Publications

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The third Neuro-Inspired Computational Elements (NICE) Workshop was held February 23-25, 2015 in Albuquerque, New Mexico. The goal of the Workshop was to bring together researchers from different scientific disciplines and application areas to provide a common point from which to develop the next generation of information processing/computing architectures that go beyond stored program architecture and Moore’s Law limits.

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Silicon usage in fixed, flat-panel photovoltaic systems can be reduced by 60 to 75% with no efficiency loss through use of arrays of mini-concentrators. These concentrators are simple trough-like reflectors that are formed in flat sheets of ~1- mm thick optical plastic. Concentration ratios of 2.55X can be achieved on rooftops and 4.0X on walls while collecting all of the direct sun and scattered skylight. The concentrators are fabricated in optical plastic— preferably polycarbonate for its high refractive index. The panels are typically 1mm thick so the weight of a panel is ~1kg/m². In addition to the rooftop, wall and window blind designs, a design is proposed that can be tilted toward the sun position at the equinox. These systems are all designed so they can be mass-produced.

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Microsystems Enabled Photovoltaics (MEPV) is a relatively new field that uses microsystems tools and manufacturing techniques familiar to the semiconductor industry to produce microscale photovoltaic cells. The miniaturization of these PV cells creates new possibilities in system designs that can be used to reduce costs, enhance functionality, improve reliability, or some combination of all three. In this article, we introduce analytical tools and techniques to estimate the costs associated with a hybrid concentrating photovoltaic system that uses multi-junction microscale photovoltaic cells and miniaturized concentrating optics for harnessing direct sunlight, and an active c-Si substrate for collecting diffuse sunlight. The overall model comprises components representing costs and profit margin associated with the PV cells, concentrating optics, balance of systems, installation, and operation. This article concludes with an analysis of the component costs with particular emphasis on the microscale PV cell costs and the associated tradeoffs between cost and performance for the hybrid CPV design.

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Microsystems-enabled photovoltaics (MEPV) can potentially meet increasing demands for light-weight, portable, photovoltaic solutions with high power density and efficiency. The study in this report examines failure analysis techniques to perform defect localization and evaluate MEPV modules. CMOS failure analysis techniques, including electroluminescence, light-induced voltage alteration, thermally-induced voltage alteration, optical beam induced current, and Seabeck effect imaging were successfully adapted to characterize MEPV modules. The relative advantages of each approach are reported. In addition, the effects of exposure to reverse bias and light stress are explored. MEPV was found to have good resistance to both kinds of stressors. The results form a basis for further development of failure analysis techniques for MEPVs of different materials systems or multijunction MEPVs. The incorporation of additional stress factors could be used to develop a reliability model to generate lifetime predictions for MEPVs as well as uncover opportunities for future design improvements.

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Microsystems-enabled photovoltaics (MEPV) has great potential to meet the increasing demands for light-weight, photovoltaic solutions with high power density and efficiency. This paper describes effective failure analysis techniques to localize and characterize nonfunctional or underperforming MEPV cells. The defect localization methods such as electroluminescence under forward and reverse bias, as well as optical beam induced current using wavelengths above and below the device band gap, are presented. The current results also show that the MEPV has good resilience against degradation caused by reverse bias stresses. © 2013 IEEE.

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After years in the field, many materials suffer degradation, off-gassing, and chemical changes causing build-up of measurable chemical atmospheres. Stand-alone embedded chemical sensors are typically limited in specificity, require electrical lines, and/or calibration drift makes data reliability questionable. Along with size, these "Achilles' heels" have prevented incorporation of gas sensing into sealed, hazardous locations which would highly benefit from in-situ analysis. We report on development of an all-optical, mid-IR, fiber-optic based MEMS Photoacoustic Spectroscopy solution to address these limitations. Concurrent modeling and computational simulation are used to guide hardware design and implementation.

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Microsystems-enabled photovoltaic (MEPV) technology is a promising approach to lower the cost of solar energy to competitive levels. This paper describes current development efforts to leverage existing silicon integrated circuit (IC) failure analysis (FA) techniques to study MEPV devices. Various FA techniques such as light emission microscopy and laser-based fault localization were used to identify and characterize primary failure modes after fabrication and packaging. The FA results provide crucial information used in provide corrective actions and improve existing MEPV fabrication techniques. © 2013 IEEE.

Microsystems-enabled photovoltaic (MEPV) technology is a promising approach to lower the cost of solar energy to competitive levels. This paper describes current development efforts to leverage existing silicon integrated circuit (IC) failure analysis (FA) techniques to study MEPV devices. Various FA techniques such as light emission microscopy and laser-based fault localization were used to identify and characterize primary failure modes after fabrication and packaging. The FA results provide crucial information used in provide corrective actions and improve existing MEPV fabrication techniques. © 2013 IEEE.

Back-contacted, ultrathin (<10 μm), and submillimeter-sized solar cells made with microsystem tools are a new type of cell that has not been optimized for performance. The literature reports efficiencies up to 15% using thicknesses of 14 μm and cell sizes of 250 μm. In this paper, we present the design, conditions, and fabrication parameters necessary to optimize these devices. The optimization was performed using commercial simulation tools from the microsystems arena. A systematic variation of the different parameters that influence the performance of the cell was accomplished. The researched parameters were resistance, Shockley-Read-Hall (SRH) lifetime, contact separation, implant characteristics (size, dosage, energy, and ratio between the species), contact size, substrate thickness, surface recombination, and light concentration. The performance of the cell was measured with efficiency, open-circuit voltage, and short-circuit current. Among all the parameters investigated, surface recombination and SRH lifetime proved to be the most important. Through completing the simulations, an optimized concept solar cell design was introduced for two scenarios: high and low quality materials/passivation. Simulated efficiencies up to 23.4% (1 sun) and 26.7% (100 suns) were attained for 20-μm-thick devices. Copyright © 2012 John Wiley & Sons, Ltd. Back-contacted, ultrathin (<10 μm), and submillimeter-sized solar cells made with microsystem tools are a new type of cell that has not been optimized for performance. In this paper, we present the design conditions and fabrication parameters necessary to optimize these devices via simulations. Through completing the simulations, an optimized concept solar cell design was introduced for two scenarios: high and low quality materials/passivation. Simulated efficiencies up to 23.4% (1 sun) and 26.7% (100 suns) were attained for 20-μm-thick devices. Copyright © 2012 John Wiley & Sons, Ltd.

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Microsystem technologies have the potential to significantly improve the performance, reduce the cost, and extend the capabilities of solar power systems. These benefits are possible due to a number of significant beneficial scaling effects within solar cells, modules, and systems that are manifested as the size of solar cells decrease to the sub-millimeter range. To exploit these benefits, we are using advanced fabrication techniques to create solar cells from a variety of compound semiconductors and silicon that have lateral dimensions of 250 - 1000 μm and are 1 - 20 μm thick. These fabrication techniques come out of relatively mature microsystem technologies such as integrated circuits (IC) and microelectromechanical systems (MEMS) which provide added supply chain and scale-up benefits compared to even incumbent PV technologies. © The Electrochemical Society.

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Microsystems Enabled Photovoltaics (MEPV) is a relatively new field that uses microsystems tools and manufacturing techniques familiar to the semiconductor industry to produce microscale photovoltaic cells. The miniaturization of these PV cells creates new possibilities in system designs that may be able to achieve the US Department of Energy (DOE) price target of $1/Wp by 2020 for utility-scale electricity generation. In this article, we introduce analytical tools and techniques to estimate the costs associated with a concentrating photovoltaic system that uses microscale photovoltaic cells and miniaturized optics. The overall model comprises the component costs associated with the PV cells, concentrating optics, balance of systems, installation, and operation. Estimates include profit margin and are discussed in the context of current and projected prices for non-concentrating and concentrating photovoltaics. Our analysis indicates that cells with a width of between 100 and 300 μm will minimize the module costs of the initial design within the range of concentration ratios considered. To achieve the DOE price target of $1/Wp by 2020, module efficiencies over 35% will likely be necessary. © 2013 IEEE.

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Microsystems-enabled photovoltaics (MEPVs) are microfabricated arrays of thin and efficient solar cells. The scaling effects enabled by this technique results in great potential to meet increasing demands for light-weight photovoltaic solutions with high power density. This paper covers failure analysis techniques used to support the development of MEPVs with a focus on the laser beam-based methods of LIVA, TIVA, OBIC, and SEI. Each FA technique is useful in different situations, and the examples in this paper show the relative advantages of each method for the failure analysis of MEPVs. Copyright © 2013 ASM International® All rights reserved.

We present ultra-thin single crystal mini-modules built with specific power of 450 W/kg capable of voltages of >1000 V/cm2. These modules are also ultra-flexible with tight bending radii down to 1 mm. The module is composed of hundreds of back contact microcells with thicknesses of approximately 20 μm and diameters between 500-720 μm. The cells are interconnected to a flexible circuit through solder contacts. We studied the characteristics of several mini-modules through optical inspection, evaluation of quantum efficiency, measurement of current-voltage curves, and temperature dependence. Major efficiency losses are caused by missing cells or non-interconnected cells. Secondarily, damage incurred during separation of 500 μm cells from the substrate caused material detachment. The detachment induced higher recombination and low performance. Modules made with the larger cells (720 μm) performed better due to having no missing cells, no material detachment and optimized AR coatings. The conversion efficiency of the best mini module was 13.75% with a total Voc = 7.9 V. © 2013 IEEE.

In this paper we propose a stacked multi-junction solar cell design that allows the intimate contact of the individual cells while maintaining low resistive losses. The cell design is presented using an InGaP and GaAs multi-junction cell as an illustrative example. However, the methodologies presented in this paper can be applied to other III-V cell types including InGaAs and InGaAsP cells. The main benefits of the design come from making small cells, on the order of 2×10-3 cm2. Simulations showed that series resistances should be kept to less than 5 ω for devices up to 400 μm in diameter to keep resistance power losses to less than 1%. Low resistance AuBe/Ni/Au ohmic contacts to n-type InGaP are also demonstrated with contact resistivity of 5×10-6 ωcm-2 when annealed at 420°C. © 2013 IEEE.

We calculate voltage-matching considerations for stacked independent cells. The calculations show that designs using independent junctions that are voltage matched can achieve better efficiency across temperature, spectrum, and a yearly metric compared to traditional monolithic cells. Voltage matching is shown to be relatively insensitive to temperature and spectrum, but dependent on open circuit voltage as a measure of cell efficiency. Voltage matching can usually yield yearly efficiencies of 98%-99% of the efficiency of a system with each junction operating at its own maximum power point. © 2013 IEEE.

We present ultra-thin single crystal mini-modules built with specific power of 450 W/kg capable of voltages of >1000 V/cm2. These modules are also ultra-flexible with tight bending radii down to 1 mm. The module is composed of hundreds of back contact microcells with thicknesses of approximately 20 μm and diameters between 500-720 μm. The cells are interconnected to a flexible circuit through solder contacts. We studied the characteristics of several mini-modules through optical inspection, evaluation of quantum efficiency, measurement of current-voltage curves, and temperature dependence. Major efficiency losses are caused by missing cells or non-interconnected cells. Secondarily, damage incurred during separation of 500 μm cells from the substrate caused material detachment. The detachment induced higher recombination and low performance. Modules made with the larger cells (720 μm) performed better due to having no missing cells, no material detachment and optimized AR coatings. The conversion efficiency of the best mini module was 13.75% with a total Voc = 7.9 V. © 2013 IEEE.

Microsystems Enabled Photovoltaics (MEPV) is a relatively new field that uses microsystems tools and manufacturing techniques familiar to the semiconductor industry to produce microscale photovoltaic cells. The miniaturization of these PV cells creates new possibilities in system designs that may be able to achieve the US Department of Energy (DOE) price target of $1/Wp by 2020 for utility-scale electricity generation. In this article, we introduce analytical tools and techniques to estimate the costs associated with a concentrating photovoltaic system that uses microscale photovoltaic cells and miniaturized optics. The overall model comprises the component costs associated with the PV cells, concentrating optics, balance of systems, installation, and operation. Estimates include profit margin and are discussed in the context of current and projected prices for non-concentrating and concentrating photovoltaics. Our analysis indicates that cells with a width of between 100 and 300 μm will minimize the module costs of the initial design within the range of concentration ratios considered. To achieve the DOE price target of $1/Wp by 2020, module efficiencies over 35% will likely be necessary. © 2013 IEEE.

A 100X magnification, ±3° field of view micro-concentrating optical array has been developed with better than 90% transmission for a microsystems-enabled photovoltaic (MEPV) prototype module using 250 μm diameter multi-junction "stacked" PV cells. Renewable Energy and the Environment Congress. © 2013.

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Microelectronics and microsystems have been part of the key technologies that enabled the incredible pace of development we have seen over the last five to six decades. This paper presents a basic view in terms of technology development supporting new approaches to generation and transfer of knowledge for critical activities, one of the key ones being the ability to capture, store and more efficiently use energy. © 2012 SPIE.

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In this paper, we demonstrate gate-all-around (GAA) single crystalline nanowires (SiNWs) that are fabricated using top-down standard CMOS front-end processes. The GAA silicon nanowires are fabricated in well-defined locations with high-quality electrical contacts, and controlled geometry and alignment. These SiNW FETs fabricated in this process have demonstrated repeatable electrical performance with threshold voltages of ∼0.2V and subthreshold slopes of ∼80mV/dec. The p-i-n silicon nanowires are highly sensitive to the intensity and polarization of the incident light. The results in this work demonstrate that individual SiNWs are good candidates for high resolution optical sensing and allow for tuning of the optical properties of the nanoscale devices by precise control of the nanowire geometry and orientation of the incident light. These top-down fabricated SiNWs can be easily integrated in high density arrays for enhanced light absorption, resulting in imaging sensors with nanoscale spatial resolution. © 2011 IEEE.

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We present an approach to create ultrathin (<20μm) and highly flexible crystalline silicon sheets on inexpensive substrates. We have demonstrated silicon sheets capable of bending at a radius of curvature as small as 2mm without damaging the silicon structure. Using microsystem tools, we created a suspended submillimeter honeycomb-segmented silicon structure anchored to the wafer only by small tethers. This structure is created in a standard thickness wafer enabling compatibility with common processing tools. The procedure enables all the high-temperature steps necessary to create a solar cell to be completed while the cells are on the wafer. In the transfer process, the cells attach to an adhesive flexible substrate which, when pulled away from the wafer, breaks the tethers and releases the honeycomb structure. We have previously demonstrated that submillimeter and ultrathin silicon segments can be converted into highly efficient solar cells, achieving efficiencies up to 14.9% at a thickness of 14μm. With this technology, achieving high efficiency (>15%) and highly flexible photovoltaic (PV) modules should be possible. © 2011 IEEE.

We present an approach to create ultrathin (<20μm) and highly flexible crystalline silicon sheets on inexpensive substrates. We have demonstrated silicon sheets capable of bending at a radius of curvature as small as 2mm without damaging the silicon structure. Using microsystem tools, we created a suspended submillimeter honeycomb-segmented silicon structure anchored to the wafer only by small tethers. This structure is created in a standard thickness wafer enabling compatibility with common processing tools. The procedure enables all the high-temperature steps necessary to create a solar cell to be completed while the cells are on the wafer. In the transfer process, the cells attach to an adhesive flexible substrate which, when pulled away from the wafer, breaks the tethers and releases the honeycomb structure. We have previously demonstrated that submillimeter and ultrathin silicon segments can be converted into highly efficient solar cells, achieving efficiencies up to 14.9% at a thickness of 14μm. With this technology, achieving high efficiency (>15%) and highly flexible photovoltaic (PV) modules should be possible. © 2011 IEEE.

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Microsystem-Enabled Photovoltaic (MEPV) cells allow solar PV systems to take advantage of scaling benefits that occur as solar cells are reduced in size. We have developed MEPV cells that are 5 to 20 microns thick and down to 250 microns across. We have developed and demonstrated crystalline silicon (c-Si) cells with solar conversion efficiencies of 14.9%, and gallium arsenide (GaAs) cells with a conversion efficiency of 11.36%. In pursuing this work, we have identified over twenty scaling benefits that reduce PV system cost, improve performance, or allow new functionality. To create these cells, we have combined microfabrication techniques from various microsystem technologies. We have focused our development efforts on creating a process flow that uses standard equipment and standard wafer thicknesses, allows all high-temperature processing to be performed prior to release, and allows the remaining post-release wafer to be reprocessed and reused. The c-Si cell junctions are created using a backside point-contact PV cell process. The GaAs cells have an epitaxially grown junction. Despite the horizontal junction, these cells also are backside contacted. We provide recent developments and details for all steps of the process including junction creation, surface passivation, metallization, and release.

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Micro-optical 5mm lenses in 50mm sub-arrays illuminate arrays of photovoltaic cells with 49X concentration. Fine tracking over ±10° FOV in sub-array allows coarse tracking by meter-sized solar panels. Plastic prototype demonstrated for 400nm<λ<1600nm. © 2010 Copyright SPIE - The International Society for Optical Engineering.

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Thin and small form factor cells have been researched lately by several research groups around the world due to possible lower assembly costs and reduced material consumption with higher efficiencies. Given the popularity of these devices, it is important to have detailed information about the behavior of these devices. Simulation of fabrication processes and device performance reveals some of the advantages and behavior of solar cells that are thin and small. Three main effects were studied: the effect of surface recombination on the optimum thickness, efficiency, and current density, the effect of contact distance on the efficiency for thin cells, and lastly the effect of surface recombination on the grams per Watt-peak. Results show that high efficiency can be obtained in thin devices if they are well-passivated and the distance between contacts is short. Furthermore, the ratio of grams per Watt-peak is greatly reduced as the device is thinned.

We present a newly developed microsystem enabled, back-contacted, shade-free GaAs solar cell. Using microsystem tools, we created sturdy 3 {micro}m thick devices with lateral dimensions of 250 {micro}m, 500 {micro}m, 1 mm, and 2 mm. The fabrication procedure and the results of characterization tests are discussed. The highest efficiency cell had a lateral size of 500 {micro}m and a conversion efficiency of 10%, open circuit voltage of 0.9 V and a current density of 14.9 mA/cm{sup 2} under one-sun illumination.

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We present a newly developed microsystem enabled, back-contacted, shade-free GaAs solar cell. Using microsystem tools, we created sturdy 3 {micro}m thick devices with lateral dimensions of 250 {micro}m, 500 {micro}m, 1 mm, and 2 mm. The fabrication procedure and the results of characterization tests are discussed. The highest efficiency cell had a lateral size of 500 {micro}m and a conversion efficiency of 10%, open circuit voltage of 0.9 V and a current density of 14.9 mA/cm{sup 2} under one-sun illumination.

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Elastic averaging is introduced as a methodology for the fabrication and assembly of multi-element, micro-optic arrays. Its performance and use is evaluated in the demonstration of a high efficiency, photovoltaic tracking system. © 2010 Optical Society of America.

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We have developed a high sensitivity (<pico Tesla/{radical}Hz), non-cryogenic magnetometer that utilizes a novel optical (interferometric) detection technique. Further miniaturization and low-power operation are key advantages of this magnetometer, when compared to systems using SQUIDs which require liquid Helium temperatures and associated overhead to achieve similar sensitivity levels.

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This work utilized advanced engineering in several fields to find solutions to the challenges presented by the integration of MEMS/NEMS with optoelectronics to realize a compact sensor system, comprised of a microfabricated sensor, VCSEL, and photodiode. By utilizing microfabrication techniques in the realization of the MEMS/NEMS component, the VCSEL and the photodiode, the system would be small in size and require less power than a macro-sized component. The work focused on two technologies, accelerometers and microphones, leveraged from other LDRD programs. The first technology was the nano-g accelerometer using a nanophotonic motion detection system (67023). This accelerometer had measured sensitivity of approximately 10 nano-g. The Integrated NEMS and optoelectronics LDRD supported the nano-g accelerometer LDRD by providing advanced designs for the accelerometers, packaging, and a detection scheme to encapsulate the accelerometer, furthering the testing capabilities beyond bench-top tests. A fully packaged and tested die was never realized, but significant packaging issues were addressed and many resolved. The second technology supported by this work was the ultrasensitive directional microphone arrays for military operations in urban terrain and future combat systems (93518). This application utilized a diffraction-based sensing technique with different optical component placement and a different detection scheme from the nano-g accelerometer. The Integrated NEMS LDRD supported the microphone array LDRD by providing custom designs, VCSELs, and measurement techniques to accelerometers that were fabricated from the same operational principles as the microphones, but contain proof masses for acceleration transduction. These devices were packaged at the end of the work.

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Acoustic sensing systems are critical elements in detection of sniper events. The microphones developed in this project enable unique sensing systems that benefit significantly from the enhanced sensitivity and extremely compact foot-print. Surface and bulk micromachining technologies developed at Sandia have allowed the design, fabrication and characterization of these unique sensors. We have demonstrated sensitivity that is only available in 1/2 inch to 1 inch studio reference microphones--with our devices that have only 1 to 2mm diameter membranes in a volume less than 1cm{sup 3}.

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Low Temperature Cofired Ceramic (LTCC) has proven to be an enabling medium for microsystem technologies, because of its desirable electrical, physical, and chemical properties coupled with its capability for rapid prototyping and scalable manufacturing of components. LTCC is viewed as an extension of hybrid microcircuits, and in that function it enables development, testing, and deployment of silicon microsystems. However, its versatility has allowed it to succeed as a microsystem medium in its own right, with applications in non-microelectronic meso-scale devices and in a range of sensor devices. Applications include silicon microfluidic ''chip-and-wire'' systems and fluid grid array (FGA)/microfluidic multichip modules using embedded channels in LTCC, and cofired electro-mechanical systems with moving parts. Both the microfluidic and mechanical system applications are enabled by sacrificial volume materials (SVM), which serve to create and maintain cavities and separation gaps during the lamination and cofiring process. SVMs consisting of thermally fugitive or partially inert materials are easily incorporated. Recognizing the premium on devices that are cofired rather than assembled, we report on functional-as-released and functional-as-fired moving parts. Additional applications for cofired transparent windows, some as small as an optical fiber, are also described. The applications described help pave the way for widespread application of LTCC to biomedical, control, analysis, characterization, and radio frequency (RF) functions for macro-meso-microsystems.

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Micromachined microphones with diffraction-based optical displacement detection are introduced. The approach enables interferometric displacement detection sensitivity in a system that can be optoelectronically integrated with a multichip module into mm3 volumes without beamsplitters, focusing optics, or critical alignment problems. Prototype devices fabricated using Sandia National Laboratories' silicon based SwIFT-Lite™ process are presented and characterized in detail. Integrated electrostatic actuation capabilities of the microphone diaphragm are used to perform dynamic characterization in vacuum and air environments to study the acoustic impedances in an equivalent circuit model of the device. The characterization results are used to predict the thermal mechanical noise spectrum, which is in excellent agreement with measurements performed in an anechoic test chamber. An A weighted displacement noise of 2.4 × 10-2 Å measured from individual prototype 2100 μm × 2100 μm diaphragms demonstrates the potential for achieving precision measurement quality microphone performance from elements 1 mm2 in size. The high sensitivity to size ratio coupled with the ability to fabricate elements with precisely matched properties on the same silicon chip may make the approach ideal for realizing high fidelity miniature microphone arrays (sub-cm2 aperture) employing recently developed signal processing algorithms for sound source separation and localization in the audio frequency range. © 2005 Acoustical Society of America.

A microflame-based detector suit has been developed for sensing of a broad range of chemical analytes. This detector combines calorimetry, flame ionization detection (FID), nitrogen-phosphorous detection (NPD) and flame photometric detection (FPD) modes into one convenient platform based on a microcombustor. The microcombustor consists in a micromachined microhotplate with a catalyst or low-work function material added to its surface. For the NPD mode a low work function material selectively ionizes chemical analytes; for all other modes a supported catalyst such as platinum/alumina is used. The microcombustor design permits rapid, efficient heating of the deposited film at low power. To perform calorimetric detection of analytes, the change in power required to maintain the resistive microhotplate heater at a constant temperature is measured. For FID and NPD modes, electrodes are placed around the microcombustor flame zone and an electrometer circuit measures the production of ions. For FPD, the flame zone is optically interrogated to search for light emission indicative of deexcitation of flame-produced analyte compounds. The calorimetric and FID modes respond generally to all hydrocarbons, while sulfur compounds only alarm in the calorimetric mode, providing speciation. The NPD mode provides 10,000:1 selectivity of nitrogen and phosphorous compounds over hydrocarbons. The FPD can distinguish between sulfur and phosphorous compounds. Importantly all detection modes can be established on one convenient microcombustor platform, in fact the calorimetric, FID and FPD modes can be achieved simultaneously on only one microcombustor. Therefore, it is possible to make a very universal chemical detector array with as little as two microcombustor elements. A demonstration of the performance of the microcombustor in each of the detection modes is provided herein.

Low-temperature co-fired ceramic (LTCC) enables development and testing of critical elements on microsystem boards as well as nonmicroelectronic meso-scale applications. We describe silicon-based microelectromechanical systems packaging and LTCC meso-scale applications. Microfluidic interposers permit rapid testing of varied silicon designs. The application of LTCC to micro-high-performance liquid chromatography (?-HPLC) demonstrates performance advantages at very high pressures. At intermediate pressures, a ceramic thermal cell lyser has lysed bacteria spores without damaging the proteins. The stability and sensitivity of LTCC/chemiresistor smart channels are comparable to the performance of silicon-based chemiresistors. A variant of the use of sacrificial volume materials has created channels, suspended thick films, cavities, and techniques for pressure and flow sensing. We report on inductors, diaphragms, cantilevers, antennae, switch structures, and thermal sensors suspended in air. The development of 'functional-as-released' moving parts has resulted in wheels, impellers, tethered plates, and related new LTCC mechanical roles for actuation and sensing. High-temperature metal-to-LTCC joining has been developed with metal thin films for the strong, hermetic interfaces necessary for pins, leads, and tubes.

The objective of this LDRD was to develop microdevice strategies for dealing with samples to be examined in biological detection systems. This includes three sub-components: namely, microdevice fabrication, sample delivery to the microdevice, and sample processing within the microdevice. The first component of this work focused on utilizing Sandia's surface micromachining technology to fabricate small volume (nanoliter) fluidic systems for processing small quantities of biological samples. The next component was to develop interfaces for the surface-micromachined silicon devices. We partnered with Micronics, a commercial company, to produce fluidic manifolds for sample delivery to our silicon devices. Pressure testing was completed to examine the strength of the bond between the pressure-sensitive adhesive layer and the silicon chip. We are also pursuing several other methods, both in house and external, to develop polymer-based fluidic manifolds for packaging silicon-based microfluidic devices. The second component, sample processing, is divided into two sub-tasks: cell collection and cell lysis. Cell collection was achieved using dielectrophoresis, which employs AC fields to collect cells at energized microelectrodes, while rejecting non-cellular particles. Both live and dead Staph. aureus bacteria have been collected using RF frequency dielectrophoresis. Bacteria have been separated from polystyrene microspheres using frequency-shifting dielectrophoresis. Computational modeling was performed to optimize device separation performance, and to predict particle response to the dielectrophoretic traps. Cell lysis is continuing to be pursued using microactuators to mechanically disrupt cell membranes. Novel thermal actuators, which can generate larger forces than previously tested electrostatic actuators, have been incorporated with and tested with cell lysis devices. Significant cell membrane distortion has been observed, but more experiments need to be conducted to determine the effects of the observed distortion on membrane integrity and cell viability. Finally, we are using a commercial PCR DNA amplification system to determine the limits of detectable sample size, and to examine the amplification of DNA bound to microspheres. Our objective is to use microspheres as capture-and-carry chaperones for small molecules such as DNA and proteins, enabling the capture and concentration of the small molecules using dielectrophoresis. Current tests demonstrated amplification of DNA bound to micron-sized polystyrene microspheres using 20-50 microliter volume size reactions.

Microelectromechanical systems (MEMS) comprise a new class of devices that include various forms of sensors and actuators. Recent studies have shown that microscale cantilever structures are able to detect a wide range of chemicals, biomolecules or even single bacterial cells. In this approach, cantilever deflection replaces optical fluorescence detection thereby eliminating complex chemical tagging steps that are difficult to achieve with chip-based architectures. A key challenge to utilizing this new detection scheme is the incorporation of functionalized MEMS structures within complex microfluidic channel architectures. The ability to accomplish this integration is currently limited by the processing approaches used to seal lids on pre-etched microfluidic channels. This report describes Sandia's first construction of MEMS instrumented microfluidic chips, which were fabricated by combining our leading capabilities in MEMS processing with our low-temperature photolithographic method for fabricating microfluidic channels. We have explored in-situ cantilevers and other similar passive MEMS devices as a new approach to directly sense fluid transport, and have successfully monitored local flow rates and viscosities within microfluidic channels. Actuated MEMS structures have also been incorporated into microfluidic channels, and the electrical requirements for actuation in liquids have been quantified with an elegant theory. Electrostatic actuation in water has been accomplished, and a novel technique for monitoring local electrical conductivities has been invented.

Fast and quantitative analysis of cellular activity, signaling and responses to external stimuli is a crucial capability and it has been the goal of several projects focusing on patch clamp measurements. To provide the maximum functionality and measurement options, we have developed a patch clamp array device that incorporates on-chip electronics, mechanical, optical and microfluidic coupling as well as cell localization through fluid flow. The preliminary design, which integrated microfluidics, electrodes and optical access, was fabricated and tested. In addition, new designs which further combine mechanical actuation, on-chip electronics and various electrode materials with the previous designs are currently being fabricated.

This paper demonstrates a simple technique for building n-channel MOSFETs and complex micromechanical systems simultaneously instead of serially, allowing a more straightforward integration of complete systems. The fabrication sequence uses few additional process steps and only one additional masking layer compared to a MEMS-only technology. The process flow forms the MOSFET gate electrode using the first level of mechanical polycrystalline silicon, while the MOSFET source and drain regions are formed by dopant diffusions into the substrate from subsequent levels of heavily doped poly that is used for mechanical elements. The process yields devices with good, repeatable electrical characteristics suitable for a wide range of digital and analog applications.

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Sandia National Labs has developed an autonomous, hand-held system for sensitive/selective detection of gas-phase chemicals. Through the sequential connection of microfabricated preconcentrators (PC), gas chromatography columns (GC) and a surface acoustic wave (SAW) detector arrays, the MicroChemLab{trademark} system is capable of selective and sensitive chemical detection in real-world environments. To date, interconnection of these key components has primarily been achieved in a hybrid fashion on a circuit board modified to include fluidic connections. The monolithic integration of the PC and GC with a silicon-based acoustic detector is the subject of this work.

Retinal prosthesis projects around the world have been pursuing a functional replacement system for patients with retinal degeneration. In this paper, the concept for a micromachined conformal electrode array is outlined. Individual electrodes are designed to float on micromachined springs on a substrate that will enable the adjustment of spring constants-and therefore contact force-by adjusting the dimensions of the springs at each electrode. This also allows the accommodation of the varying curvature/topography of the retina. We believe that this approach provides several advantages by improving the electrode/tissue interface as well as generating some new options for in-situ measurements and overall system design.

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