Finger Width Research Articles

Fine line metallization by coextrusion technology for next generation solar cells

This paper introduces the application of a coextrusion printing as a contact and mask-free fine line metallization technology for direct printing of narrow grid lines with a strongly enhanced aspect ratio. Coextrusion printed grid lines enhance short circuit current and lower series resistance through a higher number of filigree fingers. The silver and sacrificial paste that merge inside the nozzle are simultaneously extruded onto the wafer and form a silver paste structure smaller than every design feature inside the nozzle. After contact firing the grid lines become as narrow as 35µm with an aspect ratio up to 0.7. A further shrinkage potential down to 23.7µm width with an aspect ratio up to 0.62 has been demonstrated. Coextrusion printed grid lines outperform screen printed grid lines in a whole slew of geometrical and optical properties. As for example grid line width and height variation is as low as ±0.5µm and the optical effective finger width is far smaller than the screen printed effective finger width. Due to these low effective finger widths the absolute effective shading of 96 coextrusion printed grid lines is less than half of the 80 screen printed grid lines. The calculated short circuit current gain, due to the lower effective shading was experimentally confirmed accordingly. Furthermore a benchmark test in a production like environment was performed. Hereby an absolute cell efficiency gain of +0.25% over screen printed metallization was confirmed and a cell efficiency gain of over +0.35% to +0.4% abs. can be assumed to be achieved by using a direct contacting coextrusion silver paste, which is comparable to state of the art screen printing pastes.

Corner and finger formation in Hele-Shaw flow with kinetic undercooling regularisation

We examine the effect of a kinetic undercooling condition on the evolution of a free boundary in Hele-Shaw flow, in both bubble and channel geometries. We present analytical and numerical evidence that the bubble boundary is unstable and may develop one or more corners in finite time, for both expansion and contraction cases. This loss of regularity is interesting because it occurs regardless of whether the less viscous fluid is displacing the more viscous fluid, or vice versa. We show that small contracting bubbles are described to leading order by a well-studied geometric flow rule. Exact solutions to this asymptotic problem continue past the corner formation until the bubble contracts to a point as a slit in the limit. Lastly, we consider the evolving boundary with kinetic undercooling in a Saffman-Taylor channel geometry. The boundary may either form corners in finite time, or evolve to a single long finger travelling at constant speed, depending on the strength of kinetic undercooling. We demonstrate these two different behaviours numerically. For the travelling finger, we present results of a numerical solution method similar to that used to demonstrate the selection of discrete fingers by surface tension. With kinetic undercooling, a continuum of corner-free travelling fingers exists for any finger width above a critical value, which goes to zero as the kinetic undercooling vanishes. We have not been able to compute the discrete family of analytic solutions, predicted by previous asymptotic analysis, because the numerical scheme cannot distinguish between solutions characterised by analytic fingers and those which are corner-free but non-analytic.

Assessment of variability of finger millet (Eleusine coracana (L) Gaertn) landraces germplasm in Northern Nigeria

Germplasm identification and characterization is an important link between conservation and utilization of plant genetic resources. The present study was conducted to characterize the morphological diversity of 10 germplasm accessions of Finger millet (Eleusine coracana (L) Gaertn) collected from diverse locations spread across the geographic Northern Nigeria during the 2008, 2009 and 2010 cropping seasons. The seeds of the accessions were planted in a randomized complete block design (RCBD) with three replications in each of two locations-Keffi and Gwagwalada, during the three cropping seasons. The field studies for the three seasons in the two locations followed uniform agricultural practices. Field data was collected on morphological traits such as plant height, leaf length, leaf diameter, finger length, finger width, number of fingers and 1000 seed weight were recorded in accordance with standard finger millet descriptors. The results obtained, showed that plant height in accession Ex-Kwi was significantly different from all the other nine accessions while the highest leaf length which was recorded in Ex-Riyom was significantly different (p < 0.05) from only accession Ex-Dantse. Similarly, significant variations were observed in the number and length of fingers, and 1000 seed weight across all the accessions tested, over the three cropping seasons in the multilocational trial. Evaluation of phenotypic and genotypic characters of the different accessions revealed that the genotypes expressed significant genetic diversity for plant height, 1000 seed weight, leaf length and number of tillers than all the other traits assessed at p < 0.05 level of significance. These results tend to suggest a high variability existing among the selected morphological traits. Specifically, 87% of the variations were explained by the ANOVA model leaving only 13% unexplained. The cluster analysis based on morphological traits revealed six major distinct groups with one landrace forming independent cluster for the pooled analysis for the three years.

Contact-free and pose-invariant hand-biometric-based personal identification system using RGB and depth data

Hand-biometric-based personal identification is considered to be an effective method for automatic recognition. However, existing systems require strict constraints during data acquisition, such as costly devices, specified postures, simple background, and stable illumination. In this paper, a contactless personal identification system is proposed based on matching hand geometry features and color features. An inexpensive Kinect sensor is used to acquire depth and color images of the hand. During image acquisition, no pegs or surfaces are used to constrain hand position or posture. We segment the hand from the background through depth images through a process which is insensitive to illumination and background. Then finger orientations and landmark points, like finger tips or finger valleys, are obtained by geodesic hand contour analysis. Geometric features are extracted from depth images and palmprint features from intensity images. In previous systems, hand features like finger length and width are normalized, which results in the loss of the original geometric features. In our system, we transform 2D image points into real world coordinates, so that the geometric features remain invariant to distance and perspective effects. Extensive experiments demonstrate that the proposed hand-biometric-based personal identification system is effective and robust in various practical situations.

Optimized grid design for thin film solar panels

There is a gap in efficiency between record thin film cells and mass produced thin film solar panels. In this paper we quantify the effect of monolithic integration on power output for various configurations by modeling and present metallization as a way to improve efficiency of solar panels. Grid design and finger dimension optimization was performed monolithically integrated solar panels by modeling under standard conditions and with variation of boundary conditions such as transparent conductor used, conductivity of the metallic pattern and low light intensity. For each, the optimal cell and grid dimensions as well as the power output is presented. In contrast to previous studies that focus on 100μm wide grid lines, our grid finger width was varied between over a wide range and a finger width of 20μm was shown to give optimal results. We included mapping the power output for 20μm, 60μm and 100μm wide grid lines as function of cell length, finger spacing and TCO sheet resistance and show that also for wide fingers efficiency improvement of more than 15% is possible. This provides not only optimization of grid dimensions, but also the sensitivity of the power output with respect to the finger dimensions, TCO sheet resistance and the cell length. These results indicate that the application of a grid is a robust solution which allows for a considerable variation (>25%) in the parameter window around the optimum configuration with only small impact (<2%) on the power output.

Impact of fluid elasticity on miscible viscous fingering

An experimental study is performed to investigate the impact of fluid elasticity on miscible viscous fingering. Rectilinear flow experiments are performed by displacing aqueous Boger fluids (constant-viscosity elastic fluids) with water. The observations are compared to those in Newtonian fluids (glycerol solutions) of the same viscosity. Elasticity is observed to reduce the width of fingers, leading to formation of thinner and longer fingers in fully developed flow. The shielding effect is reduced due to fluid elasticity resulting in growth of multiple fingers as compared to a single thick dominant finger observed for Newtonian fluids. The dominant wave number for the onset of instabilities is observed to be higher in more elastic fluids i.e. the interface breaks down into greater number of fingers in the more elastic fluid. Data is presented to show that fluid elasticity retards the growth of fingers. Elastic effects are observed to reduce the thin film of the displaced fluid on the walls of the Hele–Shaw cells.

21.2%-efficient fineline-printed PERC solar cell with 5 busbar front grid

We evaluate industrial-type PERC solar cells applying a 5 busbar front grid and fineline-printed Ag fingers. We obtain finger widths down to 46 µm when using a stencil with 40 µm opening for the finger print, whereas the busbar is printed in a separate printing step with a different Ag paste (dual print). This compares to finger widths of 62 µm to 66 µm when applying print-on-print. The 5 busbar front grid with the best dual print process reduces the shadowing loss of the front grid to 4.0% compared to 5.8% for a conventional 3 busbar front grid printed with print-on-print. The 1.8% reduction in shadowing loss results in equal parts from the reduced finger width with dual print as well as from a reduced total busbar width of the 5 busbar design. The resulting PERC solar cells with 5 busbars demonstrate independently confirmed conversion efficiencies of 21.2% compared to 20.6% efficiency of the 3 busbar PERC solar cell. The increased conversion efficiency is primarily due to an increased short-circuit current resulting from the reduced shadowing loss. To our knowledge, 21.2% conversion efficiency is the highest value reported so far for industry typical silicon solar cells with printed metal front and rear contacts. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Clinical implications of the middle temporal vein with regard to temporal fossa augmentation.

The middle temporal vein (MTV) traverses the temporal fossa between the superficial and deep layers of the deep temporal fascia. During filler injection into a deficient temporal fossa, filling agents may be inadvertently injected into the MTV, which results in vascular complications. To investigate the course of the MTV to enable safe filler injection in the temple area. The course and diameter of the MTV were measured in 18 hemifaces from 9 Korean cadavers. The MTV was located 23.5 and 18.5 mm above the zygomatic arch at the jugale and the zygion, respectively. The diameter of the MTV at its thickest point was 5.1 mm. A splitting and reuniting pattern, such that the MTV occupied more space than a single trunk, was observed in 28% of cases. We propose that the safest area for filler injection in temporal fossa augmentation is one finger width above the zygomatic arch.

45-nm CMOS SOI Technology Characterization for Millimeter-Wave Applications

This paper presents an in-depth study of a 45-nm CMOS silicon-on-insulator (SOI) technology. Several transistor test cells are characterized and the effect of finger width, gate contact, and gate poly pitch on transistor performance is analyzed. The measured peak ft is 264 GHz for a 30 × 1007 nm single-gate contact relaxed-pitch transistor and the best fmax of 283 GHz is achieved by a 58 × 513 nm single-gate contact regular pitch transistor. The measured transistor performance agrees well with the simulations including R/C extraction up to the top metal layer. Passive components are also characterized and their performance is predicted accurately with design kit models and electromagnetic simulations. Low-noise amplifiers from Q- to W-band are developed in this technology and they achieve state-of-the-art noise-figure values.

Ni/Cu electroplating, a worthwhile alternative to use instead of Ag screen-printed front side metallization of conventional solar cells

For commercial purposes, it is necessary to manufacture high-efficiency and low-cost solar cells using simple processes. The front contact formation is one of the most critical steps in solar cell processing. Although silver paste screen-printed solar cells are the most widespread on the photovoltaic market, their efficiency is strongly limited as a result of shading and resistive losses, or more precisely the high contact resistance. Cu metallization for crystalline Si solar cells has attracted much attention as an alternative to the screen-printing technology. The low-cost Ni/Cu metal contact is regarded as the next generation of metallization processes to still improve the efficiency with a low specific contact resistance; it is formed using low-cost electroless plating and electroplating. A diffusion barrier should be placed between Cu and Si, to prevent Cu diffusion. Ni is shown to be an adequate barrier to Cu diffusion. For these reasons, geometry optimization of metal contacts of the front face, deposited by commercial processes, is investigated in this paper, in order to improve the spectral response of conventional multicrystalline mc-Si silicon solar cells. Their efficiency variation is analyzed as a function of changes in cell parameters (finger separation distance, height and width of finger, sheet resistance emitter...) using simulation programs in MATLAB, using contours to represent the efficiency evolution in terms of two variables. Efficiency gain of more than 0.7% has been achieved in this study. The simulation results were then compared with experimental data in order to be validated.

RF characteristics of 0.13-μm NMOS transistors for millimeter-wave application

Purpose – The purpose of this paper is to present the high-frequency performance of 0.13-μm n-type metal-oxide-semiconductor (NMOS) transistors with various multi-finger configurations for implementation in millimeter-wave (mm-wave) frequency. Design/methodology/approach – A folded-like double-gate transistor layout is designed to enable the transistor to work in the mm-wave region. Different sizes of transistors with variation in finger width (WF ) and number of fingers (NF ) were fabricated to determine the optimum size of the transistor. The extrinsic parasitic elements of selected transistors were extracted and investigated. The radio frequency (RF) performance of these samples were then analyzed and compared. Findings – The proposed layout performed well with the highest maximum oscillation frequency (fmax ) achieved at 122 GHz. Based on the comparison done, the optimum WF obtained for the layout is at 2.0 μm. It is found that the extrinsic parasitic capacitance is more dominant than the parasitic resistance in affecting the fmax . In s-parameter analysis, it is observed that the transistor with the least NF has smaller variance in small-signal gain throughout the measurement frequency. The maximum stable gain for the samples is also found to be roughly similar and independent of NF . Originality/value – A new layout structure for an NMOS transistor that works in mm-wave frequency is proposed. Experimental analyses presented here cover for both NF and WF , unlike others which focus on either NF or WF only.

Identification of transcriptome-derived microsatellite markers and their association with the growth performance of the mud crab (Scylla paramamosain).

Microsatellite markers from a transcriptome sequence library were initially isolated, and their genetic variation was characterized in a wild population of the mud crab (Scylla paramamosain). We then tested the association between these microsatellite markers and the growth performance of S. paramamosain. A total of 129 polymorphic microsatellite markers were identified, with an observed heterozygosity ranging from 0.19 to 1.00 per locus, an expected heterozygosity ranging from 0.23 to 0.96 per locus, and a polymorphism information content (PIC) ranging from 0.21 to 0.95 per locus. Of these microsatellite markers, 30 showed polymorphism in 96 full-sib individuals of a first generation family. Statistical analysis indicated that three microsatellite markers were significantly associated with 12 growth traits of S. paramamosain. Of these three markers, locus Scpa36 was significantly associated with eight growth traits, namely, carapace length, abdomen width (AW), body height (BH), fixed finger length of the claw, fixed finger width of the claw, fixed finger height of the claw, meropodite length of pereiopod 2, and meropodite length of pereiopod 3 (MLP3) (P<0.05). Locus Scpa75 was significantly associated with five growth traits, namely, internal carapace width, AW, carapace width at spine 8, distance between lateral spine 2 (DLS2), and MLP3 (P<0.05). Locus Spm30 was significantly associated with BH, DLS2, and body weight (P<0.05). Further analysis suggested a set of genotypes (BC at Scpa36, BC and BD at Scpa75, and AC at Spm30) that have great potential in the selection of S. paramamosain for growth traits. These findings will facilitate the development of population conservation genetics and molecular marker-assisted selective breeding of S. paramamosain and other closely related species.

GaN/Si based single SAW resonator temperature sensor operating in the GHz frequency range

The paper presents the manufacturing and characterization of GaN based SAW (surface acoustic wave) type temperature sensors. In contrast with most SAW sensor structures, manufactured on classical piezoelectric materials where delay lines or two port resonators have been used, in this paper, the resonance frequency shift vs. temperature for a single resonator structure was used for temperature measurements. It is demonstrated that the single resonator SAW structures ensure better performances in terms of sensitivity and losses compared with two port resonator structures. The sensor structure was manufactured using deep submicron e-beam nano-lithographic process on GaN/Si (finger width and interdigit spacing of 200nm) and resonance frequencies higher than 5GHz have been obtained at room temperature. The high resonance frequency ensures an increase of the sensitivity of the sensor structure. The sensor was characterized by “on wafer” resonance frequency shift and sensitivity measurements in the 23–150°C temperature range using S11 reflection parameter. The resonance frequency shift vs. temperature and the sensitivity for the sensor structures assembled on a special ceramic carrier, were measured, in a cryostat, in the −268–+150°C temperature range. Sensitivities higher than 300kHz/°C, (corresponding to values higher than 50ppm/°C) have been obtained.

Efficiency loss prevention in monolithically integrated thin film solar cells by improved front contact

AbstractFor thin film solar cells, there is a large gap between the record efficiencies and panel power output. It was found that for a “typical industrial” CIGS cell efficiency of 15.5%, the efficiency drops to 11.7% when it is operating under the circumstances of a monolithically integrated solar panel. Part of this gap is due to limited conductivity and transmittance of the front contact. By application of a metallic grid, the conductivity can be improved by over two order of magnitude at a transmittance loss of only a few percent as was shown experimentally. In addition, modeling was used to quantify the impact of such approach on the power output of monolithically integrated solar panels. This model includes optical and resistive losses, as well as related losses caused by the inhomogeneity of the operating voltage over the surface. Both power output and the different types of losses are mapped out for various cell configurations. Optimization of transparent conductive oxide resistance, cell length, finger width, and finger spacing of grids was performed and led to an efficiency improvement from 11.7% to 13.8% when the front contact is upgraded with a metallic grid consisting of 20 µm wide parallel fingers positioned perpendicular to the interconnect. Further optimization for a wide variety of cell and grid configurations show that for a technically more feasible size of 100 µm wide fingers, the calculated efficiency is still 13.5%. Finally, the power output is mapped out for a large number of configurations as to create an overview and insight in the interdependencies of cell configuration and finger dimensions. Copyright © 2014 John Wiley &amp; Sons, Ltd.

ISGP: Iterative sequential geometric programming for precise and robust CMOS analog circuit sizing

In this paper, a fast yet accurate CMOS analog circuit sizing method, referred to as Iterative Sequential Geometric Programming (ISGP), has been proposed. In this methodology, a correction factor has been introduced for each parameter of the geometric programming (GP) compatible device and performance model. These correction factors are updated using a SPICE simulation after every iteration of a sequential geometric programming (SGP) optimization. The proposed methodology takes advantage of SGP based optimization, namely, fast convergence and effectively optimum design and at the same time it uses SPICE simulation to fine tune the design point by rectifying inaccuracy that may exists in the GP compatible device and performance models. In addition, the ISGP considers the requirement of common centroid layout and yield aware design centering for robust final design point specifying the number of fingers and finger widths for each transistor which makes the design point ready for layout.The methodology has been validated in a 0.18μm CMOS technology by sizing a number of opamp circuits targeting reasonably aggressive specification. In the examples it has been observed that SPICE simulation within ISGP methodology decreases error in some of the circuit parameters from 80% to less than 1% and that of some device parameters from 700% to less than 1%. For each example the design iteration converges rapidly within 7 iterations which take only 4mins using an Intel Core 2 Duo, 2.53GHz processor. Robustness of the final design points has been observed through PVT analysis and Monte Carlo simulation.

Morphological Characterization of Fingermillet [Eleusine coracana (L.) Gaertn] Germplasm

Genetic variability and correlation coefficients analyses were carried out in 305 fingermillet genotypes between 13 grain yield and yield related traits. Highly significant mean sum of squares due to genotypes and wide range of variability were noticed among the genotypes for all the characters studied. High values for phenotypic and genotypic coefficients were recorded for grain yield per plant and flag leaf blade length, indicating that more variability is present in the germplasm for these characters. All the characters recorded high heritability in the present study indicated that these characters were relatively less influenced by environmental factors and phenotypic selection would be effective for the improvement of these characters. High estimates of variability together with high heritability and high genetic advance were observed for flag leaf sheath width, flag leaf blade width and 1000 grain weight, which indicated that these characters were governed by additive genes and selection would be effective for improvement of such characters. Highly significant positive correlation observed for the characters like days to 50 per cent flowering, productive tillers per plant, plant height, 1000 grain weight, flag leaf sheath length, days to maturity, flag leaf blade length and finger width with grain yield per plant, indicated the possibility of simultaneous improvement of these characters by selection.

Realization of a self-powered ZnO MSM UV photodetector with high responsivity using an asymmetric pair of Au electrodes

We demonstrate a novel ZnO self-powered photodetector based on the asymmetric metal-semiconductor-metal structure: one Au interdigitated electrode with wide fingers and the other one with narrow fingers.

A Roadmap for PERC Cell Efficiency towards 22%, Focused on Technology-related Constraints

Presently, the crystalline silicon (c-Si) photovoltaic (PV) industry is switching from standard cells to PERC cells to increase cell efficiency from about 18% to about 20%. This paper gives a roadmap for increasing PERC cell efficiency further towards 22%. Which equipment and which process conditions are feasible to go beyond 20% efficiency? To help answer this as generally as possible, we conduct state-of-the-art modelling in which we sweep the inputs that represent major technology-related constraints, such as diffusion depth, metal finger width and height, alignment tolerances, etc. (these are assigned to the x- and y-axes of our graphs). We then predict the optimum device parameters resulting from these restrictions (shown as contour lines). There are many different ways to achieve 22%. Our modelling predicts, for example, that 60μm wide screen-printed metal fingers are sufficiently narrow if the alignment tolerance (width of the n++ region) is below 90μm. The rear may be contacted with 30μm wide openings of the Al2O3/SiNx stack and with local J0,BSF values as high as 900 fA/cm2. If these requirements cannot be met, they may be compensated by improvements in other device parts. Regardless of this, the wafer material requires a SRH lifetime of at least 1ms at excess carrier densities near 1014 cm-3.

Paste Rheology Correlating With Dispensed Finger Geometry

Dispensing technology in crystalline silicon solar cell metallization offers the possibility to improve contact finger geometries compared with the dominating screen-printing approach. However, an optimum contact formation strongly depends on paste rheology and process parameters. In this study, a method is introduced to predetermine dispensed contact geometries by extracting specific rheological parameters from oscillating strain sweeps, allowing for paste optimization prior to printing tests. For this reason, four different dispensing pastes were processed and compared with a commercially available screen-printing paste. Oscillating strain sweeps were conducted with all pastes, in order to determine characteristic values for complex shear modulus G <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> and yield stress τy. In the following, p-type Cz-Si solar cells were processed, which were equipped with dispensed contact fingers using the four rheologically investigated dispensing pastes and compared with samples with an all screen-printed front-side grid. Effects like paste spreading or necking could be isolated and referred to the different pastes and printing processes. Various form parameters that describe specific characteristics of resulting finger geometries were introduced. The elastic part G' of the complex shear modulus G <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> was found to have the major impact on resulting finger widths, aspect ratios, and a macroscopic contact angle between the finger and the wafer surface.

Photolithographic fabrication of high-performance all-solid-state graphene-based planar micro-supercapacitors with different interdigital fingers

Here we demonstrated the fabrication of ultrahigh rate, all-solid-state, planar interdigital graphene-based micro-supercapacitors (MSCs) manufactured by methane plasma-assisted reduction and photolithographic micro-fabrication of graphene oxide films on silicon wafers. Notably, the electrochemical performance of MSCs is significantly enhanced by increasing the number of the interdigital fingers from 8 to 32 and minimizing the finger width from 1175 to 219 μm, highlighting the critical importance of adjusting the number and widths of the fingers in the fabrication of high-performance MSCs. The fabricated graphene-based MSCs delivered an area capacitance of 116 μF cm−2 and a stack capacitance of 25.9 F cm−3. Furthermore, they offered a power density of 1270 W cm−3 that is much higher than that of electrolytic capacitors, an energy density of ∼3.6 mW h cm−3 that is comparable to that of lithium thin-film batteries, and a superior cycling stability of ∼98.5% capacitance retention after 50000 cycles. More importantly, the microdevice can operate well at an ultrahigh scan rate of up to 2000 V s−1, which is three orders of magnitude higher than that of conventional supercapacitors.