Selective Laser-induced Etching Research Articles

88‐3: Fast Selective Laser‐Induced Etching and Asymmetric 3D Hologram Laser Beam for Narrow Bezel Thin Display †

Here we demonstrate fast selective laser‐induced etching (SLE) process with three‐dimensional (3D) hologram optics to reduce display bezel thickness with cost effective methods. To apply fast SLE for display manufacturing, one‐side etching process should be presumed to protect display active area. We developed one‐side selective laser‐induced etching with asymmetric 3D hologram laser beam satisfying with commercial mechanical strength. Faster etch process having etch rate 10 µm/min than common SLE, 1~3 µm/min was developed. Furthermore, we achieve that bezel thickness is 100 µm shorter than wheel scribing and CNC grinding.

Ultra‐high Aspect Ratio TGV Perforation Utilizing Selective Laser‐induced Etching with Nanochannels

At present, perforation of high aspect ratio through glass vias (TGVs) is one of the primary factors limiting the development of glass interposers. This study is based on a large number of experiments, combined with mechanistic analysis, to realize the perforation of ultra‐high/high aspect ratio fused silica TGVs using selective laser‐induced etching (SLE). Firstly, the effect of the number of pulses as well as other laser parameters on the etching selectivity is systematically investigated. It is found that the formation of nanochannels in fused silica is crucial in determining the high selectivity. Subsequently, a model based on diffusion theory is proposed to mathematically explain the reasons for the high selectivity generation. Finally, the perforations of TGVs with diameters of 5.4 µm ‐ 26.4 µm, aspect ratios of 11.7 ‐ 61.3 and vertical sidewalls are achieved, at a laser treatment speed of approximately 10,000 TGVs per minute. This research can serve as an essential reference for the manufacturing of TGVs with high aspect ratios and glass interposers with high interconnection density.This article is protected by copyright. All rights reserved.

Local analysis of micro mixing for the Villermaux-Dushman protocol by using the imaging UV-Vis spectroscopy

The Villermaux-Dushman protocol with UV-Vis analytics is an established tool to characterize the global micro mixing performance in process equipment. The local mixing process is described by a micro mixing model (incorporation model), originally designed for turbulent flows. The novel imaging UV-Vis spectroscopy used in this work uncovers locally resolved micro mixing phenomena in a laminar split-and-recombine (SAR) mixer unit manufactured from selective laser-induced etching (SLE). The local absorbance is recorded with a high spatial resolution camera through a telecentric lens and post-processed into local concentration fields of components. The method unveils discrepancies of the micro mixing time determined from the conventional incorporation model in laminar flow and the locally recorded mixing process. The micro mixing time rather needs to be seen as a mean micro mixing time instead. Furthermore, the spatial information obtained by the imaging UV-Vis spectroscopy gives insight into local micro mixing and selectivity, yielding new approaches to equipment optimization.

Effect of in-plane and out-of-plane bifurcated microfluidic channels on the flow of aggregating red blood cells.

The blood flow through our microvascular system is a renowned difficult process to understand because the complex flow behavior of blood is intertwined with the complex geometry it has to flow through. Conventional 2D microfluidics has provided important insights, but progress is hampered by the limitation of 2-D confinement. Here we use selective laser-induced etching to excavate non-planar 3-D microfluidic channels in glass that consist of two generations of bifurcations, heading towards more physiological geometries. We identify a cross-talk between the first and second bifurcation only when both bifurcations are in the same plane, as observed in 2D microfluidics. Contrarily, the flow in the branch where the second bifurcation is perpendicular to the first is hardly affected by the initial distortion. This difference in flow behavior is only observed when red blood cells are aggregated, due to the presence of dextran, and disappears by increasing the distance between both generations of bifurcations. Thus, 3-D structures scramble in-plane flow distortions, exemplifying the importance of experimenting with truly 3D microfluidic designs in order to understand complex physiological flow behavior.

Extensional rheometry of mobile fluids. Part I: OUBER, an optimized uniaxial and biaxial extensional rheometer

Numerical optimization of a “six-arm cross-slot” device yields several three-dimensional shapes of fluidic channels that impose close approximations to an ideal uniaxial (biaxial) stagnation point extensional flow under the constraints of having four inlets and two outlets (two inlets and four outlets) and for Newtonian creeping flow. One of the numerically designed geometries is considered suitable for fabrication at the microscale, and numerical simulations with the Oldroyd-B and Phan-Thien and Tanner models confirm that the optimal flow fields are observed in the geometry for both constant viscosity and shear thinning viscoelastic fluids. The geometry, named the optimized uniaxial and biaxial extensional rheometer (OUBER), is microfabricated with high precision by selective laser-induced etching of a fused-silica substrate. Employing a refractive index-matched viscous Newtonian fluid, microtomographic-particle image velocimetry enables the measurement of the flow field in a substantial volume around the stagnation point. The flow velocimetry, performed at low Reynolds number (<0.1), confirms the accurate imposition of the desired and predicted flows, with a pure extensional flow at an essentially uniform deformation rate being applied over a wide region around the stagnation point. In Part II of this paper [Haward et al., J. Rheol. 67, 1011–1030 (2023)], pressure drop measurements in the OUBER geometry are used to assess the uniaxial and biaxial extensional rheometry of dilute polymeric solutions, in comparison to measurements made in planar extension using an optimized-shape cross-slot extensional rheometer [OSCER, Haward et al., Phys. Rev. Lett. 109, 128301 (2012)].

Preclinical-grade microendoscope for optical coherence tomography and angiography inside the bladder

We present a preclinical-grade, forward-viewing endomicroscope for in-contact optical coherence tomography (OCT) and optical coherence angiography (OCA) imaging through the working channel of a conventional cystoscope. Beam scanning is achieved with a fiber scanner driven by a tubular piezoelectric actuator. A focusing lens at the fiber tip helps engineering of the operation frequency within a compact probe length to avoid lateral undersampling. Microstructuring of fused silica through selective laser-induced etching was used for manufacturing a self-aligning housing for the probe head. The entire micro-optical system is assembled and encapsulated within a custom-developed sterilizable packaging with 4.5 mm outer diameter. The presented design and fabrication strategy can be used for any forward-viewing probe, independent of its imaging modalities. We demonstrate OCT imaging within a 2.1-mm diameter field of view at a transverse resolution of 19 μm and microvasculature visualization through OCA. The presented probe’s mechanical characteristics and optical performance make it particularly attractive for outpatient care use in the detection of tissue pathology inside the bladder. The presented fabrication methodology provides a reliable strategy for enabling preclinical trials with endoscopic imaging probes.

A 3D Miniaturized Glass Magnetic-Active Centrifugal Micropump Fabricated by SLE Process and Laser Welding

A miniaturized pump to manipulate liquid flow in microchannels is the key component of microfluidic devices. Many researchers have demonstrated active microfluidic pumps, but most of them still required additional large peripherals to operate their micropumps. In addition, those micropumps were made of polymer materials so that their application may be limited to a variety of fields that require harsh conditions at high pressures and temperatures or organic solvents and acid/base. In this work, we present a 3D miniaturized magnetic-driven glass centrifugal pump for microfluidic devices. The pump consists of a volute structure and a 3D impeller integrated with two magnet disks of Φ1 mm. The 3D pump structure was 13 mm × 10.5 mm × 3 mm, and it was monolithically fabricated in a fused silica sheet by selective laser-induced etching (SLE) technology using a femtosecond laser. The pump operation requires only one motor rotating two magnets. It was Φ42 mm × 54 mm and powered by a battery. To align the shaft of the motor to the center of the 3D glass pump chip, a housing containing the motor and the chip was fabricated, and the overall size of the proposed micropump device was 95 mm × 70 mm × 75 mm. Compared with other miniaturized pumps, ours was more compact and portable. The output pressure of the fabricated micropump was between 215 Pa and 3104 Pa, and the volumetric flow rate range was 0.55 mL/min and 7.88 mL/min. The relationship between the motor RPM and the impeller RPM was analyzed, and the flow rate was able to be controlled by the RPM. With its portability, the proposed pump can be applied to produce an integrated and portable microfluidic device for point-of-care analysis.

A Novel Approach for Visualizing Mixing Phenomena of Reactive Liquid-Liquid Flows in Milli- and Micro-Channels

Modular milli- and micro-structured systems represent a promising approach to exploit the potential of micro-process technology, including precise reaction control and scale-up. A major drawback of micro-structured devices is fouling and mixing mechanisms need to be investigated phenomenologically to better understand the processes that lead to fouling. Previous work was conducted to resolve 3D concentration fields by means of Laser-Induced Fluorescence (LIF) using a Confocal Laser Scanning Microscope (CLSM) (Frey et al., J Flow Chem, 2021, 11, 599–609). While the CLSM-LIF method yields detailed insight into concentration fields down to a few micrometers, it is limited to stationary flow structures only. Aubin et al. (Chemical Engineering Science, 2010, 65, 2065–2093) give a comprehensive review of methods to analyze mixing behavior. Most recent optical measurement methods rely on the detection of a single compound in mixtures. In case of reactive mixing, Tthe state of the art procedures to locally visualize micro mixing relies on tracking a reaction product which forms on molecular scale. In literature, only small micro-structures are manufactured from transparent materials, however larger milli-structures often lack optical accesses with sufficient quality. Selective laser-induced etching (SLE) is a new technique which enables the fabrication of larger milli-structures in transparent materials that are relevant for industry-scale applications. This work develops a method based on a concept of Kexel et al. (Chemie Ingenieur Technik, 2021, 93, 830–837) visualizing the selectivity of a competitive-consecutive gas-liquid reaction in a Taylor bubble flow. The main goal of this work is the analysis of the absorbance spectra of bromothymol blue (BTB) at different pH values in a miscible liquid-liquid system in a fused silica split-and-recombine mixer. The milli-structure of the mixer is manufactured by means of SLE. Backlight at different wavelengths is pulsed matching the recording frequency. In contrast to conventional UV/Vis setups, the absorbance is recorded locally within the mixer. The proposed method yields the 2D concentration distribution of multiple species with high spatial resolution. The spatially resolved reactant and product distribution unveils micro mixing and can yield important information about local root causes of fouling.

Non-Newtonian flows and instabilities in 3D glass microfluidic devices

<h2>Abstract</h2> In this virtual seminar we will discuss the use of selective laser-induced etching (SLE) for the fabrication of glass microfluidic devices, in particular for the study of non-Newtonian fluid dynamics problems [1]. SLE enables the precise monolithic fabrication of three-dimensional (3D) channels and structures embedded in a rigid and transparent fused-silica substrate, and thus provides opportunities for a wealth of novel microscale flow experiments. We will highlight various recent and ongoing microfluidic projects from our laboratory that have been made possible by SLE fabrication. Our focus will be on flows of viscoelastic wormlike micellar and polymer solutions in microscale geometries featuring, for instance, slender rigid or cantilevered posts [2,3]. 3D intersections [4,5], and axisymmetric contraction/expansions [6]. We make use of state-of-the-art quantitative techniques such as high-speed flow-induced birefringence imaging and volumetric 3-component micro-particle image velocimetry to characterize and understand purely-elastic and inertioelastic flow instabilities arising in these complex systems.

A Thermocycler Using a Chip Resistor Heater and a Glass Microchip for a Portable and Rapid Microchip-Based PCR Device.

This study proposes a rapid and inexpensive thermocycler that enables rapid heating of samples using a thin glass chip and a cheap chip resistor to overcome the on-site diagnostic limitations of polymerase chain reaction (PCR). Microchip PCR devices have emerged to miniaturize conventional PCR systems and reduce operation time and cost. In general, PCR microchips require a thin-film heater fabricated through a semiconductor process, which is a complicated process, resulting in high costs. Therefore, this investigation substituted a general chip resistor for a thin-film heater. The proposed thermocycler consists of a compact glass microchip of 12.5 mm × 12.5 mm × 2 mm that could hold a 2 μL PCR sample and a surface-mounted chip resistor of 6432 size (6.4 mm × 3.2 mm). Improving heat transfer from the chip resistor heater to the PCR reaction chamber in the microchip was accomplished via the design and fabrication of a three-dimensional chip structure using selective laser-induced etching, a rapid prototyping technique that allowed to be embedded. The fabricated PCR microchip was combined with a thermistor temperature sensor, a blower fan, and a microcontroller. The assembled thermocycler could heat the sample at a maximum rate of 28.8 °C/s per second. When compared with a commercially available PCR apparatus running the same PCR protocol, the total PCR operating time with a DNA sample was reduced by about 20%.

Manufacturing and assembly of an all-glass OCT microendoscope

We present a forward-looking, fiber-scanning endomicroscope designed for optical coherence tomography (OCT) and OCT-Angiography (OCT-A) imaging through the working channel of commercial gastrointestinal endoscopes and cystoscopes. 3.4 mm in outer diameter and 11.9 mm in length, the probe is capable of high-resolution volumetric imaging with a field-of-view of up to 2.6 mm and an imaging depth of up to 1.5 mm at a lateral resolution of 19 µm. A high-precision lens mount fabricated in fused silica using selective laser-induced etching (SLE) allows the tailoring of the optical performance for different imaging requirements. A glass structure fabricated by the same method encapsulates the optical and mechanical components, providing ease of assembly and alignment accuracy. The concept can be adapted to high resolution OCT/-A imaging of various organs, particularly in the gastrointestinal tract and bladder.

Advances in manufacturing spinal cord implant using 3D selective laser induced etching of fused silica

Spinal cord injury (SCI) results in its dysfunction and can lead to permanent paralysis. We developed a mechanical microconnector system (mMS) to support regeneration after the SCI. This paper describes a new fabrication process of the mMS using selective laser induced etching (SLE). This technique enables the 3D microstructuring of fused silica and promises rapid and highly individualizable mMS. We show that the SLE process enhances the fabrication with regard to complexity, speed and quality. An individual mMS is produced in less than 48h hours with structures from 4µm to 1mm.

Integration of segmented microflow chemistry and online HPLC/MS analysis on a microfluidic chip system enabling enantioselective analyses at the nanoliter scale.

In this work, we introduce an approach to merge droplet microfluidics with an HPLC/MS functionality on a single chip to analyze the contents of individual droplets. This is achieved by a mechanical rotor-stator interface that precisely positions a microstructured PEEK rotor on a microfluidic chip in a pressure-tight manner. The developed full-body fused silica chip, manufactured by selective laser-induced etching, contained a segmented microflow compartment followed by a packed HPLC channel, which were interconnected by the microfluidic PEEK rotor on the fused silica lid with hair-thin through-holes. This enabled the targeted and leakage-free transfer of 10 nL fractions of droplets as small as 25 nL from the segmented microflow channel into the HPLC compartment that operated at pressures of up to 60 bar. In a proof of concept study, this approach was successfully applied to monitor reactions at the nanoliter scale and to distinguish the formed enantiomers.

Viscous flow through microfabricated axisymmetric contraction/expansion geometries

We employ a state-of-the-art microfabrication technique (selective laser-induced etching) to fabricate a set of axisymmetric microfluidic geometries featuring a 4:1 contraction followed by a 1:4 downstream expansion in the radial dimension. Three devices are fabricated: the first has a sudden contraction followed by a sudden expansion, the second features hyperbolic contraction and expansion profiles, and the third has a numerically optimized contraction/expansion profile intended to provide a constant extensional/compressional rate along the axis. We use micro-particle image velocimetry to study the creeping flow of a Newtonian fluid through the three devices and we compare the obtained velocity profiles with finite-volume numerical predictions, with good agreement. This work demonstrates the capability of this new microfabrication technique for producing accurate non-planar microfluidic geometries with complex shapes and with sufficient clarity for optical probes. The axisymmetric microfluidic geometries examined have potential to be used for the study of the extensional properties and non-linear dynamics of viscoelastic flows, and to investigate the transport and deformation dynamics of bubbles, drops, cells, and fibers.Graphic abstract

Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs.

Pressure limitations of many microfluidic platforms have been a significant challenge in microfluidic experimental studies of fractured media. As a result, these platforms have not been fully exploited for direct observation of high-pressure transport in fractures. This work introduces microfluidic platforms that enable direct observation of multiphase flow in devices featuring surrogate permeable media and fractured systems. Such platforms provide a pathway to address important and timely questions such as those related to CO2 capture, utilization and storage. This work provides a detailed description of the fabrication techniques and an experimental setup that may serve to analyze the behavior of supercritical CO2 (scCO2) foam, its structure and stability. Such studies provide important insights regarding enhanced oil recovery processes and the role of hydraulic fractures in resource recovery from unconventional reservoirs. This work presents a comparative study of microfluidic devices developed using two different techniques: photolithography/wet-etching/thermal-bonding versus Selective Laser-induced Etching. Both techniques result in devices that are chemically and physically resistant and tolerant of high pressure and temperature conditions that correspond to subsurface systems of interest. Both techniques provide pathways to high-precision etched microchannels and capable lab-on-chip devices. Photolithography/wet-etching, however, enables fabrication of complex channel networks with complex geometries, which would be a challenging task for laser etching techniques. This work summarizes a step-by-step photolithography, wet-etching and glass thermal-bonding protocol and, presents representative observations of foam transport with relevance to oil recovery from unconventional tight and shale formations. Finally, this work describes the use of a high-resolution monochromatic sensor to observe scCO2 foam behavior where the entirety of the permeable medium is observed simultaneously while preserving the resolution needed to resolve features as small as 10 µm.

High quality terahertz glass wave plates.

In this paper we present four λ/2-wave plates made out of fused silica glass for operation in the terahertz frequency range. The design of the wave plates is based on form birefringence. They were fabricated by selective laser-induced etching resulting in a series of glass bars separated by air grooves. Wave plates operating at single, two and several frequencies were designed, fabricated and characterized.

Steady viscoelastic flow around high-aspect-ratio, low-blockage-ratio microfluidic cylinders

We employ a state-of-the-art microfabrication technique (selective laser-induced etching, SLE) to produce microfluidic cylinder geometries that explore new geometrical regimes. Using SLE, two microchannels are fabricated in monolithic fused silica substrate with height H=2 mm and width W=0.4 mm (aspect ratio α=H/W=5) containing cylinders of radius r=0.02 mm (blockage ratio β=2r/W=0.1), centered at the channel mid-width, W/2. An ‘sc’ channel contains a single cylinder, while a ‘dc’ channel contains two axially-aligned cylinders separated by a distance L=1 mm (L=50r). Compared with cylinder geometries fabricated by soft lithography (which typically have α ≪ 1 and β ≳ 0.5), these rigid glass devices provide a quasi-two-dimensional flow along the direction of the cylinder axis and also more clearly reveal the effects of the strong extensional wake regions located at the leading and trailing stagnation points. Using flow velocimetry and quantitative birefringence measurement techniques, we study the behaviour of a well-characterized viscoelastic polymer solution in flow around the cylinders. The small cylinder radii result in low inertia and very high elasticity numbers El ≈ 2400. For the sc device, we report strong flow modification effects around the cylinder as the flow rate is incremented. This is associated with the deformation of polymer molecules primarily in the upstream wake region, leading to the onset of a purely elastic flow asymmetry upstream of the cylinder. Stretched polymer molecules are advected around the cylinder and relax downstream of the cylinder, resulting in an extremely long elastic wake extending for > 300r downstream. In the dc channel, at lower flow rates, similar flow modification effects are observed to develop around, and downstream of, both cylinders. However, at higher flow rates the wake of the first cylinder extends > 50r downstream, and begins to interact with the second cylinder. The second cylinder becomes encapsulated by the wake of the first and is effectively obviated from the flow field. The results will be of relevance to understanding practical applications of viscoelastic fluids, for example in particle suspension and porous media flows, and also for benchmarking against numerical simulations using viscoelastic constitutive models.

Simulation of the dynamics of heat accumulation during in-volume modification with ultrashort laser pulses

Working with ultrashort pulsed (USP) laser systems with high repetition rates ≥ 100 kHz, heat accumulation effects evolve and subsequently the absorption becomes linear. As a consequence, the process dynamics change significantly. Structuring glasses with those USP Lasers leads to melted lines that are used for waveguides, welding or selective laser-induced etching whose resulting qualities are strongly depending of the structuring results and given smoothness. We perform simulations during in-volume modification processes, by recalculating the absorption behavior in between the iteration steps of heat accumulation. The simulation results provide explanations for smoothness or non-smoothness of modifications comparable to experiments in glass.

Selective Laser-Induced Etching of 3D Precision Quartz Glass Components for Microfluidic Applications—Up-Scaling of Complexity and Speed

By modification of glasses with ultrafast laser radiation and subsequent wet-chemical etching (here named SLE = selective laser-induced etching), precise 3D structures have been produced, especially in quartz glass (fused silica), for more than a decade. By the combination of a three-axis system to move the glass sample and a fast 3D system to move the laser focus, the SLE process is now suitable to produce more complex structures in a shorter time. Here we present investigations which enabled the new possibilities. We started with investigations of the optimum laser parameters to enable high selective laser-induced etching: surprisingly, not the shortest pulse duration is best suited for the SLE process. Secondly we investigated the scaling of the writing velocity: a faster writing speed results in higher selectivity and thus higher precision of the resulting structures, so the SLE process is now even suitable for the mass production of 3D structures. Finally we programmed a printer driver for commercial CAD software enabling the automated production of complex 3D glass parts as new examples for lab-on-a-chip applications such as nested nozzles, connectors and a cell-sorting structure.

Zero-dead-volume interfaces for two-dimensional electrophoretic separations.

We present the study on the sample transfer characteristics of two different microfluidic interfaces for 2D-CE . These interfaces were manufactured using two different microfabrication technologies: one was obtained via the classical photolithography-wet etching-anodic-bonding process; and the other was obtained via the selective laser-induced etching process. The comparison of the two interfaces, and an intact capillary as a reference, was made via the CE separation of amino acids (arginine and lysine) under different bulk flow conditions, with and without applying bias potential to the secondary channels. The influence on peak shapes, migration times, and repeatabiliy were evaluated.