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We measured the response time zR and the ambipolar diffusion length Lamb in amorphous (a-Si:H) and microcrystalline silicon films (μ-Si:H) prepared by hot-wire chemical vapor deposition (HW-CVD). The response times in the amorphous and microcrystalline HW films were larger by factors of 100 and 1000, respectively, than in standard PE-CVD a-Si:H films (1-2 μs). The ambipolar diffusion length of the HW-CVD films was about twice as large as in conventional glow-discharge films. Strong doping of microcrystalline HW films with trimethylboron (TMB) led to a reduction of the response time. The results hint to a positive effect of the compact microstructure of HW-CVD films. We suggest the dark conductivity activation energy, Eact, and response time, τR, to be used as suitable parameters to describe optoelectronic film properties.

The visible photoluminescence (PL) properties (emission and excitation spectra) of hydrogenated amorphous carbon (a-C:H) have been investigated for polymer-like thin films grown at low substrate temperature and small ion energies. For a large number of a-C:H films grown in three reactors (dual-mode plasma, radio frequency plasma and electron cyclotron resonance plasma) the emission spectra appear as a sum of three peaks with energies (a) 2.28 eV, (b) 2.65 eV and (c) 2.95 eV, being independent of the excitation energy (3.54 eV or 4.13 eV). Their relative intensities depend on the growth parameters while their positions are almost independent. Preliminary picosecond time-resolved PL data indicate a decrease of the decay time for increasing emission energies. A two-phase model of a-C:H is proposed to explain the PL excitation spectra.

A single, square, voltage pulse is used to accelerate both the immobilization kinetics of DNA molecules on a functionalized thin film silicon dioxide surface and the hybridization of complementary DNA strands to immobilized DNA molecules. The voltage pulse is applied to an integrated thin-film metal electrode beneath the functionalized surface. The duration and magnitude of the voltage pulse are compatible with silicon microelectronics circuits. During immobilization, covalent thiol bonding to the functionalized surface occurs during a single pulse lasting only 100 ns. Hybridization to the immobilized complementary strand occurs during 100 μs pulses.

Thin-film MEMS molecular sensors are fabricated at temperatures below 110°C on glass substrates. The microelectromechanical structure consists of a surface micromachined bilayer bridge of phosphorous-doped hydrogenated amorphous silicon and aluminum with a patterned SiO2 layer on the top. Specific binding of DNA to functionalized SiO2 on the bridge is confirmed using fluorescence microscopy. Microbridges are electrostatically actuated and the resonance frequency measurements are performed in vacuum in the initial state after fabrication, after the chemical functionalization of the SiO2surface and after DNA immobilization. The sensor is able to detect the functionalization molecular layer, the cross-linker molecular layer, and the DNA molecules attached to the surface through a shift in its resonance frequency. The binding of molecules to the surface results in a shift of the resonance frequency due to contributions from surface stresses and mass loading.

The resonance of electrostatically actuated thin-film a-Si:H microbridges immersed in de-ionized water is detected and characterized. When the operating medium changes from vacuum to air, a small decrease of 5% of the resonance frequency occurs and the quality factor decreases from approximately 1000 to 100. The operation of the microresonators in deionized water produces a 60% shift in resonance frequency to lower values and the quality factor decreases to 10. Appropriate actuation conditions at resonance in water are used to avoid electrolysis and electrode field screening. The detection of the resonance frequency of a microbridge operating in solutions with high conductivities, up to 8 mS/cm, and viscosities up to 0.2 Pa.s is demonstrated.

Thin-film silicon micromachined bridge actuators are fabricated at temperatures below 110°C on flexible polyethylene terephthalate plastic substrates. The micromechanical structures are electrostatically actuated both at the resonance frequency and at below-resonance frequencies, and the resulting deflection is optically monitored. Deflections up to 100 nm are measured below the resonance frequency with subnanometric precision. Resonance frequencies in the MHz range are observed in vacuum with quality factors of the order of 100. The movement is studied as a function of the geometrical dimensions of the actuators, of the actuation voltage and of the measurement pressure. The experimental data are analyzed using an electromechanical model. The performance of hydrogenated amorphous silicon based resonators on PET substrates is compared to that of similar microstructures on glass substrates.

This paper describes the fabrication and characterization of thin-film nanocrystalline silicon microresonators processed at temperatures below 110°C on glass substrates. The microelectromechanical structures consist of surface micromachined bridges of boron-doped hydrogenated nanocrystalline silicon (p+-nc-Si:H) deposited at 100°C by hot-wire chemical vapor deposition (HWCVD). The microbridges, which are suspended over an Al gate electrode, are electrostatically actuated and the mechanical resonance is detected in vacuum using an optical setup. The resonance frequency and energy dissipation in p+-nc-Si:H based resonators are studied as a function of the geometrical dimensions of the microstructures. Resonance frequencies between 700 kHz and 36 MHz and quality factors as high as 2000 are observed. A Young's modulus of 160 GPa for the structural bridge film is extracted from the experimental data using an electromechanical model and the main intrinsic energy dissipation mechanisms in nc-Si:H microresonators are discussed.

This paper reports on the fabrication of novel all-polymer microbridge electrostatic actuators based on conductive polymers and using surface micromachining on glass substrates. The electromechanical properties of the microbridges are studied using electrostatic actuation and optical and electrical detection. The pull-in phenomena and a dependence of the bridge deflection with the square of the applied voltage are observed. Compared to the silicon-based microbridges, the polymer structures present higher deflection amplitude for the same applied electrical force. The resonance frequency of the polymer bridges occurs in the MHz range and with quality factors of the order of 100 when measured in vacuum. The mechanical properties of the polymer device are affected by the residual stresses.

Single square voltage pulses were used to enhance by 7 and 9 orders of magnitude the rate of covalent immobilization and hybridization, respectively, of single stranded DNA probes on a chemically functionalized thin film surface (silicon dioxide) using 2 mm size electrodes. These electrodes were scaled down to 20 μm. Photolithography was used to define the electrode voltage line, ground line, and functionalized thin-film area on a plastic substrate (polyimide). At all electrode dimensions, electric field-assisted DNA immobilization and hybridization can be achieved in the microsecond time scale, far faster than the 2 hr or 16 hr needed for immobilization and hybridization, respectively, without the electric field. Pulse conditions optimized with the large-size electrodes (2 mm) were used in the microelectrodes.

Bottom-gate amorphous silicon thin-film transistors were fabricated on a polyethylene terephthalate substrate. The maximum processing temperature was 100°C. The transistor characteristics are comparable, although still inferior, to those of standard amorphous silicon transistors fabricated on glass substrates. To obtain these characteristics, an extended anneal the processing temperature was required. The devices were fabricated using separately optimized low-temperature active layer, contact layer and gate dielectric layer. To achieve good electronic properties for these layers, hydrogen dilution was required.

The piezoresistive behavior of n-type and p-type microcrystalline silicon films deposited on polyethylene terephthalate plastic substrates by hot-wire, and radio-frequency, plasma-enhanced chemical vapor deposition, at a substrate temperature of 100/spl deg/C, is studied. The crystallite size was 10 nm for hot-wire films and 6.5 nm for radio-frequency films and the crystalline fraction varied between 50 to 80%. A four-point bending jig allowed the application of positive and negative strains in the films. Repeated measurements of the relative changes in the resistance of the samples during the strained condition showed reversible behavior, with p-type microcrystal line films having positive gauge factor in the range from 25 to 30 and n-type /spl mu/c-Si:H films having negative values of gauge factor from -40 to -10. The induced strain in the films varied in the interval between 0 and /spl plusmn/0.3%. The films were used in the as-deposited size (50 mm /spl times/ 10 mm) as sensors, utilizing their piezoresistive properties to map the contour of an acrylic model with the shape of an Archimedes' spiral. Micron-sized devices were patterned and used to map the shape of the same model.

The perpendicular transport of electrons and holes in a-Si:H,F/a-SiGe:H,F multilayers is reported. Particular emphasis is placed on a-SiGe:H,F layers with low (E/sub opt/ or approximately=300 AA) periods, the transport properties are improved beyond the baseline values. At short periods the transport properties are improved above the first-order behavior by a reduction in the density of recombination centers. At long periods the transport properties are improved by an effect whose nature is not understood at present. >

The initial stages of microcrystalline silicon growth of n+ doped films prepared by rf plasma enhanced chemical vapor deposition (PECVD) and of intrinsic films prepared by hot-wire chemical vapor deposition (HW-CVD) are studied using atomic force microscopy, Raman spectroscopy and parallel dark conductivity measurements. The effect of the use of a plasma hydrogen treatment, of chamber conditioning prior to this treatment, of the type of substrate (glass or c-Si) used and the effects of a seed layer on the film properties are discussed.

Electronic properties of polymer-like hydrogenated amorphous carbon films, grown in a RF-assisted microwave plasma reactor, have been studied using optical absorption and photoluminescence spectroscopies. Using a Forouhi-Bloomer parametrization of π-π* transitions, two regimes are evidenced for increasing C atom density : a decrease of the optical gap Eππ* at constant (H/H+C) content attributed to sp2C clustering, followed by some H elimination with minor changes in Eππ* due to cross-linking of polymer chains. The photoluminescence efficiency in the visible range (peak at ≈ 2.3 eV) is found to decrease over four orders of magnitude at the onset of the cross-linking regime. This quenching is attributed to stress-induced non-radiative centers.

Deposition of n and p-type amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon thin films on polyethylene terephthalate (PET) at substrate temperatures (Tsub) of 100°C and 25°C (RT) prepared by hot-wire (HW) chemical vapor deposition and radio-frequency (RF) plasma-enhanced chemical vapor deposition is studied as a function of hydrogen dilution. Doping is achieved by addition of phosphine (ntype) and diborane (p-type) to the gas phase reactive mixture. At Tsub=100°C, n-type a-Si:H is obtained by HW with dark conductivity σd10−4 ω−1cm−1 and by RF with σd~10−3 ω−1cm−1. P-type a-Si:H is obtained by HW with σd=8×10−7 ω−1cm−1 and by RF with σd=6×10−7 ω−1cm−1. Decreasing the temperature of deposition to 25°C decreases the sd of RF n-type amorphous samples to 5×10−5 ω−1cm−1 but the σd of p-type samples remains unchanged. RT HW a-Si:H films show a decrease of sd both for ntype film (σd=4×10−6 ω−1cm−1) and p-type film (σd=1.2×10−7 ω−1cm−1). N-type µc-Si:H was obtained by HW with σd=7×10−2 ω−1cm−1 and by RF with σd>10−2 ω−1cm−1 at 100°C. Using the same Tsub, p-type µc-Si:H was deposited by HW and by RF with σd~0.5 ω−1cm−1. At RT, only p-type µc-Si:H films could be prepared using HW (σd~1 ω−1cm−1) and RF (σd=4×10−3 ω−1cm−1). The structural properties of the films were studied using Raman spectroscopy. The structural and transport properties were correlated.

The very-high-frequency glow discharge (VHF-GD) is a high-rate deposition method for amorphous silicon based on the use of plasma excitation frequencies in the range 30-150 MHz. Thereby the high-energy tail of the electron energy density function is enhanced, increasing the deposition rate R, without a corresponding increase in electric field and ion bombardment. Here, an extensive set of optoelectronic properties (σdark, Ea, σph, CPM, PDS, TOF, SSPG, steady-state Hecht plot) is presented for samples prepared by VHF-GD for the above frequency range and R≈12-15 AA/s. Emphasized are hole transport properties. With values of (μDτt)h by TOF (time of flight) around 3*10-10 but up to ≈5*10-9 cm2V-1, VHF-GD is judged to be adequate for solar-cell applications.

Thin-film cantilever and bridge structures composed of a-Si:H, SiN x , μc-Si and Al were fabricated on glass using low temperature surface micromachining processing for mechanical integrity determination and eletrostatic actuation. The free standing length of these structures ( L max ) is related to their thickness ( h ) with a relationship L max (bridges) ≈ 100 h and L max (cantilevers) ≈ 50 h . Although these empirical relations are in qualitative agreement with the structural properties of the structures, the constant as well as the yield for free standing structures is expected to be affected by the processing parameters. Electromechanical actuation of these structures was achieved by applying an electric field between a bottom electrode and a top Al layer of the bridge or cantilever. The critical voltage necessary for the structure to bend enough to touch the bottom electrode is proportional to L −2 where L is the length of the structure. A mechanical model used to predict the bending of the structures as a function of the applied voltage confirms that dependence.

Three dimensional microstructures have been made on glass substrates using surface micromachining techniques. Bridge structures were fabricated using both hydrogenated amorphous silicon and microcrystalline silicon. A low density silicon nitride with an etch rate of 100 Å/s in buffered HF was used as the sacrificial layer. As an example of how micromachining can be applied to large area electronics, thin film transistors (TFT) with the dielectric replaced by an air-gap were fabricated. The electrical characteristics of the first working devices are presented.

A hydrogenated amorphous silicon photodetector on a glass substrate is used for the integrated, real-time detection of chemiluminescent reactions in solution. The light emission at 425 nm resulting from the horseradish peroxidase-catalyzed oxidation of luminol is detected by a p-i-n amorphous silicon photodiode operated at zero bias. The limit of detection of the present device is in the range of nanomole of horseradish peroxidase per liter.

The photocurrent decay in n-type GaN films prepared by low-pressure chemical vapor deposition (LPCVD) was measured in the ms-to-s time range using steady-state UV light and in the μs time regime using short high-power pulses from higher harmonics of a Nd:YAG laser. A power law time dependence is observed with exponents ranging from −0.1 to −0.3, which is an indication of a broad distribution of trapping states inside the band gap. Combining Hall effect results and the magnitude of the initial slope of the photocurrent decay we estimate a mobility-lifetime product of 2.1×10−4 cm2/V for photogenerated electrons at times below a few μs. Slow transients might be a handicap for applications of GaN in UV detectors.

The conductivity and the structural properties of thin films deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) from silane and hydrogen at a substrate temperature of 220 °C are shown to be strongly dependent on the filament temperature, Tfil, and process pressure, p. Amorphous silicon films are obtained at low pressures, p < 3 × 10−2Torr, for Tfil ∼ 1900 °C and FH2 = FSiH4. At this TfilJU, high deposition rates are observed, both with and without hydrogen dilution, and no silicon was deposited on the filaments. At Tfil ∼ 1500 °C, a transition from a-Si:H for p > 0.3 Torr to microcrystalline silicon (μc-Si:H) for p < 0.1 Torr occurs. In this temperature regime, silicon growth on the filaments is observed. /ic-Si:H growth both without hydrogen dilution and also in very thin films (∼ 0.05 μm) is achieved. Raman and X-Ray spectra give typical grain sizes of 10 – 20 nm, with a crystalline fraction higher than 50%. For both, Tju ∼ 1500 °C, p > 0.3 Torr and Tfil ∼ 1900 °C and p ∼ 2.7 × 10−2Torr, an increase of the crystalline fraction from 0 to ∼ 30% is observed when the hydrogen dilution, FH2/FSiH4, increases from 1 to > 4.

Microresonators based on thin film hydrogenated amorphous silicon microbridges were fabricated by surface micromachining on flexible polyethylene terephthalate (PET) substrates with a maximum processing temperature of 110°C. An aluminum sacrificial layer is used which is patterned by either wet etching or lift-off. Resonance in the MHz range was observed using electrostatic actuation. Processing of the microbridges on PET with sacrificial layer patterned by lift-off has higher yield than by etching. Bending measurements show that the thin film silicon microbridges on PET can withstand a higher compressive strain (-2.5%) than tensile strain (1.25%).

High-quality thin film transistors (TFT) with hydrogenated amorphous silicon (a-Si:H) deposited by hot-wire (HW) chemical vapor deposition as the active layer at growth rates above 20 Å/s are compared to TFTs with a-Si:H deposited by RF glow discharge at 1 Å/s. The subgap absorption measured by the constant photocurrent method and steady-state photoconductivity measured between source and drain are used to characterize the a-Si:H in the TFT. The activation energy of the dark conductivity is measured as a function of the gate voltage to obtain the position of the Fermi level. The effect of a bias stress on the TFT transfer curve is obtained.

The electron and hole transport in bandgap-engineered amorphous silicon/germanium alloys (a-Si,Ge:H,F) is studied using steady-state conductivity, time-of-flight and the voltage-bias dependence of the photocurrent. We investigate graded-bandgap structures and sawtooth multilayers. We find that in graded-bandgap structures the mobility-lifetime (μτ) products for both electron and holes show strong asymmetry in the direction of the compositional grading. We report for the first time on the optoelectronic properties of a-Si:H,F/a-Si,Ge:H,F sawtooth superlattices.

Organ-on-a-chip in vitro platforms accurately mimic complex microenvironments offering the ability to recapitulate and dissect mechanisms of physiological and pathological settings, revealing their major importance to develop new therapeutic targets. Bone diseases, such as osteoarthritis, are extremely complex, comprising of the action of inflammatory mediators leading to unbalanced bone homeostasis and de-regulation of sensory innervation and angiogenesis. Although there are models to mimic bone vascularization or innervation, in vitro platforms merging the complexity of bone, vasculature, innervation, and inflammation are missing. Therefore, in this study a microfluidic-based neuro-vascularized bone chip (NVB chip) is proposed to 1) model the mechanistic interactions between innervation and angiogenesis in the inflammatory bone niche, and 2) explore, as a screening tool, novel strategies targeting inflammatory diseases, using a nano-based drug delivery system. It is possible to set the design of the platform and achieve the optimized conditions to address the neurovascular network under inflammation. Moreover, this system is validated by delivering anti-inflammatory drug-loaded nanoparticles to counteract the neuronal growth associated with pain perception. This reliable in vitro tool will allow understanding the bone neurovascular system, enlightening novel mechanisms behind the inflammatory bone diseases, bone destruction, and pain opening new avenues for new therapies discovery.