Publications

Vector network analyzers provide a convenient way to measure scattering parameters of a variety of microwave devices. However, these instruments, unlike oscilloscopes for example, require a relatively high degree of user knowledge and expertise. Due to the complexity of the instrument and of the calibration process, there are many ways in which an incorrect measurement may be produced. We routinely use check standards to verify that the network analyzer is operating properly. In the past, these measurements were recorded manually and, sometimes, interpretation of the results was problematic. To aid our measurement assurance, a software program was developed to automatically measure a check standard and compare the new measurements with an historical database of measurements of the same device. The program acquires new measurement data from selected check standards, plots the new data against the mean and standard deviation of prior data for the check standard, and updates the database files for the check standard. The program is entirely menu-driven requiring little additional work by the user. This paper describes the function of the software, including a discussion of its capabilities, and the way in which the software is used in our lab. Finally, some examples are given showing how the software can detect potential measurement problems.

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.

The design of complex systems is difficult at best, but as a design becomes intensively dependent on the computer processing of external and internal information, the design process quickly borders chaos. This situation is exacerbated with the requirement that these systems operate with a minimal quantity of information, generally corrupted by noise, regarding the current state of the system. Establishing performance requirements for such systems is particularly difficult. This paper briefly sketches a general systems design approach with emphasis on the design of computer based decision processing systems subject to parameter and environmental variation. The approach will be demonstrated with application to an on-board diagnostic (OBD) system for automotive emissions systems now mandated by the state of California and the Federal Clean Air Act. The emphasis is on developing approach for establishing probabilistically based performance requirements for computer based systems.

The goal is to provide a high level of confidence that critical software driven event sequences are maintained in the face of hardware failures and harsh or unstable operating environments. The technical approach includes in-situ (embedded in the software) dynamic (run-time) fault management for ensuring critical event sequences in high consequence software. Our method is based on deriving a mathematical description of the critical software controlled event sequence, embedding check points and update points around the critical events into the target code, and adding a module that implements the functionality of the underlying mathematical model. This methodology is inspired by previous work in path expressions. This paper discusses the perceived problems, a brief overview of path expressions, the proposed methods, and a discussion of the differences between the proposed methods and traditional path expression usage and implementation.

The Downhole Dynamometer Database is a compilation of test data collected with a set of five downhole tools built by Albert Engineering under contract to Sandia National Laboratories. The downhole dynamometer tools are memory tools deployed in the sucker rod string with sensors to measure pressure, temperature, load, and acceleration. The acceleration data is processed to yield position, so that a load vs. position dynagraph can be generated using data collected downhole. With five tools in the hole at one time, all measured data and computed dynagraphs from five different positions in the rod string are available. The purpose of the Database is to provide industry with a complete and high quality measurement of downhole sucker rod pumping dynamics. To facilitate use of the database, Sandia has developed a Microsoft Windows-based interface that functions as a visualizer and browser to the more than 40 MBytes of data. The interface also includes a data export feature to allow users to extract data from the database for use in their own programs. This paper includes a description of the downhole dynamometer tools, data collection program, database content, and a few illustrations of the data contained in the downhole dynamometer database.

We discuss the integration of the SANDROS path planner into a general robot simulation and control package with the inclusion of a fast geometry engine for distance calculations. This creates a single system that allows the path to be computed, simulated, and then executed on the physical robot. The architecture and usage procedures are presented. Also, we present examples of its usage in typical environments found in our organization. The resulting system is as easy to use as the general simulation system (which is in common use here) and is fast enough (example problems are solved in seconds) to be used interactively on an everyday basis.

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.