Low-cost Patterning Technique Research Articles

Inkjet printing aided patterning of transparent metal mesh for wearable tactile and proximity sensors

Fabrication of an electronic device involves patterning that contributes a substantial cost to it. Development of an unconventional and low-cost patterning technique is thus the goal-post. Herein, an exclusive, simple and large-scale patterning technique for metal mesh is established. The steps involve the formation of a crackle template on a transparent substrate by spray coating, inkjet printing polyvinyl alcohol (PVA) solution followed by drying, metal deposition and template lift-off. An interdigitated electrode (IDE) with a finger-gap of ∼ 300 µm over a large electrode area (30 × 30 cm2) is accomplished with such a simple process. The patterning technique is further utilized to fabricate an IDE on flexible poly(ethylene terephthalate) (PET) substrate for the application of a transparent multifunctional capacitive sensor with proximity (up to 9 cm) and touch sensing ability.

Laser-induced graphitization of a forest-based ink for use in flexible and printed electronics

Laser-induced graphitization (LIG) is a method of converting a carbon-rich precursor into a highly conductive graphite-like carbon by laser scribing. This method has shown great promise as a versatile and low-cost patterning technique. Here we show for the first time how an ink based on cellulose and lignin can be patterned using screen printing followed by laser graphitization. Screen printing is one of the most commonly used manufacturing techniques of printed electronics, making this approach compatible with existing processing of various devices. The use of forest-based materials opens the possibility of producing green and sustainable electronics. Pre-patterning of the ink enables carbon patterns without residual precursor between the patterns. We investigated the effect of the ink composition, laser parameters, and additives on the conductivity and structure of the resulting carbon and could achieve low sheet resistance of 3.8 Ω sq−1 and a high degree of graphitization. We demonstrated that the process is compatible with printed electronics and finally manufactured a humidity sensor which uses lignin as the sensing layer and graphitized lignin as the electrodes.

Green photonics integrated circuit for NGOA coherent receivers

The recent advances in coherent optical systems enable the use of efficient modulation formats, such as quadrature phase shift keying (QPSK). In this framework, we present an integrated 90° hybrid 2 × 4 coupler based on self-patternable organic–inorganic hybrid thin films fabricated using direct laser writing. The device was coupled to balanced photodiodes, resulting in an optical coherent receiver with capacity to extract the modulated data. The device performance was demonstrated for a transmission over 40 km (G.652 fiber) with a 20 Gb/s QPSK, yielding a 2.5 dB power penalty (BER = 3.8 × 10−3), being the best figures of merit for waveguides processed by low-cost patterning techniques. Furthermore, the hybrid materials are thermally and mechanically stable than polymers, with lower fiber-to-device insertion losses. Therefore, the proposed optical coherent receiver is an easy processed and cost-effective approach for the next generation of optical access networks.

GaAs Solar Cells on Nanopatterned Si Substrates

Integrating III–Vs onto Si is a promising route toward tandem photovoltaics and cost mitigation of III–V substrates. While many III–V/Si photovoltaic integration approaches have been studied, epitaxial growth on Si allows for fewer processing steps compared to other approaches. However, current epitaxial pathways utilize expensive techniques, such as thermal cycle annealing or thick buffer layers to control defect densities, undermining the low-cost goal of integrating III–Vs with Si. Here, we present single-junction GaAs solar cells grown directly on Si using selective area growth as an alternative low-cost technique to control material quality with a much thinner buffer. We demonstrate a 10.4%-efficient GaAs device grown on a V-grooved Si substrate, which achieved an antiphase domain-free III–V/Si interface and a threading dislocation density of 2 × 107 cm –2, despite the lack of a graded buffer. We compare this growth on V-grooved Si to solar cells grown on polished Si with and without a patterned silica buffer layer, which demonstrate efficiencies of 6.5% and 6.8%, respectively; the polished Si was patterned using nanoimprint lithography, which is a low-cost patterning technique compatible with III–V selective area growth. Cracking is found to be a critical challenge that hinders solar cell performance and is exacerbated by the V-grooved Si surface topography. The results in this paper provide a promising pathway toward high-efficiency, low-cost III–V/Si tandem photovoltaics.

Insights into Drying of Noncircular Sessile Nanofluid Droplets toward Multiscale Surface Patterning Using a Wall-Less Confinement Architecture.

Surface patterning with functional colloids is an important research area because of its widespread applicability in domains such as nanoelectronics, pharmaceutics, semiconductors, and photovoltaics among others. In this endeavor, we propose a low-cost patterning technique that aspires to eliminate the more expensive methodologies that are presently in practice. Using a simple document stamp on which patterns of any geometry can be embossed, we are able to print 2D millimeter-scale "wall-less confinement" using an ink-based hydrophobic fence on any plasma-treated superhydrophilic surface. The confinement is subsequently filled with nanocolloidal liquid(s). Using confinement geometry, we are able to control the 3D shape of the droplet to exhibit multiple interfacial curvatures. The droplet in the "wall-less confinements" evaporates naturally, exhibiting unique geometry (curvature)-induced flow structures that induce the nanoparticles to self-assemble into functional patterns. We have also shown that by modifying the geometry of the pattern, evaporation, flow, and particle deposition dynamics get altered, leading to precipitate topologies from macro- to microscales. We present two such geometrical designs that demonstrate the capability of modifying both macroscopic and microscopic features of the final precipitate. We have also provided a description of the physical mechanisms of the drying process by resolving the unique flow pattern using a combination of imaging and microparticle image velocimetry. These provide insights into the coupled dynamics of evaporation and flow responsible for the evolution of particle deposition pattern. Precipitate characterization using scanning electron microscopy and dark-field microscopy highlights the transformation in the deposit morphology.

Large-area omnidirectional antireflection coating on low-index materials

Large-area subwavelength dielectric hexagonal lattices of cylindrical pillars on quartz substrates that provide high optical transmittance at all angles of incidence under different polarizations of light, and are fabricated using low-cost patterning techniques, are demonstrated and analyzed. Transmittance >85% for angles of incidence in excess of 70° is demonstrated at visible and near-infrared wavelengths, and the structures employed are shown to be superior at visible wavelengths to tapered “moth eye” surfaces for practically achievable dimensions. Detailed analytical calculations and numerical simulations elucidating the impact of feature size, height, periodicity, and refractive index are presented.

Flexible Optical Chemical Sensor Platform for BTX

Abstract An in-plane flexible sensor platform for BTXs detection was developed using low-cost patterning techniques and foil-based optical components. The platform was produced by a combination of laser patterning, inkjet printing and capillary filling. Key optical components such as lightguides, optical cladding layers and metallic interconnections were realized on low cost substrates such as paper and PET. The sensing mechanism is based on the change in fluorescence spectra of a reporter dye, supported over a porous matrix. Detection limits down to 1 ppm for benzene, toluene and xylene have been measured. Response times down to a few seconds were observed for different gas concentrations.

Towards Low-Cost Manufacturing of Organic Solar Cells: Multi Criteria Assessment of Fabrication Technologies

Solution-processed organic solar cells have recently gained considerable attention and are becoming a future solar technology option. This study is intended to improve the assessment of the operation parameters of these manufacturing technologies in order to propose a low-cost patterning technique suitable for a successful high-volume manufacturing of full organic solar cells. The assessment will take into account quantitative and qualitative parameters, such as technical issues, environmental impact or reproducibility of the fabrication output. Multi-criteria decision making methods will be used to model the problem of fabrication technique selection, combining these techniques with fuzzy numbers which serve to assess the criteria valued with linguistic labels.

UV nanoimprint lithography process optimization for electron device manufacturing on nanosized scale

Imprint specific process parameters like the residual layer thickness and the etch resistance of the UV polymers for the substrate etch process have to be optimized to introduce UV nanoimprint lithography (UV NIL) as a high-resolution, low-cost patterning technique for research and industry into electron device manufacturing. Additionally, UV NIL processes have to be compatible with conventional silicon (Si) semiconductor processing. Within this work, the minimization of the residual layer thickness by using a multi-drop ink-jet system, which was integrated into the imprint stepper NPS300 from S-E-T-(formerly SUSS MicroTec), in combination with a low viscous UV polymer from Asahi Glass Company is shown. The etch resistance of different UV polymers against the poly-Si etch process was increased by 50% with an appropriate post-exposure bake. A poly-Si dry etch process was used to pattern the gates of short channel MOSFETs. After optimizing the poly-Si etch, properly working short channel MOSFETs with a minimum gate length of about 90 nm were fabricated demonstrating successfully the compatibility of UV NIL with conventional Si semiconductor processing on nanosized scale.

Custom-specific UV nanoimprint templates and life-time of antisticking layers

UV nanoimprint lithography (UV NIL) is attracting more and more interest, because of its potential to become a high-resolution, low-cost patterning technique. To establish UV NIL as a low-cost patterning technique, the costs of single templates, today obtained from 6025 quartz mask blanks, have to be reduced and the life-time of the antisticking layers has to be optimized. Within this work, a process flow was developed to obtain 49 UV nanoimprint templates with a dimension of 12.5×12.5mm2 out of a fused silica substrate with a diameter of 150mm. After sawing, etching, and cleaning, the template surfaces were covered with an antisticking layer. Next, the templates were glued onto a template holder to enable their handling with the nanoimprint tool NPS300 from Süss MicroTec. With this process flow, the prize of one single template was strongly reduced compared to quartz templates obtained from 6025 quartz mask blanks. In addition, the life-time of antisticking layers was investigated. For this purpose, the change of the surface tension of antisticking layers after an increasing number of imprints into different UV curing materials was measured and the best combination of antisticking layer and UV curing material was figured out. Finally, silicon substrates were patterned with the optimized template.

Surface characterization of imprinted resist above glass transition temperature

Nanoimprint lithography is a high resolution and low cost patterning technique. Many difficulties have been overcome from the process point of view. This article is dedicated to the resist pattern characterization when they are annealed above the glass transition temperature of the material. This approach may be directly transposed to imprint process optimization when the demolding scheme is performed above the glass transition temperature. Simple model describing shape evolution with temperature is proposed and correlation with demolding process is presented. The results showed that a stamp release well above glass transition temperature is possible and may slightly impact the initial imprinted shape. Furthermore, this work may be transposed to determine temperature evolution of polymer dynamic viscosity.

UV nanoimprint materials: Surface energies, residual layers, and imprint quality

UV nanoimprint lithography is attracting more and more interest, because it has the potential of becoming a high-resolution, low-cost patterning technique. The availability of suitable UV curing materials is mandatory for successful imprinting. Within this work, a systematic investigation of commercially available photocuring materials was conducted to provide an overview of the properties of these materials. Their wetting behavior with respect to different substrate surfaces was characterized and their surface tensions were determined from their contact angles against two specifically selected solid surfaces: This method is presented here for the first time. The adhesion properties of the UV curing materials to different substrate surfaces and to the mold were investigated and necessary curing times were estimated. Additionally, the dependence of the residual layer thickness on the viscosity and the initial dispensed volume of UV curing materials was analyzed. It was found that the resist formulation of the UV curing materials strongly influences the surface tension as well as the adhesion to different substrate surfaces. Furthermore, the experiments verified that the thickness of the residual layer for UV curing materials increases with the square root of their viscosity which is predicted by theory. To demonstrate the suitability of the UV curing materials, first imprints with the prototype imprint tool, Nano Patterning Stepper 300 from Süss MicroTec, with pattern sizes down to 50nm are shown.

P‐42: Metal Patterning on Flexible Substrates Suitable for Roll‐to‐Roll Processes

AbstractA simple, low‐cost patterning technique suitable for high volume manufacturing of thin film transistors is proposed. This method utilizes photolithographic templates and electroless plating to generate high‐resolution metal patterns on flexible substrates. A major advantage of the process comes from simultaneous copper deposition and template dissolution that reduces the effective number of processing steps.