Aspect Ratio Features Research Articles

Simulation of buckling of internal features during selective laser sintering of metals

Additive manufacturing (AM) processes, such as Selective Laser Sintering (SLS), have enabled the fabrication of geometrically complicated designs. However, undesired distortions due to thermally-induced residual stresses may lead to loss of tolerance or failure of the part. One potential failure mode is buckling, particularly when realizing high aspect ratio features, like for infill, to minimize weight. In this paper, we address distortions and part failures due to buckling by using a finite element model to predict residual stress distributions and sintering induced distortions. Initially, we conduct a transient thermal simulation to determine the Heat Affected Zone (HAZ), which is then used in the thermomechanical simulation. In addition, we imposed perturbations on the mechanical mesh based on the buckling eigenmodes. Finally, a thermomechanical viscoplastic analysis was performed layer-by-layer to obtain the final residual stress state and subsequent distortions that occur after cooling down to ambient temperature. A model was used to describe the evolution of porosity due to laser sintering, and then a model of the effects of porosity on the viscoplastic constitutive properties of the sintered material was used in the thermomechanical simulation. Modeling results are compared against experimental specimens using a Durelli (aka, Theta) specimen geometry fabricated with a 3D Systems ProX 200 Selective Laser Sintering (SLS) machine. The geometry of the specimen represents an internal feature with a high aspect ratio that is prone to buckling, and the dimensions were modified based on the simulation results to confirm the ability of the modeling approach to provide accurate mitigation of buckling-induced distortions.

Strike‐slip reactivation of segmented normal faults: Implications for basin structure and fluid flow

AbstractReverse reactivation of normal faults, also termed “inversion”, has been extensively studied, whereas little is known about the strike‐slip reactivation of normal faults. At the same time, recognizing strike‐slip reactivation of normal faults in sedimentary basins is critical, as it may alter and impact basin physiography, accommodation and sediment supply and dispersal. Motivated by this, we present a study of a reactivated normal fault zone in the Liassic limestones and shales of Somerset, UK, to elucidate the effects of strike‐slip reactivation of normal faults, and the inherent deformation of relay zones that separate the original normal fault segments. The fault zone, initially extensional, exhibits a series of relay zones between right‐stepping segments, with the steps between the segments having subsequently become contractional due to sinistral strike‐slip movement. The relay zones have therefore been steepened and are cut by a series of connecting faults with reverse and strike‐slip components. The studied fault zone, and comparison with larger‐scale natural examples, leads us to conclude that the relays turned contractional steps are associated with (a) complex fault and fracture networks that accommodate shortening, (b) anomalously high numbers of fractures and faults, (c) layer‐parallel slip and (d) folding and uplift. Comparison with published statistics from global relay zones shows that whereas the reactivated relay zones feature aspect ratios similar to those of unreactivated relay zones, bed dips within reactivated relay zones are significantly steeper than unreactivated relay zones. Given the potential of reactivated relay zones to form areas of local uplift, they may affect basin structure and may also form potential traps for hydrocarbon or other fluids. The elevated faulting and fracturing, on the other hand, means reactivated relays are also likely loci for enhanced up‐fault flow.

Factors Influencing Drying Induced Pattern Collapse

The collapse of high aspect ratio features is a daunting challenge facing the semiconductor industry. The complex physics and dynamics that govern this process are not entirely understood. Through the use of optical video imaging we have observed pattern collapse in real time. It was found that the liquid meniscus reconfigures itself laterally along the length of the structure as opposed to the expected top-to-bottom drying. Herein, we report on our observations and the physics of drying high aspect ratio structures.

Copper Electrodeposition in Blind Mesoscale through-Silicon-Vias

Copper (Cu) electrodeposition (ECD) in through-silicon-vias (TSVs) is an essential technique required for high-density 3-D integration of complex semiconductor devices. Cu ECD most commonly utilizes an acid sulfate electrolyte containing a finely tuned three-additive combination of inhibiting and Cu2+ aquo complex catalyzing species to produce void free deposits through the depth of high aspect ratio features. Despite their proven efficacy in filling micro- and nanoscale features, these three-additive electrolytes have not been shown to be viable for filling ICs at the mesoscale (> 100 µm). This is likely explained by the seminal curvature enhanced adsorbate coverage (CEAC) mechanism that describes the adsorption/desorption action of the additive species to an electrode surface. [1], [2] This mechanism theorizes that the interaction between the constituent additives and the rate of Cu2+ reduction is highly dependent on the local curvature of the electrode surface. In addition, these systems often require finely tuned ECD techniques like the use of pulse plating regimes, tightly controlled additive concentrations, and relatively low applied current densities (< 10 mA/cm2). To overcome the deficiencies of the three-additive acid sulfate chemistry that the CEAC mechanism describes, a single-additive chemistry was developed for the purposes of filling conformally conductive high aspect ratio features exclusively from the bottom-up by Moffat, T.P. and Josell, D. [3-5] This chemistry relies on a specific polyether suppressor additive, which induces voltammetric hysteresis and a positive feedback action as metal deposition disrupts Cl--suppressor complexes at the cathode surface. The acid sulfate resistive Cu electrolyte developed by Moffat, T.P. and Josell, D. utilizes 1 M CuSO4 + 0.5 M H2SO4 in addition to µM level concentrations of chloride and polyether suppressor species.[3-5] To investigate the functionality of a novel chemistry, the work outlined herein relies on the same mechanism and utilizes the same polyether suppressor and chloride concentration ranges, but instead uses a 1.25 M CH3SO3H + 0.25 M H2SO4 electrolyte. This electrolyte exhibits a greater Cu solubility, requires a lower concentration of acid, thus increasing the Cu plating rate while still retaining the same S-NDR mechanics as developed by Moffat, T.P. and Josell.[3-5] Upon adoption of the above-described chemistry, several issues were explored. The importance of convection on plating profiles within mesoscale (600 μm depth, 5:1 aspect ratio) blind TSVs is examined. In addition, potentiostatic methods are used to explore the process window for achieving bottom-up feature filling in the mesoscale TSVs described above. However, these potentiostatic techniques rely on the use of a reference electrode in solution, which is not a viable setup in industrial wafer-scale production tools. Thus, a galvanostatic approach is outlined and shown to be a viable alternative based on resulting fill profiles. The values used for the current density were calculated by comparing the breakdown potential of the suppressor molecule with the current reading at that set potential. Using only the area of the feature bottoms, a current density was calculated and fixed during subsequent plating experiments. This method is potentially problematic as the non -referenced electrochemical potential will maintain some unknown hysteresis, but initial results are shown to be promising. This galvanostatic approach, using the novel single additive chemistry is currently being explored for subsequent implementation into full wafer plating apparatus. Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. Andricacos, P.C., et al., Damascene copper electroplating for chip interconnections. Ibm Journal of Research and Development, 1998. 42(5): p. 567-574.Moffat, T.P., et al., Superconformal film growth: Mechanism and quantification. Ibm Journal of Research and Development, 2005. 49(1): p. 19-36.Moffat, T. P., and D. Josell. "Extreme bottom-up superfilling of through-silicon-vias by damascene processing: suppressor disruption, positive feedback and turing patterns." Journal of The Electrochemical Society 159.4 (2012): D208-D216.Josell, D., D. Wheeler, and T. P. Moffat. "Modeling extreme bottom-up filling of through silicon vias." Journal of The Electrochemical Society 159.10 (2012): D570-D576.Wheeler, Daniel, Thomas P. Moffat, and Daniel Josell. "Spatial-temporal modeling of extreme bottom-up filling of through-silicon-vias." Journal of The Electrochemical Society 160.12 (2013): D3260-D3265.

(Invited) Continued Device Miniaturization Enabled By New Materials Innovations and Advanced Patterning Schemes

The microelectronics industry continues to experience high demand for new materials innovation driven by the need for solutions in the advanced patterning space. As device features and critical dimensions continue to shrink, the complexity of chip fabrication increases at an exponential rate. With this increase in complexity, many issues and challenges arise. For instance, with more steps and smaller dimensions, Edge Placement Error (EPE) becomes a key limiting factor towards enabling future nodes. EPE is the error between the intended and actual placements of desired features in a device. Smaller device features afford tighter tolerance specifications and smaller error budgets. Advanced devices require multiple patterning steps, which increase the potential for errors and misalignments. EPE can have detrimental effects on device performance due to contact shorts and open circuits, often leading to poor device yields. One way to limit the effects of EPEs is to use self-alignment patterning schemes. Selective deposition and selective etch processes are both key enablers for the development of self-aligned processes in semiconductor fabrication. Figure 1(a) shows a standard contact patterning flow without self-alignment. Selective deposition can relax the lithography and overlay requirements, as shown in Figure 1(b), and greatly decrease EPE by enabling self-alignment patterning schemes. Furthermore, as devices continue to shrink, conventional etch processes suffer from poor etch control and line edge roughness and thus can also contribute to EPE for future nodes. Atomic layer Etch (ALE) is an emerging etch technique that uses two or more precursors in a sequential fashion where the surface modification during precursor exposure is self-limiting leading to highly controllable etches that are very smooth and conformal. In addition, the filling of high aspect ratio features is also a key enabler to complicated multi-patterning flows (such as reverse tone patterning). Although there has been remarkable progress on these fronts, further developments are needed to ensure the scalability of microelectronics devices. This presentation will focus on insights and recent research results in the quest for enabling new patterning schemes through the development of new selective ALD processes, thermal ALE processes, and methods for the gap fill of high aspect ratio features. Figure 1

(Invited) Atomic Layer Deposition of Tungsten-Rich Tungsten Carbide Films Using WCl6 and AlH2(tBuNCH2CH2NMe2) as Precursors

Atomic layer deposition (ALD) is a thin film deposition procedure where growth occurs in a layer-by-layer fashion. Growth of a binary material AB occurs first by passing a gaseous stream of a precursor containing element A over the substrate, to afford a monolayer of the precursor on the surface. Then, an inert gas purge is carried out to remove excess precursor and any reaction products. Next, a gaseous stream of a precursor containing element B is passed over the substrate. This precursor reacts with the monolayer on the surface containing element A to afford the desired material AB. Finally, a second inert gas purge is conducted to remove any excess precursor and reaction products. These four steps constitute a growth cycle. A key feature of ALD is its self-limiting nature, in which the precursor containing element A reacts with surface reactive sites until they are all consumed. At this point, growth ceases, to afford a monolayer of the precursor on the substrate surface. Self-limiting growth gives excellent conformal coverage of high aspect ratio features because the growth is controlled by surface reactive sites, and also allows sub-nanometer control of film thicknesses by adjusting the number of growth cycles. The success of ALD is directly related to the chemical precursors that are used to deliver the desired elements for a given material. ALD precursors must combine good volatility, thermal stability at the deposition temperature, as well as high reactivity toward a second precursor to afford the desired material. The reaction products must be volatile so that they are not incorporated into the growing film. Moreover, chemical precursors must have chemical reaction paths built into them so that the desired materials are obtained. These properties are difficult to incorporate into molecules, and lack of appropriate precursors represents a major bottleneck for the wider applications of ALD. This tutorial will review ALD precursors that have been reported for a variety of materials. Emphasis will be focused on obtaining volatility, high thermal stability, and high reactivity toward a second precursor. Examples will be chosen where chemical reactivity is designed into the precursors to obtain desired materials with high purities. Difficult current challenges in ALD include design of precursors for the growth of electropositive element films, integration of appropriate ALD precursor chemistry into manufacturing processes, and the possibility of precursor design to achieve inherent area-selective deposition. Additional future challenges related to ALD precursors and chemistry encompass the emerging atomic layer etching (ALE) and atomic layer clean (ALC) techniques. The importance of precursors and chemistry in future ALD, ALE, and ALC processes will be highlighted.

Precision Au Electrocoating of Double Sided Aligned Si Gratings for High Energy X-Ray Phase Contrast Imaging

State of the art grating fabrication currently limits the maximum source energy that can be used in lab based x-ray phase contrast imaging (XPCI) systems. In order to move to higher source energies, and image thicker and more dense materials, new grating fabrication methods are needed. In previous work we developed a differentiating mold construction technique that replaces photodefinable organic templates1 with high aspect ratio silicon (Si) deep reactive ion etching (DRIE) followed by precision electrodeposition of gold (Au)2. Combining DRIE with precision electro-coating enabled the fabrication of un-supported Au absorption gratings with aspect ratios as high as 50:1 and grating areas as large as 100 cm2. Further pushing this grating fabrication to enable the use of higher energy x-ray sources, we developed a new modality for grating fabrication that involves precision alignment of etched features on both sides of a substrate, effectively doubling the thickness of the. This double sided grating fabrication approach was applied to make a phase grating out of DRIE Si. In this work, we couple double sided Si DRIE with precision gold (Au) electrodeposition to fabricate absorption gratings for high energy lab based XPCI. A 250 µm deep, 2 µm wide, and 4 µm pitch absorption grating was fabricated by aligning and etching 125 µm deep grating features on both sides of a Si wafer. The Si grating features are patterned and etched on an 8 µm pitch with the width of the Si features patterned at 2 µm. Fabricating uniform, high aspect ratio features across large areas on both sides of a substrate is difficult due to the need to temporarily protect one side of the grating while processing on the opposite side of the substrate. After both sides are processed, this temporary support material must be removed without damaging the gratings on either side of the substrate. At these feature sizes, surface tension forces after wet processing are strong enough to collapse the grating features and must be carefully avoided. Our integration approach for accommodating these challenges is illustrated in Figure 1. Alignment features are first patterned and etched into both sides of the substrate. The front side gratings are then patterned with reference to the front side field image alignment marks and etched into the Si. Plasma enhanced tetraethylorthosilicate (PETEOS) SiO2 is then deposited to protect the front side gratings during backside processing. The backside gratings are similarly aligned using the alignment marks on the backside of the substrate. After the gratings on both sides of the substrate are etched, a selective wet etch is used to remove the supportive oxide and a critical point dryer is used to prevent surface tension forces from damaging the Si bars. A conformal platinum (Pt) plating seed metal is deposited by atomic layer deposition (ALD) and Au is precisely electroplated at a uniform thickness of 2 μm throughout the depth of the Si grating. The Au serves as a high x-ray absorbing material finalizing the fabrication process. In this work, we provide details on our fabrication approach and measurements of our final grating geometries. Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. [1] - High Aspect Ratio Gratings for X-Ray Phase Contrast Imaging: J. Mohr, T. Grund, D. Kunka, J. Kenntner, J. Leuthold, J. Meiser, J. Schulz and M. Walter, International Workshop on X-Ray and Neutron Phase Imaging with Gratings, Tokyo, Japan, 2012; [2] - Extensively long high aspect ratio gold analyzer gratings: A. E., Hollowell, C. L. Arrington, J. J. Coleman, P. S. Finnegan, A. M. Rowen, and A. L. Dagel, X-ray and Neutron Phase Imaging with Gratings, Bethesda, MD, 2015 [3] – Double Sided Grating Fabrication for High Energy X-Ray Phase Contrast Imaging: A. E. Hollowell, C. L. Arrington, P. Finnegan, K. Musick, P. Resnick, S. Volk, and A. L. Dagel, Material Science in Semiconductor Processing, 2018, under review. Figure 1

Superconformal Cu Electrodeposition

State of the art manufacturing of semiconductor devices involves electrodeposition of copper for device wiring and chip stacking. The success of the electroplating process depends on electrolyte additives that affect the local deposition rate to yield void-free superconformal, or bottom–up filling of trenches and vias that comprise 3D interconnects. Quantitative chemical process models have been shown to be effective in describing the filling of high aspect ratio features that range from nanometers (on-chip wiring1) to micrometers (through-silicon-vias2) to millimeters (printed circuit boards) in scale. Nevertheless, much remains to be known about the molecular nature of the additives and the competitive, co-adsorption dynamics involved in both suppression and acceleration of metal deposition. Accordingly, a variety of surface science tools, such as scanning tunneling microscopy (STM) and surface-enhanced infrared absorption spectroscopy (SEIRAS) are being used to investigate additive function. This lecture will focus on recent SERIAS experiments that reveal the important role of adsorbate water interactions, i.e. hydrophilicity, in the design and operation of additives used for superconformal film growth.

Deep Dry Etching of Silicon with Scallop Size Uniformly Larger than 300 nm

High aspect ratio features in silicon have broad applications in micro-electro-mechanical systems, microfluidic control and advanced packaging. This structure is usually fabricated by Bosch process, and the corresponding scallop should be controlled. Obtaining large scallop size seems easier than that of small scallop, however, it is a big challenge to obtain uniform large scallop. Herein, by using dry etching system, we demonstrate a novel high aspect ratio silicon trench with scallop size uniformly larger than 300 nm in both single crystal silicon and polycrystalline silicon. Additionally, the difference between single crystal silicon etching and polycrystalline silicon etching is compared. This work is beneficial to understanding the silicon etching mechanism in Bosch process and has potential applications in microelectronic and microfluidic devices.

Powering the Internet of Things

Internet connected devices are limited by the performance of microbatteries that power them. In this issue of Joule, Hur et al. develop microbatteries with tall 3D electrodes that have high areal energy densities. These microbatteries were fabricated on a silicon wafer using silicon and polymer processing that are compatible with microelectronics, paving the way for future microbattery and microelectronics integration.

Aqueous Solution-Processed Multifunctional SnO2 Aggregates for Highly Efficient Dye-Sensitized Solar Cells

A room temperature based environmentally friendly aqueous solution synthesis route was developed to fabricate highly dispersed small SnO2 nanoparticles (3–5 nm) without the application of any pressurized reaction vessel or organic solvents. The subsequent treatments, that is, dialyzing and freezing, allow for the acquision of dual-function nanostructures with sheet-like feature and large aspect ratio except for the ordinary irregular aggregates. Dye-sensitized solar cells (DSCs) constructed with the resultant multifunctional SnO2 showed an outstanding photovoltaic conversion efficiency (PCE) of 6.92% and an unexpected JSC of 19.5 mA cm–2 at an optimized thickness of 14.1 μm. The excellent performance can be ascribed to the effective coordination of the favorable features (i.e., strong light scattering, large dye loading capability, and fast electron transport) via rational film thickness control as indicated by diffused reflectance spectra, UV–vis absorption spectra, and electrochemical impedance spectros...

Drop-in Electrodeposition Processes for Void-Free, High Aspect Ratio Structures of Five Metals

Superconformal electrodeposition processes enable void- and seam-free metal filling of high aspect ratio features from tens of nanometers to hundreds of micrometers in size. There are two known mechanisms underlying such processes: Curvature Enhanced Accelerator Coverage (CEAC) and S-shaped Negative Differential Resistance (S-NDR). Voltammetric measurements on planar substrates can quantify kinetics in models based on both mechanisms, enabling accurate, a-priori prediction of filling from a particular electrolyte in a particular size and aspect ratio feature. I will summarize the chemistries and associated mechanisms for superconformal Cu, Ag, Au, Co, and Ni feature filling, including experiment and model predictions, for processes that are drop-in compatible with those presently used for fabrication of Cu damascene and through silicon via interconnects.

UV Assisted Densification of Perhydropolysilazane (PHPS) Based Spin-on Glass in High Aspect Ratio Gap Fill Structure

As device dimensions scale, defect-free, robust gap filling in high aspect ratio structures such as STI and inter-gate spaces becomes increasingly challenging. This is due to very high aspect ratio (AR) of gap fill structure (AR > 7:1), shrinking CDs (<20nm) and nearly vertical sidewalls gate profiles (>88deg). The Spin-On Dielectric such as (SOD) PerHydroPolySilazane (PHPS) is preferred choice as it provides defect-free and structure agnostic gap fill (1). As coated, the PHPS film has a long polymeric chain of hydrogen terminated -Si-N-Si- network with high % of N and terminal H. The film as-coated has very high etch rate in HF based chemistry. The film structure needs to be fully converted into a dense, cross-linked network of SiO2 via silanol condensation reaction during steam anneal carried out at ≤600C. However, as the critical dimension reaches below 20nm, the inability of steam to diffuse to the bottom of high aspect ratio features results in oxide density gradient leaving very weak oxide near the bottom of trench. High temperature anneal (> 600⁰C) is not feasible for inter-gate gap fill due to its impact on junction. Non-thermal approaches are needed to improve the oxide quality inside high aspect ratio features. The use of monochromatic UV radiation for low temperature conversion of PHPS film is well documented (2). Here, broadband UV (200nm-450nm) was explored to assess its effectiveness in improving In-Trench oxide density post steam anneal. The effect of three UV conditions (UV-A, UV-B, UV-C) and modified steam anneal condition on structure and composition of as-coated PHPS film was assessed using FTIR (Fig. 1) and XPS Depth Profiling (Fig. 2). In blanket experiments, the densification effect by UV of as-coated PHPS films was assessed post-steam anneal by measuring through-thickness wet etch rate (Fig. 3). This was done by sequential etching of annealed films in 100:1 dHF chemistry (400s) followed by thickness measurement. The average relative (to thermal oxide) wet etch rate of blanket oxide films exposed to various UV conditions and modified anneal conditions is listed in Table 1. FTIR and XPS depth profiles (Fig. 1) of UV treated PHPS films show significant modulation with UV conditions. The more aggressive the UV conditions, the lower the overall %N. Data also suggests that UV treated films have progressively higher O2 and reduced N at more aggressive UV conditions. This is because the effective breaking of Si-H, N-H and SI-N bonds in UV treated films which loosen the backbone structure, thereby facilitating oxygen/moisture diffusion relative to as-coated film. Low-temperature O2 soak step prior to steam anneal was found to be very effective in achieving denser oxide post-anneal for UV cured films. However, due to limited O2 diffusivity of oxygen in as-coated PHPS film due to denser network for non-UV treated PHPS films, O2 soak prior to steam anneal is more effective only at higher temperature. Optimized UV and anneal conditions from the blanket study were further explored on integrated wafers consiting of 7nm dimension inter-gate gap fill. These structures were filled with PHPS and treated with different UV conditions prior to annealing and planarization. In-Trench wet etch rate was obtained by sequentially measuring In-trench wet etch rate of oxide similar to the blanket film etch study. In each cycle, the wafer was exposed for 60s in 100:1 HF chemistry. Optical Scatterometry was used to measure In Trench oxide recess amount per etch cycle as well as cumulative oxide recess after 5 sequential etch cycles (5X 60s HF (100:1)) (fig. 4). Table 2 displays average In Trench wet etch rate comparison between the UV treated films and control cell post-steam anneal. The blanket wet etch rate data in Table 1 suggest 18% lowering just by modifying anneal for non-UV cell. Insertion of UV between spin coating and anneal helps further reduction in blanket wet etch rates (UV-A > UV-B > UV-C). UV-C condition had 34% reduction in blanket etch rate. However, blanket etch rate trend with UV condition did not quite translate to the In-Trench wet etch rate. While the overall in-trench wet etch performance for UV treated cells was better than control, the UV-A and UV-B conditions had lower in-trench WERR than UV-C condition. These results will be explained in the light of moisture sensitivity of UV exposed PHPS films as a function of UV conditions and its impact on overall wet etch rate post-anneal. References Trivedi et al., J. Vac. Sci. Technol. B, Vol 27, No. 6, pp 3145-3148Prager et al., Chem. Eur. J., 2009, vol. 15, pp 675-683 Figure 1

Superconformal Cu Electrodeposition: Seiras and STM Study of the Polyether-SPS-Cl System

State of the art manufacturing of semiconductor devices involves electrodeposition of copper for device wiring and chip stacking. The success of the electroplating process depends on electrolyte additives that affect the local deposition rate to yield void-free superconformal, or bottom–up filling of trenches and vias that comprise 3D interconnects. Quantitative chemical process models have been shown to be effective in describing the filling of high aspect ratio features that range from nanometers to millimeters in scale. Nevertheless, much remains to be known about the molecular nature of the additives and the competitive, co-adsorption dynamics involved in both suppression and acceleration of metal deposition. Accordingly, a variety of surface science tools, such as STM and SEIRAS, are being used to investigate additive function. These studies point to controlling interface hydrophilicity as a key principle in the design and operation of additives used for superconformal film growth.

Trade-off between Photon Management Efficacy and Material Quality in Thin-Film Solar Cells on Nanostructured Substrates of High Aspect Ratio Structures

Although texturing of the transparent electrode of thin-film solar cells has long been used to enhance light absorption via light trapping, such texturing has involved low aspect ratio features. With the recent development of nanotechnology, nanostructured substrates enable improved light trapping and enhanced optical absorption via resonances, a process known as photon management, in thin-film solar cells. Despite the progress made in the development of photon management in thin-film solar cells using nanostructures substrates, the structural integrity of the thin-film solar cells deposited onto such nanostructured substrates is rarely considered. Here, we report the observation of the reduction in the open circuit voltage of amorphous silicon solar cells deposited onto a nanostructured substrate with increasing areal number density of high aspect ratio structures. For a nanostructured substrate with the areal number density of such nanostructures increasing in correlation with the distance from one edge of the substrate, a correlation between the open circuit voltage reduction and the increase of the areal number density of high aspect ratio nanostructures of the front electrode of the small-size amorphous silicon solar cells deposited onto different regions of the substrate with graded nanostructure density indicates the effect of the surface morphology on the material quality, i.e., a trade-off between photon management efficacy and material quality. This observed trade-off highlights the importance of optimizing the morphology of the nanostructured substrate to ensure conformal deposition of the thin-film solar cell.

Exploiting atomic layer deposition for fabricating sub-10 nm X-ray lenses

Moving towards significantly smaller nanostructures, direct structuring techniques such as electron beam lithography approach fundamental limitations in feature size and aspect ratios. Application of nanostructures like diffractive X-ray lenses requires feature sizes of below 10nm to enter a new regime in high resolution X-ray microscopy. As such dimensions are difficult to obtain using conventional electron beam lithography, we pursue a line-doubling approach. We demonstrate that this method yields structure sizes as small as 6.4nm. X-ray lenses fabricated in this way are tested for their efficiency and microscopic resolution. In addition, the line-doubling technique is successfully extended to a six-fold scheme, where each line in a template structure written by electron beam lithography evolves into six metal lines.

Bio-inspired textures for functional applications

Textures are abundantly exploited in nature for securing superior functionalities including adhesion, color manipulation, anti-reflection, and drag management. Over millions of years, these advanced properties are endowed to various organisms on the planet to survive and adapt in harsh environmental conditions. Texture characteristics such as feature size, shape, periodicity, aspect ratio, orientation and hierarchy are critical in nature’s ‘tool-box’. Manufacturing of cutting-edge products require multi-functionalities for efficiency, durability and sustainability for improving the quality of life of growing population. This paper analyzes and discusses convergence and underlying science and engineering of well proven natural strategies of surface textures and their effective synthetic implementation in engineered products.

A High Aspect Ratio Serpentine Structure for Use As a Strain-Insensitive, Stretchable Transparent Conductor.

The development of strain-insensitive stretchable transparent conductors (TCs) is essential for manufacturing stretchable electronics. Despite recent progress, achieving a high optoelectronic performance under applied strain of 50% continues to present a significant challenge in this research field. Herein, an ultratall and ultrathin high aspect ratio serpentine metal structure is described that exhibits a remarkable stretching ability (the resistance remains constant under applied strain of 100%) and simultaneously provides an excellent transparent conducting performance (with a sheet resistance of 7.6 Ω -1 and a transmittance of 90.5%). It is demonstrated that the highly stretchable transparent conducting properties can be attributed to the high aspect ratio feature. A high aspect ratio (aspect ratio of 17-367) structure permits facile deformation of the serpentine structure with in-plane motion, leading to a high stretching ability. In addition, this structural feature avoids the classic tradeoff between optical transmittance and electrical conductance, providing a high electrical conductance without decreasing the optical transmittance. The practical utility of these devices is tested by using these TCs as stretchable interconnectors among LEDs or in wearable VOC gas sensors.

Design and Fabrication Challenges for Millimeter-Scale Three-Dimensional Phononic Crystals

While phononic crystals can be theoretically modeled with a variety of analytical and numerical methods, the practical realization and comprehensive characterization of complex designs is often challenging. This is especially important for the nearly limitless possibilities of periodic, three-dimensional structures. In this contribution, we take a look at these design and fabrication challenges of different 3D phononic elements based on recent research using additive manufacturing. Different fabrication technologies introduce specific limitations in terms of, e.g., material choices, minimum feature size, aspect ratios, or support requirements that have to be taken into account during design and theoretical modeling. We discuss advantages and disadvantages of additive technologies suitable for millimeter and sub-millimeter feature sizes. Furthermore, we present comprehensive experimental characterization of finite, simple cubic lattices in terms of wave polarization and propagation direction to demonstrate the substantial differences between complete phononic band gap and application oriented directional band gaps of selected propagation modes.

Review Article: Active scanning probes: A versatile toolkit for fast imaging and emerging nanofabrication

With the recent advances in the field of nanotechnology, measurement and manipulation requirements at the nanoscale have become more stringent than ever before. In atomic force microscopy, high-speed performance alone is not sufficient without considerations of other aspects of the measurement task, such as the feature aspect ratio, required range, or acceptable probe-sample interaction forces. In this paper, the authors discuss these requirements and the research directions that provide the highest potential in meeting them. The authors elaborate on the efforts toward the downsizing of self-sensed and self-actuated probes as well as on upscaling by active cantilever arrays. The authors present the fabrication process of active probes along with the tip customizations carried out targeting specific application fields. As promising application in scope of nanofabrication, field emission scanning probe lithography is introduced. The authors further discuss their control and design approach. Here, microactuators, e.g., multilayer microcantilevers, and macroactuators, e.g., flexure scanners, are combined in order to simultaneously meet both the range and speed requirements of a new generation of scanning probe microscopes.