Special Issue "Printable and Flexible Electronics for Sensors"

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

Deadline for manuscript submissions: closed (31 May 2019).

Special Issue Editors

Prof. Jin-Woo Choi
E-Mail Website
Guest Editor
School of Electrical Engineering and Computer Science, Louisiana State University, Baton Rouge, LA, 70803, USA
Interests: BioMEMS; lab-on-a-chip; inkjet-printed sensors; paper-based sensors
Prof. Edward Song
E-Mail Website
Guest Editor
Department of Electrical and Computer Engineering, University of New Hampshire, Durham, NH 03824, USA
Interests: BioMEMS; molecular imprinting; graphene FET-based sensors; aptamer-based sensing

Special Issue Information

Dear Colleagues,

Printable and flexible electronic materials have gained a tremendous amount of interest both in academia and in industry, due to their potential impact in many areas including advanced manufacturing, healthcare, diagnostics, wearables, renewable energy, and defense, to name a few. What is the future of printable and flexible electronics? What is the current state of the art? In this Special Issue, we focus on the latest advancements, current challenges, and new opportunities in the world of printable and flexible electronics. We will cover both fundamentals and applications. Fundamentals include novel materials, manufacturing techniques, and characterization, among others. Applications include chemical and biological sensing, point-of-care diagnostics, detection of explosives and nerve agents, foodborne pathogens, environmental monitoring, toxic gas detection, and micro- and nano-actuators, as well as 3D-printed electronics. We invite emerging investigators and experts in the field to contribute commentaries, perspectives, future outlooks, and insightful reviews on related topics. We will also discuss technological breakthroughs and the latest developments in the formats of both short communications and full papers. The goal of this Special Issue is to stimulate the community by addressing the key issues on the topic in the hope that printable and flexible electronics will make a greater impact in our society.

Prof. Jin-Woo Choi
Prof. Edward Song
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 papers will be 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 1400 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.

Keywords

  • Biosensor
  • Nanomaterial
  • Diagnostics
  • Nano-imprinting
  • 3D printing
  • Wearable
  • Flexible
  • MEMS
  • NEMS
  • Paper-based microfluidics
  • Lab-on-a-chip
  • Inkjet printing
  • Gas sensing

Published Papers (9 papers)

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Research

Open AccessArticle
A Polymer Asymmetric Mach–Zehnder Interferometer Sensor Model Based on Electrode Thermal Writing Waveguide Technology
Micromachines 2019, 10(10), 628; https://doi.org/10.3390/mi10100628 - 20 Sep 2019
Abstract
This paper presents a novel electrode thermal writing waveguide based on a heating-induced refractive index change mechanism. The mode condition and the electrode thermal writing parameters were optimized, and the output patterns of the optical field were obtained in a series of simulations. [...] Read more.
This paper presents a novel electrode thermal writing waveguide based on a heating-induced refractive index change mechanism. The mode condition and the electrode thermal writing parameters were optimized, and the output patterns of the optical field were obtained in a series of simulations. Moreover, the effect of various adjustments on the sensing range of the nanoimprint M–Z temperature sensor was analyzed theoretically. A refractive index asymmetry Mach–Zehnder (M–Z) waveguide sensor with a tunable refractive index for a waveguide core layer was simulated with a length difference of 946.1 µm. The optimal width and height of the invert ridge waveguide were 2 μm and 2.8 μm, respectively, while the slab thickness was 1.2 μm. The sensing accuracy was calculated to range from 2.0896 × 104 to 5.1252 × 104 in the 1.51–1.54 region. The sensing fade issue can be resolved by changing the waveguide core refractive index to 0.001 via an electrode thermal writing method. Thermal writing a single M–Z waveguide arm changes its refractive index by 0.03. The sensor’s accuracy can be improved 1.5 times by the proposed method. The sensor described in this paper shows great prospects in organism temperature detection, molecular analysis, and biotechnology applications. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessFeature PaperArticle
Sustainable Fully Printed UV Sensors on Cork Using Zinc Oxide/Ethylcellulose Inks
Micromachines 2019, 10(9), 601; https://doi.org/10.3390/mi10090601 - 12 Sep 2019
Abstract
Low-cost and large-scale production techniques for flexible electronics have evolved greatly in recent years, having great impact in applications such as wearable technology and the internet of things. In this work, we demonstrate fully screen-printed UV photodetectors, successfully fabricated at a low temperature [...] Read more.
Low-cost and large-scale production techniques for flexible electronics have evolved greatly in recent years, having great impact in applications such as wearable technology and the internet of things. In this work, we demonstrate fully screen-printed UV photodetectors, successfully fabricated at a low temperature on a cork substrate, using as the active layer a mixture of zinc oxide nanoparticles and ethylcellulose. The photoresponse under irradiation with a UV lamp with peak emission at 302 nm exhibited a quasi-quadratic behavior directly proportional to the applied voltage, with a photocurrent of about 5.5 and 20 μA when applying 1.5 V and 5 V, respectively. The dark current stayed below 150 nA, while the rise and falling times were, respectively, below 5 and 2 s for both applied voltages. The performance was stable over continuous operation and showed a degradation of only 9% after 100 bending cycles in a 45 mm radius test cylinder. These are promising results regarding the use of this type of sensor in wearable applications such as cork hats, bracelets, or bags. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessFeature PaperArticle
Fabrication of Simultaneously Implementing “Wired Face-Up and Face-Down Ultrathin Piezoresistive Si Chips” on a Film Substrate by Screen-Offset Printing
Micromachines 2019, 10(9), 563; https://doi.org/10.3390/mi10090563 - 26 Aug 2019
Abstract
We realized the implementation of an ultrathin piezoresistive Si chip and stretchable printed wires on a flexible film substrate using simple screen-offset printing technology. This process does not require a special MEMS fabrication equipment and is applicable to face-up chips where electrodes are [...] Read more.
We realized the implementation of an ultrathin piezoresistive Si chip and stretchable printed wires on a flexible film substrate using simple screen-offset printing technology. This process does not require a special MEMS fabrication equipment and is applicable to face-up chips where electrodes are formed on the top surface of the chip, as well as to face-down chips where electrodes are formed on the bottom surface of the chip. This fabrication process is quite useful in the field of flexible hybrid electronics (FHE) as a method for mounting and wiring electronic components on a flexible substrate. In this study, we confirmed that face-up and face-down chips could be mounted on polyimide film tape. Furthermore, it was confirmed that the two types of chips could be simultaneously mounted even if they exist on the same substrate. Five-μm-thick piezoresistive Si chips were transferred and wired on a polyimide film tape using screen-offset printing, and a band-plaster type blood pulse sensor was fabricated. Moreover, we successfully demonstrated that the blood pulse could be measured with neck, inner elbow, wrist, and ankle. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessArticle
Flexible Multi-Layer Semi-Dry Electrode for Scalp EEG Measurements at Hairy Sites
Micromachines 2019, 10(8), 518; https://doi.org/10.3390/mi10080518 - 04 Aug 2019
Abstract
One of the major challenges of daily wearable electroencephalogram (EEG) monitoring is that there are rarely suitable EEG electrodes for hairy sites. Wet electrodes require conductive gels, which will dry over the acquisition time, making them unstable for long-term EEG monitoring. Additionally, the [...] Read more.
One of the major challenges of daily wearable electroencephalogram (EEG) monitoring is that there are rarely suitable EEG electrodes for hairy sites. Wet electrodes require conductive gels, which will dry over the acquisition time, making them unstable for long-term EEG monitoring. Additionally, the electrode–scalp impedances of most dry electrodes are not adequate for high quality EEG collection at hairy sites. In view of the above problems, a flexible multi-layer semi-dry electrode was proposed for EEG monitoring in this study. The semi-dry electrode contains a flexible electrode body layer, foam layer and reservoir layer. The probe structure of the electrode body layer enables the electrode to work effectively at hairy sites. During long-term EEG monitoring, electrolytes stored in the reservoir layer are continuously released through the foam layer to the electrode–scalp interface, ensuring a lower electrode–scalp contact impedance. The experimental results showed that the average electrode–scalp impedance of the semi-dry electrode at a hairy site was only 23.89 ± 7.44 KΩ at 10 Hz, and it was lower than 40 KΩ over a long-term use of 5 h. The electrode performed well in both static and dynamic EEG monitoring, where the temporal correlation with wet electrode signals at the hairy site could reach 94.25% and 90.65%, respectively, and specific evoked EEG signals could be collected. The flexible multi-layer semi-dry electrode can be well applied to scalp EEG monitoring at hairy sites, providing a promising solution for daily long-term monitoring of wearable EEGs. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessArticle
Patterned Metal/Polymer Strain Sensor with Good Flexibility, Mechanical Stability and Repeatability for Human Motion Detection
Micromachines 2019, 10(7), 472; https://doi.org/10.3390/mi10070472 - 15 Jul 2019
Abstract
Wearable health monitoring smart systems based on flexible metal films are considered to be the next generation of devices for remote medical practice. However, cracks on the metallic surface of the films and difficulty in repeatability are the key issues that restrict the [...] Read more.
Wearable health monitoring smart systems based on flexible metal films are considered to be the next generation of devices for remote medical practice. However, cracks on the metallic surface of the films and difficulty in repeatability are the key issues that restrict the application of such wearable strain sensors. In this work, a flexible wearable strain sensor with high sensitivity and good repeatability was fabricated based on a patterned metal/polymer composite material fabricated through nanoimprint lithography. The mechanical properties were measured through cyclic tension and bending loading. The sensor exhibited a small ΔR/R0 error line for multiple test pieces, indicating the good mechanical stability and repeatability of the fabricated device. Moreover, the sensor possesses high sensitivity with gauge factors of 10 for strain less than 50% and 40 for strain from 50% to 70%. Various activities were successfully detected in real-time, such as swallowing, closing/opening of the mouth, and multi-angle bending of elbow, which illustrates the proposed sensor’s potential as a wearable device for the human body. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessArticle
Inkjet Printing of Functional Electronic Memory Cells: A Step Forward to Green Electronics
Micromachines 2019, 10(6), 417; https://doi.org/10.3390/mi10060417 - 22 Jun 2019
Cited by 1
Abstract
Nowadays, the environmental issues surrounding the production of electronics, from the perspectives of both the materials used and the manufacturing process, are of major concern. The usage, storage, disposal protocol and volume of waste material continue to increase the environmental footprint of our [...] Read more.
Nowadays, the environmental issues surrounding the production of electronics, from the perspectives of both the materials used and the manufacturing process, are of major concern. The usage, storage, disposal protocol and volume of waste material continue to increase the environmental footprint of our increasingly “throw away society”. Almost ironically, society is increasingly involved in pollution prevention, resource consumption issues and post-consumer waste management. Clearly, a dichotomy between environmentally aware usage and consumerism exists. The current technology used to manufacture functional materials and electronic devices requires high temperatures for material deposition processes, which results in the generation of harmful chemicals and radiation. With such issues in mind, it is imperative to explore new electronic functional materials and new manufacturing pathways. Here, we explore the potential of additive layer manufacturing, inkjet printing technology which provides an innovative manufacturing pathway for functional materials (metal nanoparticles and polymers), and explore a fully printed two terminal electronic memory cell. In this work, inkjetable materials (silver (Ag) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)) were first printed by a piezoelectric Epson Stylus P50 inkjet printer as stand-alone layers, and secondly as part of a metal (Ag)/active layer (PEDOT:PSS)/metal (Ag) crossbar architecture. The quality of the individual multi-layers of the printed Ag and PEDOT:PSS was first evaluated via optical microscopy and scanning electron microscopy (SEM). Furthermore, an electrical characterisation of the printed memory elements was performed using an HP4140B picoammeter. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessArticle
Plasma-Induced Bubble Microjet Metallization of Elastomer
Micromachines 2019, 10(6), 389; https://doi.org/10.3390/mi10060389 - 11 Jun 2019
Abstract
As the development of flexible materials and advanced materials progresses, innovative wiring methods for these materials are attracting attention. In this study, we investigated a new wiring technology using plasma-induced microbubbles for elastomer without any surface treatment. Our technology includes three main points. [...] Read more.
As the development of flexible materials and advanced materials progresses, innovative wiring methods for these materials are attracting attention. In this study, we investigated a new wiring technology using plasma-induced microbubbles for elastomer without any surface treatment. Our technology includes three main points. (1) Unlike electroless plating and other conventional methods, it does not require complicated pre-surface treatment processes before wiring. (2) A wiring resolution of 500 micro meter can be reached quickly and economically. (3) Robust metallic adhesion on a wide range of materials can be successfully carried out with precise positioning. Here, by applying our method, we adhered nickel nanoparticles to a latex rubber substrate and demonstrated the electrical conductivity of the created line. The result suggests that our method has potential as an innovative wiring technology to precisely, robustly, and simply fabricate an electric circuit without any complicated procedures or pre-treatment. Our method can contribute to microfabrication technologies. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessArticle
Reduced Carboxylate Graphene Oxide based Field Effect Transistor as Pb2+ Aptamer Sensor
Micromachines 2019, 10(6), 388; https://doi.org/10.3390/mi10060388 - 11 Jun 2019
Abstract
Aptamer functionalized graphene field effect transistor (apta-GFET) is a versatile bio-sensing platform. However, the chemical inertness of graphene is still an obstacle for its large-scale applications and commercialization. In this work, reduced carboxyl-graphene oxide (rGO-COOH) is studied as a self-activated channel material in [...] Read more.
Aptamer functionalized graphene field effect transistor (apta-GFET) is a versatile bio-sensing platform. However, the chemical inertness of graphene is still an obstacle for its large-scale applications and commercialization. In this work, reduced carboxyl-graphene oxide (rGO-COOH) is studied as a self-activated channel material in the screen-printed apta-GFETs for the first time. Examinations are carefully executed using lead-specific-aptamer as a proof-of-concept to demonstrate its functions in accommodating aptamer bio-probes and promoting the sensing reaction. The graphene-state, few-layer nano-structure, plenty of oxygen-containing groups and enhanced LSA immobilization of the rGO-COOH channel film are evidenced by X-ray photoelectron spectroscopy, Raman spectrum, UV-visible absorbance, atomic force microscopy and scanning electron microscope. Based on these characterizations, as well as a site-binding model based on solution-gated field effect transistor (SgFET) working principle, theoretical deductions for rGO-COOH enhanced apta-GFETs’ response are provided. Furthermore, detections for disturbing ions and real samples demonstrate the rGO-COOH channeled apta-GFET has a good specificity, a limit-of-detection of 0.001 ppb, and is in agreement with the conventional inductively coupled plasma mass spectrometry method. In conclusion, the careful examinations demonstrate rGO-COOH is a promising candidate as a self-activated channel material because of its merits of being independent of linking reagents, free from polymer residue and compatible with rapidly developed print-electronic technology. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessArticle
Flexible Metal/Polymer Composite Films Embedded with Silver Nanowires as a Stretchable and Conductive Strain Sensor for Human Motion Monitoring
Micromachines 2019, 10(6), 372; https://doi.org/10.3390/mi10060372 - 04 Jun 2019
Cited by 2
Abstract
To avoid conductive failure due to the cracks of the metal thin film under external loads for the wearable strain sensor, a stretchable metal/polymer composite film embedded with silver nanowires (AgNWs) was examined as a potential candidate. The combination of Ag film and [...] Read more.
To avoid conductive failure due to the cracks of the metal thin film under external loads for the wearable strain sensor, a stretchable metal/polymer composite film embedded with silver nanowires (AgNWs) was examined as a potential candidate. The combination of Ag film and AgNWs enabled the fabrication of a conductive film that was applied as a high sensitivity strain sensor, with gauge factors of 7.1 under the applied strain of 0–10% and 21.1 under the applied strain of 10–30%. Furthermore, the strain sensor was demonstrated to be highly reversible and remained stable after 1000 bending cycles. These results indicated that the AgNWs could act as elastic conductive bridges across cracks in the metal film to maintain high conductivity under tensile and bending loads. As such, the strain sensor engineered herein was successfully applied in the real-time detection and monitoring of large motions of joints and subtle motions of the mouth. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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