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The thermal stability and contact resistance of TaAlN thin films as electrical contacts to SiGe thermoelectric elements are reported. We demonstrate that a sharp interface is maintained after the device annealed at 800 °C for over 100 h, indicating that no interdiffusion takes place between TaAlN and SiGe. A specific contact resistivity of (2.1 ± 1.3) × 10−6 Ω-cm2 for p-type SiGe and (2.8 ± 1.6) × 10−5 Ω-cm2 for n-type SiGe is demonstrated after the high temperature annealing. These results show that TaAlN is a promising contact material for high temperature thermoelectrics such as SiGe.

Organic and inorganic thin film transistors (TFTs) are fabricated, simulated, and tested for circuit applications. The devices are based on polycrystalline cadmium sulfide (CdS) and pentacene thin films. Both devices are simulated and analyzed using two-dimensional finite element simulation methodology. For CdS, grain boundary and uniform trap distribution approaches are implemented. It is assumed that traps due to grain boundaries are uniformly distributed throughout the film. For pentacene a Poole-Frenkel mobility model is employed. After matching device simulation with experimental data, the SPICE model parameters are extracted for circuit simulation. The devices are tested for both analog and digital circuits. operational amplifier (OPAMP) and inverter circuits are tested. Two OPAMP topologies are compared and the results are discussed. One of the topologies is based on all n-type transistors using CdS TFT and the other topology is the two-stage Miller compensated CMOS design based on CdS and pentacene TFTs. The operational amplifiers have an open-loop voltage gain of 25.9dB and 29.7dB respectively. The performance of the CMOS design is found to be limited by performance of pentacene transistor. Display Omitted

Microelectrode arrays (MEAs) enable non-invasive recording of supra-threshold signals, i.e. action potentials or spikes, from a variety of cultured electrically active cells. While this label-free technology has been shown to be useful for pharmacological and toxicological studies, a major limitation has been the reliance on expensive recording substrates that have been manufactured with the intent of re-use. Prior work by our group has demonstrated an approach for fabricating MEAs using conventional liquid crystal display manufacturing techniques. Here, we describe and characterize the UT Dallas planar MEA which is fabricated with low cost materials and processes. We compare the performance of the UT Dallas MEAs, which consist of exposed gold microelectrodes with patterned parylene insulation over traces, with well-established commercially available MEAs using cultured murine cortical networks. Detailed electrophysiological comparisons show virtually identical performance between MEA types with respect to network metrics including recording yield across the array, network spike rate and burst rate, and virtually identical pharmacological responses to a diverse set of neuropharmacological agents.

We compute thermal conductivity ( κ ) of magnesium silicide (Mg 2 Si) with point defects and nanoparticles through molecular dynamics simulation. To describe an alloy with complex defect structures, the extended modified embedded atom method is utilized in this simulation study. The calculated phonon dispersion and κ of pristine Mg 2 Si are in close agreement with first-principles calculations and experimental results. We compared the effect of intrinsic point defects and nanoparticles on heat transfer in Mg 2 Si at the same stoichiometry. We find that point defects could be more effective than nanoparticles to reduce κ . The geometric size effect is also investigated for Mg and Si nanoparticles. Smaller Mg nanoparticles can significantly reduce κ . However, Si nanoparticles demonstrate little size effect on κ . Our simulation results show that phonon transport in Mg 2 Si has more contribution from strain scattering than mass defect scattering. These findings can provide guidance for experiments to more effectively engineer bulk Mg 2 Si with nanostructured defects for thermoelectric applications.

By using a single host for both blue and orange phosphorescent dopants, a simple and efficient white organic light emitting-diode is reported. The dual-emissive-layer white device achieves a peak external quantum efficiency of 16.9 ± 0.9% and power efficiency of 44.1 ± 2.3 lm/W without out-coupling enhancement. Analysis of the device working mechanism determines that the blue dopant molecules can form a bridge to facilitate electron transport into the adjacent orange emitting-layer. The orange emission originates from both the direct electron trapping by the orange dopant and incomplete blue–orange energy transfer mechanisms. The origin of the voltage-dependent color shift of the device is quantitatively determined according to the working mechanism. Possible solution to reducing the color-shift is also provided based on the calculation and analytical results.

The electronic structure of group VA impurities in PbTe is investigated by first principles calculations. Our findings show that these impurities can act as either donors or acceptors, depending on whether they occupy Pb or Te lattice sites. The impurities introduce a defect state at ∼0.3 eV above the conduction band minimum if they stay at Pb sites, whereas they introduce a state at the edge of the PbTe valence band if they stay at Te sites. The implications of our calculations on the thermoelectric efficiency of PbTe are also discussed.

The effect of a polycrystalline silicon (poly-Si) seeding layer on the properties of relaxor Pb(Zr0.53,Ti0.47)O3–Pb(Zn1/3,Nb2/3)O3 (PZT–PZN) thin films and energy-harvesting cantilevers was studied. We deposited thin films of the relaxor on two substrates, with and without a poly-Si seeding layer. The seeding layer, which also served as a sacrificial layer to facilitate cantilever release, was found to improve morphology, phase purity, crystal orientation, and electrical properties. We attributed these results to reduction of the number of nucleation sites and, therefore, to an increase in relaxor film grain size. The areal power density of the wet-based released harvester was measured. The power density output of the energy harvester with this relaxor composition and the poly-Si seeding layer was 325 μW/cm2.

Today's state-of-the-art phosphorescent organic light-emitting diodes (PhOLEDs) must rely on the host-guest doping technique to decrease triplet quenching and increase device efficiency. However, doping is a sophisticated device fabrication process. Here, a Pt(II)-based complex with a near unity photoluminescence quantum yield and excellent electron transporting properties in the form of neat film is reported. Simplified doping-free white PhOLED and yellow-orange PhOLED based on this emitter achieve rather low operating voltages (2.2–2.4 V) and very high power efficiencies of approximately 80 lm W−1 (yellow-orange) and 50 lm W−1 (white), respectively, without any light extraction enhancement. Furthermore, the efficient white device also exhibits high color stability. No color shift is observed during the entire operation of the device. Analysis of the device's operational mechanism has been postulated in terms of exciton and polaron formation and fate. It is found that using the efficient neat Pt(II)-complex as a homogeneous emitting and electron transporting layer and an ambipolar blue emitter are determining factors for achieving such a high efficiency.

By introducing a neat Pt(II)-based phosphor with a remarkably short decay lifetime, a simplifi ed doping-free phosphorescent organic light-emitting diode (OLED) with a forward viewing external quantum effi ciency (EQE) and power effi ciency of 20.3 ± 0.5% and 63.0 ± 0.4 lm W − 1 , respectively, is demonstrated. A quantitative analysis of how triplet-triplet annihilation (TTA) and tripletpolaron annihilation (TPA) affect the device EQE roll-off at high current densities is performed. The contributions from loss of charge balance associated with charge leakage and fi eld-induced exciton dissociation are found negligible. The rate constants k TTA and k TPA are determined by time-resolved photoluminescence experiments of a thin fi lm and an electrically-driven unipolar device, respectively. Using the parameters extracted experimentally, the EQE is modeled versus electric current characteristics of the OLEDs by taking both TTA and TPA into account. Based on this model, the impacts of the emitter lifetime, quenching rate constants, and exciton formation zone upon device effi ciency are analyzed. It is found that the short lifetime of the neat emitter is key for the reduction of triplet quenching.

The structural, optical and dielectric characteristics of PMMA–TMSPM–SiO2 hybrid thin films, synthesized by sol–gel, were studied as a function of the molar concentration of the coupling agent (TMSPM) in the hybrid precursor solution. It was possible to obtain very homogenous films, with improved thermal stability and variable organic and inorganic composition. The hybrid films showed high uniformity, excellent optical transparency and tunable refractive index from 1.447 to 1.490 at 633 nm depending on the PMMA fraction in the films. The formation of both organic and inorganic components and their interaction in the hybrid material were confirmed by the analysis of the ATR–FTIR spectra, suggesting changes in the film structure caused by the variations of the TMSPM concentration. The dielectric constant of the hybrid films, determined from capacitance–voltage (C–V) measurements performed in metal–insulator–metal (MIM) configuration, had unexpectedly high values between 5 and 14, increasing with decreasing TMSPM molar ratio. Such high dielectric constant values were attributed to highly polarizable OH and C C groups in the hybrid films, OH being part of the residual precursor solvents and C C the result of incomplete conversion of precursor monomer (MMA) into polymer (PMMA), as shown by FTIR measurements. Furthermore, the dielectric constant of the hybrid films was modeled according to an effective media approximation model, taking into account the constituting organic and inorganic phases, residual O H and C C groups.

We have demonstrated a low temperature process for a ferroelectric non-volatile random access memory cell based on a one-transistor–one-capacitor (1T1C) structure for application in flexible electronics. The n-channel thin film transistors (TFTs) and ferroelectric capacitors (FeCaps) are fabricated using cadmium sulfide (CdS) as the semiconductor and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer as the ferroelectric material, respectively. The maximum processing temperature for the TFTs is 100 °C and 120 °C for the FeCaps. The TFT shows excellent access control of the FeCap in the 1T1C memory cell, and the stored polarization signals are undisturbed when the TFT is off. The fabricated 1T1C memory cell was also evaluated in a FRAM circuit. The memory window on the bit line was demonstrated as 2.3 V, based on the 1T1C memory cell with a TFT having dimensions of 80 μm/5 μm (W/L) and a FeCap with an area of 0.2 × 10−3 cm2 using a bit line capacitor of 1 nF pre-charged at 17.2 V. The 1T1C memory cell is fabricated using photolithographic processes, allowing the integration with other circuit components for flexible electronics systems.

Fabrication and characterization of integrated hybrid complementary metal oxide semiconductor devices (CMOS) using 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PC) and cadmium sulfide (CdS) as the active layers deposited using solution based processes are demonstrated. The n- and p-type thin film transistors (TFTs), inverters, and NAND gate devices were fabricated using photolithography-based techniques. The hybrid CMOS technology demonstrated is compatible with large-area and mechanically flexible substrates given the low temperature processing ( 2 /V s, respectively. The inverters exhibited a DC gain of ≈52 V/V with full rail-to-rail switching. The NAND logic gates switch rail-to-rail with a transition point of V DD /2.

There is an interest in higher-ZT thermoelectric materials for high-watt-density cooling of electronics. Reducing thermal conductivity through increased phonon scattering in nanomaterials has been shown to be effective and is being investigated by many groups. Solution-based synthesis is a method for making thermoelectric nanomaterials that can provide particle sizes

Alternating layers of TiO 2 nanosheets and poly(ethylenimine) were sequentially dip coated onto a polyethylene naphthalate substrate (PEN) using layer-by-layer assembly. UV–vis spectroscopy shows a linear growth of the PEI/nanosheets bilayer on the PEN substrate. The cross-section microstructure of the LBL film was studied using scanning electron microscopy (SEM). Helium permeability measurement showed that the titania nanosheet/PEI bilayers reduced the permeation rate of He through the coated PEN film.

Planar microelectrode arrays (MEAs) permit the long-term, non-invasive monitoring of electrically active cells. Compared to disposable plastic chambers and cultured dishes used for in vitro tests, MEAs are typically reused in experiments since they are expensive. Here, we report the design and demonstration of a low-cost novel MEA using conventional liquid crystal display manufacturing techniques. The resulting MEA is flexible, conducive for neuronal culture, and capable of monitoring extracellular potentials at a signal-to-noise ratio comparable to standard commercially available MEAs. The design layout is consistent with results from finite-element modeling. Electrochemical impedance and input referred noise have been measured for the fabricated MEA. Finally, it was demonstrated that spike activity of the cultured cortical neurons on the MEA is sensitive to pharmacological blocker tetrodotoxin (TTX).

Lead zirconate titanate, Pb(Zr 0.53 ,Ti 0.47 )O 3 or PZT, thin films and integrated cantilevers have been fabricated for energy harvesting applications. The PZT films were deposited on PECVD SiO 2 /Si substrates with a sol–gel derived ZrO 2 buffer layer. It is found that lead content in the starting solution and ramp rate during film crystallization are critical to achieving large-grained films on the ZrO 2 surface. The electrical properties of the PZT films were measured using metal–ferroelectric–metal and inter-digital electrode structures, and revealed substantial improvement in film properties by controlling the process conditions. Functional cantilevers are demonstrated using the optimized films with output of 1.4 V peak-to-peak at 1 kHz and 2.5 g.

The electrical fatigue characteristics of 100 nm thick, solution processed poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer thin film Metal-Ferroelectric-Metal (MFM) capacitors have been studied. After one million stress cycles at an electric field of 1.4 MV/cm and 500 Hz switching frequency, 87% of the initial switching polarization is maintained, with the non-switching polarization remaining low. The kinetics of the switching polarization were studied before and after electrical stress. Fatigue increases the required activation field for switching polarization and suppresses switchable polarization. The activation field increases after electrical stress and higher activation fields were required for higher electric field stressing. The reduction in switchable polarization is approximately 10% of the initial switching polarization for all electric fields and frequencies studied. We demonstrated that under operating conditions compatible with flexible electronic applications, the optimized ferroelectric thin film capacitor reported shows stable switching polarization and acceptable fatigue after electrical stress.

In this work we report the performance of permeation barriers based on organic/inorganic multilayer stacks. We have used PMMA-SiO2 (poly methyl methacrylate-silica) hybrid films synthesized through a sol–gel route as organic–inorganic components, whereas Al2O3 thin films were used as the inorganic component. The hybrid layers were deposited by dip coating and the Al2O3 by atomic layer deposition (ALD), films were prepared on polyethylene naphthalene (PEN) substrates. The permeability of the films and stacks is evaluated using helium as the diffusion gas in a custom made ultra-high vacuum system. The results show that permeability for PEN is reduced from 5 × 10−3 g/m2-day to about 9 × 10−5 g/m2-day for the best multiple barrier evaluated. Increased barrier properties are due to the increasing in the path and hence the lag-time of the permeating gas. In particular, we report the surface roughness of the different layers and its impact on the barrier performance. The hybrid layers reduced notably the roughness of the bare PEN substrate improving the quality of the Al2O3 layer in the barrier. The optical transmittance of the barriers in the visible region is higher than 80% in all the studied cases.

Organic–inorganic hybrid thin films have been prepared by a modified sol–gel route using tetraethyl orthosilicate as the inorganic (silica) source, methyl methacrylate (MMA) as the organic source, and 3-trimetoxysilylpropyl methacrylate as the coupling agent. The films were prepared by spin coating on Si (100) p-type substrates and subsequently heat-treated at 90 °C. Fourier transform infrared results reveal a set of absorption bands associated with the formation of both PMMA and SiO2 phases in the hybrid films. Capacitance–voltage (C–V) characterization was carried out on metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures, with the hybrid films as the insulator layer to evaluate the electrical properties. We present a detailed comparative analysis of the dielectric constant obtained from C–V characterization in the frequency range of 1 kHz–1 MHz. For the PMMA-SiO2 hybrid material the dielectric constant values obtained were around 9.5 at 1 MHz which is superior to the values reported for thermally grown SiO2 and pure PMMA materials. The interface state density for PMMA-SiO2 on Si was approximately 1010 cm−2, which is comparable to the standard SiO2/Si structures. Due to the electrical behavior and low processing temperatures this hybrid dielectric is a very promising candidate for flexible electronic devices and its subsequent implementation does not require complex equipment.

0.9Pb(Zr0.53,Ti0.47)O3-0.1Pb(Zn1/3,Nb2/3)O3 (PZT–PZN) thin films and integrated cantilevers have been fabricated. The PZT–PZN films were deposited on SiO2/Si or SiO2/Si3N4/SiO2/poly-Si/Si membranes capped with a sol–gel-derived ZrO2 buffer layer. It is found that the membrane layer stack, lead content, existence of a template layer of PbTiO3 (PT), and ramp rate during film crystallization are critical for obtaining large-grained, single-phase PZT–PZN films on the ZrO2 surface. By controlling these parameters, the electrical properties of the PZT–PZN films, their microstructure, and phase purity were significantly improved. PZT–PZN films with a dielectric constant of 700 to 920 were obtained, depending on the underlying stack structure.

The impact of thermal treatment and thickness on the polarization and leakage current of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer thin film capacitors has been studied. The evolution of the film morphology, crystallinity and bonding orientation as a function of annealing temperature and thickness were characterized using multiple techniques. Electrical performance of the devices was correlated with the material properties. It was found that annealing at or slightly above the Curie temperature (Tc) is the optimal temperature for high polarization, smooth surface morphology and low leakage current. Higher annealing temperature (but below the melting temperature Tm) favors larger size β crystallites through molecular chain self-organization, resulting in increased film roughness, and the vertical polarization tends to saturate. Metal–Ferroelectric–Metal (MFM) capacitors consistently achieved Ps, Pr and Vc of 8.5 μC/cm2, 7.4 μC/cm2 and 10.2 V, respectively.

This work reports the preparation and characterization of hafnium (IV) oxide (HfO2) nanoparticles grown by derived sol-gel routes that involves the formation of an organic polymeric network. A comparison between polymerized complex (PC) and polymer precursor (PP) methods is presented. For the PC method, citric acid (CA) and ethylene glycol (EG) are used as the chelating and polymerizable reagents, respectively. In the case of PP method, poly(acrylic acid) (PAA) is used as the chelating reagent. In both cases, different precursor gels were prepared and the hafnium (IV) chloride (HfCl4) molar ratio was varied from 0.1 to 1.0 for the PC method and from 0.05 to 0.5 for the PP method. In order to obtain the nanoparticles, the precursors were heat treated at 500 and 800 °C. The thermal characterization of the precursor gels was carried out by thermogravimetric analysis (TGA) and the structural and morphological characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns of the samples obtained by both methods shows the formation of HfO2 at 500 °C with monoclinic crystalline phase. The PC method exhibited also the cubic phase. Finally, the HfO2 nanoparticles size (4 to 11 nm) was determined by TEM and XRD patterns.

In this study, HfxZr1-xO2 (0 < x < 1) thin films were deposited on silicon wafers using a dip-coating technique and by using a precursor solution prepared by the Pechini route. The effects of annealing temperature on the structure and morphological properties of the proposed films were investigated. HfxZr1-xO2 thin films with 1, 3 and 5 layers were annealed in air for 2 h at 600 and 800 °C and the structural and morphological properties studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results show that the films have monoclinic and tetragonal structure depending of the Hf and Zr concentration. SEM photographs show that all films consist of nanocrystalline grains with sizes in the range of 6 - 13 nm. The total film thickness is about 90 nm.

In the present study a complete analysis of the morphological and electrical properties of PZT layers with composition 53Zr-47Ti is presented. Three different samples composed of 3, 6, and 9 PZT layers were analyzed on a substrate consisting of ZrO2-SiO2-Si structures. The PZT and ZrO2 layers were deposited via Sol-Gel, whereas the SiO2 layer, on every sample, was deposited via PECVD. SEM results showed morphology of very small granules on the 3 layered thin-film samples (12 nm), on the 6 layered thin-film samples a mixture of small and large size (100-300 nm) granule formation was observed, with the 9 layered thin-film samples exhibiting very large granule sizes (bigger than 300 nm). XRD results showed that increasing the number of deposited layers caused an incremental increase on the detected peak intensities, aided in the promotion of the perovskite phase, and diminished the presence of the pyrochlore phase. It was also observed, during electrical measurements, that increasing the number deposited layers directly increased the overall capacitance of the thin-film structure. This effect was attributed primarily to the large amount of perovskite and large size of grains presented on thick samples.

In this work we demonstrate a novel integration approach to fabricate CMOS circuits on plastic substrates (poly-ethylene naphthalate, PEN). We use pentacene and amorphous silicon (a-Si:H) thin-film transistors (TFTs) as p-channel and n-channel devices, respectively. The maximum processing temperature for n-channel TFTs is 180 °C and 120 °C for the p-channel TFTs. CMOS circuits demonstrated in this work include inverters, NAND, and NOR gates. Carrier mobilities for nMOS and pMOS after the CMOS integration process flow are 0.75 and 0.05 cm2/V s, respectively. Threshold voltages (Vt) are 1.14 V for nMOS and −1.89 V for pMOS. The voltage transfer curve of the CMOS inverter showed a gain of 16. Correct logic operation of integrated flexible NAND and NOR CMOS gates is also demonstrated. In addition, we show that the pMOS gate dielectric is likely failing after electrical stress.

In this work, we present reliability results of MIM (Metal–Insulator–Metal) capacitors fabricated with parylene as the dielectric, deposited at room temperature. We have evaluated the time dependent dielectric breakdown (TDDB) of parylene-based MIM capacitors as a function of constant DC voltage stress, area and dielectric thickness of the capacitor. Mean-time-to-failure (MTTF) of parylene evaluated at different stress voltages shows a power law distribution over the applied voltage range and device area, with MTTF driven by the number of defects. Defect density in the parylene capacitors is also reported and is calculated to be ∼1.2 × 10 3 defects/cm 2 .

Transmission electron microscopy (TEM) characterization of nickel contacts to bulk bismuth tellurium selenide [Bi2(Te,Se)3] is reported. Samples were prepared in a dual column focused ion beam/scanning electron microscope (FIB/SEM) system using a lift-out technique, with ion beam energy and exposure times carefully optimized to minimize sample damage. Diffusion of Ni into Bi2(Te,Se)3 was observed and the formation of a nickel telluride (NiTe) interfacial region confirmed after heat treatment at 200 °C. Selected area diffraction patterns provided evidence of a modified bismuth telluride–like structure at the interface, identified by analytical electron microscopy to be composed of Ni and Bi2(Te,Se)3. Copyright © 2009 John Wiley & Sons, Ltd.

Multilayer composites that utilize polymeric and brittle inorganic films are essential components for extending the lifetimes and exploiting the flexibility of many electronic devices. However, crack formation within the brittle inorganic layers that arise from defects as well as the flexing of these multilayer composite materials allows the influx of atmospheric water, a major source of device degradation. Thus, a composite material that can initiate self-healing upon the influx of environmental water through defects or stress-induced cracks would find potential applications in multilayer composite materials for permeation barriers. In the present study, the reactive metal oxide precursor TiCl4 is encapsulated within the pores of a degradable polymer, poly(lactic acid) (PLA). Electrospun PLA fibers are found to be reactive to atmospheric water leading to the hydrolysis of the degradable polymer shell and subsequent release of the reactive metal oxide precursor. Release of the reactive TiCl4 from the pores results in hydrolysis of the metal oxide precursor, forming solid titanium oxides at the surface of the fibers. The efficacy of this self-healing delivery system is also demonstrated by the integration of these reactive fibers in the polymer planarization layer, poly(methyl methacrylate), of a multilayer film, upon which an alumina barrier layer is deposited. The introduction of nanocracks in the alumina barrier layer lead to the release of the metal oxide precursor from the pores of the fibers and the formation of titanium dioxide nanoparticles within the crack and upon the thin film surface. In this study the first delivery system that may find utility for the self-healing of multilayer barrier films through the site-specific delivery of metal oxide nanoparticles through smart reactive composite fibers is established.

The thermal stability of fully silicided (FUSI) NiSi with arsenic or boron doping on silicon on insulator (SOI) was investigated. After the stacks were subjected to a typical back-end of line (BEOL) thermal annealing in a N"2 ambient, abnormal oxidation of As doped FUSI NiSi stacks is observed by X-ray photoelectron spectroscopy (XPS), and confirmed by high-resolution transmission electron microscopy (HRTEM). X-ray diffraction (XRD) results show Ni-rich phases like Ni"3Si are formed due to abnormal oxidation of FUSI NiSi. In contrast to As doped stacks, no phase transformation nor abnormal oxidation are observed for B doped stacks under similar annealing. However, backside secondary ion mass spectrometry (SIMS) results indicate B penetration through a 3nm SiON layer into the Si channel after N"2 annealing for 4h at 400^oC. There is no evidence for Ni diffusion into the Si channel for B doped stacks. However, Ni penetration into the Si channel is observed for As doped stacks due to the enhancement of abnormal oxidation of FUSI NiSi.

We explore the effects of conventional photo lithographic patterning of the active layer of poly (3-hexylthiophene) (P3HT) organic thin film transistors (OTFT) on device performance. The performance of the devices was monitored in each step of the patterning process. We successfully developed a patterning process which is compatible with plastic substrates and P3HT as the organic semiconductor. In this process, parylene and atomic layer deposition (ALD) Al 2 O 3 were used as capping layers. Al 2 O 3 and parylene/P3HT were etched using Al etchant and O 2 plasma reactive ion etching (RIE), respectively. The degradation occurred primarily during the ALD Al 2 O 3 deposition and capping layer etching. There was a 30% degradation in mobility, a 1–2× reduction in drive current, and an increase in threshold voltage after the ALD Al 2 O 3 deposition. In the capping layer etching, a near 50% degradation in mobility was observed. The patterned devices have a mobility of 0.02 cm 2 /V s, which is 1000× better than photo lithographically patterned P3HT OTFTs previously reported in the literature, and comparable to un-patterned P3HT devices.

We have demonstrated that an experimental cross-wire junction set-up can be used to measure the I–V characteristics of a self-assembled monolayer (SAM) stabilized metal quantized point contact. The increased stability due to the presence of the SAM allows the measurement of the I–V characteristics. However, the SAM also provides additional conductance paths in addition to the pure metal point contact. The presence of the SAM may contribute to the non-integral quantum conductance transition and the non-linear I–V characteristics of the quantum contact. Nonetheless, a straight I–V curve is obtained for the Au quantized point contact from 0 to 1 V with a conductance of approximately 1G0, in contrast to previous work reported in the literature.

A high-k/metal film stack in a conventional complementary metal oxide semiconductor (CMOS) flow is a key candidate in the semiconductor industry for replacing the existing poly-silicon gate and silicon dioxide (SiO2) gate dielectric to reduce poly depletion and gate leakage. During conventional CMOS integration, the high-k/metal film stack is exposed to a high thermal budget process. In this work, an atomic layer deposition (ALD)-based hafnium oxide (HfO2)/titanium nitride (TiN) film stack (representative of the high-k/metal film stack) was annealed at 1000 °C to determine any change in the physical and electrical properties, such as thickness, surface roughness, density, sheet resistance, refractive index, extinction coefficient, composition, C–V characteristics, work function and etch rate. Although there was no significant electrical impact, some significant physical changes have been observed, which impact the process of integrating high-k/metal film stacks, especially in dual metal gate CMOSs.

We present the effect of poly (3-hexylthiophene) (P3HT) thickness on the performance of organic thin film transistors (OTFTs). The P3HT film thickness varies from 11to186nm. The devices have channel lengths of 5, 10, 20, 40, and 80μm and a channel width of 500μm. The mobility and on/off ratio are up to 0.08cm2∕Vs and 7×103, respectively. The drain current and the mobility increase with thickness. At the same P3HT thickness, the drain current and mobility become higher when the channel length is reduced. The on/off ratio decreases quickly and then saturates for thickness >64nm. Short channel devices have higher on/off ratio than long channel devices. For short channel devices (5μm), the on/off ratio does not change significantly with thickness. The devices with shorter channel length and thicker P3HT films tend to have smaller threshold voltages. The threshold voltage saturates for long channel (20–80μm) devices, for films thicker than 110nm. The gate leakage (ID offset) is higher for thicker film devices. The performance dependence as a function of P3HT film thickness can be explained by the bulk conductance model and the SiO2 surface potential change. Our results suggest that the performance of P3HT OTFTs should be optimized based on the specific application.

Gate bias induced leakage current and drain current offset limit device performance in poly 3-hexylthiophene (P3HT) organic thin film transistors (OTFTs). The drain current offset distorts the drain current in the linear region of the transistor performance curve, making it difficult to extract device parameters. A higher drain current offset corresponds to higher leakage current, which contributes to poor drain current modulation. The drain current offset increases when the semiconductor doping density is higher or when the P3HT film is thicker. We propose that the most probable mechanism for the leakage and drain current offset is uncontrolled expansion of drain/source electrodes. Based on the proposed mechanisms, the drain current offset is dramatically reduced by patterning the active region to reduce non-channel leakage.

This article describes a study of the static friction and wear of coated microelectromechanical systems (MEMS) surfaces using thermally actuated friction microdevices. In order to characterize static friction and wear, a tribological deep reactive ion etched silicon test microstructure is developed. Reproducibility of the data is proven by testing multiple devices in parallel. Conformal coatings consisting of atomic layer deposited (ALD) TiO2 or ZrO2 and successive ionic layer adsorption and reaction (SILAR) deposited MoS2 or ZrO2 films are applied on the MEMS silicon test devices. The effect of film roughness and humidity on friction and wear is studied by exposing the coated MEMS devices to a relative humidity varying between 5% and 100%. The coatings were found to behave differently, ZrO2 and MoS2 decreasing the coefficient of friction compared to uncoated devices, while TiO2 presented a decrease in the coefficient of friction only at higher humidity. The wear data for the ALD coated devices, quantifie...

Different mutants of Cowpea Mosaic Virus (CPMV) have been used as scaffolds to bind 2 and 5 nm gold nanoparticles through gold−sulfur bond formation at specific locations on the virus to produce patterns of specific interparticle distances. TEM images confirm that the bound gold particles produce patterns of gold nanoparticles that correlate well with models built from the known locations of the inserted cysteine groups on the capsid. These results demonstrate that it is possible to use CPMV mutants as nanoscale scaffolds to place gold nanoparticles at fixed interparticle distances.

Physical and electrical properties of hafnium silicate (HfSixOy) dielectric films prepared by room-temperature UV/ozone (O3) oxidation of hafnium silicide (HfSi2) are reported. Angle-resolved x-ray photoelectron spectroscopy was used to determine chemical bonding at the film interface and within the bulk film. These films, with 12 at. % Hf composition, have a dielectric constant (κ) of ∼8–9 and exhibit a flat-band voltage shift of 60 mV. The leakage current density at VFB+1 V is 4.7×10−5 A/cm2 for a 4.7-nm-thick film (capacitance equivalent thickness=2.6 nm) and breakdown strength was >8 MV/cm.

The effect of different small-signal ac voltage amplitudes on C–V curves characterized by thin SiO2 based p-type MOS capacitor with aluminum gate is reported. When the small-signal ac voltage is comparable to the gate bias, the thickness of SiO2 thin films extracted from the accumulation capacitance is found to be independent of small-signal ac voltage amplitudes, but the flat band voltage shift and interface state density associated with the variation of depletion layer capacitance are dependent on small-signal ac voltage amplitudes. They all increase with the small-signal ac voltage amplitudes. The experimental results reveal that the optimum small-signal ac voltage should be less than 100 mV. The mechanisms involving the depletion layer changes with small-signal ac voltages in SiO2 thin films are also discussed in this paper.

Screened samples of two different commercial phosphors were aged at 1.5 keV under nominally identical conditions in five different vacuum systems. After aging to doses of ∼5 C/cm2 the changes in cathodoluminescence (CL) spectral output and photoluminescence properties were determined, and x-ray photoemission spectroscopy (XPS) and Auger analyses were performed. We observed that while the CL degradation was similar for all systems at low electron doses, the aging rates diverged at high doses, suggesting an increasing importance of the vacuum environment. Post-aged CL spectra showed distinct redshifts in all cases, and the most heavily degraded samples displayed XPS-determined increases in surface carbon levels. The data suggest an extrinsic CL aging mechanism; a model involving the conversion of surface hydrocarbons to a metallic graphite phase agrees with the data.

We examine conductance phenomenon for Au quantum point contacts (QPC) formed using a crossed-wire geometry experimental set-up. When one of the wires is coated with a self-assembled monolayer of an alkanethiol, we find that a conductance plateau indicative of a QPC can be stable for tens of seconds, exceeding typical periods of stability by several orders of magnitude. This extended stability is attributed to the inhibition of the diffusion of Au atoms away from the contact area by the presence of the self-assembled monolayer.

We have developed a chemical sensor based on a capacitor design that utilizes molecular sieves as the dielectric phase. In this study, thin films of vanadium aluminum phosphate (VAPO-5), the isostructural manganese aluminum phosphate (MnAPO-5) and magnesium aluminum phosphate (MAPO-36) were deposited onto titanium nitride-coated silicon wafers by laser ablation. The molecular sieve films function as the dielectric phase and were patterned with Au/Pd to complete the capacitor. The molecular sieve-based sensors exhibited capacitance changes upon exposure to CO2, CO, N2 and H2O at room temperature. Significant responses to CO2 and CO were registered at levels as low as 50 and 100 ppm, respectively.

A simulation based comparative study of the polarization hysteresis of the ferroelectric capacitor using various ferroelectric models is presented. A 2-dimensional finite element device-level model was implemented using SILVACO's ATLAS device simulator to generate the polarization hysteresis characteristics for Au/Poly(vinylidene fluoride-trifluoroethylene)/Au metal-insulator-metal (MIM) device. Landau free energy expression for electric field in terms of polarization is also implemented in the MATLAB to produce the polarization hysteresis curve of polycrystalline ferroelectrics. The main drawback of these models was their inability to predict polarization saturation at the same electric field limits for which the experimental device was saturating. A new model for ferroelectric hysteresis based on curve fitting algorithm is derived that forces the polarization to be saturated at desired electric field. The MATLAB simulation of this model and the experimental hysteresis is compared which shows an excellent level of agreement.

We investigate the impact of various dopants (Na, Ag, Cd, Zn, Al, Ga, In, Tl, Ge, and Sn) on the electronic structure of Mg2Si by first principles calculations using a hybrid functional that does not need a band gap correction. We find that for Na and Ge in Mg2Si, the impurity-induced states do not affect the density of states at both edges of the valence band and the conduction band. Ag- and Sn affect slightly the density of states at the valence band edge, while Cd and Zn affect slightly the density of state at the conduction band edge. Al and In could modify significantly the density of states at the conduction band edge. Ga introduces states just at the bottom of the conduction band. Tl introduces states in the band gap. This study provides useful information on optimizing the thermoelectric efficiency of Mg2Si.

We investigated the impact of doping group III elements (Al, Ga, In and Tl) on the electronic structure of PbTe by first principles calculations. The impurity-induced defect level changes with respect to the charge state of the impurity. We find that among the four elements, Tl is the best candidate for the enhancement of thermoelectric efficiency, consistent with the experimental data.

About 25 A of CaF 2 was epitaxially grown on Si(111) at substrate temperatures of 25, 300, 600 and 800°C. The analysis was carried out by non-destructive depth profiling using angle-resolved core level X-ray photoelectron spectroscopy. Ca 2p, F 1s and Si2p regions were investigated. The spectra of the bulk material indicate a shift towards lower binding energy for the Ca 2p and F 1s core levels in the samples relative to the surface spectra. Near the interface, CaSi bonds were found to be present. No evidence of FSi bonds was found. From the binding energy differences between Ca2p and Si2p and between F 1s and Si 2p core levels, a qualitative picture of the bonding near the interface was drawn. In an intermediate region between the surface and the interface, the amount of fluorine lost or the number of CaSi bonds formed is more in the high temperature samples than that in the low temperature samples. At the interface, the number of CaSi bonds was found to be dependent upon the deposition conditions. The amount of fluorine near the interface region was more for the low temperature samples than for the high temperature samples. The electrical properties (CV curves) of the samples exhibit a pinned interface for the high temperature samples and an unpinned interface for low temperature samples.

We investigate the band offsets and stability for Ni/Bi2Te3and Co/Bi2Te3interfaces by first principles calculations. It is found that the surface termination strongly affects the band offsets. Ni and Co are found to form Ohmic contacts to Bi2Te3. The interface formation energies for Co/Bi2Te3interfaces are much lower than those of Ni/Bi2Te3interfaces. Our calculations are consistent with the experimental data.

The template syntheses of rhodium(III) phthalocyanine complexes within the supercage structures of zeolites X and Y are reported. These ship-in-a-bottle compounds are characterized by elemental analysis, UV-Vis, IR, XRD and X-ray photoelectron spectroscopy. The effect of temperature on the encapsulation process is also discussed.

A dipole moment model explaining Vt tuning in HfSiON gated nFETs is proposed and its impact on performance and reliability is presented. La, Sc, Er, and Sr dopants are utilized due to their differing electronegativities and ionic radii. These dopants tune Vt in the range of 250-600 mV. Vt tuning is found to be proportional to the net dipole moment associated with the Hf-O and rare earth (RE)-O bonds at the high-k/SiO2 interface. The magnitude of this interfacial dipole moment is determined by the electronegativities and ionic radii of the RE cations. LaOx is the most effective dopant based on Vt, mobility, and reliability

We demonstrate electrical properties of rare earth (RE)-doped HfO2 and ZrO2 for application as higher permittivity (k) dielectrics in logic and memory devices. X-ray diffraction (XRD) results show that Dy, Er, and Gd doping stabilizes the higher-k tetragonal phase rather than the lower-k monoclinic phase. This preferred tetragonal phase results in a k~30. Initial electrical results show ~3 nm higher-k enables an equivalent oxide thickness (EOT) of 0.93 nm. Alternatively, ~7nm higher-k reduces leakage currents 1000x relative to HfO2 achieving

The adsorption kinetics of octadecanethiol (ODT) and p-nitrobenzenethiol (NBT) from ethanol solutions has been studied by means of contact angle, optical ellipsometry, angle-resolved X-ray photoelectron spectroscopy (ARXPS), and grazing angle attenuated total reflection Fourier transform infrared (FTIR) measurements. ODT data were used as a reference for the kinetics studies of film growth. The growth of self-assembled monolayers from dilute solutions follows Langmuir isotherm adsorption kinetics. A saturated film is formed within 5 h after immersion in solutions of concentrations ranging from 0.0005 to 0.01 mM. The density of the monolayer depends on the concentration of the solution.