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A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "E：Engineering and Technology".

Deadline for manuscript submissions: closed (31 January 2022) | Viewed by 29645

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Special Issue Editors

Prof. Dr. Yee Cheong Lam

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Guest Editor

School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
Interests: microfluidics; laser material interaction; injection molding

Prof. Dr. Rafael Taboryski

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Guest Editor

DTU Nanolab, National Centre for Nano Fabrication and Characterization, Technical University of Denmark, Ørsted Plads, Building 347, DK-2800 Kgs. Lyngby, Denmark
Interests: micro- and nanofabrication; fabrication of polymer micro- and nanostructures; anti-reflecting surfaces; plasmonic metasurfaces; microfluidics; surface wetting properties
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Manufacturing is an important and challenging field, upon which the wellbeing of our society is dependent. The increasing demands for miniaturisation have resulted in steady innovations and developments in micro- and nanofabrication. Generally speaking, there are two distinct approaches, namely top-down or bottom-up fabrication processes. Top-down fabrication is well established, but has continuously been undergoing considerable advancements driven by the semiconductor and manufacturing industries; new processes, approaches, and equipment are constantly being developed for improving the reliability of processes, lowering their cost, and making them more environmentally friendly and able to satisfy new demands and applications.

This Special Issue of Micromachines focuses on top-down micro- and nanofabrication. It will serve as a platform for communication of the latest developments and innovations in top-down micro- and nanofabrication and/or their applications. Researchers are invited to contribute with manuscripts that address the various challenges and opportunities in this field. Contributions covering the following topics, in addition to any related to the topic of the Special Issue, are welcome:

Precision machining;
Laser machining;
Die manufacturing;
New lithographical methods;
Manufacturing system/equipment and tools;
Surface properties and characterization;
Reliability, consistency, and metrology;
Semiconductor/optical/bio/medical applications;
Precision molding and forming;
Non-traditional manufacturing technology.

Prof. Dr. Yee Cheong Lam
Prof. Dr. Rafael J. Taboryski
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Related Special Issue

Micro/Nano Fabrication in Micromachines (10 articles)

Published Papers (10 papers)

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Research

Jump to: Review

15 pages, 15668 KiB

Open AccessArticle

Multi-Foci Laser Separation of Sapphire Wafers with Partial Thickness Scanning

by Celescia Siew Mun Lye, Zhongke Wang and Yee Cheong Lam

Micromachines 2022, 13(4), 506; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13040506 - 24 Mar 2022

Cited by 3 | Viewed by 1736

Abstract

With multi-foci laser cutting technology for sapphire wafer separation, the entire cross-section is generally scanned with single or multiple passes. This investigation proposes a new separation technique through partial thickness scanning. The energy effectivity and efficiency of the picosecond laser were enhanced through a two-zone partial thickness scanning by exploiting the internal reflection at the rough exit surface. Each zone spanned only one-third thickness of the cross-section, and only two out of three zones were scanned consecutively. A laser beam of 0.57 W and 50 kHz pulse repetition rate was split into 9 foci, each with a 2.20 μm calculated focused spot diameter. By only scanning the top two-thirds sample thickness, first its middle section then upper section, a cleavable sample could result. This was achieved with the lowest energy deposition at the fastest scanning speed of 10 mm/s investigated. Although with partial thickness scanning only, counter intuitively, the cleaved sample had a previously unattained uniform roughened sidewall profile over the entire thickness. This is a desirable outcome in LED manufacturing. As such, this proposed scheme could attain a cleavable sample with the desired uniformly roughened sidewall profile with less energy usage and faster scanning speed. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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12 pages, 2195 KiB

Open AccessArticle

Realization of Three-Dimensionally MEMS Stacked Comb Structures for Microactuators Using Low-Temperature Multi-Wafer Bonding with Self-Alignment Techniques in CMOS-Compatible Processes

by Adrian J. T. Teo and King Ho Holden Li

Micromachines 2021, 12(12), 1481; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12121481 - 29 Nov 2021

Cited by 4 | Viewed by 2419

Abstract

A high-aspect-ratio three-dimensionally (3D) stacked comb structure for micromirror application is demonstrated by wafer bonding technology in CMOS-compatible processes in this work. A vertically stacked comb structure is designed to circumvent any misalignment issues that could arise from multiple wafer bonding. These out-of-plane comb drives are used for the bias actuation to achieve a larger tilt angle for micromirrors. The high-aspect-ratio mechanical structure is realized by the deep reactive ion etching of silicon, and the notching effect in silicon-on-insulator (SOI) wafers is minimized. The low-temperature bonding of two patterned wafers is achieved with fusion bonding, and a high bond strength up to 2.5 J/m² is obtained, which sustains subsequent processing steps. Furthermore, the dependency of resonant frequency on device dimensions is studied systematically, which provides useful guidelines for future design and application. A finalized device fabricated here was also tested to have a resonant frequency of 17.57 kHz and a tilt angle of 70° under an AC bias voltage of 2 V. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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18 pages, 8479 KiB

Open AccessArticle

Multi-Foci Division of Nonlinear Energy Absorption on Ultrashort Pulse Laser Singulation of Sapphire Wafers

by Celescia Siew Mun Lye, Zhongke Wang and Yee Cheong Lam

Micromachines 2021, 12(11), 1328; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12111328 - 28 Oct 2021

Cited by 2 | Viewed by 1580

Abstract

The multi-foci division of through thickness nonlinear pulse energy absorption on ultrashort pulse laser singulation of single side polished sapphire wafers has been investigated. Firstly, it disclosed the enhancement of energy absorption by the total internal reflection of the laser beam exiting from an unpolished rough surface. Secondly, by optimizing energy distribution between foci and their proximity, favorable multi-foci energy absorption was induced. Lastly, for effective nonlinear energy absorption for wafer separation, it highlighted the importance of high laser pulse energy fluence at low pulse repetition rates with optimized energy distribution, and the inadequacy of increasing energy deposition through reducing scanning speed alone. This study concluded that for effective wafer separation, despite the lower pulse energy per focus, energy should be divided over more foci with closer spatial proximity. Once the power density per pulse per focus reached a threshold in the order of 1012 W/cm², with approximately 15

μ

m between two adjacent foci, wafer could be separated with foci evenly distributed over the entire wafer thickness. When the foci spacing reduced to 5

μ

m, wafer separation could be achieved with pulse energy concentrated only at foci distributed over only the upper or middle one-third wafer thickness. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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10 pages, 3304 KiB

Open AccessArticle

Fabrication of Multifocal Microlens Array by One Step Exposure Process

by Wei Yuan, Yajuan Cai, Cheng Xu, Hui Pang, Axiu Cao, Yongqi Fu and Qiling Deng

Micromachines 2021, 12(9), 1097; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12091097 - 11 Sep 2021

Cited by 6 | Viewed by 2125

Abstract

Microlenses can be widely used in integrated micro-optical systems. However, in some special applications, such as light field imaging systems, multifocal microlens arrays (MLA) are expected to improve imaging resolution. For the fabrication of multifocal MLA, the traditional fabrication method is no longer applicable. To solve this problem, a fabrication method of multifocal MLA by a one step exposure process is proposed. Through the analyses and research of photoresist AZ9260, the nonlinear relationship between exposure dose and exposure depth is established. In the design of the mask, the mask pattern is corrected according to the nonlinear relationship to obtain the final mask. The continuous surface of the multifocal MLA is fabricated by the mask moving exposure. The experimental results show that the prepared multifocal MLA has high filling factor and surface fidelity. What is more, this method is simple and efficient to use in practical applications. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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9 pages, 3240 KiB

Open AccessArticle

Laser Grinding of Single-Crystal Silicon Wafer for Surface Finishing and Electrical Properties

by Xinxin Li, Yimeng Wang and Yingchun Guan

Micromachines 2021, 12(3), 262; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12030262 - 04 Mar 2021

Cited by 6 | Viewed by 2771

Abstract

In this paper, we first report the laser grinding method for a single-crystal silicon wafer machined by diamond sawing. 3D laser scanning confocal microscope (LSCM), X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), laser micro-Raman spectroscopy were utilized to characterize the surface quality of laser-grinded Si. Results show that SiO₂ layer derived from mechanical machining process has been efficiently removed after laser grinding. Surface roughness Ra has been reduced from original 400 nm to 75 nm. No obvious damages such as micro-cracks or micro-holes have been observed at the laser-grinded surface. In addition, laser grinding causes little effect on the resistivity of single-crystal silicon wafer. The insights obtained in this study provide a facile method for laser grinding silicon wafer to realize highly efficient grinding on demand. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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13 pages, 3340 KiB

Open AccessArticle

Dry Film Photoresist-Based Microfabrication: A New Method to Fabricate Millimeter-Wave Waveguide Components

by Sadia Farjana, Mohamadamir Ghaderi, Sofia Rahiminejad, Sjoerd Haasl and Peter Enoksson

Micromachines 2021, 12(3), 260; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12030260 - 03 Mar 2021

Cited by 7 | Viewed by 3610

Abstract

This paper presents a novel fabrication method based on dry film photoresists to realize waveguides and waveguide-based passive components operating at the millimeter-wave frequency (30–300 GHz). We demonstrate that the proposed fabrication method has a high potential as an alternative to other microfabrication technologies, such as silicon-based and SU8-based micromachining for realizing millimeter-wave waveguide components. Along with the nearly identical transfer of geometrical structures, the dry film photoresist offers other advantages such as fewer processing steps, lower production cost, and shorter prototyping time over the conventional micromachining technologies. To demonstrate the feasibility of the fabrication process, we use SUEX dry film to fabricate a ridge gap waveguide resonator. The resonator is designed to exhibit two resonances at 234.6 and 284 GHz. The measured attenuation at 234 GHz is 0.032 dB/mm and at 283 GHz is 0.033 dB/mm for the fabricated prototype. A comparative study among different existing technologies indicates that the reported method can give a better unloaded Q-value than other conventional processes. The measured unloaded Q-values are in good agreement with the simulated unloaded Q-values. The signal attenuation indicates that SUEX dry film photoresists can be used to fabricate passive devices operating at millimeter-wave frequencies. Moreover, this new fabrication method can offer fast and low-cost prototyping. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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12 pages, 5215 KiB

Open AccessArticle

Electrical Resistance Reduction Induced with CO₂ Laser Single Line Scan of Polyimide

by Zhongke Wang, Kok Keat Tan and Yee Cheong Lam

Micromachines 2021, 12(3), 227; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12030227 - 24 Feb 2021

Cited by 7 | Viewed by 1866

Abstract

We conducted a laser parameter study on CO₂ laser induced electrical conductivity on a polyimide film. The induced electrical conductivity was found to occur dominantly at the center of the scanning line instead of uniformly across the whole line width. MicroRaman examination revealed that the conductivity was mainly a result of the multi-layers (4–5) of graphene structure induced at the laser irradiation line center. The graphene morphology at the line center appeared as thin wall porous structures together with nano level fiber structures. With sufficient energy dose per unit length and laser power, this surface modification for electrical conductivity was independent of laser pulse frequency but was instead determined by the average laser power. High electrical conductivity could be achieved by a single scan of laser beam at a sufficiently high-power level. To achieve high conductivity, it was not efficient nor effective to utilize a laser at low power but compensating it with a slower scanning speed or having multiple scans. The electrical resistance over a 10 mm scanned length decreased significantly from a few hundred Ohms to 30 Ohms when energy dose per unit length increased from 0.16 J/mm to 1.0 J/mm, i.e., the laser power increased from 5.0 W to 24 W with corresponding power density of 3.44 × 10 W/cm² to 16.54 W/cm² respectively at a speed of 12.5 mm/s for a single pass scan. In contrast, power below 5 W at speeds exceeding 22.5 mm/s resulted in a non-conductive open loop. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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15 pages, 4954 KiB

Open AccessArticle

Redeposition-Free Deep Etching in Small KY(WO₄)₂ Samples

by Simen Mikalsen Martinussen, Raimond N. Frentrop, Meindert Dijkstra and Sonia Maria Garcia-Blanco

Micromachines 2020, 11(12), 1033; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11121033 - 24 Nov 2020

Cited by 1 | Viewed by 2439

Abstract

KY(WO₄)₂ is a promising material for on-chip laser sources. Deep etching of small KY(WO₄)₂ samples in combination with various thin film deposition techniques is desirable for the manufacturing of such devices. There are, however, several difficulties that need to be overcome before deep etching of KY(WO₄)₂ can be realized in small samples in a reproducible manner. In this paper, we address the problems of (i) edge bead formation when using thick resist on small samples, (ii) sample damage during lithography mask touchdown, (iii) resist reticulation during prolonged argon-based inductively coupled plasma reactive ion etching (ICP-RIE), and (iv) redeposited material on the feature sidewalls. We demonstrate the etching of 6.5 µm deep features and the removal of redeposited material using a wet etch procedure. This process will enable the realization of waveguides both in ion-irradiated KY(WO₄)₂ as well as thin KY(WO₄)₂ membranes transferred onto glass substrate by bonding and subsequent polishing. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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19 pages, 3151 KiB

Open AccessArticle

Rapid Fabrication of Membrane-Integrated Thermoplastic Elastomer Microfluidic Devices

by Alexander H. McMillan, Emma K. Thomée, Alessandra Dellaquila, Hussam Nassman, Tatiana Segura and Sasha Cai Lesher-Pérez

Micromachines 2020, 11(8), 731; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11080731 - 28 Jul 2020

Cited by 9 | Viewed by 6762

Abstract

Leveraging the advantageous material properties of recently developed soft thermoplastic elastomer materials, this work presents the facile and rapid fabrication of composite membrane-integrated microfluidic devices consisting of Flexdym^TM polymer and commercially available porous polycarbonate membranes. The three-layer devices can be fabricated in under 2.5 h, consisting of a 2-min hot embossing cycle, conformal contact between device layers and a low-temperature baking step. The strength of the Flexdym^TM-polycarbonate seal was characterized using a specialized microfluidic delamination device and an automated pressure controller configuration, offering a standardized and high-throughput method of microfluidic burst testing. Given a minimum bonding distance of 200 μm, the materials showed bonding that reliably withstood pressures of 500 mbar and above, which is sufficient for most microfluidic cell culture applications. Bonding was also stable when subjected to long term pressurization (10 h) and repeated use (10,000 pressure cycles). Cell culture trials confirmed good cell adhesion and sustained culture of human dermal fibroblasts on a polycarbonate membrane inside the device channels over the course of one week. In comparison to existing porous membrane-based microfluidic platforms of this configuration, most often made of polydimethylsiloxane (PDMS), these devices offer a streamlined fabrication methodology with materials having favourable properties for cell culture applications and the potential for implementation in barrier model organ-on-chips. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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Review

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25 pages, 2161 KiB

Open AccessReview

Biomimetic Functional Surfaces towards Bactericidal Soft Contact Lenses

by Tianyu Mao and Fengzhou Fang

Micromachines 2020, 11(9), 835; https://doi.org/10.3390/mi11090835 - 31 Aug 2020

Cited by 9 | Viewed by 3158

Abstract

The surface with high-aspect-ratio nanostructure is observed to possess the bactericidal properties, where the physical interaction between high-aspect-ratio nanostructure could exert sufficient pressure on the cell membrane eventually lead to cell lysis. Recent studies in the interaction mechanism and reverse engineering have transferred the bactericidal capability to artificial surface, but the biomimetic surfaces mimicking the topographical patterns on natural resources possess different geometrical parameters and surface properties. The review attempts to highlight the recent progress in bactericidal nanostructured surfaces to analyze the prominent influence factors and cell rupture mechanism. A holistic approach was utilized, integrating interaction mechanisms, material characterization, and fabrication techniques to establish inclusive insights into the topographical effect and mechano-bactericidal applications. The experimental work presented in the hydrogel material field provides support for the feasibility of potentially broadening applications in soft contact lenses. Full article

(This article belongs to the Special Issue Top-Down Micro- or Nanofabrication and Its Applications)

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