High-resistivity Films Research Articles

Fluoride Contamination Induced ${\rm NiSi}_{2}$ Film Formation in a Gate NiSi Line

Undulate high-resistance nickel silicide film is found in a gate electrode of a logic device. The undulate film is caused by fluoride contamination derived from a chemical dry-cleaning process for silicon (Si) substrate prior to nickel (Ni) sputtering. The undulate film was composed of a thicker nickel monosilicide (NiSi) film nearby a Si hillock and a thinner nickel disilicide (NiSi2) film on the hillock. These results indicate that fluoride contamination impeded Ni diffusion during the initial silicidation. At the same time, vacancies are left by excess Ni diffusion at a clean Ni-Si interface. Then, the thin nickel silicide film is transformed into NiSi2 because of the excess thermal budget during the second silicidation. Where the vacancies filled up by Si, a Si hillock is formed.

The effect of substrate pore size on the network interconnectivity and electrical properties of dropcasted multiwalled carbon nanotube thin films

Abstract

Conductivity and photoconductivity of granular silver films on a sapphire substrate

The photoelectric properties of a high-resistance silver film on sapphire, consisting of granules 15–20 nm across with the same intervals between them, have been investigated. The ohmic conductivity of the film increased with temperature. Photoconductivity is detected in the film when optical radiation with wavelengths up to the red limit of the photoelectric effect acts on it. A sign change of the photocurrent is detected in the photoconductivity spectrum when the current through the film increases under the action of radiation with wavelength less than 460 nm, whereas it decreases when the wavelength is greater than 460 nm. A conductivity and photoconductivity model is proposed that is based on doping of the dielectric substrate due to the metallic nanoparticles placed on it and the motion of electrons over traps in the substrate. The position of the bottom of the conduction band of the dielectric relative to the Fermi level for silver is calculated in terms of the model.

Overcharge Protection Effect of Cyclohexylbenzene and New Overcharge Protection Agent for Lithium Ion Batteries

We investigated the overcharge protection property of cyclohexylbenzene (CHB). CHB prevents overcharging by consuming the overcharge current through the electrochemical reaction of CHB. However, the CHB reactants do not increase resistance, and the overcharge reaction will restart after the CHB reaction has finished. A new overcharge protection agent (OPA) needed to be developed that has a shut-down function. We developed the new OPA, which consists of a polymer with an aromatic group and a high polar functional group. The new OPA forms a high-resistance film during overcharging, and its concept is validated.

Exchange Field-Mediated Magnetoresistance in the Correlated Insulator Phase of Be films

We present a study of the proximity effect between a ferromagnet and a paramagnetic metal of varying disorder. Thin beryllium films are deposited onto a 5 nm thick layer of the ferromagnetic insulator EuS. This bilayer arrangement induces an exchange field, H(ex), of a few tesla in low-resistance Be films with sheet resistance R≪R(Q), where R(Q)=h/e2 is the quantum resistance. We show that H(ex) survives in very high-resistance films and, in fact, appears to be relatively insensitive to the Be disorder. We exploit this fact to produce a giant low-field magnetoresistance in the correlated-insulator phase of Be films with R≫R(Q).

Effect of annealing atmosphere (Ar vs. air) and temperature on the electrical and optical properties of spin-coated colloidal indium tin oxide films

Colloidal indium tin oxide (ITO) ~6 nm nanoparticles synthesized in-house were deposited by spin coating on fused silica substrates, resulting in high resistivity films due to the presence of passivating organics. These films were annealed at various temperatures ranging from 150 to 750 °C in air and argon atmospheres. The films are very transparent in the as-coated form, and they retain high transparency upon annealing, except the films annealed at 300 °C in argon, which became brown due to incomplete pyrolysis of the organics. Thermogravimetric analysis and Raman characterization showed that the removal of organics increases with an increase in the annealing temperature, and that this removal is more efficient in the oxidizing atmosphere of air, especially in the 300–450 °C temperature range than in Ar. Although ITO defect chemistry suggests that argon annealing should result in higher carrier concentration than air annealing, the faster removal of insulating organics upon annealing in air resulted in significantly lower film resistivity at intermediate annealing temperatures for films annealed in air than in Ar. At higher annealing temperatures, both Ar and air annealing, resulted in comparable film resistivities (the lowest achieved was ~100 Ω cm).

Cross-plane electronic and thermal transport properties of p-type La0.67Sr0.33MnO3/LaMnO3 perovskite oxide metal/semiconductor superlattices

Lanthanum strontium manganate (La0.67Sr0.33MnO3, i.e., LSMO)/lanthanum manganate (LaMnO3, i.e., LMO) perovskite oxide metal/semiconductor superlattices were investigated as a potential p-type thermoelectric material. Growth was performed using pulsed laser deposition to achieve epitaxial LSMO (metal)/LMO (p-type semiconductor) superlattices on (100)-strontium titanate (STO) substrates. The magnitude of the in-plane Seebeck coefficient of LSMO thin films (<20 μV/K) is consistent with metallic behavior, while LMO thin films were p-type with a room temperature Seebeck coefficient of 140 μV/K. Thermal conductivity measurements via the photo-acoustic (PA) technique showed that LSMO/LMO superlattices exhibit a room temperature cross-plane thermal conductivity (0.89 W/m·K) that is significantly lower than the thermal conductivity of individual thin films of either LSMO (1.60 W/m·K) or LMO (1.29 W/m·K). The lower thermal conductivity of LSMO/LMO superlattices may help overcome one of the major limitations of oxides as thermoelectrics. In addition to a low cross-plane thermal conductivity, a high ZT requires a high power factor (S2σ). Cross-plane electrical transport measurements were carried out on cylindrical pillars etched in LSMO/LMO superlattices via inductively coupled plasma reactive ion etching. Cross-plane electrical resistivity data for LSMO/LMO superlattices showed a magnetic phase transition temperature (TP) or metal-semiconductor transition at ∼330 K, which is ∼80 K higher than the TP observed for in-plane resistivity of LSMO, LMO, or LSMO/LMO thin films. The room temperature cross-plane resistivity (ρc) was found to be greater than the in-plane resistivity by about three orders of magnitude. The magnitude and temperature dependence of the cross-plane conductivity of LSMO/LMO superlattices suggests the presence of a barrier with the effective barrier height of ∼300 meV. Although the magnitude of the cross-plane power factor is too low for thermoelectric applications by a factor of approximately 10−4—in part because the growth conditions chosen for this study yielded relatively high resistivity films—the temperature dependence of the resistivity and the potential for tuning the power factor by engineering strain, oxygen stoichiometry, and electronic band structure suggest that these epitaxial metal/semiconductor superlattices are deserving of further investigation.

Electrochemical behavior of graphite anode during anode effect in cryolite molten salts

Anodic electrochemical behavior was studied on graphite anode at 1000°C in cryolite-alumina molten salt by means of cyclic voltammetry. The high current peak in a typical cyclic voltammogram was discussed. It is considered that a type of oxyfluoroaliminate complex anions reacts with carbon to form a high-resistance CF film on the anode surface at a high potential. The passivation potential is 3.28 V in 0.5% alumina-containing electrolyte, and the passivation potential increases with alumina content increasing which indicates that the alumina content determines the anodic process in the cryolite-alumina molten salt system.

Electrical contact resistance effect on resistance spot welding

The effects of local electrical contact resistance on transport variables, cooling rate, solute distribution, and nugget shape after solidification responsible for microstructure of the fusion zone during resistance spot welding are realistically and systematically investigated. The model accounts for electromagnetic force, heat generation and contact resistances at the faying surface and electrode–workpiece interfaces and bulk resistance in workpieces. Contact resistances are composed of film and constriction resistances, as functions of hardness, temperature, electrode force and surface condition. The computed results show that the bulk dynamic electrical resistance cannot reliably reflect transport processes and nugget shape, unless the local constriction resistance and electric current density are known. Regardless of high film resistance, nugget growth and transport processes are independent of film resistance due to delayed response time of local electric current in the early stage. A decrease in constriction resistance, however, delays nugget formation, enhances convection and solute mixing, and changes circulation direction of the stronger convection cell during cooling period.

Electrically conductive and high temperature resistant superhydrophobic composite films from colloidal graphite

Electrically conductive and self-cleaning superhydrophobic films (water contact angles >160°, droplet roll off angles <5°) were fabricated by simply solution casting sub-micron polytetrafluoroethylene (Teflon) particle dispersed alcohol-based colloidal graphite solutions. The process is very suitable for forming conductive superhydrophobic coatings on glasses, metals, ceramics and high performance polymers such as polyimide (Kapton®). The solutions were deposited on microscope glass slides and Kapton® films by drop casting. After solvent evaporation under ambient conditions, the coatings were annealed to melt Teflon. Upon melting, Teflon particles fused into one another forming a hydrophobic polymer matrix. The degree of superhydrophobicity and the surface morphology of the coatings together with their electrical conductivity were studied in detail by varying Teflon-to-graphite weight fractions. A number of applications can be envisioned for these coatings such as electrode materials for energy conversion devices, high performance electromagnetic shielding materials, flexible electronic components and heat exchanger surfaces, to name a few.

Adhesion Characteristics of Magnetron-Sputter-Deposited Copper on Smooth Cycloolefin for Realizing Wiring with High-Frequency Signal Propagation

Copper wiring formation on a resin material with a low dielectric constant, a low dielectric loss and a smooth surface is indispensable to realize high-frequency signal propagation with fine wiring patterns. Cycloolefin polymer (COP) resin is a promising material to meet these requirements. We propose adhesive copper seed layer formation on the COP by magnetron sputtering as an alternative to the electroless deposition which usually requires an intentional roughnessinduced process to obtain practical adhesion between the resin and the metal. The proposed process steps include plasma nitridation of the COP surface, thin CuN film deposition and Cu film deposition before the electroplating. Excellent adhesion strength between the COP and the metal, greater than 1 kN/m, can be obtained while maintaining a smooth surface, which is attributed to the strong chemical bond generated between the nitrided COP surface and the CuN film. The coplanar transmission line was fabricated using the proposed process steps with semi-additive processes, and we found that the introduction of relatively high-resistive CuN film does not cause degradation of the propagation characteristics.

Impedance of Hot-Electron Bolometer Mixers at Terahertz Frequencies

This paper discusses the current distribution in thin-film devices, especially in a hot-electron bolometer (HEB) mixer at terahertz frequencies, and the consequences of different current distributions on the device impedance. We first present an approximate analytical model from which we derive a proposed rule of thumb for deciding when the film is thin enough to support a current distribution that is uniform in the transverse direction. We then verify this rule by performing electromagnetic simulations. Our conclusion is that the current distribution in thin films with a relatively high DC resistivity and small film thickness with respect to the skin depth is essentially uniform up to 8 THz. These results are crucial, e.g., for understanding radiation coupling between an HEB and an antenna and indispensable when analyzing detectors and receivers based on bolometric properties of thin films.

CdZnS/CdTe 이종접합의 커패시턴스-전압 특성에 관한 연구

본 연구에서는 CdZnS와 CdTe로 구성되는 이종접합 소자를 제작하고 커패시턴스-전압 특성을 조사하였다. CdS/CdTe 접합의 경우, 역방향 바이어스가 증가함에 따라 공핍층의 폭이 커져 커패시턴스 값이 약간 감소하였으나 CdZnS/CdTe 접합에서는 CdTe 박막 내에서의 공핍층 폭이 바이어스에 크게 영향을 받지 않아 커패시턴스 값이 역방향 바이어스에 따라 거의 변화가 없었다. 바이어스 전압을 인가하지 않은 상태에서의 공핍층 폭은 높은 CdZnS 박막의 비저항 및 낮은 캐리어 농도로 인해 CdS/CdTe 접합보다 CdZnS/CdTe 접합에서 보다 큰 값을 나타내었다. CdZnS/CdTe 태양전지의 개방전압은 Zn의 비율이 커짐에 따라 CdZnS 박막과 CdTe 박막의 전자 친화력 차이의 감소로 인하여 크게 증가하였으나, Zn 비율이 0.35 이상인 경우 오히려 감소함을 알 수 있었다. 또한 CdZnS 박막의 높은 비저항이 태양전지의 직렬저항을 상승시켜 전지의 변환 효율은 오히려 감소함을 알 수 있었다. In this work, we fabricated the CdZnS/CdTe heterojunction and investigated the C-V characteristics to determine the depletion width and the charge density distribution. A parallel experiment on CdS/CdTe heterojunction was also carried out for comparison. The depletion region width, for CdZnS/CdTe heterojunction, was nearly constant, regardless of bias voltage. However, the depletion region was wider than that of CdS/CdTe heterojunction due to high resistivity of CdZnS film. The interface charge density of CdZnS/CdTe heterojunction was increased linearly with the bias voltage and showed lower values than those for CdS/CdTe junction. The open circuit voltage of CdZnS/CdTe heterojunction solar cells increased with zinc mole ratio due to reducing of the electron affinity difference between CdZnS and CdTe films. However, the increase of series resistance due to the high resistivity of Cd1-xZnxS films results in reducing conversion efficiency.

The properties of plasma-enhanced atomic layer deposition (ALD) ZnO thin films and comparison with thermal ALD

Zinc oxide (ZnO) thin films were prepared by plasma-enhanced atomic layer deposition (PE-ALD) using oxygen plasma as a reactant and the properties were compared with those of thermal atomic layer deposition (TH-ALD) ZnO thin films. While hexagonal wurzite phase with preferential (002) orientation was obtained for both cases, significant differences were observed in various aspects of film properties including resistivity values between these two techniques. Photoluminescence (PL) measurements have shown that high resistivity of PE-ALD ZnO thin films is due to the oxygen interstitials at low growth temperature of 200°C, whose amount decreases with increasing growth temperature. Thin film transistors (TFT) using TH- and PE-ALD ZnO as an active layer were also fabricated and the device properties were evaluated comparatively.

Thin film chip resistors with high resistance and low temperature coefficient of resistance

High resistance thin film chip resistors (0603 type) were studied, and the specifications are as follows: 1 kΩ with tolerance about ±0.1% after laser trimming and temperature coefficient of resistance (TCR) less than ±15×10−6/°C. Cr-Si-Ta-Al films were prepared with Ar flow rate and sputtering power fixed at 20 standard-state cubic centimeter per minute (sccm) and 100 W, respectively. The experiment shows that the electrical properties of Cr-Si-Ta-Al deposition films can meet the specification requirements of 0603 type thin film chip resistors when the deposition time was about 11 min and deposition films were annealed at 500 °C for 120 min. The morphologies of Cr-Si-Ta-Al film surfaces were examined by scanning electron microscopy (SEM). The analysis suggests that Ta and Al may be distributed in CrSi2 film with mixed form of several structures (e.g., bridge-like, capillary-like or island-like structures), and such a structure distribution is responsible for high film resistance and low TCR of Cr-Si-Ta-Al film.

Effect of Gold Addition on Electrical and Optical Properties of NiO Films by Rf Sputtering

The NiO-Au composite films with Au contents of 0 to 33.7 at.% are deposited on glass substrates. The high electrical resistivity (ρ) of Au-doped NiO films with Au contents below 1.0 at.% is difficlut to measure by four point probe. The ρ value could be reduced to 30.4 Ω-cm as Au content of 1.4 at.% is added into NiO film. It is reduced significantly to 0.375 Ω-cm as Au content is increased to 13.6 at.%. Further increasing the Au content to 33.7 at.%, the ρ value of NiO film is further decreased to 4 x 10-4 Ω-cm. On the other hand, the transmittance of Au doped NiO films also decreases with increasing Au contents. The transmittance for pure NiO film is as high as 96 %. As the Au contents of 1.4, 13.6, and 33.7 % are added into NiO film, they are decreased drastically to 45 %, 20 %, and 9 % respectively. The XRD patterns of Au-doped NiO films with Au content below 9.6 at.% only appear NiO peaks and their (200) peaks shift slightly to low angle as Au content is increased. When Au content is added to above 9.6 at.%, the NiO crystalline become worse. In addition, further increasing the Au content to above 13.6 at.%, the (111) peak of Au also appears in XRD patterns. This indicating that the Au atoms instead of part of Ni atoms results in the enlargement of NiO lattice for Au-doped NiO film with lower Au contents, but large amount of Au atoms are precipitated from the NiO lattice when the content of Au in the NiO film is increased to above 13.6 at.%.

Development of atmospheric pressure CVD processes for highquality transparent conductive oxides

For the past decade TNO has been involved in the research and development of atmospheric pressure CVD (APCVD) and plasma enhanced CVD (PECVD) processes for deposition of transparent conductive oxides (TCO), such as tin oxide and zinc oxide. It is shown that by combining precursor development, fundamental gas phase and surface chemistry studies, process optimization and modeling-based reactor design, the demanding product requirements and cost issues of different types of thin film PV can be met. Our studies on the APCVD deposition of SnO2:F reveal the influence of different types of precursors and process conditions on the transmittance, morphology and conductance of the film. It is shown that a high transmittance (80%) and low resistivity (4.0·10-4Ω·cm) film can be obtained in combination with an intrinsic surface structure that enhances the light trapping effect. © 2009 Published by Elsevier Ltd.

Corrosion Behavior of Surface-Treated Implant Ti-6Al-4V by Electrochemical Polarization and Impedance Studies

Implant materials for orthopedic and heart surgical services demand a better corrosion resistance material than the presently used titanium alloys, where protective oxide layer breaks down on a prolonged stay in aqueous physiological human body, giving rise to localized corrosion of pitting, crevice, and fretting corrosion. A few surface treatments on Ti alloy, in the form of anodization, passivation, and thermal oxidation, followed by soaking in Hank solution have been found to be very effective in bringing down the corrosion rate as well as producing high corrosion resistance surface film as reflected from electrochemical polarization, cyclic polarization, and Electrochemical Impedance Spectroscopy (EIS) studies. The XRD study revealed the presence of various types of oxides along with anatase and rutile on the surface, giving rise to high corrosion resistance film. While surface treatment of passivation and thermal oxidation could reduce the corrosion rate by 1/5th, anodization in 0.3 M phosphoric acid at 16 V versus stainless steel cathode drastically brought down the corrosion rate by less than ten times. The mechanism of corrosion behavior and formation of different surface films is better understood from the determination of EIS parameters derived from the best-fit equivalent circuit.

Epitaxial Growth of High-Resistivity CdTe Thick Films Grown Using a Modified Close Space Sublimation Method

This paper reports the growth of high-resistivity CdTe thick epitaxial films of single crystal nature using a modified close space sublimation method (MCSS) in a Te-rich environment. We propose that the high Te2 partial pressure results in an increased concentration of TeCd antisites acting as deep donors to produce the high-resistivity CdTe, as well as improved quality of thick films. This is in agreement with the deep-donor model introduced by Fiderele et al. [Cryst. Res. Technol. 38 (2003) 588]. The thick films have a µeτe value in the order 10-4 cm2 V-1 and as expected, the TeCd antisites appeared not to act as electron traps.

Different origins of the yellow luminescence in as-grown high-resistance GaN and unintentional-doped GaN films

The yellow luminescence (YL) in as-grown high-resistance (HR) and unintentional-doped (UID) GaN films grown by metal organic chemical vapor deposition has been investigated by means of photoluminescence and monoenergetic positron annihilation spectroscopy. It is found there is stronger YL in UID-GaN with higher concentration of gallium vacancy (VGa), suggesting that VGa-involved defects are the origin responsible for the YL in UID-GaN. Contrastly, there is much stronger YL in HR-GaN that is nearly free from VGa, suggesting that there is another origin for the YL in HR-GaN, which is thought as the carbon-involved defects. Furthermore, it is found that the HR-GaN film with shorter positron diffusion length Ld exhibits stronger YL. It is suggested that the increased wave function overlap of electrons and holes induced by the extremely strong space localization effect of holes deduced from the short Ld is the vital factor to enhance the YL efficiency in HR-GaN.