Probe Resistivity Measurements Research Articles

Effects of Sn doping in Hg 1− xSn xBa 2Ca 2Cu 2O 8+δ superconductors

Tin-doped samples of Hg 1− x Sn x Ba 2Ca 2Cu 3O 8+ δ (hereafter symbolized as (Hg 1− x Sn x )-1223) with x = 0, 0.05, 0.1, 0.2, 0.4 and 0.5 have been synthesized in sealed silica tubes by the solid state reaction method. The precursor can be prepared in air. The effects of Sn doping on the formation and stability, microstructure of grain growth and critical temperature of the (Hg 1− x Sn x )-1223 superconductor have been investigated by X-ray diffraction, scanning electron microscopy (SEM) and electron probe microanalysis (EDS), thermogravity analysis, resistance measurements and ac susceptibility measurement techniques. Experimental results show that a small amount of Sn doped in Hg-1223 promotes the formation of the triple CuO 2-layer superconducting compound. The stability of the product compounds is also enhanced. Sn doping may play a role as a nucleating centre. The T c for Sn-doped samples (Hg 1− x Sn x )-1223 with x ≤ 0.1 does not notably change as compared with the pure Hg-1223 phase (about 134 K). Sn doping is favourable for synthesizing the Hg-1223 superconductor. However, further increasing of Sn doping into the sample leads to a deterioration on both T c and the fraction of superconducting phase.

Morphological and Microstructural Stability of Boron‐Doped Diamond Thin Film Electrodes in an Acidic Chloride Medium at High Anodic Current Densities

Boron‐doped diamond thin films have been examined before and after high‐current‐density electrolysis to investigate the morphological and microstructural stability of this new electrode material. The diamond thin films were used to generate chlorine from a solution of 1.0 M + 2.0 M NaCl at current densities of 0.05 and 0.5 A/cm2 for times up to 20 h. Comparative studies were made using common “graphitic” electrodes including highly oriented pyrolytic graphite, glassy carbon, and Grafoil®. The electrodes were characterized using four‐point probe resistivity measurements, atomic force microscopy, scanning electron microscopy, Raman spectroscopy, x‐ray photoelectron spectroscopy, and cyclic voltammetry. In all cases, no severe morphological or microstructural damage (i.e., corrosion) was observed on films exposed to the highest current density. There were surface compositional changes in the forms of oxygenation and nondiamond carbon impurity etching that produced an increase in the reaction overpotential. Specifically, the overpotential was supposed to result from a combination of decreased surface conductivity due to the formation of carbon‐oxygen functional groups and loss of kinetically active redox sites due to the oxidative etching of nondiamond carbon impurities.

The role of temperature gradient in the growth of Bi-system whiskers

This is the first report that an appropriate temperature gradient plays a catalytic role in the growth of Bi-system whiskers. Bi-system whiskers are grown out only under a temperature gradient of 2–5 C/cm, but not under other cases. The fact strongly supports the tip growth mechanism. Magnetization measurement and four probe resistance measurement show that these whiskers have perfect superconducting properties.

The effects of fluorine ion implantation on the formation of SIMOX structure

The effects of fluorine ion implantation on the formation and characteristics of SOI/SIMOX structure have been investigated by the combined implantation of high dose oxygen and lower dose fluorine into silicon. After high temperature annealing, fluorine atoms migrated to the Si surface, showing an anomalous out-diffusion behavior. The SOI structure is very different from that of non-fluorinated samples. A polycrystalline silicon layer was formed between the silicon overlayer and the buried oxide. Furthermore, the lower energy F + implantation affected the SOI structure more significantly and a Si-rich layer was formed in the buried oxide. The electrical properties of the silicon overlayer were analyzed by spreading resistance probe and Hall measurements. © 1997 Elsevier Science S.A. All rights reserved.

The Conversion of Czochralski Silicon from P-Type to N-Type by Hydrogen Plasma Enhanced Thermal Donor Formation

ABSTRACTOur experiments show a hydrogen plasma assisted creation of p-n junctions in p-type Cz silicon due to a hydrogen enhanced thermal donor (TD) formation at temperatures ≤450 °C. Applying DC or HF plasma treatments a conversion of p-type into n-type Cz silicon by TD formation occurs. One can distinguish one step processes (p-n junction formation appears just after the plasma exposure) and two step processes (p-n junction formation requires subsequent post hydrogenation annealing). The samples are studied by depth resolved spreading resistance probe (SRP), capacitance-voltage (CV) and Hall measurements. For the one step processes a kinetic model for hydrogen enhanced TD formation is presented.

Oxygen Gettering and Thermal Donor Formation at Post-Implantation Annealing of Hydrogen Implanted Czochralski Silicon

ABSTRACTThe effect of oxygen gettering by buried defect layers at post-implantation annealing of hydrogen implanted Czochralski (Cz) grown silicon has been investigated. Hydrogen ions were implanted with an energy of 180 keV and doses of 2.7.1016cm−2 into p-type Cz and for comparison into p-type float zone (Fz) Si. The samples were annealed at temperatures between 400 °C and 1200 °C in a forming gas ambient and examined by secondary ion mass spectrometry (SIMS) in order to measure the hydrogen and oxygen concentration profiles. Spreading resistance probe (SRP) measurements were used to obtain depth resolved profiles of the resistivity. The observed changes of the resistivity after post-implantation annealing of hydrogen implanted Cz and Fz Si can be explained by hydrogen enhanced thermal donor formation processes (oxygen or hydrogen related) and charges at the SiOx precipitates. The effective oxygen gettering in hydrogen implanted Cz silicon is attributed to hydrogen enhanced diffusion of oxygen to buried defect layers.

Influence of in-process copper incorporation on the quality of diamond-like carbon films deposited by pulsed laser deposition technique

Copper-incorporated carbon films have been prepared on Si(100) and Corning (7059) glass substrates by the pulsed excimer laser deposition technique using KrF radiation (λ = 248 nm). Cold-pressed composite pellets, having compositions from 2 at. % to 11 at. % copper in carbon, were used as targets for ablation. Good quality, scratch-proof films were obtained at a laser energy density of 2−3 J/cm2 and a substrate temperature of 50 °C. The films were characterized by x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), UV-visible spectrometry, ellipsometry, and four-point probe resistivity measurements. Under similar deposition conditions, films obtained from composite targets of lower copper concentration are seen to have better diamond-like character as compared to those obtained from a pure graphite target. At such low concentrations, copper is seen to cluster in the form of nanoparticles. As the copper concentration increases in the films, they tend to acquire disordered graphitic network with degraded DLC characteristics, and the size of copper agglomerates increases from about 5 nm (for the 2 at. % case) to 85 nm (for the 11 at. % case). It is seen that an increase in the copper content leads to modifications in the carbon network, additional interband transitions, and reduction of the band gap.

In-situ resistivity measurements during the oxygenation of YBa 2Cu 3O 7−δ and Gd 0.8Y 0.2Ba 2Cu 3O 7−δ single crystals

We report on measurements of the electrical resistivity during the oxygenation of single crystals of YBa 2Cu 3O 7−δ and Gd 0.8Y 0.2Ba 2Cu 3O 7−δ. Real four-point probe resistivity measurements were performed between room temperature and 650°C in pure oxygen atmosphere. The crystals were kept at each temperature as long as they reached an equilibrium state with no further changes in the resistivity. From the R( t) curves we were able to calculate the chemical diffusion coefficient for various temperatures between 380 and 600°C. In contrast to some literature the diffusion coefficients for oxygen in- and out diffusion were found to have the same value. The values of the diffusion coefficient for the different temperatures obey an Arrhenius law, thus allowing a determination to be made of the activation energy for oxygen diffusion. For Gd 0.8Y 0.2Ba 2Cu 3O 7−δ crystals D 0 was determined to be 4.94 × 10 −5 cm 2/s. The activation energy ΔE was found to be 0.52 eV. For YBa 2Cu 3O 7−δ crystals the activation energy ΔE was determined to be about 0.8 eV. The very low values compared to the results of other authors, which we obtained for the diffusion coefficient of oxygen in our crystals are in good agreement with the small impurity content we found in these crystals and with the observed long time, which is required for a full oxygenation.

Minimizing the size of force-controlled point contacts on silicon for carrier profiling

The spatial distribution of charge carriers in semiconducting structures can be derived from conductive properties. In this report silicon cantilevers with integrated tips and coated with boron‐doped chemical vapor deposited diamond have been used for the first time to establish electrically reliable point contacts on silicon. The relation between the applied force and the nanoindentation characteristics has been investigated in a range from 10 to 150 μN. The threshold value necessary to pierce the native oxide layer has been obtained and is found to depend on the peculiar coating of each tip. The data are correlated with the current–voltage characteristics of the contacts. The impedance of point contacts on homogeneously doped p‐ and n‐type silicon with known resistivity has been measured and calibration curves have been plotted for nanospreading resistance probe measurements. It is found that only above the threshold for plastic deformation can useful electrical characterizations be performed.

Perpendicular current giant magnetoresistance in 0.4 μm diameter Co-Cu multilayer sensors

We have fabricated a novel giant magnetoresistive (GMR) multilayer (ML) flux sensor that is designed to operate in the current perpendicular to the plane (CPP) mode. The CPP-GMR sensor is a 0.4 /spl mu/m diameter, 0.09 /spl mu/m tall Co-Cu ML pedestal. The sensors are patterned using electron beam lithography. The Al/sub 2/O/sub 3/-TiC substrate is coated with a sputter deposited Al/sub 2/O/sub 3/ film that is polished to <0.2 nm root mean square (RMS) roughness. Contact to the bottom of the CPP-GMR sensor is made by depositing and Co-Cu multilayers onto a smooth 0.45 /spl mu/m thick Mo-Si ML stack. The top contact is self-aligned to the CPP-GMR sensor. This is accomplished, in part, by chemical mechanical polishing (CMP). The top and bottom contacts are electrically isolated by a plasma enhanced chemical vapor deposited (PECVD) Si/sub 3/N/sub 4/ film. The configuration of the contacts allows four point probe resistance measurements. The CPP-GMR coefficient for these 0.4 /spl mu/m diameter sensors is 13%.

Synthesis of low resistivity complex oxides on MgO using Pt as buffer layer

Highly crystalline SrRuO3 (SRO) and La0.5Sr0.5CoO3 (LSCO) thin films were deposited on (100) Pt/ MgO by pulsed laser deposition. The films were mainly (001) textured normal to the substrate surface with a high degree of in-plane orientation with respect to the substrate’s major axes. These films were characterized using x-ray diffraction, Rutherford backscattering, four-point probe resistivity measurement, and transmission electron microscopy. The room temperature resistivity for LSCO and SRO films on Pt/MgO was found to be ∼35 and ∼40 μΩ-cm, respectively. An ion beam minimum channeling yield of ∼43% and ∼33% was obtained for LSCO and SRO films, respectively. The interface between Pt and oxide was found to be smooth and free from any interfacial diffusion. This result showed that high-quality low resistivity oxide thin films can be deposited on Pt.

Influence of the substrate doping level on spreading resistance profiling

A study has been performed of spreading resistance probe measurements on a series of 200-nm-deep boron implants into p-type substrates with varying doping levels ranging from 3×1014 up to 4×1017/cm3. All implants were performed under the same conditions and with the same dose. However, routinely generated spreading resistance carrier profiles from different sites consistently indicate abnormally high doses and shoulder peak artifacts at the back side of the implant profile for the more highly doped substrates. It is proposed that these artifacts can be related to pressure-enhanced carrier spilling effects underneath the probes. When performing a Laplace-based correction and hence neglecting any carrier spilling effects, the correction factor scheme reacts upon the position of the on-bevel junction position instead of on the vertical junction position which can be considerably deeper in the presence of pressure-enhanced spilling. The observed artifacts can be reduced within Laplace calculations by allowing for more barrier resistance and consequently a larger contact radius.

Electroplating of poly(tetrafluoroethylene) using plasma enhanced chemical vapor deposited titanium nitride as an interlayer

A low-temperature process for titanium nitride (TiN) deposition by means of an electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition process was applied to poly(tetrafluoroethylene) (PTFE). Tetrakis(dimethylamido)titanium introduced into the downstream region of a nitrogen ECR plasma was used as a precursor for TiN deposition at 100 °C. The thin TiN films (thickness 15–30 nm) act as interlayers to activate the electroless deposition of copper followed by an electroplating process. Prior to the deposition of the interlayer, the samples were treated on a biased susceptor with argon ions to enhance the adhesion of the TiN interlayer. This metallization procedure avoids the use of toxic and pollutive etching agents and yields adherent copper layers on PTFE. Films were characterized by four-point probe resistivity measurements, atomic force microscopy, and secondary ion mass spectrometry.

Rapid formation of the high-T c phase in (Bi,Pb)-Sr-Ca-Cu-O superconductor via the sol-gel method

Bi-Pb-Sr-Ca-Cu-O powder was synthesized by the oxalate gel method. A sample with the composition of Bi1.7Pb0.4Sr1.6Ca2.4Cu3.6Oy was used in this study. After pyrolysis of the gel precursor at 500 °C for 5 h, the resulting powder was calcined at 850 °C for another 5 h. The black powder was pressed into pellets and sintered at 852 °C for 5 h. The high-Tc phase was formed more easily in the sample with excess calcium and copper than in the theoretical composition. (Bi,Pb)2Sr2Ca2Cu3Oy (above 90%) was prepared as above within a relatively short time. Characterization of (Bi,Pb)2Sr2Ca2Cu3Oy superconductor by X-ray diffraction, scanning electron microscopy, electron probe microanalysis, resistivity measurement and magnetic measurement, is reported.

Depth Profiles for Hydrogen‐Enhanced Thermal Donor Formation in Silicon: Spreading Resistance Probe Measurements

Hydrogen enhancement of formation rates for oxygen‐related thermal donors in Si has been investigated for dependence on: the source of hydrogen, hydrogen isotope, and exposure time and temperature. Hydrogen injection efficiency is an important variable and depth profiles are dependent upon the surface preparation of samples exposed in an electron cyclotron resonance plasma where ion energies are ≤35 eV. Formation rates up to at 400°C have been observed. A sublinear dependence of the donor formation rate on beam current under 50 keV ion implantation is interpreted as a competition between oxygen‐hydrogen and hydrogen‐hydrogen interactions. Dependence on isotope mass and on exposure time in the plasma indicates hydrogen is the diffusing species that determines the penetration depth for the enhanced donor formation. Peculiar box‐like depth profiles and high formation rates near the advancing front produced in RF plasma exposures are suggestive of hydrogen accumulation near the advancing front. The temperature dependence for the penetration depth gives an activation energy of . This energy is attributed to trap‐limited diffusion wherein hydrogen lowers the energy barrier for the oxygen motion necessary to form thermal donors.

Study on Ti-SiO2 Reaction - Thermodynamic Approach

AbstractInteractions between Ti and SiO2 thin films have been studied in self-aligned transistor process in the MOS Integrated Circuits Technology. A thermodynamic study of this interaction was conducted on the titanium and silicon dioxide chemistry. The Gibbs free energy was analyzed in the 25 to 1000°C range and it was concluded that the 11/3 Ti + SiO2 --&gt; 1/3 Ti5 Si3 + 2 Ti reaction has the lowest free energy. Ti thin films were deposited by sputtering over dry silicon oxide and then sintered in atmospheric pressure furnace - RTP at argon ambient. The samples were analyzed by X-RAY Diffraction (XRD), Rutherford Backscatering Spectroscopy (RBS) and fourpoint- probe resistivity measurements. It was showed that experimental results can be modeled by theoretical analysis.

Structural and magnetic properties of the anion-deficient LaVO 3−δ

The anion deficient LaVO 3−δ ( δ = 0.08) was prepared by solid state reactions using V 2O 3 and pre-dried La 2O 3 in an evacuated induction furnace. The oxygen content was estimated by thermogravimetric analysis (TGA). Rietveld profile analysis of powder X-ray diffraction data shows that this sample adopts an orthorhombically distorted perovskite structure, isostructural with GdFeO 3; space group Pnma, a = 5.5509(1), b = 7.8441(2), c = 5.5513(s) A ̊ . Four probe resistivity measurements indicates that LaVO 3−δ is semiconducting over the experimental temperature range. The magnetic properties of LaVO 3−δ are strongly dependent on the sample cooling history. LaVO 3−δ undergoes a paramagnetic to antiferromagnetic transition at ca. 140 K under zero-field-cooled condition. When cooled in a magnetic field of H appl ≤ 5 kG, however, the anomalous diamagnetic behaviour is observed below ca. 140 K. These properties are discussed in terms of the structure-property relationship, and comparisons are made to the previous results on the stoichiometric LaVO 3.

Structural, optical, and electrical properties of epitaxial chalcopyrite CuIn3Se5 films

Single crystal CuIn3Se5 epitaxial films have been synthesized on GaAs(001) by a hybrid sputtering and evaporation technique. The microstructure, microchemistry, and selected electrical and optical properties of the films have been investigated by scanning electron microscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy, cathodoluminescence, optical absorption and reflection, and four-point probe resistivity measurements. The results showed that the CuIn3Se5 crystals have an ordered point defect structure, a band gap of ≥1.18 eV, an optical absorption coefficient of about 15 000 cm−1 at a photon energy of 1.35 eV, and a film resistivity of ≳105 Ω cm. The results suggest the presence of band tails giving rise to subgap radiative recombination and absorption. Antiphase domain boundaries, stacking faults, and nanotwins were observed in the epitaxial layers and were reduced in number by rapid thermal annealing.

Repeated compressive stress increase with 400 °C thermal cycling in tantalum thin films due to increases in the oxygen content

Stresses which build up in thin films such as tantalum, during thermal processing, can cause major reliability problems in electronic and x-ray optics applications. We demonstrate that 50–200 nm thick sputtered β-Ta thin films undergo repeated compressive stress increases when thermally cycled to 400 °C (at a rate of 10 °C/min) and back in a purified He ambient because of small amounts of oxygen gettered by the tantalum. The oxygen contamination results from the poor quality of the atmospheric seal on the quartz annealing chamber. As-deposited Ta thin films have a compressive stress ranging from −1 to −4 GPa. The compressive stress buildup was monitored in situ and was shown to increase −0.5 GPa on average after each thermal cycle for a final value from −6 to −7 GPa after seven cycles. After being cycled thermally seven times any perturbation of the film such as a four-point probe resistivity measurement can cause the film to instantaneously crack in a serpentine pattern, relieving the large compressive stress. Auger electron spectroscopy depth profiling analysis was used to determine that the as-deposited film contained 1 at. % oxygen which increased to 8%–12% after seven thermal cycles with an approximate doubling in resistivity. The −0.5 GPa average compressive stress increase in Ta thin films when cycled to 400 °C is attributed to a 1.3% increase in oxygen concentration leading to a Ta unit cell expansion of 0.6%.

Study of low-resistivity oxides on Pt/MgO

Abstract Highly crystalline SrRuO3 (SRO) and La0.5Sr0.5CoO3 (LSCO) thin films were deposited on Pt/MgO(100) by pulsed laser deposition. The films were mainly (001) textured normal to the substrate surface with a high degree of in-plane orientation with respect to the substrate's major axes. These films were characterized using X-ray diffraction, Rutherford backscattering, four-point probe resistivity measurement and transmission electron microscopy. The room-temperature resistivities for LSCO and SRO films on Pt/MgO were found to be 35 and 40μωcm respectively. Ion beam minimum channelling yields of 43 and 33% were obtained for LSCO and SRO films respectively. The interface between Pt and oxide was found to be smooth and free from any interfacial diffusion. This result showed that high-quality low-resistivity oxide thin films can be deposited on Pt.