We investigated continuous fabrication of a large area 2-D metamaterial comprising a metal dot array on a dielectric coated substrate. We demonstrated patterning of metal dots arrays of varying patterns and shapes with diameter of about 2.5 μm and metal-to-metal spacing from 0.3 to 2.5 μm using a nano-imprinting stamp on a roller. The pattern was first fabricated on a standard photolithography mask, reproduced onto a silicon wafer master mold, and then transferred to a flexible polymer mold that was wrapped around a metal roller. The method was used to pattern a thin Al layer on top of SiO2 on a flexible polymer substrate. The aluminum was coated with a resist and the roller moved over the substrate with adjustable speed and pressure to imprint the fine pattern into the resist. The resist was cured, and a very thin layer of residual resist was removed by RIE, followed by a standard etching treatment for patterning the aluminum layer.

The as-etched pattern had very few defects and the optical properties of the metamaterial were excellent and correlated well with simulations. This work has shown that low cost, rapid roll-to-roll processing of 2-D metamaterial structures is possible.

We have simulated the angle-dependent absorption and thermal emittance of two dimensional metallic and metallodielectric photonic crystals (PCs) with rigorous scattering matrix methods- where Maxwell's equations are solved in Fourier space. These metallic photonic crystals exhibit strong thermal emittance and absorption peaks in the normal direction. This peak splits into multiple peaks at larger and shorter wavelengths away from the normal direction. The thermal emission at different wavelengths is redistributed into different emission angles. There is partial suppression of photon emission at long wavelengths and enhancement at the shorter wavelength spectral range where the thermal emittance has a maximum. Angle-dependent measurements of the emission in metallo-dielectric photonic crystals are performed. Simulations compare well with these measurements and are consistent with the surface plasmon model. The strong dependence of the absorption with angle is very important for thermo-photovoltaic devices.

Metallo-dielectric photonic crystals are sharp thermal emitters at infrared wavelengths, and are being employed in sensors. We describe the theory of thermal emission and enhanced absorption in these photonic crystals using a scattering matrix approach, where Maxwell's equations are solved in Fourier space. A sub-wavelength hole array in a metal layer is coupled to a two-dimensional photonic crystal of the same periodicity in these metallo-dielectric photonic crystals. The sub-wavelength hole array has an enhanced transmission mode that couples to a weakly guided mode of the photonic crystal having similar modal character. The transmissive mode of the hole array is absorbed by the photonic crystal to create a sharp absorption and reflective minimum. The enhanced absorption is investigated in different lattice symmetries.

We have simulated metallo-dielectric photonic crystals that are sharp thermal emitters at infrared wavelengths, and are being employed in gas sensors. The simulations were performed with a rigorous scattering matrix approach where Maxwell's equations are solved in Fourier space. These metallo-dielectric photonic crystals consist of a sub-wavelength hole array in a metal layer coupled to a two-dimensional photonic crystal of the same periodicity. The sub-wavelength hole array has an enhanced transmission mode that couples to a guided mode of the photonic crystal. The transmissive mode of the hole array is absorbed by the photonic crystal to create a sharp absorption and reflective minimum feature found for a range of lattice spacing. The structure thermally emits in a narrow band of wavelengths controlled by the lattice spacing that can be tuned over the infrared region. The underlying physics of this emissive device is modeled with rigorous scattering matrix simulations.

We examined lanthanum doped lead barium titanate films for temperature measurements of photonic crystal - MEMS devices. Films were deposited by sol-gel techniques and crystallized in air above 650°C. X-ray diffraction spectra consistent with the perovskite structure were detected. The room temperature dielectric constant was ∼570 at 10 kHz of La-doped (0.3 mol%) Pb0.3Ba0.7TiO3 films. These films had a remanent polarization of ∼20μC/cm2 and a coercive field of 145 kV/cm. The leakage current density was ∼ 2×10−7 amps/cm2 at 100 kV/cm field. The resistivity of the films extracted from the linear region of the I-V data (electric fields in excess of 100 kV/cm) measured as a function of temperature shows an increase in resistivity at temperatures above Tc (120°C for BaTiO3 and 240°C for Pb0.3Ba0.7TiO3) of the film consistent with positive coefficient of resistance (PTCR) effect. However, the change in resistance was small when compared to bulk samples of similar compositions.

MEMS devices have unique packaging considerations compared to conventional semiconductor devices. They tend to have relatively large die size and many architectures cannot tolerate elevated temperatures. Often these devices require a vacuum environment for efficient operation. While advances have been made in hermetic packaging of MEMS devices, vacuum packaging remains elusive. One significant problem in developing vacuum sealing has been the inability to determine, readily and non-destructively, the vacuum level inside the package. We have previously described the development of a silicon MEMS-based chip design, “SensorChip™,” with integrated photonic crystal and reflective optics, which uses narrow-band optical emission and absorption for selective identification of gas and chemical species. Because the power consumption required to maintain a specific temperature is directly related to the vacuum level, these devices effectively serve as microscopic Pirani gauges – local vacuum sensors in the moderate vacuum range (0.01 to 1.0 torr) of interest to MEMS devices. Using the membrane itself as a vacuum gauge during sealing has proven to be an invaluable tool in developing a robust vacuum seal in a leadless chip carrier package. It has enabled us to optimize choice of design, materials and processing.

We are reporting on the analysis of a new design for a thermal source exploiting Si-based suspended micro-bridge structures. A device consists of a metal film perforated by a periodic array of apertures extending into the Si substrate and each of size on order of the wavelength of the light. This perforated film permits resonant coupling of the incident radiation from the underlying silicon photonic crystal with surface plasmons at the metal surface. The coupling provides for unusually high optical emission efficiencies when the structure is thermally excited. The radiation emitted exhibits an enhancement over a narrow wavelength range in the infrared and its spectral response is highly dependent on the direction of observation. The positions of the main resonances, for both reflection and emission from our structures, scale linearly with the periodicity of the metallo-dielectric structure. As one moves off normal incidence, a single main resonance splits into several smaller resonances whose locations scale roughly linearly with observation angle. These structures have been used as emitter/detector sensor chips to selectively detect industrial pollutants like carbon dioxide. Control of the wavelength of resonance, bandwidth and direction of emission play an important role in improving the sensitivity and selectivity of these gas sensors.

A new type of gas sensor was developed that combines the principles of bolometric infrared detectors with photonic crystals.1,2 This paper describes a quantitative model used to optimize the materials, geometry, and electrical properties of this suspended membrane MEMS device. Fundamentally the model is concerned with the thermal response of the device using temperature dependent thermal conductivity, specific heat, and electrical resistance to calculate conduction, convection, and radiation losses for a negative temperature coefficient of resistance material. Variations in the electrical drive circuit, dc and ac response, low and high frequency sinusoidal and random noise, along with an exacting calculation of expected signal were used to improve design. The model follows the time evolution of the system. We show how look-up tables with scaling (derived from exact, off-line finite element models for thermal conduction, spectral emission, etc.) provided sufficiently accurate estimates with rapid calculation to enable running the model on a standard PC type computer. The simulations matched the experimental results, accurately predicted the unstable operating regimes, and maximized the signal to noise ratio for the device.

Here we describe the evolution of a silicon, MEMS-based chip design developed for infrared gas and chemical detection. The “Sensor-Chip,” with integrated photonic crystal and reflective optics, employs narrow-band optical emission/absorption for selective identification of gas and chemical species. Gas concentration is derived from attenuated optical power, which results in a change in device set point. This change in temperature results in a change in device resistance, via the TCR of the Si. Thermal non-uniformity across the device results in optical “noise” and accelerates localized thermal and electrical failures. This paper reports the influence of processing and design, on achieving uniformly heated, high reliability devices. Specifically, we examine the role of contacts, drive scheme, and device thermal distribution on chip design. Experimentally the temperature uniformity was characterized using an infrared camera. Experimental results indicate that the design of the contact areas in combination with the device design is essential for the reliable performance of the Sensor-Chip. Redesigned devices were fabricated and demonstrated as highly-selective gas and chemical sensors.

We have developed a thermally stimulated narrow-band infrared source for sensing, spectroscopy and thermophotovoltaic applications by combining the unique advantages of two different structures: a photonic crystal that consists of an array of holes etched into a dielectric substrate and a periodically perforated metallic thin film. The dielectric photonic crystal structure is passive and exhibits a strong absorption at resonance. This acts as a radiation reservoir for the conductive array, which plays an active role through plasmon interactions and is opaque at all wavelengths except those at which coupling occurs. We have fabricated the arrays on silicon, silicon dioxide and silicon nitride substrates using MEMS-based processing methods. Infrared spectroscopic studies were used to characterize reflection, absorption and emission in the 2 to 14 micron range showing narrow band resonance. Spectral tuning was accomplished by controlling symmetry and lattice spacing of the arrays. The effects of the etch depth, metal and dielectric properties have been studied experimentally and theoretically. These structures have been used as an emitter/detector sensor chip to selectively detect industrial pollutants like carbon dioxide.

A sensor chip has been designed and tested that uses a MEMS strip heater as both source and detector of infrared radiation. An optical cavity reflects infrared radiation back onto the source filament. Changes in reflected light intensity modify heater temperature, and the measured signal is a change in resistance. The effects of processing on electrical and thermal isolation were characterized and used to evaluate device performance. Thermally isolated, uniformly heated emitters are achieved using a backside release etch process. The fully released devices demonstrated superior electric to thermal-optical conversion, with the requisite narrow band emission for CO2 detection. Using these sensor-chips, CO2 detection was demonstrated, with projected sensitivities ≤0.1%.

Photonic bandgap structures have received much attention as optical and infrared filters with controllable narrow-band absorbance. There is a need, however, for the same kind of control of the thermal emittance of surfaces for applications ranging from control of radiative heat transfer to gas absorption spectroscopy. We report on the fabrication of photonic bandgap structures on silicon surfaces using standard lithographic techniques. Substrate resistivity varied from n− to n+ and in some cases background surface emissivity was suppressed with a high reflectivity coating such as aluminum. We have measured the infrared reflectance and emittance of these patterned surfaces. Peak absorption wavelength and spectral purity (linewidth) correlate with photonic bandgap feature size and spacing as well as surface conductivity. We demonstrate band emission with a sharp short wavelength cut-off from these structures when heated.

The homoleptic compound erbium{tris[bis (trimethylsilyl)]amide} displays high doping ability for incorporation of the rare earth element into epitaxially grown semiconducting host materials for fabrication of temperature-independent, monochromatic solid state optoelectronic devices. Electronic characteristics derived from erbium doped semiconducting films have been obtained. Several more volatile and lower melting representatives of this class of compounds have been synthesized, characterized by various analytical techniques and examined for their suitability to incorporate optically-active erbium centers into a semiconducting environment.

Thin films of yttria stabilized zirconia (YSZ) were deposited by metal organic chemical vapor deposition (MOCVD) on cobalt-chromium (Co-Cr) alloys used for orthopaedic implants. TMHD derivatives were preferred for the metalorganic sources over the less expensive fluorinated beta-diketonates as the latter left up to 1% fluorine in the film, as determined by Auger spectroscopy. Crystalline cubic structure of these YSZ films was verified by X-ray diffraction. Columnar grain growth gave a rough surface on thicker YSZ films, which increased wear of the mating polyethylene component during simulation tests. YSZ films under one micron thick were mirror smooth and reduced wear of the polymer component by 70% compared to uncoated Co-Cr. Film adhesion was excellent.

Rare earth elements are important as dopants in the preparation of semiconductors, particularly for temperature-independent optical devices. The compound Er{N\Si(CH3)3]2}3 has been demonstrated to be a suitable source compound for erbium doping of semiconducting materials. Further investigations of this and related compounds have been carried out. New compounds have been characterized by 1H NMR, FTIR, TGA and elemental analysis techniques. Vapor pressures and decomposition profiles have been examined for these compounds.

The objective of this research was to demonstrate heteroepitaxial growth of yttria stabilized cubic zirconia on single crystal silicon substrates by chemical vapor deposition (CVD) using metalorganic source materials. We succeeded in depositing extremely smooth, well aligned films of zirconia on silicon substrates, both the <100> and <111> orientations, without an oxide interfacial layer. Experimental variables investigated included varying zirconia source materials, substrate temperatures, oxygen concentration, gas flow rates, yttria doping, substrate orientation, and cobalt-silicide as an oxygen diffusion barrier. ZrO2 films were predominantly tetragonal when deposited in the absence of oxygen while cubic phase material could be put down at 750°C with oxygen background. Films deposited from TMHD zirconium contained no measurable carbon contamination. Deposits from trifluoro-acetylacetonate Zr contained small amounts of fluorine, even in the presence of water vapor, and some carbon when hydrogen was used as a diluent gas.

The overall objective of this research is to develop source materials for doping AIGaAs. We compared Er(C5H5)3 to Er{N[Si(CH3)3]2)3 for purity, decomposition kinetics and doping of germanium films deposited from Ge(CH3)4 in a hydrogen atmosphere. Cyclopentadienyl erbium left large amounts of carbon both in pure metal films, and in the germanium film, at low pressure and temperatures to 850°C. Bis-(tri-methylsilyl) erbium amide decomposed cleanly without carbon, nitrogen or silicon in the deposited film.

Thin films of lead-titanate were deposited by chemical vapor deposition (CVD) using tetraethyl lead and titanium isopropoxide. Good high frequency hysteresis curves were obtained with platinum contacts. Low resistance of the material (estimated at 108 ohm-cm) affected low frequency measurements.

Optimized experimental parameters (pressure, temperature, gas flows, oxidizer) were derived from a designed experimental matrix using response surface methodology. This approach significantly reduced the number of deposition trials required.

Different materials were investigated for use as diffusion barriers between silicon and yttrium barium copper oxide (YBCO). Ion beam assisted deposition (IBAD) of 300nm zirconia films at room temperature prevented interdiffusion at sintering temperatures over 800°C. Similar MgO and indium-tin oxide films did not prevent degradation at elevated temperatures. All films deposited on top of YBCO reduced the effects of extended atmospheric exposure.

Mass analyzed and non-mass analyzed carbon ion beams were used to deposit coatings on polished silicon wafers. Extremely, hard dense coatings that are structurally similar to i-carbon as determined by Ramon spectroscopy were achieved with high current beams of methane and argon. Residual contaminants of oxygen and nitrogen were minimized.