Simple Processing Sequence Research Articles

New wiggles from old cables: Data processing and imaging considerations

Distributed acoustic sensing (DAS) using fiber-optic cables as sensors has become a standard measurement technique in many industrialized settings. Geophysical applications have been mainly commercialized in the borehole environment. When deployed on the seabed (SB), horizontal analysis of DAS data poses new challenges due to the particularity of the receiver response and characteristics of DAS data. Recent acquisition of a 2D towed-streamer (TS) survey following the path of a communication cable (installed in 1998), which is interrogated continuously throughout the TS acquisition, enables us to jointly analyze SB-DAS and conventional TS data recorded using modern hydrophone streamer from acquisition, through different processing stages up to a migrated image. The SB-DAS recording from the old communication cable enables us to generate excellent P-wave and converted wave (PS) images of the subsurface. However, care is needed when recovering the high spatial frequencies damped by the nature of DAS measurements (which also may depend on the hardware used) and demonstrating the recovery of the signal within the data processing (DP) sequence. Our focus is on the challenges associated with the DP of entrenched marine cables. Given a simple TS processing sequence as a reference, we examine an equivalent recommended practice for signal analysis, DP, and imaging of SB-DAS data.

Revealing the complexity of ultra-soft hydrogel re-swelling inside the brain

The brain is an ultra-soft viscoelastic matrix. Sub-kPa hydrogels match the brain's mechanical properties but are challenging to manipulate in an implantable format. We propose a simple fabrication and processing sequence, consisting of de-hydration, patterning, implantation, and re-hydration steps, to deliver brain-like hydrogel implants into the nervous tissue. We monitored in real-time the ultra-soft hydrogel re-swelling kinetics in vivo using microcomputed tomography, achieved by embedding gold nanoparticles inside the hydrogel for contrast enhancement. We found that re-swelling in vivo strongly depends on the implant geometry and water availability at the hydrogel-tissue interface. Buckling of the implant inside the brain occurs when the soft implant is tethered to the cranium. Finite-element and analytical models reveal how the shank geometry, modulus and anchoring govern in vivo buckling. Taken together, these considerations on re-swelling kinetics of hydrogel constructs, implant geometry and soft implant-tissue mechanical interplay can guide the engineering of biomimetic brain implants.

Screen-printed n-type Si solar cells with laser-doped selective back surface field

The primary challenge to the industrial application of n-type silicon solar cells is relatively complicated process flow compared to producing p-type silicon solar cells. This paper demonstrates a simple processing sequence to fabricate n-type silicon solar cells in which the boron-doped emitter and phosphorus-doped back surface field (BSF) are formed in one high-temperature step. By introducing a selective BSF structure that is formed by laser doping, the conversion efficiency of the solar cells can be further improved. The averaged conversion efficiency of 21.7% is obtained in batches with relatively large quantity of cells with tight efficiency distribution.

Structuring of Metal Layers by Electrochemical Screen Printing for Back-Contact Solar Cells

Reduction in production costs is essential for newsolar cell concepts to be competitive. A large cost factor in interdigitated back-contact solar cell manufacturing is the metallization. Several process steps are needed to form an interdigitated metal pattern out of a full faced metal layer to realize n- and p-metal contacts. Generating electrically separated conductor tracks is not only a challenge in PV but also in the circuit board sector. To drive down the costs for metal structuring, an innovative approach called electrochemical screen printing (ESP), which combines screen printing and electrochemical etching is developed in this paper. It permits localized etching of aluminum layers with very short process durations. The process speed yields 100 mm/s and is comparable with the conventional screen printing speed in solar cell manufacturing. Hence, it is faster than conventional structuring processes using masks and chemical etchants. By using a self-made water-based NaNO3 paste, narrow etched grooves (<80 μm) are formed in an aluminum layer by ESP, resulting in electrically separated aluminum regions. To increase the conductivity of the thin formed Al pattern, selective thickening is demonstrated by aluminum activation and plating nickel and copper. In this way, Al/Ni/Cu conductor tracks separated by a 70 μm trench are made out of a full faced aluminum layer using a short and simple process sequence. By electron microscopy and X-ray spectroscopy, the quality of etched regions and the structure of the formed metal stack are characterized in detail in order to assess the process sustainability.

Power-loss Analysis of Advanced PERC Cells Reaching 20.5% Energy Conversion Efficiency

We recently demonstrated at imec a relatively simple process sequence for the formation of copper based front contacts consisting of: i) defining the front contact pattern by laser ablation ii) plating of the contacts using Ni/Cu/Ag in a single plating sequence and finally iii) contact sintering. In this paper, we conduct a power loss analysis of the best 20.5% (confirmed by ISE CalLab) PERC solar cell produced on 125mm magnetically pulled CZ (m-CZ) Si with Ni/Cu/Ag contacts. Based on this power loss analysis, we estimate potential improvements in cell design enabling >21% energy conversion efficiencies.

Probabilistic facies discrimination from simultaneous seismic-inversion results in clastic reservoirs in southwestern Venezuela

Facies volumes were obtained in southwestern Venezuela reservoirs integrating rock-physics analysis and seismic-inversion results. Facies volumes showed a sandstone-shale spatial distribution that matches log data and the conceptual sedimentologic model of the reservoir. After seismic-gather conditioning, applying a simple but robust processing sequence, the signal-to-noise ratio was increased. Two angle stacks were generated to perform a simultaneous seismic inversion to obtain P- and S-wave impedance volumes. Parallel to the inversion process, rock-physics analysis was done using rock-physics templates (RPT) for constant-cement models (CCM) to discriminate between sandstone and shale. P- and S-wave impedance bivariate probabilistic density functions (PDF) were computed from well-log data as an a priori probability. Finally, these PDFs were used to classify facies from P- and S-wave impedance volumes obtained from simultaneous inversion, using a Bayesian probabilistic approach. This classification produced two facies volumes, sandstone and shale, which honored the well information and rock-physics models.

Examining Dislocations in SiC Epitaxy by Light Emission from Simple Diode Structures

With a simple processing sequence using only patterned aluminum (Al), dislocations and stacking faults were examined in thick n- epitaxial layers including a grown p+ layer on top. The thicknesses of the n- layers were 100 and 150 μm, values that are typical for fabricating 10 kV PiN diodes. High temperature sintering of the metal film was avoided making this a potentially nondestructive scheme for evaluating SiC epitaxy. Faulting of basal plane dislocations (BPDs) and the resulting forward voltage, Vf, increase were examined at current densities up to 20 A/cm2. A simple guard ring structure defined in the Al pattern was successfully used to confine the current through the epitaxial layers to the area inside of the ring. Kelvin contacts compensated for voltage drops at the Al/SiC interfaces. As a result, current-voltage characteristics and electroluminescent imaging were obtained across a known area of the PiN layer at currents densities ranging from 20 A/cm2 to 7 × 10-3 A/cm2.

17.6% efficient tricrystalline silicon solar cells with spatially uniform texture

AbstractUp to now solar cells fabricated on tricrystalline Czochralski‐grown silicon (tri‐Si) have shown relatively low short‐circuit current densities of about 31–33 mA/cm2 because the three {110}‐oriented grains cannot effectively be textured by commonly used anisotropic etching solutions. In this work, we have optimised a novel chemical texturing step for tri‐Si and integrated it successfully into our solar cell process. Metal/insulator/semiconductor‐contacted phosphorus‐diffused n+p junction silicon solar cells with a silicon‐dioxide‐passivated rear surface and evaporated aluminium contacts were manufactured, featuring a spatially uniform surface texture over all three grains on both cell sides. Despite the simple processing sequence and cell structure, an independently confirmed record efficiency of 17.6% has been achieved. This excellent efficiency is mainly due to an increased short‐circuit current density of 37 mA/cm2 obtained by substantially reduced reflection and enhanced light trapping. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Development of an emitter for industrial silicon solar cells using the doped oxide solid source diffusion technique

The aim of this paper is to demonstrate for the first time the feasibility of fabricating large-area screen-printed monocrystalline silicon solar cells using the Doped Oxide Solid Source (DOSS) diffusion technique. This process was applied to form the n +p emitter junction from highly doped sources prepared in a POCl 3 ambient. The diffusions were performed under a pure nitrogen flow in the temperature range 900–1050°C. In this investigation attention was devoted to the influence of the source doping level on the fill factor. The solar cells were fabricated on industrial quality 4-inch Cz wafers using a simple processing sequence incorporating screen-printed contacts and a TiO 2 antireflection coating deposited by spin-on. Fill factors as high as 79% were obtained. The potential benefit of retaining for passivation purposes the thin residual oxide grown during phosphorus diffusion was evaluated. These first experiments led to a cell efficiency close to 10%.

Characterization of Low Temperature Polysilicon TFTs with Self-Aligned Graded LDD Structure

AbstractA simple process sequence for fabrication of low temperature polysilicon (LTPS) TFTs with self-aligned graded LDD structure was demonstrated. The graded LDD structure was self-aligned by side-etch of Al under the photo-resist followed by excimer laser irradiation for dopant activation and laterally diffusion. The graded LDD polysilicon TFTs were suitable for high-speed operation and active matrix switches applications because they possessed low-leakage-current characteristic without sacrificing driving capability significantly and increasing overlap capacitance. The leakage current of graded LDD polysilicon TFTs at Vd = 5V and Vg = −10V could attain to below 1pA/μm without any hygrogenation process, when proper LDD length and laser activation process were applied. The on/off current ratios of these devices were also above 108. Furthermore, due to graded dopant distribution in LDD regions, the drain electric field could be reduced further, and as a result, graded LDD polysilicon TFTs provided high reliability for high voltage operation.

Easy-to-fabricate 20% efficient large-area silicon solar cells

Recently, an innovative silicon solar cell structure has been developed at ISFH which is capable of achieving very high cell efficiencies on industrial-size wafers with a simple photolithography-free processing sequence. As the corresponding solar cells essentially rely on the application of obliquely evaporated contacts they are denoted as OECO cells. In this paper the successful up-scaling of the novel OECO process from 21% efficient 4 cm 2 laboratory devices to the fabrication of large-area (⩾100 cm 2) silicon solar cells is described, and independently confirmed total area efficiencies of 20% are reported for 10×10 cm 2 OECO-type solar cells fabricated on p-type float-zone silicon.

Fabrication and characterization of a piezoelectric accelerometer

Zinc oxide based piezoelectric accelerometers were fabricated by bulk micromachining. A high yield was obtained in a relatively simple process sequence. For two electrode configurations a direction selectivity better than 100 was obtained for acceleration in the vertical direction and a selectivity of 3 for acceleration in the horizontal direction, respectively. The charge sensitivity in the vertical direction is better than 0.1 pC and a noise level of was estimated.

Simple versus complicated seismic processing in the Exmouth Sub-basin

Seismic data quality in the deeper water regions of the Exmouth Sub-basin, Western Australia is generally excellent. Both the temporal and lateral resolution are very high, allowing the identification of fine geological detail. These data contrast with the data over much of Australia’s offshore exploration and producing regions, where multiples, velocity inversions, poor reflectivity contrasts, and sea floor reefs and channels seriously degrade data quality.A quite different approach to seismic data processing is required for processing seismic data from the deeper waters of the Ex mouth Sub-basin than is normally used for the more noisy areas of offshore Australia. Rather than concentrating on processes that improve the signal-to-noise ratio of the data, it is more important to concentrate on processes that do not distort the seismic wavefield.While processing seismic data recorded in 1994 in the Exmouth Sub-basin, I found that most processes typically applied to seismic data did not lead to any improvement in quality. In fact, it was quite difficult to find processes that actually improved the quality of the data. I found that the results of processing were very susceptible to the type of deconvolution applied to the data. Conventional trace-by-trace prestack deconvolution was found to introduce reverberations, degrading the quality of the final migrated section. Shot averaged deconvolution produced vastly superior results than trace-by-trace deconvolution. Other processes such as shot domain f-k filtering, trace summation and f-k demultiple had little effect on the quality of the final section. These processes, however, can introduce subtle distortions of the wavelet, and hence should only be used if it can be demonstrated that they produce noticeable improvements.The final sequence used to process the data was extremely simple, and consisted of: (1) gain recovery; (2) large gate trace equalisation; (3) shot averaged deconvolution; (4) one pass velocity analysis; (5) NMO, mute and stack; and (6) migration followed by bandpass filtering. Probably many of the deeper water regions of Australia could benefit from the use of the simple processing sequence presented in this paper.

Process development for large-area terrestrial solar cells with-out optical confinement

In this letter a simple processing sequence is established to achieve large area solar cells in the efficiency range 8-9%

Single-Crystal Silicon: Photovoltaic Applications

The vast majority of solar cells used in the field are based on single-crystal silicon. There are several reasons for this. First, by using this material, photovoltaic manufacturers can benefit from the economies of scale of the much larger microelectronics industry, where crystalline silicon also dominates. Since lower-quality silicon is acceptable for solar cells, cell manufacturers are able not only to benefit from large production volumes, but also to use off-grade material. The relatively high efficiencies that result from this material, its excellent reliability in the field, its almost complete lack of environmental problems, and recent laboratory progress strengthen the position of this technology.Although there had been earlier work with what might be termed “cast multicrystalline silicon,” the first efficient crystalline silicon cells were reported in 1954. These cells displayed energy conversion efficiencies of about 6%, a substantial improvement over what had been previously demonstrated. Performance improved rapidly through the 1950s, with efficiencies up to about 15% demonstrated in the early 1960s. By this time, their use on spacecraft had become the major commercial purpose of the cells, with reliability a more important attribute than efficiency. The technology then stabilized for a decade. In the early 1970s, another burst of activity pushed the performance of laboratory cells to about 17%. At about this time, a simple processing sequence was developed, based on screen printing the metal contacts to the cell. Anisotropic chemical etching of the silicon to produce surface texture to reduce reflection loss was also implemented, to give the cell structure shown in Figure 1.

A 34-ns 16-Mb DRAM with controllable voltage down-converter

A high-speed 16-Mb DRAM with high reliability is reported. A multidivided column address decoding scheme and a fully embedded sense-amplifier driving scheme were used to meet the requirements for high speed. A low-power hybrid internal power supply voltage converter with an accelerated life-test function is also proposed and was demonstrated. A novel substrate engineering technology, a retrograded well structure formed by a megaelectronvolt ion-implantation process, provides a simple process sequence and high reliability in terms of soft error and latch-up immunity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modular and Hierarchical Organization of Extrastriate Visual Cortex in the Macaque Monkey

In the 1970s, a quiet revolution began in our understanding of how information processing occurs in regions beyond the primary visual cortex. Work from several laboratories indicated that there were more visual areas than just the three proposed by classic neuroanatomists. The number of extrastriate areas identified around that time was about a half dozen in various species (Zeki 1976; Allman 1977; Van Essen 1979; Tusa et al. 1981). It also became apparent during this period that the connectivity among visual areas was more complex than the simple serial processing sequence that many investigators expected to encounter.

Fabrication of diode arrays for photovoltaic characterization of silicon substrates

A simple process sequence for the fabrication of passivated mesa diode arrays for photovoltaic characterization of single/polycrystalline silicon substrates is described. These diodes are used to measure a variety of substrate and cell parameters including resistivity, minority-carrier diffusion length, Voc, Jsc, fill factor, and current-voltage characteristics for analysis of the electronic transport properties. Evaluation techniques which use these diodes for determining spatial variations in the material/device charateristics are described. These devices are also suitable for characterizing various cell fabrication processes and for analysis of crystal defects on the solar cell characteristics.