of GaN-based power devices but also for use as epitaxial transparent electrode materials for nitride based optical devices.

Crystallization and Characterization of GeSn Deposited on Si with Ge Buffer Layer by Low-temperature Sputter Epitaxy

Recently, GeSn is drawing great deal of interests as one of the candidates for group-IV-driven optical interconnect for integration with the Si complementary metal-oxide-semiconductor (CMOS) owing to its pseudo-direct band structure and high electron and hole mobilities. However, the large lattice mismatch between GeSn and Si as well as the Sn segregation have been considered to be issues in preparing GeSn on Si. In this work, we deposit the GeSn films on Si by DC magnetron sputtering at a low temperature of <TEX>$250^{\circ}C$</TEX> and characterize the thin films. To reduce the stresses by GeSn onto Si, Ge buffer deposited under different processing conditions were inserted between Si and GeSn. As the result, polycrystalline GeSn domains with Sn atomic fraction of 6.51% on Si were successfully obtained and it has been demonstrated that the Ge buffer layer deposited at a higher sputtering power can relax the stress induced by the large lattice mismatch between Si substrate and GeSn thin films.

Influence of N2 introduction on structural and optical properties of V-doped ZnO thin films grown by low-temperature reactive RF magnetron sputtering

The influences of N2 introduction to a sputtering gas on structural and optical properties of vanadium-doped ZnO (VZO) films, grown by using reactive RF magnetron sputtering on a quartz substrate at room temperature, were investigated. In the VZO films, V doping caused to form a large number of O vacancies (VO) and degraded both the c-axis orientation and optical transmittance. While, on the contrary, the ZnO(002) diffraction intensity of 3.5-at.% VZO films increased adding N2 with a partial pressure ratio (αN2) >2% reaching a maximum at αN2 =5%. The average optical transmittance (wavelengths: 450−800nm) of the 3.5-at.% VZO films was also improved by the N2 introduction and reached 74% at αN2 =5%. As a result of the analyses of the chemical binding states of the incorporated N atoms via the Raman spectroscopy and XPS, it was confirmed that the O sites were substituted by the N atoms and the amount of incorporated N increased by the high V doping. From the above, the N2 introduction was effective to suppress the VO formation even in room-temperature-grown VZO films, so it enables to improve both the c-axis orientation and optical transmittance.

Sputtered carbon as a corrosion barrier for x-ray detector windows

Sputtered amorphous carbon thin films were explored as corrosion resistant coatings on aluminum thin films to be incorporated into x-ray detector windows. The requirements for this application include high corrosion resistance, low intrinsic stress, high strains at failure, and high x-ray transmission. Low temperature sputtering was used because of its compatibility with the rest of the window fabrication process. Corrosion resistance was tested by exposure of carbon coated and uncoated Al thin films to humidity. Substrate curvature and bulge testing measurements were used to determine intrinsic stress and ultimate strain at failure. The composition and bonding of the carbon films were further characterized by electron energy loss spectroscopy, Raman spectroscopy, and carbon, hydrogen, and nitrogen elemental analyses. Samples had low compressive stress (down to.08 GPa), a high strain at failure (3%), and a low fraction of sp3 carbon–carbon bonds (less than 5%). The high breaking strain and excellent x-ray transmission of these sputtered carbon films indicate that they will work well as corrosion barriers in this application.

High hole mobility p-type GaN with low residual hydrogen concentration prepared by pulsed sputtering

We have grown Mg-doped GaN films with low residual hydrogen concentration using a low-temperature pulsed sputtering deposition (PSD) process. The growth system is inherently hydrogen-free, allowing us to obtain high-purity Mg-doped GaN films with residual hydrogen concentrations below 5 × 1016 cm−3, which is the detection limit of secondary ion mass spectroscopy. In the Mg profile, no memory effect or serious dopant diffusion was detected. The as-deposited Mg-doped GaN films showed clear p-type conductivity at room temperature (RT) without thermal activation. The GaN film doped with a low concentration of Mg (7.9 × 1017 cm−3) deposited by PSD showed hole mobilities of 34 and 62 cm2 V−1 s−1 at RT and 175 K, respectively, which are as high as those of films grown by a state-of-the-art metal-organic chemical vapor deposition apparatus. These results indicate that PSD is a powerful tool for the fabrication of GaN-based vertical power devices.

Low temperature aluminum nitride thin films for sensory applications

A low-temperature sputter deposition process for the synthesis of aluminum nitride (AlN) thin films that is attractive for applications with a limited temperature budget is presented. Influence of the reactive gas concentration, plasma treatment of the nucleation surface and film thickness on the microstructural, piezoelectric and dielectric properties of AlN is investigated. An improved crystal quality with respect to the increased film thickness was observed; where full width at half maximum (FWHM) of the AlN films decreased from 2.88 ± 0.16° down to 1.25 ± 0.07° and the effective longitudinal piezoelectric coefficient (d33,f) increased from 2.30 ± 0.32 pm/V up to 5.57 ± 0.34 pm/V for film thicknesses in the range of 30 nm to 2 μm. Dielectric loss angle (tan δ) decreased from 0.626% ± 0.005% to 0.025% ± 0.011% for the same thickness range. The average relative permittivity (εr) was calculated as 10.4 ± 0.05. An almost constant transversal piezoelectric coefficient (|e31,f|) of 1.39 ± 0.01 C/m2 was measured for samples in the range of 0.5 μm to 2 μm. Transmission electron microscopy (TEM) investigations performed on thin (100 nm) and thick (1.6 μm) films revealed an (002) oriented AlN nucleation and growth starting directly from the AlN-Pt interface independent of the film thickness and exhibit comparable quality with the state-of-the-art AlN thin films sputtered at much higher substrate temperatures.

Comparative study of RF reactive magnetron sputtering and sol-gel deposition of UV induced superhydrophilic TiOx thin films

TiOx and TiOx-like thin films were deposited on PEEK (Polyether ether ketone) substrates by low-temperature RF reactive magnetron sputtering and the sol-gel method. The resulting films were compared in terms of their properties and photoinduced hydrophilicity. Both techniques resulted in uniform films with good adhesion that can be switched to superhydrophilic after exposure to UVA radiation for similar time periods. In addition, the sputtered films can also be activated and switched to superhydrophilic by natural sunlight due to the higher absorption in the visible spectrum compared to the sol-gel films. On the other hand, the as deposited sol-films remain relatively hydrophilic for a longer time in dark compared to the sputtered film due to the differences in the morphology and the porosity of the two materials. Thus, depending on the application, either method can be used in order to achieve the desirable TiOx properties.

TiN diffusion barrier failure by the formation of Cu3Si investigated by electron microscopy and atom probe tomography

The authors investigate the interdiffusion damage of Cu/TiN stacks deposited on Si(001) substrates by low-temperature unbalanced direct current magnetron sputtering. Pristine and diffusion-annealed samples are examined by x-ray diffraction, four-point-probe resistivity measurements, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and atom probe tomography. Two relevant diffusion processes are identified. The local diffusion of Cu through defects and grain boundaries in the TiN layer leads to the formation of the η″-Cu3Si phase at the barrier/substrate interface. Three-dimensional reconstructions obtained by atom probe tomography additionally reveal the outward diffusion of Si atoms from the substrate through the TiN bulk toward the Cu top layer, eventually also resulting in the formation of a discontinuous Cu3Si surface layer.