Ultraviolet Laser Micromachining Research Articles

Fabrication of durable haemophobic surfaces on cast acrylic sheets using UV laser micromachining

A low-cost, high-speed micro-scale patterning procedure for generation of durable blood-repellent patterns on polymers using continuous wave (CW) ultra-violet (UV) laser with optical lens arrangement is demonstrated in this work. A laser engraver which can generate patterned structures in the range of 1–300 µm employing a 5 W, 445 nm CW UV laser with collimating lens arrangement was developed for this purpose. Subsequently, cell cast high impact acrylic sheets of 5 cm × 5 cm size were patterned to generate fishbone architecture like microstructures with central structure footprint 71.3 µm, peripheral structure footprint 29.8 µm and peripheral structure spacing of 77.8 µm. The patterned acrylic was evaluated for hydrophobicity and human blood-repellent nature using a contact angle goniometer. Hardness tests for checking durability of the patterned surfaces for various biomedical applications were conducted using a hardness tester. The tested Vickers hardness of the acrylic patterned sample was 17.41 HV which indicates durability of the fabricated patterns. Maximum static contact angle of 142.3° and minimum roll-off angle of 11.7° observed for blood on patterned acrylic confirm the haemophobic nature of the fabricated surfaces.

Ultraviolet laser ablation as technique for defect repair of GaN-based light-emitting diodes

Defect repair of GaN-based light-emitting diodes (LEDs) by ultraviolet laser micromachining is reported. Percussion and helical drilling in GaN by laser ablation were investigated using 248 nm nanosecond and 355 nm picosecond pulses. The influence of laser ablation including different laser parameters on electrical and optical properties of GaN-based LED chips was evaluated. The results for LEDs on sapphire with transparent conductive oxide p-type contact on top as well as for thin-film LEDs are reported. A reduction of leakage current by up to six orders in magnitude and homogeneous luminance distribution after proper laser defect treatment were achieved.

Characterization of Polymer Fiber Bragg Grating With Ultrafast Laser Micromachining

We report that the main photosensitive mechanism of poly(methyl methacrylate)-based optical fiber Bragg grating (POFBG) under ultraviolet laser micromachining is a complex process of both photodegradation and negative thermo-optic effect. We found experimentally the unique characteristics of Bragg resonance splitting and reunion during the laser micromachining process providing the evidence of photodegradation, while the mean refractive index change of POFBG was measured to be negative confirming further photodegradation of polymer fiber. The thermal-induced refractive index change of POFBG was also observed by recording the Bragg wavelength shift. Furthermore, the dynamic thermal response of the micromachined-POFBG was demonstrated under constant humidity, showing a linear and negative response of around −47.1 pm/°C.

Effect of Fluence and Pulse Overlapping on Fabrication of Microchannels in PMMA/PDMS Via UV Laser Micromachining: Modeling and Experimentation

This article presents modeling and experimental investigations on the effects of process parameters and the viability of directly fabricating microchannels in polymethyl methacrylate (PMMA) and polydimethylsiloxane (PDMS) polymers which are suitable for the fabrication of microfluidic devices due to their biocompatibility and transparent properties. Experimental work was conducted using a solid-state Nd:YAG laser with 355 nm ultraviolet (UV) wavelength and 5 ns pulse duration at various energy densities and pulse overlapping (PO). The study was focused on understanding the effects of two main process parameters: fluence and PO. This study closely investigates the effect of varying process parameters on the ablation depth and profile achieved and the resultant microchannel dimensional quality. It presents findings indicating that both process parameters have strong effects on the profile shape and variability of the microchannel width and depth. For PMMA polymer, the lowest dimensional variability for the microchannel profile is obtained with low fluence values and highest PO factor, whereas for PDMS polymer, it was observed that microchannel width and depth decreased linearly with increasing fluence and increased nonlinearly with increasing scanning rate. Further, process modeling is utilized for predicting microchannel profile and ablation depth, and these predictions were validated with experimental results obtained with pulsed laser micromachining at UV wavelength.

Deep etch of GaN by laser micromachining

AbstractTrench formation for device isolation on GaN light‐emitting diode (LED) wafers via nanosecond ultraviolet laser micromachining is demonstrated. Owing to the dissimilar ablation thresholds between GaN and sapphire, the etch process terminates automatically at the GaN/sapphire interface. It was found that optimal focus offset, optimal pulse energy and high repetition rate are essential for obtaining a trench with tapered sidewall and smooth bottom surface, which is suitable for the conformal deposition of interconnects across the trench. This technique has been successfully applied to the rapid prototyping of interconnected LED arrays on a single chip. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Precision laser micromachining of trenches in GaN on sapphire

Trench formation for device isolation on GaN light-emitting diode (LED) wafers via nanosecond ultraviolet laser micromachining is demonstrated. Trenches with smooth sidewalls and flat bottom surfaces are produced. Unlike wafer scribing with laser beams, the formation of trenches requires that the incident fluence is sufficient for laser ablation of GaN, yet low enough to prevent ablation of the sapphire substrate. Owing to the dissimilar ablation thresholds between GaN and sapphire, the etch process terminates automatically at the GaN/sapphire interface. The effect of the following parameters on the trench properties and quality has been investigated: focus offset, pulse energy, pulse repetition rate, scan speed, and the number of scan passes. It was found that optimal focus offset and pulse energy, a high pulse repetition rate, and single cycle of slow scanning are the key factors for obtaining a trench with tapered sidewall and smooth bottom surface, which is suitable for the laying of interconnects conformally across the trench for device interconnection. This technique has been successfully applied to the rapid prototyping of interconnected LED arrays on a single chip, where metal interconnects run continuously across the micromachined trenches to connect the individual LED devices.

Deep ultraviolet laser micromachining of novel fibre optic devices

A deep ultraviolet F2 laser, with output at 157-nm wavelength, has been adopted for micro-shaping the end facets of single and multi-mode silica optical fibres. The high energy 7.9-eV photons drive strong interactions in the wide-bandgap silica fibres to enable the fabrication of surface-relief microstructures with high spatial resolution and smooth surface morphology. Diffraction gratings, focusing lenses, and Mach-Zehnder interferometric structures have been micromachined onto the cleaved-fibre facets and optically characterized. F2-laser micromachining is shown to be a rapid and facile means for direct-writing of novel infibre photonic components.

Microfabrication in free-standing gallium nitride using UV laser micromachining

Gallium nitride (GaN) and related alloys are important semiconductor materials for fabricating novel photonic devices such as ultraviolet (UV) light-emitting diodes (LEDs) and vertical cavity surface-emitting lasers (VCSELs). Recent technical advances have made free-standing GaN substrates available and affordable. However, these materials are strongly resistant to wet chemical etching and also, low etch rates restrict the use of dry etching. Thus, to develop alternative high-resolution processing for these materials is increasingly important. In this paper, we report the fabrication of microstructures in free-standing GaN using pulsed UV lasers. An effective method was first developed to remove the re-deposited materials due to the laser machining. In order to achieve controllable machining and high resolution in GaN, machining parameters were carefully optimised. Under the optimised conditions, precision features such as holes (through holes, blind or tapered holes) on a tens of micrometer length scale have been machined. To fabricate micro-trenches in GaN with vertical sidewalls and a flat bottom, different process strategies of laser machining were tested and optimised. Using this technique, we have successfully fabricated high-quality micro-trenches in free-standing GaN with various widths and depths. The approach combining UV laser micromachining and other processes is also discussed. Our results demonstrate that the pulsed UV laser is a powerful tool for fabricating precision microstructures and devices in gallium nitride.

Direct-Write Planar Microultracapacitors by Laser Engineering

We have successfully employed laser direct write and micromachining to fabricate high capacity hydrous ruthenium oxide or microultracapacitors. A laser direct-write process is used to deposit uniform pads of in sulfuric acid under ambient temperature and atmospheric conditions. Ultraviolet laser micromachining is used to tailor the shape and size of the deposited material into planar electrodes. The specific capacitance of the laser-deposited materials is comparable to reported values of ∼720 F/g. The microultracapacitors demonstrate linear charge and discharge behavior at currents below 1 mA, as expected for an ideal capacitor. By studying the charge storage and power output as a function of discharge current, the power can be successfully modeled assuming only simple ohmic losses. Parallel and series combinations of these microultracapacitor cells provide the expected addition of capacitance. Maximum discharge currents of 50 mA are applied to two cells in parallel without damage to the microultracapacitor cells. The microultracapacitors exhibit high specific power and specific energy with over 1100 mW/g at approximately 9 mWhr/g for an 80 μg cell with a footprint of 2 mm2 and a thickness of 15 μm. © 2003 The Electrochemical Society. All rights reserved.

Laser-based microscale patterning of biodegradable polymers for biomedical applications

In this paper, we throw light on current state of advancements in the field of biodegradable polymers and devices targeted at biomedical applications. A short introduction involving biodegradable polymers, various fabrication techniques for patterning biodegradable polymers and an extensive coverage of ultraviolet (UV) laser micromachining of polymers is presented. We also present UV laser micromachining of biodegradable polymers for potential biomedical applications. Micro-holes and microchannels, which are important features in many micro-devices, have been etched on biodegradable polymers by UV lasers. The morphology and surface conditions of the etched micro-features in the polymers are studied using SEM and surface profilometre. The effect of laser parameters such as laser wavelength and pulse energy on the etching quality is also investigated. This work on using UV laser for ablation of biodegradable polymers is the first of its kind.

Fabrication Of Mesoscale Energy Storage Systems By Laser Direct-Write

ABSTRACTOver the last two decades, there has been a trend towards the development of smaller and more autonomous electronic devices, yet the question of how to power these microdevices with correspondingly small power sources remains. To address this problem, we employ a laser forward-transfer process in combination with ultraviolet laser micromachining, to fabricate mesoscale electrochemical power sources, such as microbatteries and micro-ultracapacitors. This direct-write laser-engineering approach enables the deposition of battery materials (hydrous ruthenium oxide, manganese oxide, lithium cobalt oxide, etc.) under ambient temperature and atmospheric conditions, resulting in films with the desired morphological and electrochemical properties. Planar and stacked cell configurations are produced and tested for their energy storage and power delivery capabilities and exhibit favorable performance in comparison to current battery technology.