Fine metal line patterning on hydrophilic non-conductive substrates based on electrohydrodynamic printing and laser sintering

We present a electrohydrodynamic (EHD) fine metal line patterning on a hydrophilic non-conductive substrate for the repair of flat panel displays. There are two crucial problems to solve for fine metal line patterning: 1) The scattering effect caused by the charges accumulated on the printed lines, 2) the unwanted thermal effect around patterned lines during sintering. We found that the scattering can be curbed by optimizing head parameters, and the unwanted thermal effect around patterned lines by directly applying laser sintering to printed lines. We achieved a 3 μm width of metal line patterns with the electrical resistivity of 17.48 μΩ cm.     

Optimization of microcrystalline silicon thin film solar cell isolation processing parameters using ultraviolet laser

This study used ultraviolet laser to perform the microcrystalline silicon thin film solar cell isolation scribing process, and applied the Taguchi method and an L₁₈ orthogonal array to plan the experiment. The isolation scribing materials included ZnO:Al, AZO transparent conductive film with a thickness of 200 nm, microcrystalline silicon thin film at 38% crystallinity and of thickness of 500 nm, and the aluminum back contact layer with a thickness of 300 nm. The main objective was to ensure the success of isolation scribing. After laser scribing isolation, using the minimum scribing line width, the flattest trough bottom, and the minimum processing edge surface bumps as the quality characteristics, this study performed main effect analysis and applied the ANOVA (analysis of variance) theory of the Taguchi method to identify the single quality optimal parameter. It then employed the hierarchical structure of the AHP (analytic hierarchy process) theory to establish the positive contrast matrix. After consistency verification, global weight calculation, and priority sequencing, the optimal multi-attribute parameters were obtained. Finally, the experimental results were verified by a Taguchi confirmation experiment and confidence interval calculation. The minimum scribing line width of AZO (200 nm) was 45.6 μm, the minimum scribing line width of the microcrystalline silicon (at 38% crystallinity) was 50.63 μm and the minimum line width of the aluminum thin film (300 nm) was 30.96 μm. The confirmation experiment results were within the 95% confidence interval, verifying that using ultraviolet laser in the isolation scribing process for microcrystalline silicon thin film solar cell has high reproducibility.     

Influence of YSZ electrolyte thickness on the characteristics of plasma-sprayed cermet supported tubular SOFC

Novel Ni–Al₂O₃ cermet-supported tubular SOFC cell was fabricated by thermal spraying. Flame-sprayed Al₂O₃–Ni cermet coating played dual roles of a support tube and an anode current collector. Y₂O₃-stabilized ZrO₂ (YSZ) electrolyte was deposited by atmospheric plasma spraying (APS) to aim at reducing manufacturing cost. The gas tightness of APS YSZ coating was achieved by post-densification process. The influence of YSZ coating thickness on the performance of SOFC test cell was investigated in order to optimize YSZ thickness in terms of open circuit voltage of the cell and YSZ ohmic loss. It was found that the reduction of YSZ thickness from 100 μm to 40 μm led to the increase of the maximum output power density from 0.47 W/cm² to 0.76 W/cm² at 1000 °C. Using an APS 4.5YSZ coating of about 40 μm as the electrolyte, the test cell presented a maximum power output density of over 0.88 W/cm² at 1030 °C. The results indicate that SOFCs with thin YSZ electrolyte require more effective cathode and anode to improve performance.     

Multi-layered Ag film pattern printed by spatially modulated pulsed laser beam

Ag film solution-deposited on the glass source substrate was selectively transferred onto a receiver substrate by a spatially modulated pulsed ultraviolet laser beam. After printing a line pattern, an additional layer was orthogonally printed over the first layer. It was found that the thickness of the first layer is a crucial factor affecting the mechanical stability of the overall pattern. When the first layer was thicker than 0.7 μm, the second layer was cracked at the junction edges regardless of its thickness. This is attributed to the vertical elongation of the second layer at the edge areas. As long as the first layer remains below 0.7 μm thick, however, a very thick additional layer could be printed without any cracks. The printed patterns were mechanically robust and exhibited good electrical contact between the layers. The threshold pulse energy density for printing was measured to be 10 mJ/cm² and this threshold level made it possible to print over square centimeters by a single pulse.     

Submicron-scale spatial compression of light beam through two-stage photonic crystals spot-size converter

Photonic crystals spot-size converter that achieved the controlling of the spot-size through two-stage conversions was proposed. The pre-conversion depended on the efficient coupling between the high quality factor resonator and photonic crystal waveguide. Nearly unity transmission efficiency of the pre-conversion can be achieved through optimizing the radii of the rods located surrounding the resonator. Nanowire waveguide with width of 0.14 μm at a distance 1.05 μm from the resonator was introduced to realize the second stage conversion. Through two-stage conversions, the light beam width was converted to 0.16 μm. The transmission efficiency and conversion ratio reached to 94.6% and 14.875 respectively in theory.     

Structuring of micro line conductor using electro-hydrodynamic printing of a silver nanoparticle suspension

The generation of a fine pattern of metallic materials from suspensions is gaining significant interest because it is the key in the fabrications of displays and printed circuit boards. In our experiments, a silver nanoparticle suspension was first deposited onto a Kapton® polyimide film by using an electro-hydrodynamic printing system, including a guide ring and pin (nozzle)-to-pin (ground) electrodes. Then after thermal curing of the particles deposited, a conductor line as fine as 32 μm in width and 0.3 μm in thickness was obtained onto the film. The resistivity of the line was about 13 μΩ?cm. The pin type ground electrode was helpful in the deposit of the silver nanoparticle suspension along a specific direction. The guide ring repressed the chaotic motion of the jet and prevented the jet from digressing from the centerline. With the electro-hydrodynamic printing method, a nozzle (inner diameter: 140 μm, outer diameter: 320 μm) much larger than an ink jet nozzle could be used.     

Long range surface plasmon polariton waveguides at 1.31 and 1.55 μm wavelengths

We investigate characteristics of gold metal strip waveguides based on long range surface plasmon polaritons (LRSPPs) along thin metal strips embedded in a polymer for practical applications at the telecommunication wavelengths of 1.31 and 1.55 μm. Guiding properties of the gold strip waveguides are theoretically and experimentally evaluated with the limited thickness and width up to ∼20 nm and ∼10 μm, respectively. The lowest propagation loss of ∼1.4 dB/cm is obtained with a 14.5-nm-thick and 2-μm-wide gold strip at 1.55 μm. With a single-mode fiber, the lowest coupling loss of ∼0.4 dB/facet is achieved with a 14.5-nm-thick and 5-μm-wide gold strip at 1.55 μm. The lowest insertion losses are obtained 8-9 dB with 1.5 cm-long gold strips of a limited thickness and width at both the wavelengths. We demonstrate a 10 Gbps optical signal transmission via the LRSPP waveguide with a 14 nm-thick, 2.5 μm-wide, and 4 cm-long gold strip. These LRSPP waveguides have potential applications for optical interconnects and communications.     

A thin film magnetic field sensor of sub-pT resolution and magnetocardiogram (MCG) measurement at room temperature

We developed a very sensitive high-frequency carrier-type thin film sensor with a sub-pT resolution using a transmission line. The sensor element consists of Cu conductor with a meander pattern (20 mm in length, 0.8 mm in width, and 18 μm in thickness), a ground plane, and amorphous CoNbZr film (4 μm in thickness). The amplitude modulation technique was employed to enhance the magnetic field resolution for measurement of the high-frequency field (499 kHz), a resolution of 7.10×10^?13 T/Hz^1/2 being achieved, when we applied an AC magnetic field at 499 kHz. The phase detection technique was applied for measurement of the low frequency field (around 1 Hz). A small phase change was detected using a dual mixer time difference method. A high phase change of 130°/Oe was observed. A magnetic field resolution of 1.35×10^?12 T/Hz^1/2 was obtained when a small AC field at 1 Hz was applied. We applied the sensor for magnetocardiogram (MCG) measurement using the phase detection technique. We succeeded in measuring the MCG signal including typical QRS and T waves, and compared the MCG with a simultaneously obtained conventional electrocardiogram (ECG) signal.     

MFM studies of magnetic domain patterns in bulk barium ferrite (BaFe12O19) single crystals

Magnetic domain patterns in bulk barium ferrite (BaFe₁₂O₁₉; BaM) single crystals on the basal plane and the prism plane were measured and studied by magnetic force microscopy (MFM). The surface domain pattern is in the form of flowers or star on the basal plane and long elongated spikes or stripe domains on the prism plane. The change in domain structure with applied field (H_app) and the thickness (T) dependence on domain width (δ) was observed. The domain width decreased from 32 to 9 μm for the crystals of 800-100 μm thicknesses, respectively.     

Highly porous 3D nanofibrous scaffolds processed with an electrospinning/laser process

Electrospinning has been widely used to produce micro/nanosized fibres. Although the method is very simple, easy, and effective for obtaining nanosized material, the fabrication of three dimensional (3D) shapes comprised of micro/nanofibres has been a major obstacle for use in tissue engineering. In this study, a new electrospinning method to fabricate controllable 3D micro/nanofibrous structure (with thickness over 3 mm) is suggested. The fabricated 3D fibrous structure was fully porous and successfully consisted of submicron-sized fibres. However, the pores in the 3D fibrous structure were too small (5–10 μm), so we used a femtosecond laser process to achieve enough cell infiltration and proliferation in the thickness direction of the 3D structure. By controlling appropriate processing conditions, we can successfully fabricate a highly porous 3D micro/nanofibrous structure with various pore sizes ranging from 189 ± 28 μm to 380 ± 21 μm. The fabricated 3D fibrous scaffolds were assessed for in vitro biological capabilities by culturing osteoblast like cells (MG63). Compared with the rapid-prototyped PCL scaffold, the 3D fibrous scaffold exhibited significantly higher biological activities (initial cell attachment and cell proliferation) due to the topographical structure of micro/nanofibres.     

Si homojunction structured near-infrared laser based on a phonon-assisted process

We fabricated several near-infrared Si laser devices (wavelength ～1300 nm) showing continuous-wave oscillation at room temperature by using a phonon-assisted process induced by dressed photons. Their optical resonators were formed of ridge waveguides with a width of 10 μm and a thickness of 2 μm, with two cleaved facets, and the resonator lengths were 250–1000 μm. The oscillation threshold currents of these Si lasers were 50–60 mA. From near-field and far-field images of the optical radiation pattern, we observed the high directivity which is characteristic of a laser beam. Typical values of the threshold current density for laser oscillation, the ratio of powers in the TE polarization and TM polarization during oscillation, the optical output power at a current of 60 mA, and the external differential quantum efficiency were 1.1–2.0 kA/cm², 8:1, 50 μW, and 1 %, respectively.     

Small-signal modeling approach to 0.1-μm metamorphic HEMTs for W-band coplanar MMIC amplifier design

We present an accurate and reliable modeling method for designing the W-band (75-110 GHz) small-signal millimeter-wave monolithic integrated circuit (MMIC) amplifiers with the GaAs-based 0.1-μm metamorphic high electron-mobility transistors (MHEMTs). For this, we propose an improved process control monitoring (PCM) pattern layout for the MHEMT modeling and a small-signal equivalent circuit model of 17 elements accounting for the feedback capacitance (C_pgd) and output conductance time delay (τ_ds). The modeling technique adopts a gradient optimizer with the initial values of the extrinsic parameter set determined from the cold-FET measurement avoiding the forward gate-biasing in a frequency range of 0.5-65 GHz and the intrinsic parameter set obtained at an operating hot-FET condition in our W-band design frequency range. On the basis of the proposed small-signal equivalent circuit model, we design and fabricate 1- and 2-stage W-band MMIC amplifiers using the MHEMTs (30-μm gate width, 2 gate fingers) and a coplanar waveguide-based MMIC process. The measurements of the fabricated MMIC amplifiers show an excellent agreement with simulation data in the design frequency range.     

Relationship between phase and generation mechanisms of THz waves in InAs

We investigated the thickness-dependent characteristics of THz waves from InAs epilayers whose thickness ranges from 0.01 to 1.74 μm. The amplitude showed monotonic increments up to 0.9 μm, followed by a saturation at 1.74 μm. Interestingly, the phase of THz waves was reversed around absorption depth and used to identify the transient dipole direction based on simulated band diagram. We could further distinguish dominant THz wave generation mechanisms, associated with the phase information.     

A study on the biological detection chip through the use of PDMS lens for the reinforcement of fluorescence receiving signal

In this study, MEMS process technology is adopted to produce microfluidic chip and PDMS lens. SU-8 thick film photo resist is coated onto silicon wafer surface in two times of spin coating, then through lithography and mold transfer technology, PDMS chip of minimal line width 100 μm and thickness 200 μm is printed. In fluorescence detection aspect, we use objective lens to couple laser optical source to optical fiber, and then have it incident to excite fluorescence sample, the excited fluorescence then passes through filter and detected by optical detector of experiment group and spectrophotometer of reference group. From the experiment result, the Hex fluorescence detection limit of the system is verified to be 1 pmol/5 μl. In addition, we have integrated PDMS lens into microfluidic chip to make generalized detection experiment, it was found that the signal measured by optical embedded type is higher than that of non-embedded type. Meanwhile, the microfluidic chip with double concave lens (135°) and10 mm PDMS focusing lens can be utilized to obtain optimal fluorescence receiving effect. The fluorescence intensity is raised by 2–3 times, and the measurement limit is lowered to 100 fmol/5 μl.     

Printable flexible cholesteric capsule display with a fine resolution of RGB subpixels

We report a method for fabricating a cholesteric liquid crystal capsule display wherein the red, green, and blue capsules are separated in the subpixels with a width of 200 μm. The mixture of a photo-isomerizable chiral dopant and a nematic liquid crystal was encapsulated by an emulsification technique, and then directly printed onto a plastic substrate. A UV light with different amount of energy was exposed through a shadow photomask, and consequently, the red, green, and blue colors were separately induced in each subpixels zone.     

Determination of diffusion length in photovoltaic crystalline silicon by modelisation of light beam induced current

The diffusion length of minority carriers is one of the most important electrical parameters to qualify silicon for photovoltaic applications. One way to evaluate this parameter is to analyse the decay of the current induced when a focused beam is scanned away from the collector using Light Beam Induced Current (LBIC) technique. The LBIC signal was numerically calculated with 2D-DESSIS software under different boundary conditions, as a function of material thickness and surface recombination velocity in order to verify the limitations of analytical models and to fit the LBIC signal measured in thin silicon samples. Samples with thickness ranging from 55 μm to 2500 μm were evaluated with diffusion length values ranging from 70 μm to 2.5 mm. Analytical expressions of the Internal Quantum Efficiency (IQE) were also used to extract the minority carrier bulk and effective diffusion lengths from surface averaged spectral response and reflectivity data in thick solar cells.     

An experimental study of the relative response of plastic scintillators to photons and beta particles

A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6 keV to 1.332 MeV and a Ni-63 beta source with a maximum energy of 66 keV. Scintillator thicknesses ranged from 10 μm to 2500 μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. These experimental findings were used to empirically determine the optimum thickness of scintillator material with which to build a low energy beta detector which discriminates against high energy gamma photons in a mixed radiation field environment.     

Effect of film thickness on the transport properties of MgB2 synthesized by spray pyrolysis

Polycrystalline MgB₂ films of different thickness have been prepared by employing spray pyrolysis technique on MgO (1 0 0) substrate. The MgB₂ and other phases have been confirmed using X-ray diffraction technique and no trace of impurities phases have been found. The resistivity behavior shows that the superconducting transition temperature lies in the range of 37–39 K with narrow transition width. The transport critical current density vary with films thickness and achieved highest value ～1.2 × 10⁶ A/cm² at 20 K for 2.0 μm thick film and its values increase as thickness increases.     

Laser machining of silicon nitride based composite cantilever structures

Cantilever structures from silicon nitride based composite ceramic materials were produced using laser cutting. A picosecond laser was used to cut two-dimensional meso sized cantilever structures up to 450 μm thickness in conductive and insulating ceramics. A practical experimental based approach was used, where various parameters of the laser cutting process were altered to produce a cut surface with a damage zone of 5–10 μm. The quality of the cut ceramics was investigated by optical and scanning electron microscopy. The results are presented along with the properties of the laser cut surface, including the damage zone, formation of cracks and the reaction products.     

Femtosecond laser-induced ZnSe nanowires on the surface of a ZnSe wafer in water

We present a simple route for ZnSe nanowire growth in the ablation crater on a ZnSe crystal surface. The crystal wafer, which was horizontally dipped in pure water, was irradiated by femtosecond laser pulses. No furnace, vacuum chamber or any metal catalyst were used in this experiment. The size of the nanowires is about 1-3 μm long and 50-150 nm in diameter. The growth rate is 1-3 μm/s, which is much higher than that achieved with molecular-beam epitaxy and chemical vapor deposition methods. Our discovery reveals a rapid and simple way to grow nanowires on designed micro-patterns, which may have potential applications in microscopic optoelectronics.