Direct Laser Patterning Research Articles

Fully laser-patterned stretchable microsupercapacitors integrated with soft electronic circuit components

Stretchable energy storage devices are prerequisites for the realization of autonomous elastomeric electronics. Microsupercapacitors (MSCs) are promising candidates for this purpose due to their high power and energy densities, potential for miniaturization, and feasibility of embedding in circuits; however, efforts to realize stretchable MSCs have mostly relied on strain-accommodating materials and have suffered from limited stretchability, low conductivity, or complicated patterning processes. Here, we designed and fabricated a stretchable MSC based on reduced-graphene-oxide/Au heterostructures patterned by facile and versatile direct laser patterning. An interconnected and stable 3D network composed of vertically oriented heterostructures was realized by high-repetition-rate femtosecond laser pulses. Upon transferring to polydimethylsiloxane (PDMS), the 3D network achieved a high conductivity of ~105 S m−1, and the conductivity could be maintained at ~104 S m−1 even at 50% strain. A fully laser-patterned stretchable electronics system was integrated with embedded MSCs, which will find applications in soft robotics, wearable electronics, and the Internet of Things.

Angle Dependent 3-D Directional Patterning of Flexible Films by Infrared Laser.

Laser direct patterning (LDP) technology has attracted great attention due to its process simplification and environmental friendliness. It is replacing the existing photo-lithography technology. Infrared (IR) laser equipment also has advantages such as low cost and long duration, although it is difficult to implement fine line width compared to ultraviolet (UV) or excimer laser. Therefore, it is very important to realize 3-D patterning system based on cheap infrared laser system. In this paper, 3-D infrared laser direct patterning system was designed by introducing an etching process on Ag paste/ITO/PET flexible film. Such 3-D patterned Ag paste/ITO/PET flexible films showed feasibility and effectiveness of 3-D laser directional patterning technologies. Etch ratio of the fabricated Ag paste/ITO/PET flexible film after 3-D infrared laser direct patterning was then systematically investigated.

Superhydrophobicity on hierarchical periodic surface structures fabricated via direct laser writing and direct laser interference patterning on an aluminium alloy

Multi-scaled hierarchical surface microstructures are fabricated on Al2024 alloy using Direct Laser Writing and Direct Laser Interference Patterning. During the manufacturing procedure two distinct laser sources are used, including an ultra-violet nanosecond laser system that produces microcell structures with different dimensions through Direct Laser Writing. Posteriorly, an infrared picosecond laser source is used to fabricate sub-micron features on the previously patterned microcells. Thus, the fabricated multi-scaled hierarchical structures are a closer representation of what is observed in nature. Water contact angle measurements are carried out in order to assess the wettability response, which revealed superhydrophobicity one week posterior to the fabrication, with measured contact angles up to 161.5 ± 3°.

Electrical and Thermal Properties of Heater-Sensor Microsystems Patterned in TCO Films for Wide-Range Temperature Applications from 15 K to 350 K.

This paper presents an analysis of the electrical and thermal properties of miniature transparent heaters for use in a wide range of temperature applications, from 15 K to 350 K. The heater structures were produced in transparent conducting oxide (TCO) layers: indium tin oxide (ITO) and ITO/Ag/ITO on polymer substrates-polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), by direct laser patterning. Thermo-resistors for temperature measurement were created in the same process, with geometry corresponding to the shape of the heating path. The thermo-resistors integrated with the heating structure allowed easy control of the thermal state of the heaters. Laser patterning provided high precision and repeatability in terms of the geometry and electrical properties of the heater-sensor structures. Measurements at temperatures from 15 K to above room temperature (350 K) confirmed the excellent dynamics of the heating and cooling processes, due to current flow. The largest value for surface heating power was over 3 W/cm2. A heater-sensor structure equipped with a small capacity chamber was successfully applied for controlled heating of small volumes of different liquids. Such structures have potential for use in research and measurements, where for various reasons controlled and accurate heating of small volumes of liquids is required.

A laser curable palladium complex ink used for fabrication of copper pattern on polyimide substrate

Abstract A simple and efficient approach for selective metallization of polyimide (PI) substrate has been developed in this work. A heat curable Pd complex ink consists of Pd salt, pH sensitive monomer N, N-dimethyl-dimethylaminoethyl methacrylate (DMAEMA), trimethylolpropane triacrylate (TMPTA), and tert-butyl peroxybenzoate (TBPB) is utilized to promote the adhesion between the Cu coating and PI substrate. After heating the spin-coated ink on PI and successive electroless deposition (ELD) of copper, a layer of copper with excellent adhesion is formed on PI substrate. The effects of this ink on catalyzing the ELD of copper and the mechanism for the enhancement of the adhesion between flexible PI substrate and copper layer are investigated by XPS and FT-IR. The copper coating plated by this method has a low resistivity (about 13.6 × 10 − 6 Ω cm) and satisfied endurance of bending. Moreover, we also demonstrate that the copper patterns can be prepared easily by integration of laser-direct patterning of the spin-coated ink and electroless Cu deposition, which is fast and effective strategy for fabricating circuit patterns on the plastic substrate.

355 nm UV laser patterning and post-processing of FR4 PCB for fine pitch components integration

Laser direct patterning of fine pitch features on standard PCB (Printed Circuit Board) was investigated. As a feasibility study, eight parameter sets were selected and the smallest achievable grooves and tracks were determined. Three regular FR4 (Flame Resistant 4) PCB substrates have been experimented with. The first two have respectively 18 µm and 35 µm bare copper conductive layer without finish while the third one has a 18 µm copper layer with ENIG (Electroless Nickel Immersion Gold) finish.Laser patterning of PCB conductive structure is a single step, maskless and purely dry operation expected to allow reaching fine pitch features, even on thick copper layers (≥ 18 µm) for which the traditional chemical wet processes encounter underetch problems. Aside PCB complete structuring, a second objective is to evaluate laser post-processing of standard patterned PCB as an economically viable technique to integrate a few fine pitch components on low cost PCBs. This process is suitable for prototyping and for small and medium series.The widths of the smallest grooves and tracks that we achieved were measured about 11 µm and 19 µm on 18 µm thick cooper layer, 13 µm and 39 µm on 35 µm thick cooper layer, and 11 µm and 38 µm on 18 µm cooper layer with ENIG finish. These values are well below what can be achieved with a wet process. Etching results are presented at high magnification both from the top and from a cross-sectioning perspective. The latter allows observation of the TAZ (Thermal Affected Zone) in the conductive layer and the damages in the FR4.

Multicomponent patterned ultrathin carbon nanomembranes by laser ablation

Carbon nanomembranes (CNMs) are a class of two-dimensional materials, which are obtained by electron beam-induced crosslinking of aromatic self-assembled monolayers (SAMs) on solid substrates. CNMs made from a single type of precursor molecule are uniform with homogeneous chemical and physical properties. We have developed a method for the fabrication of internally patterned CNMs resembling a key feature of biological membranes. Direct laser patterning is used to obtain multicomponent patterned SAMs on gold, which are subsequently crosslinked by electron irradiation. We demonstrate that the structure of internally patterned CNMs is preserved upon transfer to different substrates. The method enables rapid fabrication of patterned 2D materials with local variations in chemical and physical properties on the micrometer to centimeter scale.

Nanosecond-laser patterning of 3Y-TZP: Damage and microstructural changes

The aim of this study is to characterize in detail the microstructural changes and collateral damage induced by direct laser patterning on the surface of dental-grade zirconia (3Y-TZP) employing an interference setup with the 532 and 355nm harmonics of a Nd:YAG laser (pulse duration of 10ns).Laser-material interaction mainly results in thermal effects for both wavelengths studied. Upon laser irradiation the material locally melts producing pattern and establishing a steep thermal gradient on the surface. This generates a∼1μm thick heat affected zone where microcracking, directional recrystallization, phase transformation (from tetragonal to monoclinic, t→m) and texturization (ferroelastic domain switching) take place. In addition, surface coloration results from the activation of F-centers as a consequence of high energy radiation exposure. No chemical segregation or diffusion was detected. All these microstructural changes should be taken into account to ensure integrity and long-term reliability of the zirconia components.

Cell patterning via laser micro/nano structured silicon surfaces

The surface topography of biomaterials can have an important impact on cellular adhesion, growth and proliferation. Apart from the overall roughness, the detailed morphological features, at all length scales, significantly affect the cell-biomaterial interactions in a plethora of applications including structural implants, tissue engineering scaffolds and biosensors. In this study, we present a simple, one-step direct laser patterning technique to fabricate nanoripples and dual-rough hierarchical micro/nano structures to control SW10 cell attachment and migration. It is shown that, depending on the laser processing conditions, distinct cell-philic or cell-repellant patterned areas can be attained with a desired motif. We envisage that our technique could enable spatial patterning of cells in a controllable manner, giving rise to advanced capabilities in cell biology research.

Fabrication of transparent ITO-Ag-ITO electrodes on polyethylene terephthalate substrate by Nd:YVO4 laser direct patterning

ABSTRACTFor the realization of high conductive and transparent electrodes on flexible substrates, indium tin oxide(ITO), Ag, and ITO were sequentially deposited on polyethylene terephthalate(PET) and a Q-switched Nd:YVO4 laser was used for direct etching of the ITO–Ag-ITO films. Considering the complementary relationship between transmittance and conductivity, Ag was deposited for different sputtering times and the laser etched results were also compared and analyzed. Considering the laser etched shape, the ITO–Ag-ITO electrodes were patterned with the optimized laser beam condition. From the current-voltage characteristics and multi-meter measurement, much lower resistances were obtained from electrically isolated ITO-Ag-ITO electrode.

Environmental assessment of new technologies: Production of a Quantum Dots-Light Emitting Diode

The production of a Quantum Dots-Light Emitting Diode by Direct Laser Patterning is a new strategy to draw luminous patterns on Organic Light Emitting Diodes. The laser patterned Quantum Dots-Light Emitting Diode improves the optical performances of Organic Light Emitting Diodes introducing Quantum Dots as luminophores and avoids the use of photolithography to draw patterns, thus simplifying the manufacturing process.The purpose of this study is to describe the production of a Quantum Dots-Light Emitting Diode prototype using Direct Laser Patterning technology and to assess its environmental performance, by means of Life Cycle Assessment method, with the aim to identify the hotspots in the production chain and to support a more environmentally-friendly product design.The goal of the Life Cycle Assessment study is to evaluate the environmental impacts of the production of one Quantum Dots-Light Emitting Diode with a surface of 4 cm2 and a laser patterning surface of 25 mm2. The system boundaries were from cradle to gate and included the production of the following elements: the cadmium sulphide precursor for Quantum Dots, the organic electroluminescent polymer, the anode and cathode as well as laser patterning. Primary data were collected at laboratory scale and IMPACT 2002+ impact assessment method was used. Results show that the main hotspots are the production of the electroluminescent polymer and the indium tin oxide glass used as anode. Therefore, other materials could be used as anode and polymer with the aim to improve the environmental performances of the device. Moreover, a comparative analysis between the environmental impacts of the new patterning technology and that of the traditional photolithography shows that their environmental performances are quite similar. However, the use of the new Quantum Dots-Light Emitting Diode technology is advisable because of its better technological performance, lower costs and processing time.

Laser direct 3D patterning and reduction of graphene oxide film on polymer substrate

The graphene oxide (GO) film embossing and reduction was demonstrated under femtosecond laser pulses. The best conductivity of laser reduced GO film of 200Ω/□ was achieved for fs laser pulses energy of 35–45nJ and 10–25 pulses per µm. We demonstrate the patterned laser reduction over the embossed GO film that holds it integrity and conductivity. Laser reduced GO properties was studied by Raman, SEM and sheet resistance measurements.

Nd:YVO4 Laser Direct Patterning of Aluminum-Doped Zinc Oxide Films Sputtered Under Different Process Conditions

Nd:YVO4 Laser Direct Patterning of Aluminum-Doped Zinc Oxide Films Sputtered Under Different Process Conditions

Laser patterning of Y3Al5O12:Ce3+ ceramic phosphor platelets for enhanced forward light extraction and angular color uniformity of white LEDs.

We present a facile fabrication process to directly fabricate cone-shaped microwells arrays on single crystal Y3Al5O12:Ce3+ (YAG:Ce) ceramic phosphor platelets (CPPs) by short-pulse laser direct patterning. Compared to unpatterned YAG:Ce CPP with smooth surface, the forward-to-total ratio of emission photons of patterned YAG:Ce CPPs was enhanced from 53.2% up to 78.2%, and the total emission within 4-π degree is 6% higher. The fabricated patterns are also beneficial in increasing the color conversion efficiency of YAG:Ce CPPs by 7.6%. The patterned YAG:Ce CPPs display much better correlated color temperature (CCT) uniformity under varied currents. The angular correlated color temperature uniformity (ACU) of patterned YAG:Ce CPPs reaches as high as 0.933 compared to 0.730 of the unpatterned one. These results suggest that laser patterning of YAG:Ce CPP could effectively manipulate its luminance, chromaticity and illumination pattern, which may lead to further technological advancements for diversified applications of film-type CPPs in highly efficient white LEDs.

In search of quantum-limited contact resistance: understanding the intrinsic and extrinsic effects on the graphene–metal interface

Owing to its two-dimensional structure, graphene is extremely sensitive to surface contamination. Conventional processing techniques inevitably modify graphene’s intrinsic properties by introducing adsorbents and/or defects which limit device performance and understanding the intrinsic properties of graphene. Here we demonstrate femtosecond laser direct patterning of graphene microstructures, without the aid of resists or other chemicals, that enables us to study both intrinsic and extrinsic effects on the graphene–metal interface. The pulsed femtosecond laser was configured to ablate epitaxial graphene (EG) on a sub-micrometer scale and form a precisely defined region without damaging the surrounding material or substrate. The ablated area was sufficient to electrically isolate transfer length measurement structures and Hall devices for subsequent transport measurements. Using pristine and systematically contaminated surfaces, we found that Ni does not form bonds to EG synthesized on SiC in contrast to the well-known C–Ni bond formation for graphene synthesized on metals; known as end-contacting. Without end-contacting, the contact resistance (RC) of Ni to pristine and resist-contaminated EG are one and two orders of magnitude larger, respectively, than the intrinsic quantum limited contact resistance. The range of reported RC values is explained using carrier transmission probability, as exemplified by the Landauer–Büttiker model, which is dependent on the presence or absence of end-contacts and dopant/work-function mediated conduction. The model predicts the need for both end-contacts and a clean graphene–metal interface as necessary conditions to approach quantum limited contact resistance.

The Coupled Photothermal Reaction and Transport in a Laser Additive Metal Nanolayer Simultaneous Synthesis and Pattering for Flexible Electronics.

The Laser Direct Synthesis and Patterning (LDSP) technology has advantages in terms of processing time and cost compared to nanomaterials-based laser additive microfabrication processes. In LDSP, a scanning laser on the substrate surface induces chemical reactions in the reactive liquid solution and selectively deposits target material in a preselected pattern on the substrate. In this study, we experimentally investigated the effect of the processing parameters and type and concentration of the additive solvent on the properties and growth rate of the resulting metal film fabricated by this LDSP technology. It was shown that reactive metal ion solutions with substantial viscosity yield metal films with superior physical properties. A numerical analysis was also carried out the first time to investigate the coupled opto-thermo-fluidic transport phenomena and the effects on the metal film growth rate. To complete the simulation, the optical properties of the LDSP deposited metal film with a variety of thicknesses were measured. The characteristics of the temperature field and the thermally induced flow associated with the moving heat source are discussed. It was shown that the processing temperature range of the LDSP is from 330 to 390 K. A semi-empirical model for estimating the metal film growth rate using this process was developed based on these results. From the experimental and numerical results, it is seen that, owing to the increased reflectivity of the silver film as its thickness increases, the growth rate decreases gradually from about 40 nm at initial to 10 nm per laser scan after ten scans. This self-controlling effect of LDSP process controls the thickness and improves the uniformity of the fabricated metal film. The growth rate and resulting thickness of the metal film can also be regulated by adjustment of the processing parameters, and thus can be utilized for controllable additive nano/microfabrication.

Laser Direct Patterning of Dry Etch BCB Adhesive Layers for Low Temperature Permanent Wafer-to-Wafer Bonding

To enable advanced wafer level packaging approaches for devices like MEMS, image sensors or optical elements, wafer-to-wafer bonding processes using structured low temperature curable adhesives are required. A lot of Benzocyclobutene (BCB)-based wafer bonding works have been reported in the past showing a broad range of applications and good performance, but also some limitations such as long bond cycles and high cure temperature of 250 °C. In 2013 new process concepts were demonstrated [1], showing that wafer bond cycle time can be reduced to less than 10 min and a post bond batch cure at temperatures below 200 °C can be used to significantly shrink the overall cost of a BCB-based adhesive wafer bonding process. In order to create a patterned BCB bond layer, photo structuring of CYCLOTENE ® 4000 Resin is one solution. However, due to the decreased flow capability of that material after exposure, high bond forces and extended bonding times during wafer bonding as well as nearly flat surfaces with low topography are required for void-free bonding. To overcome these limitations, an increased material flow capability during wafer bonding is required. In this context non-photo sensitive CYCLOTENE ® 3000 Resin is suitable, since it has excellent flow capability in non-cured state. However, non-cured CYCLOTENE ® 3000 Resin cannot be structured with standard dry etching processes using a photo resist layer as mask. In order to enable patterned adhesive bonding based on CYCLOTENE ® 3000 Resin, alternative structuring methods have to be evaluated. One method was presented in [1] which is transfer printing of CYCLOTENE ® 3000 Resin from a help wafer to topography features of the device wafer. Although very good results were obtained, the method is restricted to applications with significant topography to enable the transfer printing. In this work we focus on a new structuring method for non-cured BCB layers formed from CYCLOTENE ® 3000 Resin. The layers were spin coated, baked and subsequently patterned using a 248 nm excimer laser stepper. The system features a 2.5× mask projection with a resulting exposure field of 6.5 × 6.5 mm2 and allows a direct ablation patterning of polymers. By using this method bond frame structures were patterned into 5 μm thick BCB layers at 200 mm silicon wafers. The wafers with the structured adhesive were bonded at 80 °C and 0.2 MPa for 5 minutes with 200 mm glass wafers. The bonded wafer stacks were subsequently post bond batch cured at 190 °C. Wafer dicing and shear tests of the bonded structures revealed excellent mechanical robustness of the BCB bond frames. The paper will review the new BCB wafer bond processes for supporting short cycle times with special focus on the new patterning approach by laser ablation. Process flow description as well as systematical analysis of pattern reproducibility of the new structuring method is part of the discussion.

High Performance All-Solid-State Flexible Micro-Pseudocapacitor Based on Hierarchically Nanostructured Tungsten Trioxide Composite.

Microsupercapacitors (MSCs) are promising energy storage devices to power miniaturized portable electronics and microelectromechanical systems. With the increasing attention on all-solid-state flexible supercapacitors, new strategies for high-performance flexible MSCs are highly desired. Here, we demonstrate all-solid-state, flexible micropseudocapacitors via direct laser patterning on crack-free, flexible WO3/polyvinylidene fluoride (PVDF)/multiwalled carbon nanotubes (MWCNTs) composites containing high levels of porous hierarchically structured WO3 nanomaterials (up to 50 wt %) and limited binder (PVDF, <25 wt %). The work leads to an areal capacitance of 62.4 mF·cm–2 and a volumetric capacitance of 10.4 F·cm–3, exceeding that of graphene based flexible MSCs by a factor of 26 and 3, respectively. As a noncarbon based flexible MSC, hierarchically nanostructured WO3 in the narrow finger electrode is essential to such enhancement in energy density due to its pseudocapacitive property. The effects of WO3/PVDF/MWCNTs composite composition and the dimensions of interdigital structure on the performance of the flexible MSCs are investigated.

Laser direct patterning of AgNW/CNT hybrid thin films

A hybrid material composed of silver nanowires (AgNWs) and carbon nanotubes (CNTs) is investigated by a laser direct patterning method. A femtosecond laser system with a wavelength of 1027nm and a pulse width of 380fs is applied for the patterning of AgNW/CNT hybrid film. The Gaussian and square quasi-flat-top beam profiles are used for the patterning lines. The laser fluence and overlapping rate were optimized for patterning at 67.9mJ/cm2 and 70%, respectively. The patterned AgNW/CNT film is evaluated using an optical microscope and scanning electron microscope. The partially ablated area of AgNW/CNT films around the patterned line is observed and discussed. The measurement results explain that the uniformity of the laser beam profile and the beam shape are key factors for development of AgNW/CNT films with fine edges.

Fabrication of Copper Wire Using Glyoxylic Acid Copper Complex and Laser Irradiation in Air

Preparation of a glyoxylic acid copper complex and fabrication of fine copper wire by CO2 laser irradiation in air to a thin film of that complex have been investigated. Irradiating laser to the complex thin film spin-coated on a glass substrate, thin film of metallic copper was fabricated in areas that were subjected to laser irradiation in air. The thickness of this thin copper film was approx. 30 to 40 nm, and as non-irradiated areas were etched and removed by a soluble solvent of the copper complex, fine copper wire with 200 μm width was formed by laser direct patterning. The resistivity of this thin copper film depended on the irradiation intensity of the laser and was 3.0 × 10–5 Ω·cm at 12 W intensity (sweep speed: 20 mm/s). This method enables the high-speed deposition of copper wiring in air by a printing process, indicating an inexpensive and useful process for fabricating copper wiring.