Publications

A compact optoelectronic integrated circuit (OEIC) for generation of millimeter-wave frequencies was demonstrated. It integrates a passively modelocked semiconductor ring laser, optical amplifier and high-speed photodiode for generation, amplification and detection of an optical pulse train with 30 to 90 GHz pulse-repetition frequency. This OEIC concept can be used in a wide variety of applications that require a very compact, light weight millimeter-wave source.

Microfluidic chips have the potential to be useful in bioanalytical tools for DNA, protein, and cellular studies. To realize this potential, means for introducing fluids, separating their components, and detection must be integrated in onto the chip. Semiconductor laser microcavity spectroscopy is investigated as a means for ultrasensitive detection of various fluids, cells, and particulates. Two methods for implementing this laser device, the spectra for four different types of cells, and how the transverse mode spacings can be used to caliper the cell dimensions are discussed. The current investigations of different methods for pumping fluids through the microactivity space using mechanical or electromotive forces are also discussed.

Sandia National Laboratories has developed a chip scale packaging technology called mini Ball Grid Array (mBGA). The mBGA is a flip chip die, obtained by redistributing peripheral pads in existing dies to an area array of pads 10 mils or larger in diameter with a minimum pitch of 20 mils. The peripheral pads are redistributed to area array pads using two polyimide dielectric and two metal conductor layers. mBGA can be closely tiled together on a substrate to yield a very high circuit density. In an earlier report, we presented the results on the reliability and thermal performance of mBGA on silicon and ceramic substrates. In this report, we present an mBGA cost analysis, improvement in the mBGA bump adhesion, and reliability and thermal performance of mBGA assemblies on FR-4 boards.

VRaptor, a VR system for situational training that uses trainer-defined scenarios is described. The trainee is represented by an avatar; the rest of the virtual world is populated by virtual actors, which are under the control of trainer-defined scripts. The scripts allow reactive behaviors, but the trainer can control the overall scenario. This type of training system may be very useful in supplementing physical training.

Gamma-densitometry tomography (GDT) and electrical-impedance tomography (EIT) have both been applied to a liquid-solid flow for comparison purposes. The experiment consisted of a cylinder (19 cm diameter) filled with water, in which 80 μm glass spheres were suspended by a mixer to achieve solid volume fractions of 0.01, 0.02, and 0.03. Both GDT and EIT revealed a relatively uniform distribution of solids in the measurement plane, and the average solid volume fractions from both techniques were in good agreement.

Hot electron induced degradation in 0.25 μm n-channel MOSFETs annealed in H2 or D2 containing atmospheres is reported. Threshold voltage and channel transconductance variations correlate with the growth of the interface state density evidenced by charge pumping measurements. The transistor lifetime (for a given transconductance variation) is ∼ 10-40 times shorter for H2 as opposed to D2 annealed devices.

It is shown analytically and experimentally that, when significant densities of positive and/or negative charge are trapped in the bulk of the oxide, standard thermally stimulated current (TSC) measurements at negative gate bias may not provide accurate estimates of MOS oxide-trap charge densities. Combining TSC measurements at negative bias with capacitance-voltage (C-V) measurements allows useful, self-consistent estimates of trapped electron densities in the oxide to be obtained. However, unless one can determine whether most of the trapped electrons lie in the bulk of the oxide or in border traps, unambiguous estimates of trapped positive charge densities cannot be obtained with negative or positive bias TSC, with or without C-V measurements. Implications are discussed for charge trapping in radiation-hardened thermal oxides, SIMOX buried oxides, and bipolar base oxides. © 1997 IEEE.

The dependence of single event gate rupture (SEGR) critical field on oxide thickness is examined for gate oxides from 6 to 18 nm. Capacitor data are compared to SEGR data from full integrated circuits. A I/ECR dependence is found for critical field to rupture as a function of ion linear energy transfer (LET), consistent with earlier work for power MOSFETS with oxide thicknesses from 30 to 150 nm. More importantly, critical field to rupture increases with decreasing oxide thickness, consistent with increasing oxide breakdown field prior to heavy-ion exposure. This suggests that SEGR need not be a limiting factor as future technologies scale into the deep submicron region. However, there is a great deal of uncertainty in how voltage may scale with decreasing oxide thickness, and SEGR may continue to be a concern for devices that operate at electric fields significantly higher than 5 MV/cm. © 1997 IEEE.

Radiation-induced gain degradation is compared in two types of lateral PNP bipolar devices that are identical except for the emitter doping. The devices with heavily-doped emitters (1×1020 cm-3) degrade less than the devices with lightly-doped emitters (1×1018 cm-3). Both device types are sensitive to interface-trap formation in the oxide above the emitter-base junction and the neutral base region. In addition, the devices with lightly-doped emitters experience spreading of the depletion region into the emitter, increasing their sensitivity to total-dose irradiation. The gain degradation in both device types is due to a combination of increased base current and decreased collector current. The radiation-induced decrease in collector current is more significant for devices from this technology than for other devices studied previously. Increased gain degradation is observed in heavily-doped devices irradiated at low dose rates, but the enhanced degradation appears to be due to time-dependent effects rather than true dose-rate effects. The lightly-doped devices do not exhibit a clear dose-rate trend and the gain of these devices improves during post-irradiation annealing. © 1997 IEEE.

In large scale 3D EM inverse problems it may not be possible to directly invert a full least-squares system matrix involving model sensitivity elements. Thus iterative methods must be employed. For the inverse problem, we favor either a linear or non-linear (NL) CG scheme, depending on the application. In a NL CG scheme, the gradient of the objective function is required at each relaxation step along with a univariate line search needed to determine the optimum model update. Solution examples based on both approaches will be presented.

The method of finite differences has been employed to solve a variety of 3D electromagnetic (EM) forward problems arising in geophysical applications. Specific sources considered include dipolar and magnetotelluric (MT) field excitation in the frequency domain. In the forward problem, the EM fields are simulated using a vector Helmholtz equation for the electric field, which are approximated using finite differences on a staggered grid. To obtain the fields, a complex-symmetric matrix system of equations is assembled and iteratively solved using the quasi-minimum method (QMR) method. Perfectly matched layer (PML) absorbing boundary conditions are included in the solution and are necessary to accurately simulate fields in propagation regime (frequencies>10 MHz). For frequencies approaching the static limit (<10 KHz), the solution also includes a static-divergence correction, which is necessary to accurately simulate MT source fields and can be used to accelerate convergence for the dipolar source problem.

Light induced electron transfer (ET) from nanosize semiconductors of MoS2 to organic electron acceptors such as 2,2′-bipyridine (bpy) and methyl substituted 4,4′,5,5′-tetramethyl-2,2′-bipyridine (tmb) was studied by static and time resolved photoluminescence spectroscopy. The kinetics of ET were varied by changing the nanocluster size (the band gap), the electron acceptor, and the polarity of the solvent. MoS2 is an especially interesting semiconductor material as it is an indirect semiconductor in bulk form, and has a layered covalent bonding arrangement which is highly resistant to photocorrosion.

A miniature solid-propellant rocket motor has been developed to impart a specific motion to an object deployed in space. This rocket motor effectively eliminated the need for a cold-gas thruster system or mechanical spin-up system. A low-energy igniter, an XMC4397, employing a semiconductor bridge was used to ignite the rocket motor. The rocket motor was ground-tested in a vacuum tank to verify predicted space performance and successfully flown in a Sandia National Laboratories flight vehicle program.

The thermal stability of fluorinated SiO2 films (SiOF) was found to be dependent on F content and the type of substrate upon which the film was deposited. SiOF films with a range of F concentrations were deposited using an electron cyclotron resonance (ECR) plasma upon Si, Al/Si, TiN/Al/Si, and Al/SiO2/Si substrates. Following deposition, the films were deliberately hydrated and/or annealed and their stability assessed. Hydration was found to only affect the high F content films. Capacitance changes with annealing in the high F content films were found to occur beginning at 200 °C. These changes, which were independent of substrate type, likely occurred due to desorption of H2O in the films. After annealing of the high F content films up to 400 °C, a reduction in F content was found for SiOF films on some substrates. Significant reductions were found for SiOF films on Al/Si substrates, while little or no change was found for films on TiN/Al/Si, Al/SiO2/Si, or Si substrates. Local chemical analysis of those films which showed F reduction indicated that the F profile was approximately uniform throughout the layer and did not pile-up at the interface. The substrate-dependent thermal instability exhibited by these films suggests the chemical nature or qualities of the substrate may play a role in the F reduction reaction.

An acousto-optic (AO) deflector composed of PbMoO4 was exposed to 4 MeV protons while operating under Bragg angle conditions. An ion beam in air of 1 mm width was directed normal to the crystal face and laser beam. Between exposures, the approximately 13 mm × 8.5 mm AO deflector was mechanically translated in two dimensions in front of the fixed ion beam. The AO diffraction efficiency was mapped and was observed to change as a function of ion beam location and dose rate. These effects are attributed to the induced change in the temperature distribution of the crystal, which changed the sonic velocity and refractive index. Similar effects were observed when the ion beam was directed at the acoustic transducer.

Charge collection and SEU from angled ion strikes are studied using three-dimensional simulation. The physics of charge collection in unloaded diodes and transistors is explored, as is the angular dependence of upset threshold in CMOS SRAMs. The simulation results are compared to analytical models for charge collection. Modeling fundamental transport in SRAMs, the true effective LET relationship is computed and used to analyze experimental heavy-ion data. Impacts on SEU test methodology are discussed. © 1997, IEEE. All rights reserved.

A room Co-60 source was characterized using thermoluminescent dosimeters (TLDs) and pMOS RADFETs. Measurements were made over a range of dose rates between 0.8 and 100 mrad(Si)/s. Dose enhancement (DE) was measured using RADFETs with and without gold-flashed kovar lids. DE factors ranged from 1.05 to 2.35. A method was developed to predict dose enhancement as a function of position and test configuration. This method involves separation of direct and scattered gamma dose rate contributions. ©1997 IEEE.

Finite-difference, prestack depth migrations offers significant improvements over Kirchhoff methods in imaging near or under salt structures. We have implemented a finite-difference prestack depth migration algorithm for use on massively parallel computers which is discussed. The image quality of the finite-difference scheme has been investigated and suggested improvements are discussed.

A key to reducing the risks and costs of associated with oil and gas exploration is the fast, accurate imaging of complex geologies, such as salt domes in the Gulf of Mexico and overthrust regions in U.S. onshore regions. Pre-stack depth migration generally yields the most accurate images, and one approach to this is to solve the scalar-wave equation using finite differences. Current industry computational capabilities are insufficient for the application of finite-difference, 3-D, prestack, depth-migration algorithms. High performance computers and state-of-the-art algorithms and software are required to meet this need. As part of an ongoing ACT1 project funded by the U.S. Department of Energy, we have developed a finite-difference, 3-D prestack, depth-migration code for massively parallel computer systems. The goal of this work is to demonstrate that massively parallel computers (thousands of processors) can be used efficiently for seismic imaging, and that sufficient computing power exists (or soon will exist) to make finite-difference, prestack, depth migration practical for oil and gas exploration.

We describe the metal-organic chemical vapor deposition of InAsSb/InAsP strained-layer superlattice (SLS) active regions for use in mid-infrared emitters. These SLSs were grown at 500°C, and 200 torr in a horizontal quartz reactor using trimethylindium, triethylantimony, AsH3, and PH3. By changing the layer thickness and composition we have prepared structures with low temperature (les/20 K) photoluminescence wavelengths ranging from 3.2 to 5.0 μm. Excellent performance was observed for an SLS light emitting diode (LED) and both optically pumped and electrically injected SLS lasers. An InAsSb/InAsP SLS injection laser emitted at 3.3 μm at 80 K with peak power of 100 mW.

We present a numerical method for nonisothermal, multiphase subsurface transport in heterogeneous porous media. The mathematical model considers nonisothermal two-phase (liquid/gas) flow, including capillary pressure effects, binary diffusion in the gas phase, conductive, latent, and sensible heat transport. The Galerkin finite element method is used for spatial discretization, and temporal integration is accomplished via a predictor/corrector scheme. Message-passing and domain decomposition techniques are used for implementing a scalable algorithm for distributed memory parallel computers. An illustrative application is shown to demonstrate capabilities and performance.

The second silicon revolution will be based on intelligent, integrated microsystems where multiple technologies (such as analog, digital, memory, sensor, micro-electro-mechanical, and communication devices) are integrated onto a single chip or within a multichip module. A necessary element for such systems is cost-effective, high-performance packaging. This paper examines many of the issues associated with the packaging of integrated microsystems, with an emphasis on the areas of packaging design, manufacturability, and reliability. © 1997 Published by Elsevier Science Ltd.

The Authenticated Tracking and Monitoring System (ATMS) answers the need for global monitoring of the status and location of sensitive items on a worldwide basis, 24 hours a day. The ATMS concept uses wireless sensor packs to monitor the status of the items and environmental conditions, to collect a variety of sensor event data, and to transmit the data through the INMARSAT satellite communication system, which then sends the data to appropriate ground stations for tracking and monitoring. Authentication and encryption algorithms are used throughout the system to secure the data during communication activities. A typical ATMS application would be to track and monitor the safety and security of a number of items in transit along a scheduled shipping route. The resulting tracking, timing, and status information could then be processed to ensure compliance with various agreements. Following discussions between the Australian Safeguards Office (ASO), the U.S. Department of Energy (DOE), and Sandia National Laboratories (SNL) in early 1995, the parties mutually decided to conduct and evaluate a field trial prototype ATMS to track and monitor shipments of uranium ore concentrate (UOC) from a currently operating uranium mine in Australia to a final destination in Europe. This trial is in the process of being conducted on a worldwide basis with tracking and monitoring stations located at sites in both Australia and the U.S. This paper describes the trial.

We have investigated two types of extended defects commonly found in AlN, GaN and InN films using density-functional techniques. First, basal-plane stacking faults have been studied for all three compounds. Stacking-fault energies were found to be largest in AlN and smallest in GaN consistent with density-functional results for their wurtzite/zinc-blende energy differences. In addition, the 4H and 6H structures were found to have lower energies than zinc blende for all three compounds. Second, we have investigated the electronic structure and formation energy for an edge dislocation in AlN. The full-core dislocation structure was found to have a filled electronic level approximately 0.55 eV above the valence-band edge and an empty level 1.4 eV below the conduction-band edge. An open-core structure was found to have filled and empty electronic levels closer to the middle of the energy gap. Formation energies for these two geometries suggest that the full-core structure would be expected to form in p-type material whereas both are expected in n-type material.

Amorphous carbon is an elemental form of carbon with low hydrogen content, which may be deposited in thin films by the impact of high energy carbon atoms or ions. It is structurally distinct from the more well-known elemental forms of carbon, diamond and graphite. It is distinct in physical and chemical properties from the material known as diamond-like carbon, a form which is also amorphous but which has a higher hydrogen content, typically near 40 atomic percent. Amorphous carbon also has distinctive Raman spectra, whose patterns depend, through resonance enhancement effects, not only on deposition conditions but also on the wavelength selected for Raman excitation. This paper provides an overview of the Raman spectroscopy of amorphous carbon and describes how Raman spectral patterns correlate to film deposition conditions, physical properties and molecular level structure.