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Patterned atomic layer deposition (ALD) that selectively coats sidewalls with platinum (Pt) is developed to improve performance on CMOS MEMS devices. The proposed fabrication process is the first, to our knowledge, to pattern metal ALD on high-aspect-ratio MEMS sidewalls. A reflow step for the lift-off resist is introduced to increase yield by solving stringer issues. Sidewall metallization enables higher sensitivity on capacitive sensors and eliminates dielectric charging. A Pt-coated resonator oscillator and a capacitive accelerometer are demonstrated as examples, showing the successful process results. The measurement on a Pt-coated resonator oscillator indicates much higher stability than with the original dielectric sidewalls. This metal sidewall coating also has potential for other CMOS MEMS devices, such as switches. [2020-0178]

Accelerometer metrics of performance include higher dynamic range, lower noise, lower bias instability and lower power. As with all systems, these trade-offs compete. Achieving large dynamic range in accelerometers drives design trade-offs of sensitivity and survivability at the high end and low noise and drift at the low end of the range. CMOS-MEMS technology enables deployment of system-on-chip designs comprising an array of hundreds of individual accelerometer cells integrated with low-noise readout circuits and on-chip temperature, stress, and scale-factor sensors to compensate drift. These systems range to 50 kg shock measurement with 3 mg bias instability and a path toward micro-g bias instability.

Fabrication of ultra-thin (1–20- $\mu \text{m}$ thickness) polydimethylsiloxane (PDMS) films is enabled with a hexane dilution process and an underlying gelatin release layer. The release and transfer of these films over large areas (>5 cm) allows measurement of the thickness-dependent and process-dependent mechanical properties of ultra-thin PDMS membranes, reported for the first time. The effective Young’s modulus of 1- $\mu \text{m}$ -thick PDMS, measured by bulge testing, is approximately ten times larger than that of 0.5-mm-thick material, following a continuous power-law relationship over the entire thickness range. Mesh-patterned metal electrodes of 2- $\mu \text{m}$ minimum feature size are embedded in selected membranes. Metal evaporation and subsequent reactive ion etch patterning on PDMS increases its Young’s modulus due to the increase in cross-link formation and hardening of the surface. The results are meaningful in design and fabrication of soft electronics, microsensors, microvalves, and micropumps. [2014-0382]

In this paper, a 6-element pixelated antenna with reconfigurable resonance frequency and polarization is presented. Reconfiguration is achieved by mechanically connecting/disconnecting 6 movable Ni patches to/from fixed Cu patches, hence realizing patch antennas of different sizes and shape. Each movable patch is a cantilevered plate, micro-fabricated from a Ni layer plated on an RT Duroid substrate. The Ni patch is magnetically actuated by means of an electro-permanent magnet (EPM) placed behind the ground plane of the antenna. Since the Ni patch is itself part of the radiating element, this approach eliminates the need to insert an external switch on the antenna plane. The EPM is placed behind the ground plane, therefore eliminating losses associated with bias lines generally used in pixelated antennas. Most importantly, the very low mechanical contact resistance (as low as 200 mΩ) between the Ni and Cu patch ensures high antenna efficiency. The EPM enables latching of the magnetic actuator, hence resulting in zero static configuration power consumption. Measured resonance frequency reconfigurability, radiation pattern and radiation efficiency agree well with simulated data.

In this paper, we present magnetically-actuated micromechanical Ni patches that have been monolithically integrated on a printed circuit board to demonstrate a reconfigurable pixelated antenna operating within the 5–8 GHz frequency bands. The proposed antenna is based on a monolithically integrated grid structure of movable nickel (Ni) and fixed copper (Cu) patches. The Ni patches are magnetically actuated by means of an array of switchable magnets (SMs) placed behind the ground plane of the antenna. This approach eliminates the need for bias lines, which are generally used in reconfigurable antennas and induce losses. Most importantly, the very low mechanical contact resistance (as low as 200 mΩ) between the Ni and Cu patch ensures the insertion of these devices on the antenna plane without introducing significant losses. The use of a SM for the actuation of the patch makes it such that the antenna can hold the desired configurations without consuming active power. Power is consumed only during the switching operation. To demonstrate the feasibility of the proposed idea, the four most relevant operating modes of this small antenna prototype, centered around 5.55GHz, 6.44 GHz, and 7.89 GHz, are presented.a#13

Multiple regioregular polythiophene polymers with a variety of side chains, end groups and secondary polymer chains were used as active sensing layers in a single chip chemresistor sensor array device. A custom inkjet system was used to selectively deposit the polymers onto the array of transduction electrodes. The sensor demonstrated sensitivity and selectivity for detection and discrimination of volatile organic compounds (VOCs). The conductivity responses to VOC vapors are dependent on the chemical structure of the polymers. For certain VOCs, conductivity increased in some polymers, while it decreased in others. Principal component analysis (PCA) of sensor responses was used to discriminate between the tested VOCs. These results are correlated to the chemical structures of the different polymers, and qualitative hypothesis of chemical sensing mechanisms are proposed. This research demonstrates the potential for using such devices in VOC detection and discrimination sensing applications.

We introduce a large stroke electrostatic micro-pump made with a thin PDMS diaphragm embedded with thin-film metal electrodes and bonded over a smoothly shaped Si substrate that acts as the counter electrode. The thin PDMS layer creates a highly compliant diaphragm. The spline-shaped substrate height significantly reduces electrostatic actuation voltage, and is refined in its smoothness by a modification to conventional grayscale lithography for Si MEMS. Combining the effects of the compliant diaphragm and the “zipper” electrode gap, a diaphragm displacement of 100 µm is achieved, giving a displacement volume of 1 µL/stroke and a pumping rate of 60 µL/min at 1 Hz.

This paper reports on the fabrication of ultra-thin (~10 μm) polydimethylsiloxane (PDMS) films with embedded metal electrodes of 2 μm minimum feature size, as well as the release and transfer of large area films (>5 cm). The initial motivation for this work is the development of a miniature pump actuator for moving working fluid in an electrocaloric microcooler. PDMS diaphragms with electrodes are released and transferred onto contoured silicon chambers formed by gray-scale lithography and deep-reactive ion etching.

A refrigeration system composed of silicon MEMS cooling elements is designed based on the electrocaloric (EC) effect in a P(VDF–TrFE–CFE) terpolymer, poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) 59.2/33.6/7.2 mol%. Each cooling element includes two diaphragm actuators fabricated in the plane of a silicon wafer, which drive a heat transfer fluid back and forth across terpolymer layers that are placed between them. In the EC effect, reversible temperature and entropy changes related to polarization changes appear in a material under the application and removal of an electric field. Finite element simulations are performed to explore the system performance. The effect of the applied electric field is studied, and the time lag between the electric field and the diaphragm motion is found to significantly affect the cooling power. A parametric study of the operating frequency, externally-applied temperature span, and the electric field amplitude are conducted. The results indicate that when the system is operated at a temperature span of 15 K, a cooling power density of 3 W/cm2and a percent of Carnot COP of 31% are achieved for one element.

We present a micro-machining technology which enables MEMS fabrication on standard CMOS with very dense electrical/mechanical integration. Micro-mechanical structures are fabricated alongside circuits on standard 0.5-μm 3-metal CMOS dice using four maskless dry-etch steps. The resulting laminated beams are made of CMOS metal and dielectric layers. Multi-conductor mechanical structures can carry multiple signals for actuation and sensing. Narrow vertical and lateral gaps enable efficient XYZ electrostatic actuation and fine capacitive position sensing. Experiments show that mechanical structures can be integrated 1.5 μm away from signal-processing circuits, resulting in very low parasitics, good system performance, and small die size.

The electrocaloric effect (ECE) is a phenomenon in which reversible temperature and entropy changes of a material due to polarization appear under the application and removal of an electric field. Materials with a giant ECE have recently been reported, suggesting practical application in cooling devices. In this paper, a refrigeration system composed of silicon MEMS cooling elements is designed based on the ECE in a terpolymer. Finite element simulations are performed to explore the system performance. The effect of the form of the applied electric field is studied. The time lag between the electric field and the diaphragm motion is found to affect the cooling power significantly. A parametric study of the operating frequency is also conducted. The results indicate that when the system is operated at a temperature difference of 5 K, a cooling power density of 2 W/cm2 is achieved for one element.Copyright © 2013 by ASME

A new reflected mode magneto‐optic spatial light modulator (R‐MOSLM) has been developed for miniature optical correlators and computers. A factor of 4 improvement in pixel switching sensitivity, compared to the conventional transmission mode magneto‐optic spatial light modulator, has been achieved by the use of narrower drive lines, and burying the conductor into the film. A factor of 3 higher resolution and a factor of 2 higher optical efficiency have also been achieved by the use of smaller pixels and narrower pixel gaps. The smaller pixels and improved switching sensitivity permit an order of magnitude reduction in optical path length and increase in frame rate, respectively. The progress that has been made in the design of the R‐MOSLM, issues concerning its fabrication, a comparison by finite element analysis of field modeling to experimentally determined current requirements to drive individual lines, and some optical characteristics are discussed.

This paper reports on development of AFM-like active CMOS-MEMS conductive probes and arrays. The active probes are aimed for scanning tunneling microscopy (STM) imaging and field-emission (FE) assisted nanostructure formation. Two kinds of STM tip approaches compatible with CMOS-MEMS process — Electron-Induced Beam Deposition (EBID) and Spindt tip method — are presented, and their functionality is examined. Atomic-level resolution is achieved using tips in an ultra-high vacuum (UHV) STM. The MEMS probe working in ambient STM is also demonstrated. The active probe is equipped with a transimpedance amplifier (TIA) for tip FE current measurement around a nominal value of 1 nA.

A Stirling cycle micro-refrigeration system composed of arrays of silicon MEMS cooling elements has been designed and evaluated thermodynamically. The cooling elements are each 5 mm-long, 2.25 mm-wide, have a thickness of 300 μm, and are fabricated in a stacked array on a silicon wafer. A 0.5 mm-long regenerator is placed between the compression (hot side) and expansion (cold side) diaphragms. The diaphragms are 2.25 mm circles driven electrostatically. Helium is the working fluid, pressurized at 2 bar and sealed in the system. Under operating conditions, the hot and cold diaphragms oscillate sinusoidally 90° out of phase such that heat is extracted to the expansion space and released from the compression space. The bulk silicon substrate on which the device is grown is etched with “zipping” shaped chambers under the diaphragms. The silicon enables efficient heat transfer between the gas and heat source/sink as well as reduces the dead volume of the system, thus enhancing the cooling capacity. In addition, the “zipping” shaped substrates reduce the voltage required to actuate the diaphragms. An array of vertical silicon pillars in the regenerator serves as a thermal capacitor transferring heat to and from the working gas during a cycle. In operation, the push-pull motion of the diaphragm makes a 300 μm stroke and actuates at a frequency of 2 kHz. Parametric study of the design shows the effects of phase lag, swept volume ratio between the hot space and cold space, and dead volume ratio on cooling capacity. At TH = 313.15 K and TC = 288.15 K and assuming a perfect regenerator, the thermodynamic optimization analysis gives a heat extraction rate of 0.22 W per element and cooling capacity of 30 W/cm2 for the stacked system. Evaluation of the stacked system shows that the COP will reach 6.3 if the expansion work from the cold side is recovered electrostatically and used to drive the hot side diaphragm.Copyright © 2011 by ASME

The use of gold nanoparticles coated with an organic monolayer of thiol for application in chemiresistive sensors was initiated in the late 1990s; since then, such types of sensors have been widely pursued due to their high sensitivities and reversible responses to volatile organic compounds (VOCs). However, a major issue for chemical sensors based on thiol-capped gold nanoparticles is their poor long-term stability as a result of slow degradation of the monothiol-to-gold bonds. We have devised a strategy to overcome this limitation by synthesizing a more robust system using Au nanoparticles capped by trithiol ligands. Compared to its monothiol counterpart, the new system is significantly more stable and also shows improved sensitivity towards different types of polar or non-polar VOCs. Thus, the trithiol-Au nanosensor shows great promise for use in real world applications.

In this paper, a method of fabricating active CMOS-MEMS AFM-like conductive probes with nanometer-sized probe tips for Tip-directed Field-emission Assisted Nanofabrication (TFAN) is reported. We envision an approach using tip-directed chemical vapor deposition (CVD) for the deposition of Si nanowires (SNWs), using field-emitted electrons to locally crack adsorbed precursors (silane/disilane) through direct momentum transfer. This approach will enable control of nanowire geometry during fabrication. The designed active probe consists of three key parts: a thermal bimorph structure actuator, a capacitive sensor and a field emission (FE) probe tip. Unlike the past Spindt process for FE tip fabrication, a single-step probe tip fabrication process on CMOS-MEMS chips is introduced via electron-beam lithography and evaporation technique using PMMA as resist. The mechanism and key growth conditions for Spindt-type tip formation are investigated.

This work presents the fabrication and demonstration of an electroless gold plated CMOS-MEMS chemresistor array sensor for selective detection of volatile organic compounds, with conductive polythiophene polymer used as an active sensing material. Chemresistor electrode fabrication involves post-CMOS etching and electroless plating steps. An electroless gold plating process selectively deposits gold onto the CMOS aluminum electrodes to provide ohmic contact to the polymer layer. Electroless gold techniques are optimized to provide for a sub-micron vertical gap between the chemresistor electrodes. Polymer solutions are then deposited onto electrodes using drop-on-demand inkjet printing. Measured device response to methanol, acetone, and acetonitrile vapors demonstrates feasibility.

Regioregular polythiophene-based conductive copolymers with highly crystalline nanostructures are shown to hold considerable promise as the active layer in volatile organic compound (VOC) chemresistor sensors. While the regioregular polythiophene polymer chain provides a charge conduction path, its chemical sensing selectivity and sensitivity can be altered either by incorporating a second polymer to form a block copolymer or by making a random copolymer of polythiophene with different alkyl side chains. The copolymers were exposed to a variety of VOC vapors, and the electrical conductivity of these copolymers increased or decreased depending upon the polymer composition and the specific analytes. Measurements were made at room temperature, and the responses were found to be fast and appeared to be completely reversible. Using various copolymers of polythiophene in a sensor array can provide much better discrimination to various analytes than existing solid state sensors. Our data strongly indicate that several sensing mechanisms are at play simultaneously, and we briefly discuss some of them.

We have developed and synthesized highly conductive regioregular poly(3-alkylthiophene) (rr-PAT) derivatives for use in sensor arrays on a chip. Poly(3-alkylthiophene)s are ideally suited for this application because of their excellent electrical properties, solution processability and our ability to modify their chemical structure. Here, we synthesized rr-PATs that have different side chains and different end groups. The polymers were ink-jetted onto ChemFET devices on a chip and their chemical sensing properties were tested to a variety of volatile organic compounds (VOCs). The sensors demonstrated ppm level sensitivity and selectivity to all VOCs tested, including both polar and non-polar compounds.

A new reflected mode magneto-optic spatial light modulator (R-MOSLM) has been developed for miniature optical correlators and computers. An improvement by a factor of four in pixel switching sensitivity, compared to the conventional transmission mode magneto-optic spatial light modulator (T-MOSLM), has been achieved by the use of narrower drive lines, and burying the conductor into the film. A higher resolution by a factor of three and a higher optical efficiency by a factor of two have also been achieved by the use of smaller pixels and narrower pixel gaps. The smaller pixels and improved switching sensitivity permit an order of magnitude reduction in optical path length and increase in frame rate, respectively. >

Electrostatically actuated microstructures with high-aspect-ratio laminated-beam suspensions have been fabricated using conventional CMOS processing followed by a sequence of maskless dry-etching steps. Laminated structures are etched out of the CMOS silicon oxide, silicon nitride, and aluminum layers. The key to the process is use of the CMOS metallization as an etch-resistant mask to define the microstructures. A minimum beam width and gap of 1.2 /spl mu/m and maximum beam thickness of 4.8 /spl mu/m are fabricated in a 0.8 /spl mu/m 3-metal CMOS process available through MOSIS. Structural features will scale in size as the CMOS technology improves. An effective Young's modulus of 63 GPa is extracted from resonant frequency measurements. Cantilevered structures slightly curl up with a radius of curvature of about 4.2 mm. Multi-conductor electrostatic micromechanisms, such as self-actuating springs and nested comb-drive lateral resonators, are successfully produced. Self-actuating springs are self-aligned multi-conductor electrostatic microactuators that are insensitive to curl. The resonance amplitude is 1 /spl mu/m for an 107 /spl mu/m-wide/spl times/109 /spl mu/m-long spring with an applied 11 V ac signal. Finite-element simulation using the extracted value for Young's modulus predicts the resonant frequency of the springs to within 6% of the measured values.

The pressure drop and friction factor of gas flow across an array of circular silicon micro-pillars with different diameters fabricated by deep reactive ion etch (DRIE) process were investigated. The pitch-to-diameter ratio (1.5

The electrocaloric effect in thin films of a poly(vinylidene fluoride-trifluoroethylene chlorofluoroethylene) terpolymer (62.6/29.4/8 mol. %, 11–12 μm thick) is directly measured by infrared imaging at ambient conditions. The adiabatic temperature change is estimated to be 5.2 K for an applied electric field of 90 V/μm. The temperature change is independent of the operating frequency in the range of 0.03–0.3 Hz and is stable over a testing period of 30 min. Application of this terpolymer is promising for micro-scale refrigeration.

A post-CMOS maskless dry etch process has been developed to fabricate MEMS structures compatible with commercial low-k copper interconnect processes. The micromachining in the copper low-k process enables the fabrication of an RF inductor with quality factor of 12 at 7.5 GHz and a variable capacitor operating up to 3 GHz. Reduction of fluorine concentration in the plasma for the low-k dielectric etch solves the metal delamination problems. Argon/oxygen plasma cleaning of fluorine residue from the copper surface greatly reduces the metal erosion when exposed to high humidity.

This article describes an approach for implementing a complete computer system (CPU, RAM, I/O, and nonvolatile mass memory) on a single integrated-circuit substrate (a chip)—hence, the name “single-chip computer.” The approach presented combines advances in the field of microelectromechanical systems (MEMS) and micromagnetics with traditional low-cost very-large-scale integrated circuit style parallel lithographic manufacturing. The primary barrier to the creation of a computer on a chip is the incorporation of a high-capacity [many gigabytes (GB)] re-writable nonvolatile memory (in today’s terminology, a disk drive) into an integrated circuit (IC) manufacturing process. This article presents the following design example: a MEMS-based magnetic memory that can store over 2 GB of data in 2 cm2 of die area and whose fabrication is compatible with a standard IC manufacturing process.

This paper is a report on the characteristics of a new high resolution, high frame rate, reflected R-MOSLM. This effort is aimed at the production of Miniature Ruggedized Optical Correlators for Optical Pattern Recognition. Pixel size is under one mil center to center, one-third the dimension of present transmission mode devices, thereby reducing the optical path length by an order of magnitude. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems.

The reflected mode magneto-optic spatial light modulator (R-MOSLM) has been developed over the past couple of years. This development has led to a device that has state-of-the-art performance and is producible. This SLM device is truly compatible with semiconductor manufacturing techniques and is now being fabricated in a production environment. Performance details of individual devices is presented elsewhere. However, in this paper we discuss the measured parameters of multiple devices for statistics, discuss yield and packaging, and describe the impact of its manufacturability on cost. The system description of the correlator system using these devices is reported in a companion paper.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper is a report on the advanced development and characteristics of a new high resolution, high frame rate, reflected R-MOSLM. This effort is aimed at the production of miniature ruggedized optical correlators (MROC) for optical pattern recognition. Pixel size is under one mil center to center, one third the dimension of present transmission mode devices, thereby reducing the optical path length by an order of magnitude. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems. The device research and process development has been performed at Carnegie Mellon University NSF Data Storage System Center under contract from Litton Data Systems. The Litton Electron Device Division is transitioning the device to production. The MROC system description is described in companion paper (1959-09).

The advanced development and characteristics of a new high resolution, high frame rate, reflected mode MOSLM is reported. This effort is aimed at the production of Miniature Ruggedized Optical Correlators. The device research and process development is being performed at Carnegie Mellon University NSF Data Storage System Center (formerly Magnetic Technology Center) under contract from Litton Data Systems. Pixel size is under one mil center to center, one third the dimension of present transmission mode evaluation devices. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems.

Airborne particles of diameter > 0.4 μm reaching Dye 3, Greenland during April–May 1983 were highly variable in size and concentration from day to day. Five-day backward air mass trajectories suggest the importance of long-range transport from more northerly latitudes on days with high concentrations; particle sizes were larger on these days. Lower concentrations and smaller particle sizes were associated with transport from the south. It is inferred that Dye 3 may receive material emitted from Eurasian sources and transported over the Pole, similar to inferences for more northern Arctic sites. Elemental analysis of individual particles showed an abundance of crustal material, with many particles also containing sulfur. Bulk chemical analyses of airborne particles and fresh snow, collected during three snowstorms where ice nucleation dominated, provided data which were used to estimate mass-basis scavenging ratios. Average scavenging ratios were in the range ~1000–2000 for the crustal elements Al, Fe, K, Mg, Mn, and Na. Similar values were observed for Cd, Cu and NO3−. The corresponding ratios for Pb and SO42− averaged less than 200. These ratios were used with precipitation rate data to estimate wet deposition velocities in the order of ~2 cm s−1 for the first nine species, and ~0.2 cm s−1 for Pb and SO42−. Comparing fresh and older surface snow concentrations gave an average dry deposition velocity of roughly 0.2 cm s−1 for the crustal elements, with the small fraction of large particles (~5–10 μm) dominating deposition; much smaller values were associated with the remaining species. When used with other data in the literature, the results of this study suggest that total deposition velocities of Pb and SO42− may be as small as 0.05 cm s−1 in relatively dry regions of the Arctic.

Airborne particles in fugitive emissions have been measured at a slagging fixed-bed coal-gasification pilot plant using lignite. Sampling was conducted during shutdown operations and opening of the gasifier following an aborted startup. Aerosol collected with a Sierra high-volume impactor was subjected to analysis by gas chromatography, mass spectrometry, and scanning electron microscopy; aerosol collected with an Andersen low-volume impactor was subjected to flameless atomic absorption analysis. The data show that the bulk of the trace organic material is associated with small particles: these data are similar to data on ambient air reported in the literature. Particle morphologies resemble those of fly ash from coal combustion, including smooth spheres, vesicular spheres, and crystalline material. Trace element size distributions are bimodal and resemble data for ambient air. Pb-containing particles are generally submicron, while particles containing Al, Fe, and other crustal species are mostly of supermicron size. Aluminum-based aerosol enrichment factors calculated from the lignite composition show that the composition of the aerosol resembles that of the coal, with the exception of modest enrichments of Mg, Na, As, and Pb in the submicron size range. Aerosol enrichment factors based on the earth's crustal composition are somewhat greater than those based on coal composition for several elements, suggesting potential errors in using crustal enrichment data to investigate chemical fractionation during aerosol formation.

Fugitive emissions from a slagging fixed-bed coal-gasification pilot plant were analyzed by flameless atomic absorption spectrophotometry, gas chromatography, and mass spectrometry for trace metal and trace organic species. Analysis of the size distributions of airborne particulate matter inside the plant showed an abundance of large metal-containing particles; outdoor distributions in the vicinity of the plant resembled the indoor distributions, suggesting the importance of the gasifier in influencing ambient air quality. This conclusion was further supported by identification of similar organic compounds inside and outside the plant. Trace element enrichment factors based on the earth's crustal composition were greater than those based on the composition of the lignite used in the gasifier, showing the importance of characterizing the proper source material when inverstigating chemical fraction during aerosol formation. Enrichments in the present study were much greater than those found in previous sampling during aborted start-up and cleaning procedures, where normal operating temperatures had not yet been reached. Both studies showed evidence of enrichment factors which decreased with increasing particle size. Although much of the airborne mass was associated with large particles having low respirability, the high concentrations of some metals indoors suggests that further assessment of potential occupational exposures is warranted.