AVS2014 Session TF-ThP: Thin Films Poster Session

Surface modification of forming many kinds of films must be one of the most important technologies. For especially many kinds of plating methods are already established and easy processing to the product of complicated forms. Furthermore, the composite plating which contains many kinds of small particles in the film are also fabricated and it contributes to the further improvement in the characteristic.

In this study, we focused on development of Ni composite plated films reinforced by dispersed multi-walled CNT with 50 nm in the diameter and several μm in the length using the ultrasonic vibration. An ordinary electroplating method was applied at room temperature. CNT/Ni composite plated film was examined under the conventional plating conditions of pH 4.5-4.7 using a Ni plate as an anode and a Cu plate as a cathode. The mixing weight concentrations of CNT were changed in the range of 0-0.1 wt.%CNT to the weight of the plating bath. It is necessary to prevent from aggregation of CNT in composite plated films because the aggregation parts of CNT must surely cause a loss of strength of the materials. In order to distribute CNT molecules in the plating solution, the ultrasonic vibrations was applied for 1 h before the plating process. The operation conditions was set constant as follows; the bias voltage of 3.7 V, the current density of 3.0 A/dm² and the plating time of 10 minutes. Thickness of plated film obtained was about 40 μm. Fabrication of CNT/Ni composite films of all mixing weight ratio plated on a Cu plate was confirmed with flat surfaces. But the remarkable condensation parts were observed at the surface at the weight ratio of 0.1 wt.%CNT. The X-ray diffraction experiments clearly indicated no formation of any compound between Ni metal and CNT, because only Ni crystalline diffraction patterns for all CNT concentrations were identified. Vickers hardness tests showed that the hardness increased with the increase of concentration up to 310 Hv of 0.07 wt.%CNT, and decreased after that. This maximum hardness was about twice of the value of the pure Ni plated film. The decrease of hardness over the concentration of 0.07 wt.%CNT should be due to existence of softer aggregate part CNT in the composite films. The friction and abrasion characteristics were also estimated using by a pin-on-disk tester under the load of 0.5 N with a stainless steel pin. It was clarified that the friction coefficient of the composite film with concentration of 0.07 wt.%CNT decreased to 0.5 in comparison with pure Ni coating of 0.8 and showed an unobservable abrasion mark.

From the above results, industrial validity of this study was surely able to be found out.

We fabricated dispersed C₆₀ molecules/Al nano-composite thin films using by a conventional vacuum evaporation method. The microstructural characterization of the films obtained clarified the uniform dispersion of C₆₀ molecules in Al based film. Nano-indentation hardness of Al-1.0 wt.%C₆₀ showed increase up to 3 times larger than that of Al film. These results clearly indicated that dispersion of C₆₀ molecules in the conventional films contributes to drastic improvement in mechanical properties.

In this study, we tried to establish the synthesis technology of the composite thin films containing dispersed C₆₀ molecules in order to apply practical uses in the industry fields. We focused on conventional high hardness TiN films fabricated using by RF magnetron sputtering method. For the purpose of evaporating C₆₀ molecules, the heating evaporator was equipped directly below the substrate of existing RF magnetron sputtering chamber due to prevent from the influence of plasma. It was possible to control the deposition rates of two kinds of evaporation sources to become the predetermined compositions separately.

TiN films with constant thickness of 100 nm were deposited on Si(100) water-cooled substrates using by the RF magnetron sputtering deposition method for 30 minutes. The concentration of C₆₀ molecule powder was changed in the range from 0.5 to 50 wt.%, and the evaporation temperature was controlled in the range of 473-673 K. The structure analyses of all nano-composite films prepared by X-ray diffraction method showed TiN crystalline structure, and FT-IR analysis clarified the existence of C₆₀ molecules contained in TiN films. Nano-indentation studies showed that the hardness of the composite film of 2.0 wt.%C₆₀/TiN showed the maximum hardness of 18 GPa and this value was increased up to 50 % larger than that of TiN film.

Fluorine-doped Al₂O₃ films were deposited by high-power impulse magnetron sputtering with an Al metal target at room temperature. In order to obtain better optical and mechanical properties, films were investigated under different duty cycle and different ratios of O_{2 to} CF₄ gas. The optical properties in deep ultraviolet range, microstructure, surface roughness, and crystalline structure, of fluorine-doped Al₂O₃ films have been studied. The fluorine-doped Al₂O₃ films deposited with 45/555 duty cycle and 0.6 sccm CF₄ has lowest extinction coefficient (5 × 10^-4)and highest refractive index (1.70) at 193 nm. Besides, the fluorine-doped Al₂O₃ films reveal a dense and amorphous structure.

ZnO is an interesting wurtzitic semiconducting material with a wide band-gap of 3.3 eV. It has been reported that the reduction of the optical band-gap down to 2.4 eV was observed from (ZnO)_x(GaN)_1-x powders with x = 0.81[1]. Moreover, optical band-gap of nitrogen doped ZnO (ZnON) films decreased from 3.26 to 0.9 eV with increasing the N concentration[2], while that of Zn_1-xGa_xO films was reported to be engineered from 3.3 to 4.9 eV by varying the Ga content[3]. From these facts, we believe that the band-gap of ZnGaON can be widely controllable from 0.9 to 4.9 eV by changing their chemical composition. In these previous reports, however, there have been few observations on their luminescence properties. The purpose of this study is to form ZnGaON thin films with various optical band-gaps. The substrates used in this study were c-axis sapphire substrates or glass substrates. ZnGaON thin films were deposited on these substrates by two kinds of radio frequency (RF) magnetron co-sputtering methods. One is co-sputtering (a) of GaN tablets and a ZnO target in N₂/O₂ gas flow, in which the GaN tablets were placed on the ZnO target and the number of GaN tablets (N_GaN) was varied from 0 to 3. The other is co-sputtering (b) of Ga₂O₃ tablets and Zn target in Ar/N₂ gas flow, in which the Ga₂O₃ tablets were placed on the Zn target. Samples were subsequently subjected to NH₃ treatment at 500 °C for nitridation in former co-sputtering (a) and N₂ annealing at 500 °C for improvement of crystallinity in latter co-sputtering (b). These samples were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), optical transmittance and photoluminescence (PL). First of all, we show the characterization results of films prepared by co-sputtering (a). XRD analysis showed that the crystalline quality of ZnGaON films became worse with increasing N_GaN. EDS results revealed that nitrogen doping concentration in ZnGaON films was increased only by NH₃ treatment. Optical band-gap of ZnGaON films became wider from 3.29 to 3.51 eV with increasing N_GaN from 0 to 3 due to Burnstein-Moss shift. PL spectra of ZnO films showed band-to-band emission at 380nm, while those of ZnGaON films exhibited a broad and weak peak centered at 530 nm, which results from oxygen interstitial (O_i). On the other hands, optical band-gap of ZnON films prepared by co-sputtering (b) without Ga₂O₃ tablets decreased to 1.18 eV, probably due to formation of Zn₃N₂.

[1] J. Wang et al., J. Mater. Chem., 21, 4562 (2011).

[2] L. Jensen et al., J. Phys. Chem. C, 112, 3439 (2008).

[3] J. Zhao et al., IEEE Trans Electron Devices, 56, 2995 (2009).

In progress towards spin polarization measurements, we are using a unique ultra-high vacuum (UHV) deposition chamber equipped with electron gun deposition sources, sputter deposition, and plasma oxidation to fabricate shadow-mask defined tunnel junctions. The formation of the tunnel barrier is one of the most crucial processes in junction fabrication which makes the development of an optimal growth recipe a vital step. While varying plasma oxidation process parameters, we will be growing aluminum oxide thin films as a tunnel barrier for metal/insulator/superconductor junctions. Optical spectra of the oxidation plasma and electrical characterization of the resulting junctions will be used to elucidate optimum growth conditions for our aluminum oxide tunnel barriers. The aforementioned data and experimental details will be discussed in this presentation.

In this work we present results for two types of thin films deposited by ECR–CVD: silicon oxide (SiO₂) and hydrogenated amorphous silicon (a–Si:H) with thicknesses of about 6–8nm and 3–4nm respectively. SiO₂/a–Si:H and SiO₂/a–Si:H/SiO₂ structures for potential application in Non–Volatile Memories, were deposited on p–type (100) c–Si wafers under the following conditions: a gas pressure of 2.0mTorr, an applied ECR microwave (frequency of 2.45GHz) with power of 250Watts and a substrate temperature of 20°C. The precursor gases used for SiO₂ deposition were 2% of SiH₄ diluted in Ar, Ar and O₂ with flows of 125, 5 and 2.5sccm, respectively. The a–Si:H layers were deposited without oxygen using the same SiH₄ and Ar flows. The films were subjected to furnace annealing in N₂ at temperatures in the 800–1100°C range for 60min. Different oxygen and silicon incorporation into the films were extracted using Energy Dispersive X–ray (EDX) analysis (Fig1). Information for the layer thicknesses and optical properties was carried out by Single Wavelength Ellipsometry (SWE) λ~638nm. The thickness measured was 7–11nm and 9–20nm for two and three layers, respectively. Refractive index (n) values between 1.46–1.53 that were obtained are greater than stoichiometric silicon oxide (n=1.457) reported in the literature, indicating formation of thin films rich in silicon. MOS capacitors were fabricated by r.f. sputtering of Al as top (d~0.5 µm) and back contacts. These capacitors were sintered at 450°C in forming gas (92%N₂ and 8%H₂) for 5, 10 and 20min. Electrical characterization was carried out by Capacitance–Voltage (C-V) measurements. The increase of the low temperature annealing time, leads to an improvement of the SiO₂/Si interface seen as an increase of the slope of the high frequency C–V dependence. The capacitance variation in accumulation (C_acc) is in the range of 160–180pF for two layer capacitors which correspond to a thickness of 6–7nm (Fig2). In the same way for three layers the variation of C_acc is larger and the thickness calculated is 11–17nm (Fig3). The obtained values are in agreement with the expected thickness determined by SWE. Three–layer MOS capacitors annealing in forming gas for 20min showed hysteresis in their C–V measurements with ramps varying from negative to positive voltages and back. The flat–band Voltage shift (ΔV_FB) obtained for capacitors annealed at 800°C and 1000°C were: -2.7V to -2.13V and -4.3V to -2.48V showing an hysteresis window of 0.57V and 1.82V, respectively (Fig4). By the other hand for two–region structures do not present hysteresis (Fig5) which means that three-layer structures could be a possible application as memory devices.

We report the MOCVD growth of doped thin 2-D MgZnO films on c-plane sapphire substrates for solar-blind detector applications. Spectroscopic ellipsometry (SE), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are used to determine the composition. The carrier gas is N₂. For pure ZnO, the precursors are diethylzinc (DEZ) and nitrous oxide (N₂O). When growing p-type material, 3% nitric oxide (NO) in N₂ provides N ions in the +2 oxidation state needed for doping, and growth occurs as a two-step process monitored in real time by the SE. In the first step, we use a low Zn partial pressure to induce V_Zn formation. Because V_Zn energies are low for Fermi levels from mid-gap to the conduction band edge, and because the absorption energy for N_Zn is 0.08 eV for the hexagonal close packed site of the Zn-polar surface, this allows the N to incorporate at Zn sites as N_Zn. In the second step, we use a high Zn partial pressure to drive the formation of oxygen vacancies (V_O). Growth is then followed by an appropriate annealing sequence. While substitutional N on the O sublattice is a deep acceptor, we find that acceptor complexes involving N, H and V_Zn can provide p-type ZnO films with a hole concentration of ~10¹⁸ cm^-3 at room temperature. For MgZnO growth, we use bis-cyclopentadienyl magnesium (BcMg) in addition to DEZ, N₂O, and NO. Although we deposit MgZnO, films of a quality that we consider acceptable have not yet been produced owing to the large parameter space of temperature, precursor flows, and gas pressure.

Tin (II) Monosulfide (SnS) has become an interesting new material for thin film photovoltaics (PV). The optoelectronic properties indicate that SnS is a suitable material for PV. Its high absorption coefficient, greater than 10⁴ cm^-1, and band gap near 1.3 eV are well matched with the solar spectrum. SnS also has a carrier concentration greater than 10¹⁵ cm^-3 and potential to be both n-type and p-type. With recent success in achieving 4% efficiency, SnS-based devices demonstrated their potential. However, the success comes with extensive optimization of each layer in the device, suggesting that further understanding of SnS is crucial to improving performance.

Sulfur is more volatile than tin and despite strong Sn-S bonds in tin sulfide compounds, sulfur loss to the gas phase while annealing in a vacuum environment. Therefore, it is important to start with a sulfur-rich thin film prior to annealing. Annealing of sulfur-rich sputtered tin sulfide thin films has not been done before. This work will investigate the optoelectronic properties, composition and morphology of annealed, sputtered tin sulfide thin films. Specifically, we will investigate the change in phase and improvement in material quality as a result of post-deposition heat treatments.

Tin sulfide thin films are sputtered on glass and silicon substrates from a distance of 11.5 cm at 115 W with a Ar chamber pressure of 10 mTorr. The sputter target was a 3” SnS₂ with 99.999% purity (LTS Research Laboratories, Inc.). SnS_x samples are deposited at room temperature and 150ºC. These samples are then annealed some under medium vacuum (<2x10^-6 Torr) in the deposition chamber without breaking vacuum at 200, 300, and 400°C.

Preliminary results show promise for high-quality SnS thin films. Significantly improved crystallinity was seen in sulfur-rich thin films annealed at 400ºC for 30 minutes. Morphology is not the same for film deposited with and without substrate heating, although both film exhibit a uniform SnS phase as determined by X-ray diffraction. Longer anneal times are expected to further improve crystal quality. Reasonable resistivities are seen in these annealed thin films. The presentation will include details on producing high-quality SnS thin films as well as detailed results of optoelectronic properties, composition and morphology.

Due to exceptional material properties, such as refractive index and others, the use of silicon nitride (SiN) as an optical waveguide has become common. SiN films are used in many applications, from gate dielectrics to encapsulation layers. However, the use of SiN as a waveguide is greatly affected by hydrogen incorporation, particularly at telecommunication wavelengths of ~1550 nm.

Hydrogen incorporation for plasma enhanced chemical vapor deposition (PECVD) of SiN_x is a due to the Si-H species from the use of SiH₄ as well as the standard precursor NH₃ for the N component for SiN_x. The resulting hydrogen bonds, both Si-H species and N-H species, result in absorption and thus loss in the telecommunication spectrum. In particular, the N-H bond has high absorption around 1550 nm.

Previous studies have investigated the use of N₂ as a replacement precursor for NH₃ for low-hydrogen PECVD SiN_x.^1,2 However, these studies have only investigated a few process parameters and their effect on the optical characteristics of the film. In our investigation, a detailed study was performed on a production PECVD system to look at the effect of SiH₄ flow, NH₃ flow, N₂ flow, ratios of all precursors, chamber pressure, and RF bias. The relative hydrogen content was measured for all process parameters through Fourier transform infrared spectroscopy (FTIR). Additionally, we measured the refractive index (from 375 nm to 1675 nm), deposition rate, uniformity, and stress of the SiN_x films. We are able to not only tune the relative hydrogen content of the film, but the uniformity, stress and refractive index independently, in order to fabricate SiN_x optical waveguides for photonic applications.

It was observed that although substituting N₂ in place of NH₃ for the source of N in SiN_x resulted in lower relative hydrogen content, it greatly affected the refractive index and stress of the film resulting in a film that is not ideal for photonic integrated circuits. In order to balance these film properties, we were able to exploit other process parameters, such as chamber pressure and RF bias, in order to tune the film. We also measured the insertion loss of SiN_x optical waveguides with select SiN_x films in order to further understand the role of different film properties.

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

¹S. C. Mao, et al., Opt. Express 16, 20809-20816 (2008).

²F. Karouta, et al., J. Phys. D: Appl. Phys. 45, 445301 (2012).

Polymer substrates are used for flexible organic electronics due to being lightweight, cheap, transparent and printable in continuous roll to roll manufacturing technology. However, a significant disadvantage of these materials is their high gas/vapour permeability. A permeation barrier is therefore essential when using polymer substrates in organic electronics to reduce both oxygen and moisture ingress to an acceptable level. Films deposited by atomic layer deposition (ALD) have shown to improve the barrier properties of polymeric films [1-2]. In the present study, single alumina (Al₂O₃) films were deposited onto one surface of PET substrates (Multapex, biaxially oriented, 75 µm thick) using thermal and plasma enhanced ALD. Films with thicknesses in the range of 7 - 25 nm were deposited at 100 or 120°C. The water vapour transmission rate (WVTR) of the ALD films was determined predominately by tritium permeation, but was also measured using the MOCON and Ca-tests for comparison. Thermally grown 20 nm thick alumina films were also deposited onto PET and PEN substrates with thicknesses of 75 and 125 µm to evaluate the effect of substrate type and thickness on WVTR. In addition, several mixed oxide structures such as alumina/hafnia and alumina/titania were also investigated to examine their potential for further decreasing the WVTR. Characterisation of the ALD grown films was carried out using X-ray photoelectron spectroscopy, atomic force microscopy and optical microscopy. For single Al₂O₃ layers, film thickness and deposition temperature influenced the WVTR. The WVTR decreased with increasing film thickness and deposition temperature. The deposition of ALD metal oxide films was successful in reducing water permeation through polymer substrates, demonstrating the potential of these coatings as a barrier technology for organic electronics over wide range of polymer based products.

[1] Groner MD, George SM, McLean RS, Carcia PF Appl. Phys. Lett 2006, 88, 051907

[2] Dameron AA, Davidson SD, Burton BB, Carcia PF, McLean S, George SM J. Phys. Chem. C. 2008, 112(12), 4573

Titanium-dioxide films are produced by the dip coating method, using a solution of 2-propanol and titanium isopropoxide in a concentration of 0.17M and an immersion speed of 0.122 cm/s. Films with different thickness are obtained by changing the number of immersion cycles. Analysis results indicate that the obtained films present the TiO₂ anatase structure when treated at 400 °C for 3 hrs, the film thickness ranged from 20nm to 150 nm and the rate deposition is of 18 nm/cycle.

Gas sensing studies indicate that at a work temperatures of 300 °C sensors present a significant change in electrical resistance. When analyzing sensors sensitivity as a function of propane concentration and film thickness a two-regime behavior is observed, being the sensitivity independent of the film thickness when partial pressures are above 400 ppm, and thickness dependant at lower partial pressures. The maximum sensitivity is obtained in the range from 5 ppm to 300 ppm for the film grown with 5 immersion cycles.

This study investigated the optical design of silver mirror and effected of optical properties in the radiation environment. In different optical designed by Macleod software was studied in the same radiation environment. The optical properties were measured by the integrating sphere spectrophotometer and material properties by X-ray diffraction instrument. After the 35 Krad Co-60 radiation testing, the titanium dioxide film, silicon dioxide film, pure chromium and silver film could efficient reduce the damage of the B270 substrate by radiation. In the visible light, the titanium dioxide film had smaller spectral absorption about 0.5% at 450 nm and about 25 nm spectral drift. In the metal film,△T% in visible light of the sliver film was about 0.5% and chrome film about 1.5%. So, the radiation resistance of silver film was better than chrome film. By X-Ray diffraction analysis showed that the crystalline of silver film would be slightly improved by exposure to radiation.

In this study, the effect of Mg doping concentration on the resistance switching behavior of Al₂O₃ films was investigated in conjunction with an analysis of the chemical bonding states. Mg doping concentration is increased from 0 to 8.6% with increasing Mg gun power. In micro-structure, the Al₂O₃ and Mg-doped Al₂O₃ films have amorphous structure in all conditions. In non-lattice oxygen, the concentration of non-lattice oxygen is increased with increasing Mg doping concentration in Al₂O₃ films. In order to identify the effect of only non-lattice oxygen concentration without crystal structure change, the resistance switching characteristics such as operating current, forming electric field, endurance, and retention was compared. The operating current and uniformity of endurance is increased with increasing Mg doping concentration. And also the conduction mechanism and activation energy from Poole-Frenkel equation of resistance switching characteristics of Mg-doped Al₂O₃ films was investigated. The activation energy is decreased with increasing non-lattice oxygen concentration because non-lattice oxygen is defect in Al₂O₃ films. From these findings, the resistance switching characteristics are influenced by non-lattice oxygen concentration.

Previous work in copper thin films with thickness > 30nm demonstrated excellent agreement with the semiclassical models of the resistivity size effect. Using the same methodology developed for Cu, electron scattering at surfaces and grain boundaries in polycrystalline Ni, Ru, and W films was examined. 2-200 nm thick films were prepared via DC magnetron sputtering onto thermally oxidized silicon wafers. Films with thicknesses below 10nm were encapsulated in 0.5nm thick layers of Ta to improve film stability.

Films were annealed in the range of 200°C to 900°C in Ar+3% H₂. They were characterized using X-ray reflectivity, Rutherford backscatter spectrometry, and transmission electron microscopy with precession electron diffraction techniques to measure thickness, grain size, and film continuity. Resistivity was measured using the Van Der Pauw method.

The contributions of surface and grain boundary scattering were assessed using the semiclassical models of Fuchs-Sondheimer and Mayadas-Shatzkes. Systematic deviations from model predictions were observed for films less than approximately 15nm thick in all three metals. The complex Fermi surfaces of these metals result in a variety of Fermi velocities, as several bands cross the Fermi level. This complexity may be a likely cause for the failure of the semiclassical models, which consider only an average mean free path value. The deviations are most pronounced in the thinnest films.