Studies on the optimisation of unbalanced magnetron sputtering cathodes

The optimisation is reported on the design of unbalanced magnetron (UBM) sputtering cathodes. For the study, a planar circular cathode backed by a double-coil electromagnet (compatible for a 100 mm diameter target) was developed. The variation of the structure and strength of the magnetic field in front of the target was investigated for different current combinations in the electromagnetic coils, and its effect on the sputtering process was analysed. The observations on the magnetic field geometry revealed some interesting features, such as the balancing point of the fields along the axis (null-point), and the zero axial region over the target surface (B-z = 0 ring). The positions of both could be controlled by adjusting the ratio of the electric current in the coils. The magnetic field null-point could be used as a reference for the region of homogeneous film growth. The B-z = 0 ring was the location where the glow discharge concentrated (or where the maximum target erosion occurred). The diameter of the ring determined the area covered by the discharge and thus the sputtering efficiency. The optimum substrate position can be fixed according to the position of the null-point and optimisation of sputtering can be achieved by adjusting the diameter of the B-z = 0 ring. The results of this study should be helpful in the designing of an ideal UBM using permanent magnets as well as electromagnets. (C) 1999 Elsevier Science Ltd. All rights reserved.

Non-resonant perturbation formula for interaction impedance measurement for a folded-waveguide SWS

The non-resonant perturbation formula for the measurement of interaction impedance of a folded-waveguide slow-wave structure was derived for the relevant electromagnetic field configuration at the axis of the beam-hole of the structure. Efficacy of the theory was benchmarked through virtual measurement using 3D electromagnetic modeling in CST-studio.

Photoelectron spectroscopy beamline on Indus-1 synchrotron radiation source

We describe here a photoelectron spectroscopy beamline installed on Indus-1 storage ring. Initially we give a brief description of optical and mechanical layout of beam-line. The beamline optics was designed to cover energy range from 10 eV to 200 eV and it consists of a pre-focusing mirror, a toroidal grating monochromator and a post-focusing mirror. We then discuss indigenously developed ultra high vacuum compatible work station to carry out angle integrated photoemission experiments. The beamline has been successfully commissioned and photoemission measurements on a variety of standard samples are presented.

BCS-BEC crossover induced by a synthetic non-Abelian gauge field

We investigate the ground state of interacting spin-1/2 fermions in three dimensions at a finite density (rho similar to k(F)(3)) in the presence of a uniform non-Abelian gauge field. The gauge-field configuration (GFC) described by a vector lambda equivalent to (lambda(x),lambda(y),lambda(z)), whose magnitude lambda determines the gauge coupling strength, generates a generalized Rashba spin-orbit interaction. For a weak attractive interaction in the singlet channel described by a small negative scattering length (k(F)vertical bar a(s)vertical bar less than or similar to 1), the ground state in the absence of the gauge field (lambda = 0) is a BCS (Bardeen-Cooper-Schrieffer) superfluid with large overlapping pairs. With increasing gauge-coupling strength, a non-Abelian gauge field engenders a crossover of this BCS ground state to a BEC (Bose-Einstein condensate) of bosons even with a weak attractive interaction that fails to produce a two-body bound state in free vacuum (lambda = 0). For large gauge couplings (lambda/k(F) >> 1), the BEC attained is a condensate of bosons whose properties are solely determined by the Rashba gauge field (and not by the scattering length so long as it is nonzero)-we call these bosons ``rashbons.'' In the absence of interactions (a(s) = 0(-)), the shape of the Fermi surface of the system undergoes a topological transition at a critical gauge coupling lambda(T). For high-symmetry GFCs we show that the crossover from the BCS superfluid to the rashbon BEC occurs in the regime of lambda near lambda(T). In the context of cold atomic systems, these results make an interesting suggestion of obtaining BCS-BEC crossover through a route other than tuning the interaction between the fermions.

Reduction of oxygen impurity at GaN/beta-Si(3)N(4)/Si interface via SiO(2) to Ga(2)O conversion by exposing of Si surface under Ga flux

The removal of native oxide from Si (1 1 1) surfaces was investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectra (SIMS) depth profiles. Two different oxide removal methods, performed under ultrahigh-vacuum (UHV) conditions, were carried out and compared. The first cleaning method is thermal desorption of oxide at 900 degrees C. The second method is the deposition of metallic gallium followed by redesorption. A significant decrease in oxygen was achieved by thermal desorption at 900 degrees C under UHV conditions. By applying a subsequent Ga deposition/redesorption, a further reduction in oxygen could be achieved. We examine the merits of an alternative oxide desorption method via conversion of the stable SiO(2) surface oxide into a volatile Ca(2)O oxide by a supply of Ga metals. Furthermore, ultra thin films of pure silicon nitride buffer layer were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma followed by GaN growth. The SIMS depth profile shows that the oxygen impurity can be reduced at GaN/beta-Si(3)N(4)/Si interfaces by applying a subsequent Ga deposition/redesorption. (C) 2011 Elsevier B.V. All rights reserved.

The Effect of Evacuated Backside Cavity on the Dynamic Characteristics of a Capacitive Micromachined Ultrasonic Transducer

In this paper, we investigate the effect of vacuum sealing the backside cavity of a Capacitive Micromachined Ultrasonic Transducer (CMUT). The presence or absence of air inside the cavity has a marked effect upon the system parameters, such as the natural frequency, damping, and the pull-in voltage. The presence of vacuum inside the cavity of the device causes a reduction in the effective gap height which leads to a reduction in the pull-in voltage. We carry out ANSYS simulations to quantify this reduction. The presence of vacuum inside the cavity of the device causes stress stiffening of the membrane, which changes the natural frequency of the device. A prestressed modal analysis is carried out to determine the change in natural frequency due to stress stiffening. The equivalent circuit method is used to evaluate the performance of the device in the receiver mode. The lumped parameters of the device are obtained and an equivalent circuit model of the device is constructed to determine the open circuit receiving sensitivity of the device. The effect of air in the cavity is included by incorporating an equivalent compliance and an equivalent resistance in the equivalent circuit.

Novel Mn-doped chalcopyrites

Heavily Mn-doped II-VI-V-2 semiconductors, such as CdGeP2 and ZnGeP2 have been prepared by depositing Mn on single crystalline substrate at nearly 400 T in an ultra high vacuum chamber. Well-defined ferromagnetic hysteresis with a saturation behavior appears in the magnetization curve up to above room temperature. The chemical states of the ZDGeP(2):Mn interface has been clarified by a careful in situ photoemission spectroscopy. The as-prepared surface consists of Ge-rich, metallic Mn compound. In and below the sub-surface region, dilute divalent Mn species as precursors of the DMS phase exist. No MnP phase was observed at any stage of the depth profile. Theoretical band-calculation suggests that the system with vacancies (Cd, V-c, Mn)GeP2 or a non-stoichiometric (Cd, Ge, Mn)GeP2 are ferromagnetic and energetically stable although ferromagnetism is not stable in a stoichiometric compound (Cd, Mn)GeP2. (C) 2003 Elsevier Ltd. All rights reserved.

Studies on thin film materials on acrylics for optical applications

Deposition of durable thin film coatings by vacuum evaporation on acrylic substrates for optical applications is a challenging job. Films crack upon deposition due to internal stresses and leads to performance degradation. In this investigation, we report the preparation and characterization of single and multi-layer films of TiO2, CeO2, Substance2 (E Merck, Germany), Al2O3, SiO2 and MgF2 by electron beam evaporation on both glass and PMMA substrates. Optical micrographs taken on single layer films deposited on PMMA substrates did not reveal any cracks. Cracks in films were observed on PMMA substrates when the substrate temperature exceeded 80degreesC. Antireflection coatings of 3 and 4 layers have been deposited and characterized. Antireflection coatings made on PMMA substrate using Substance2 (H2) and SiO2 combination showed very fine cracks when observed under microscope. Optical performance of the coatings has been explained with the help of optical micrographs.

Analytical Evaluation of Squeeze Film Forces in a CMUT With Sealed Air-Filled Cavity

The presence of vacuum inside the cavity of a capacitive micromachined ultrasonic transducer (CMUT) causes the membrane of the device (which is the main vibrating structural component) to deflect towards the substrate, thereby causing a reduction in the effective gap height. This reduction causes a drastic decrease in the pull-in voltage of the device limiting the DC bias at which the device can be operated for maximum efficiency. In addition, this initial deflection of the membrane due to atmospheric pressure, causes significant stress stiffening of the the membrane, changing the natural frequency of the device significantly from the design value. To circumvent the deleterious effects of vacuum in the sealed cavity, we investigate the possibility of using sealed CMUT cavities with air inside at ambient pressure. In order to estimate the transducer loss due to the presence of air in the sealed cavity, we evaluate the resulting damping and determine the forces acting on the vibrating membrane resulting from the compression of the trapped air film. We take into account the flexure of the top vibrating membrane instead of assuming the motion to be parallel-plate like. Towards this end, we solve the linearized Reynolds equation using the appropriate boundary conditions and show that, for a sealed CMUT cavity, the presence of air does not cause any squeeze film damping.

Ascent Phase Trajectory Optimization of a Generic Launch Vehicle

Trajectory optimization of a generic launch vehicle is considered in this paper. The trajectory from launch point to terminal injection point is divided in to two segments. The first segment deals with launcher clearance and vertical raise of the vehicle. During this phase, a nonlinear feedback guidance loop is incorporated to assure vertical raise in presence of thrust misalignment, centre of gravity offset, wind disturbance etc. and possibly to clear obstacles as well. The second segment deals with the trajectory optimization, where the objective is to ensure desired terminal conditions as well as minimum control effort and minimum structural loading in the high dynamic pressure region. The usefulness of this dynamic optimization problem formulation is demonstrated by solving it using the classical Gradient method. Numerical results for both the segments are presented, which clearly brings out the potential advantages of the proposed approach.

Recent Advances in Low CTE and High Density System-on-a-Package (SOP) Substrate with Thin Film Component Integration

The Packaging Research Center has been developing next generation system-on-a-package (SOP) technology with digital, RF, optical, and sensor functions integrated in a single package/module. The goal of this effort is to develop a platform substrate technology providing very high wiring density and embedded thin film passive and active components using PWB compatible materials and processes. The latest SOP baseline process test vehicle has been fabricated on novel Si-matched CTE, high modulus C-SiC composite core substrates using 10mum thick BCB dielectric films with loss tangent of 0.0008 and dielectric constant of 2.65. A semi-additive plating process has been developed for multilayer microvia build-up using BCB without the use of any vacuum deposition or polishing/CMP processes. PWB and package substrate compatible processes such as plasma surface treatment/desmear and electroless/electrolytic pulse reverse plating was used. The smallest line width and space demonstrated in this paper is 6mum with microvia diameters in the 15-30mum range. This build-up process has also been developed on medium CTE organic laminates including MCL-E-679F from Hitachi Chemical and PTFE laminates with Cu-Invar-Cu core. Embedded decoupling capacitors with capacitance density of >500nF/cm2 have been integrated into the build-up layers using sol-gel synthesized BaTiO3 thin films (200-300nm film thickness) deposited on copper foils and integrated using vacuum lamination and subtractive etch processes. Thin metal alloy resistor films have been integrated into the SOP substrate using two methods: (a) NiCrAlSi thin films (25ohms per square) deposited on copper foils (Gould Electronics) laminated on the build-up layers and two step etch process for resistor definition, and (b) electroless plated Ni-W-P thin films (70 ohms to few Kohms per square) on the BCB dielectric by plasma surface treatment and activation. The electrical design and build-up layer structure along- - with key materials and processes used in the fabrication of the SOP4 test vehicle were presented in this paper. Initial results from the high density wiring and embedded thin film components were also presented. The focus of this paper is on integration of materials, processes and structures in a single package substrate for system-on-a-package (SOP) implementation

Effect of Te addition on the optical properties of As(2)S(3) thin film

Bilayer thin films of Te/As(2)S(3) were prepared from Te and As(2)S(3) by thermal technique under high vacuum. Optical constants were calculated by analysing the transmission spectrum in the spectral range 400-1100 nm. The optical band gap decreases with the addition of Te to As(2)S(3). The decrease of optical band gap has been explained on the basis of density of states and the increase in disorder in the system. We have irradiated the as-deposited films using a diode pumped solid state laser of 532 nm wavelength to study photo-diffusion of Te into As(2)S(3). The changes were characterised by Fourier Transform Infrared and X-ray Photoelectron Spectroscopy (XPS). The optical band gap is found to be decreased with the light irradiation which is proposed due to homopolar bond formation. The core level peaks in XPS spectra give information about different bond formation. (C) 2011 Elsevier B.V. All rights reserved.

Effect of Gallium on microstructure and mechanical properties of Nb-Si eutectic alloy

In this paper, we report a significant improvement in mechanical properties of near eutectic Nb-Si alloys by addition of Gallium (Ga) and control of microstructural length scale. A comparative study of two alloys Nb-18.79 at.%Si and Nb-20.2 at.%Si-2.7 at.%Ga were carried out. The microstructure refinements were carried out by vacuum suction casting in water cooled thick copper mold. It is shown that addition of Ga suppresses Nb(3)Si phase and promotes beta-Nb(5)Si(3) phase. The microstructural length scale and in particular eutectic spacing reduces significantly to 50-100 nm in suction cast ternary alloys. Compression test shows a strength of 2.8 +/- 0.1 GPa and plasticity of 4.3 +/- 0.03%. In comparison, the binary Nb-18.79 at.%Si alloy processed under identical conditions exhibit coarser length scale (300-400 nm) and brittle behavior. The fracture toughness of Ga containing suction cast alloy shows a value of 24.11 +/- 0.5 MPa root m representing a major improvement for bulk Nb-Si eutectic alloy. (C) 2011 Elsevier Ltd. All rights reserved.

Knudsen effusion measurements on Cr Mn alloys

The equilibrium partial pressures of Mn over bcc Cr--Mn alloys have been measured using Knudsen cell technique in the temp. range 1200-1500K. The alloys in particulate form were contained in thoria crucibles inside Knudsen cells made of tungsten. The rates of mass loss of each cell under vacuum was monitered as a function of time at constant temp. using a microbalance. Activities exhibit mild negative deviations from Raoult's law, contrary to indications from an earlier study using a fused salt emf technique. The Cr--Mn system is characterized by negative enthalpy and excess entropy of mixing. There is close similarity between the composition dependence of enthalpy and excess entropy. These findings suggest strong vibrational and negligible magnetic contributions to excess entropy of mixing in bcc phase at high temp. 10 ref.--AA

Stress Evolution With Temperature in Titanium-Rich NiTi Shape Memory Alloy Films

The effect of deposition temperature on residual stress evolution with temperature in Ti-rich NiTi films deposited on silicon substrates was studied. Ti-rich NiTi films were deposited on 3? Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 degrees C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 degrees C and the lowest for the film deposited and annealed at 300 degrees C. All the three films were found to be amorphous in the as-deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 degrees C) was similar for all three films although the spike in tensile stress, which occurs at similar to 330 degrees C, was significantly higher in the film deposited and annealed at 300 degrees C. All the films were also found to undergo partial crystallisation on heating up to 450 degrees C and this resulted in decrease in the stress values around 5560 degrees C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 degrees C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.