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17 pages, 5422 KiB

Open AccessArticle

Imaging Conductivity Changes in Monolayer Graphene Using Electrical Impedance Tomography

by Anil Kumar Khambampati, Sheik Abdur Rahman, Sunam Kumar Sharma, Woo Young Kim and Kyung Youn Kim

Micromachines 2020, 11(12), 1074; https://doi.org/10.3390/mi11121074 - 1 Dec 2020

Cited by 8 | Viewed by 2871

Abstract

Recently, graphene has gained a lot of attention in the electronic industry due to its unique properties and has paved the way for realizing novel devices in the field of electronics. For the development of new device applications, it is necessary to grow [...] Read more.

Recently, graphene has gained a lot of attention in the electronic industry due to its unique properties and has paved the way for realizing novel devices in the field of electronics. For the development of new device applications, it is necessary to grow large wafer-sized monolayer graphene samples. Among the methods to synthesize large graphene films, chemical vapor deposition (CVD) is one of the promising and common techniques. However, during the growth and transfer of the CVD graphene monolayer, defects such as wrinkles, cracks, and holes appear on the graphene surface. These defects can influence the electrical properties and it is of interest to know the quality of graphene samples non-destructively. Electrical impedance tomography (EIT) can be applied as an alternate method to determine conductivity distribution non-destructively. The EIT inverse problem of reconstructing conductivity is highly non-linear and is heavily dependent on measurement accuracy and modeling errors related to an accurate knowledge of electrode location, contact resistances, the exact outer boundary of the graphene wafer, etc. In practical situations, it is difficult to eliminate these modeling errors as complete knowledge of the electrode contact impedance and outer domain boundary is not fully available, and this leads to an undesirable solution. In this paper, a difference imaging approach is proposed to estimate the conductivity change of graphene with respect to the reference distribution from the data sets collected before and after the change. The estimated conductivity change can be used to locate the defects on the graphene surface caused due to the CVD transfer process or environment interaction. Numerical and experimental results with graphene sample of size 2.5 × 2.5 cm are performed to determine the change in conductivity distribution and the results show that the proposed difference imaging approach handles the modeling errors and estimates the conductivity distribution with good accuracy. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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14 pages, 2188 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Graphene-Based Contacts for Optoelectronic Devices

by Susana Fernández, Antonio Molinero, David Sanz, José Pablo González, Marina de la Cruz, José Javier Gandía and Julio Cárabe

Micromachines 2020, 11(10), 919; https://doi.org/10.3390/mi11100919 - 1 Oct 2020

Cited by 12 | Viewed by 3762

Abstract

Hybrid transparent contacts based on combinations of a transparent conductive oxide and a few graphene monolayers were developed in order to evaluate their optical and electrical performance with the main aim to use them as front contacts in optoelectronic devices. The assessment of [...] Read more.

Hybrid transparent contacts based on combinations of a transparent conductive oxide and a few graphene monolayers were developed in order to evaluate their optical and electrical performance with the main aim to use them as front contacts in optoelectronic devices. The assessment of the most suitable strategies for their fabrication was performed by testing different protocols addressing such issues as the protection of the device structure underneath, the limitation of sample temperature during the graphene-monolayer transfer process and the determination of the most suitable stacking structure. Suitable metal ohmic electrodes were also evaluated. Among a number of options tested, the metal contact based on Ti + Ag showed the highest reproducibility and the lowest contact resistivity. Finally, with the objective of extracting the current generated from optoelectronic devices to the output pins of an external package, focusing on a near future commercial application, the electrical properties of the connections made with an ultrasonic bonding machine (sonic welding) between the optimized Ti + Ag metal contacts and Al or Au micro-wires were also evaluated. All these results have an enormous potential as hybrid electrodes based on graphene to be used in novel designs of a future generation of optoelectronic devices, such as solar cells. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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12 pages, 4324 KiB

Open AccessArticle

Inkjet-Printed Graphene-Based 1 × 2 Phased Array Antenna

by Mahmuda Akter Monne, Peter Mack Grubb, Harold Stern, Harish Subbaraman, Ray T. Chen and Maggie Yihong Chen

Micromachines 2020, 11(9), 863; https://doi.org/10.3390/mi11090863 - 18 Sep 2020

Cited by 20 | Viewed by 3860

Abstract

Low-cost and conformal phased array antennas (PAAs) on flexible substrates are of particular interest in many applications. The major deterrents to developing flexible PAA systems are the difficulty in integrating antenna and electronics circuits on the flexible surface, as well as the bendability [...] Read more.

Low-cost and conformal phased array antennas (PAAs) on flexible substrates are of particular interest in many applications. The major deterrents to developing flexible PAA systems are the difficulty in integrating antenna and electronics circuits on the flexible surface, as well as the bendability and oxidation rate of radiating elements and electronics circuits. In this research, graphene ink was developed from graphene flakes and used to inkjet print the radiating element and the active channel of field effect transistors (FETs). Bending and oxidation tests were carried out to validate the application of printed flexible graphene thin films in flexible electronics. An inkjet-printed graphene-based 1 × 2 element phased array antenna was designed and fabricated. Graphene-based field effect transistors were used as switches in the true-time delay line of the phased array antenna. The graphene phased array antenna was 100% inkjet printed on top of a 5 mil flexible Kapton^® substrate, at room temperature. Four possible azimuth steering angles were designed for −26.7°, 0°, 13°, and 42.4°. Measured far-field patterns show good agreement with simulation results. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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13 pages, 3410 KiB

Open AccessArticle

Camphor-Based CVD Bilayer Graphene/Si Heterostructures for Self-Powered and Broadband Photodetection

by Dung-Sheng Tsai, Ping-Yu Chiang, Meng-Lin Tsai, Wei-Chen Tu, Chi Chen, Shih-Lun Chen, Ching-Hsueh Chiu, Chen-Yu Li and Wu-Yih Uen

Micromachines 2020, 11(9), 812; https://doi.org/10.3390/mi11090812 - 27 Aug 2020

Cited by 11 | Viewed by 4579

Abstract

This work demonstrates a self-powered and broadband photodetector using a heterojunction formed by camphor-based chemical vaper deposition (CVD) bilayer graphene on p-Si substrates. Here, graphene/p-Si heterostructures and graphene layers serve as ultra-shallow junctions for UV absorption and zero bandgap junction materials (<Si bandgap [...] Read more.

This work demonstrates a self-powered and broadband photodetector using a heterojunction formed by camphor-based chemical vaper deposition (CVD) bilayer graphene on p-Si substrates. Here, graphene/p-Si heterostructures and graphene layers serve as ultra-shallow junctions for UV absorption and zero bandgap junction materials (<Si bandgap (1.1 eV)) for long-wave near-infrared (LWNIR) absorption, respectively. According to the Raman spectra and large-area (16 × 16 μm²) Raman mapping, a low-defect, >95% coverage bilayer and high-uniformity graphene were successfully obtained by camphor-based CVD processes. Furthermore, the carrier mobility of the camphor-based CVD bilayer graphene at room temperature is 1.8 × 10³ cm²/V·s. Due to the incorporation of camphor-based CVD graphene, the graphene/p-Si Schottky junctions show a good rectification property (rectification ratio of ~110 at ± 2 V) and good performance as a self-powered (under zero bias) photodetector from UV to LWNIR. The photocurrent to dark current ratio (PDCR) value is up to 230 at 0 V under white light illumination, and the detectivity (D*) is 8 × 10¹² cmHz^1/2/W at 560 nm. Furthermore, the photodetector (PD) response/decay time (i.e., rise/fall time) is ~118/120 μs. These results support the camphor-based CVD bilayer graphene/Si Schottky PDs for use in self-powered and ultra-broadband light detection in the future. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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11 pages, 8315 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improved High-Yield PMMA/Graphene Pressure Sensor and Sealed Gas Effect Analysis

by Ying Liu, Yong Zhang, Xin Lin, Ke-hong Lv, Peng Yang, Jing Qiu and Guan-jun Liu

Micromachines 2020, 11(9), 786; https://doi.org/10.3390/mi11090786 - 19 Aug 2020

Cited by 8 | Viewed by 3140

Abstract

Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the [...] Read more.

Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the graphene pressure sensor suffers a lot. This is one of the main obstacles towards graphene commercial applications. In this paper, we utilized polymethylmethacrylate (PMMA)/graphene heterostructure to isolate graphene from the ambient environment and enhance its strength simultaneously. PMMA/graphene pressure sensors, with the finite-depth cavities and the through-hole cavities separately, were made for comparative study. The through-hole device obtained a comparable sensitivity per unit area to the state of the art of the bare graphene pressure sensor, since there were no leaking cracks or defects. Both the sensitivity and stability of the through-hole sensor are better than those of the sensor with 285-nm-deep cavities, which is due to the sealed gas effect in the pressure cavity. A modified piezoresistive model was derived by considering the pressure change of the sealed gas in the pressure cavity. The calculated result of the new model is consistent with the experimental results. Our findings point out a promising route for performance optimization of graphene pressure sensors. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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10 pages, 3801 KiB

Open AccessArticle

Low Power Consumption 3D-Inverted Ridge Thermal Optical Switch of Graphene-Coated Polymer/Silica Hybrid Waveguide

by Yue Cao, Yunji Yi, Yue Yang, Baizhu Lin, Jiawen Lv, Haowen Zhao, Fei Wang and Daming Zhang

Micromachines 2020, 11(8), 783; https://doi.org/10.3390/mi11080783 - 18 Aug 2020

Cited by 1 | Viewed by 2521

Abstract

An inverted ridge 3D thermal optical (TO) switch of a graphene-coated polymer/silica hybrid waveguide is proposed. The side electrode structure is designed to reduce the mode loss induced by the graphene film and by heating the electrode. The graphene layer is designed to [...] Read more.

An inverted ridge 3D thermal optical (TO) switch of a graphene-coated polymer/silica hybrid waveguide is proposed. The side electrode structure is designed to reduce the mode loss induced by the graphene film and by heating the electrode. The graphene layer is designed to be located on the waveguide to assist in the conduction of heat produced by the electrode. The inverted ridge core is fabricated by etching and spin-coating processes, which can realize the flat surface waveguide. This core improves the transfer of the graphene layer and the compatibility of the fabrication processes. Because of the opposite thermal optical coefficient of polymer and silica and the high thermal conductivity of the graphene layer, the 3D hybrid TO switch with low power consumption and fast response time is obtained. Compared with the traditional TO switch without graphene film, the power consumption of the proposed TO switch is reduced by 41.43% at the wavelength of 1550 nm, width of the core layer (a) of 3 μm, and electrode distance (d) of 4 μm. The rise and fall times of the proposed TO switch are simulated to be 64.5 μs and 175 μs with a d of 4 μm, and a of 2 μm, respectively. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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17 pages, 4661 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of Fully Flexible Tactile Pressure Sensor with Bilayer Interlaced Bumps for Robotic Grasping Applications

by Lingfeng Zhu, Yancheng Wang, Deqing Mei and Chengpeng Jiang

Micromachines 2020, 11(8), 770; https://doi.org/10.3390/mi11080770 - 12 Aug 2020

Cited by 22 | Viewed by 5753

Abstract

Flexible tactile sensors have been utilized in intelligent robotics for human-machine interaction and healthcare monitoring. The relatively low flexibility, unbalanced sensitivity and sensing range of the tactile sensors are hindering the accurate tactile information perception during robotic hand grasping of different objects. This [...] Read more.

Flexible tactile sensors have been utilized in intelligent robotics for human-machine interaction and healthcare monitoring. The relatively low flexibility, unbalanced sensitivity and sensing range of the tactile sensors are hindering the accurate tactile information perception during robotic hand grasping of different objects. This paper developed a fully flexible tactile pressure sensor, using the flexible graphene and silver composites as the sensing element and stretchable electrodes, respectively. As for the structural design of the tactile sensor, the proposed bilayer interlaced bumps can be used to convert external pressure into the stretching of graphene composites. The fabricated tactile sensor exhibits a high sensing performance, including relatively high sensitivity (up to 3.40% kPa⁻¹), wide sensing range (200 kPa), good dynamic response, and considerable repeatability. Then, the tactile sensor has been integrated with the robotic hand finger, and the grasping results have indicated the capability of using the tactile sensor to detect the distributed pressure during grasping applications. The grasping motions, properties of the objects can be further analyzed through the acquired tactile information in time and spatial domains, demonstrating the potential applications of the tactile sensor in intelligent robotics and human-machine interfaces. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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12 pages, 3243 KiB

Open AccessArticle

An Electrochemical Immunosensor for Sensitive Detection of the Tumor Marker Carcinoembryonic Antigen (CEA) Based on Three-Dimensional Porous Nanoplatinum/Graphene

by Aihua Jing, Qiong Xu, Wenpo Feng and Gaofeng Liang

Micromachines 2020, 11(7), 660; https://doi.org/10.3390/mi11070660 - 3 Jul 2020

Cited by 30 | Viewed by 3257

Abstract

Carcinoembryonic antigen (CEA) is an important broad-spectrum tumor marker. The quantitative detection of a low concentration of CEA has important medical significance. In this study, three-dimensional porous graphene-oxide-supported platinum metal nanoparticles (3DPt/HGO) composites were prepared by a wet chemical method and modified on [...] Read more.

Carcinoembryonic antigen (CEA) is an important broad-spectrum tumor marker. The quantitative detection of a low concentration of CEA has important medical significance. In this study, three-dimensional porous graphene-oxide-supported platinum metal nanoparticles (3DPt/HGO) composites were prepared by a wet chemical method and modified on an electrode with enhanced conductivity, a large surface area, and good adsorption of immobilizing antibodies (Ab₁). Horseradish peroxidase (HRP)-functionalized Au nanoparticles were fabricated to label the secondary antibodies (Ab₂). The proposed immunosensor showed a good linear relationship in the range of 0.001–150 ng/mL for CEA and a detection limit of 0.0006 ng/mL. The immunosensor had high sensitivity, good stability and reproducibility, and has great application prospects for the clinical diagnosis of cancer. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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19 pages, 2616 KiB

Open AccessArticle

Graphene Aerogels for In Situ Synthesis of Conductive Poly(para-phenylenediamine) Polymers, and Their Sensor Application

by Sahin Demirci, Mehmet Can and Nurettin Sahiner

Micromachines 2020, 11(7), 626; https://doi.org/10.3390/mi11070626 - 27 Jun 2020

Cited by 8 | Viewed by 2816

Abstract

In this study, macroporous graphene aerogels (GAs) were synthesized by chemical reduction of graphene oxide sheets and were used as a support material for in situ synthesis of conductive poly(para-phenylenediamine) (p(p-PDA)). The in situ synthesis of p(p-PDA) in GA was carried out by [...] Read more.

In this study, macroporous graphene aerogels (GAs) were synthesized by chemical reduction of graphene oxide sheets and were used as a support material for in situ synthesis of conductive poly(para-phenylenediamine) (p(p-PDA)). The in situ synthesis of p(p-PDA) in GA was carried out by using a simple oxidation polymerization technique. Moreover, the prepared conductive p(p-PDA) polymers in the networks of GAs were doped with various types of acids such as hydrochloric acid (HCl), nitric acid (HNO₃), sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), respectively. The prepared GA and different acid-doped forms as GA/p(p-PDA) composites were characterized by FT-IR, TGA, and conductivity measurements. The observed FT-IR peaks at 1574 cm⁻¹, and 1491 cm⁻¹, for stretching deformations of quinone and benzene, respectively, confirmed the in situ synthesis of P(p-PDA) polymers within GAs. The conductivity of GAs with 2.17 × 10⁻⁴ ± 3.15 × 10⁻⁵ S·cm⁻¹ has experienced an approximately 250-fold increase to 5.16 × 10⁻² ± 2.72 × 10⁻³ S·cm⁻¹ after in situ synthesis of p(p-PDA) polymers and with HCl doping. Conductivity values for different types of acid-doped GA/p(p-PDA) composites were compared with the bare p(p-PDA) and their undoped forms. Moreover, the changes in the conductivity of GA and GA/p(p-PDA) composites upon CO₂ gas exposure were compared and their sensory potential in terms of response and sensitivity, along with reusability in CO₂ detection, were evaluated. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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11 pages, 2661 KiB

Open AccessArticle

Dynamically Tunable Phase Shifter with Commercial Graphene Nanoplatelets

by Muhammad Yasir and Patrizia Savi

Micromachines 2020, 11(6), 600; https://doi.org/10.3390/mi11060600 - 20 Jun 2020

Cited by 10 | Viewed by 2887

Abstract

In microwave frequency band the conductivity of graphene can be varied to design a number of tunable components. A tunable phase shifter based on commercial graphene nanoplatelets is introduced. The proposed configuration consists of a microstrip line with two stubs connected with a [...] Read more.

In microwave frequency band the conductivity of graphene can be varied to design a number of tunable components. A tunable phase shifter based on commercial graphene nanoplatelets is introduced. The proposed configuration consists of a microstrip line with two stubs connected with a taper. On each side of the stubs there is a gap, short circuited through a via, where the commercial graphene nanoplatelets are drop casted. By applying a DC bias voltage that alters the graphene resistance the phase of the transmitted signal through the microstrip line can be varied. In order to maximize the phase shift of the transmitted signal and minimize the insertion loss, the length of the taper and the stubs are optimized by the help of circuit model and full-wave simulations. A prototype working at 4GHz is fabricated and measured. A phase variation of 33 degrees is acquired with an amplitude variation of less than 0.4 dB. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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13 pages, 8295 KiB

Open AccessArticle

Conductance Tunable Suspended Graphene Nanomesh by Helium Ion Beam Milling

by Fayong Liu, Zhongwang Wang, Soya Nakanao, Shinichi Ogawa, Yukinori Morita, Marek Schmidt, Mayeesha Haque, Manoharan Muruganathan and Hiroshi Mizuta

Micromachines 2020, 11(4), 387; https://doi.org/10.3390/mi11040387 - 7 Apr 2020

Cited by 9 | Viewed by 4441

Abstract

This paper demonstrates that the electrical properties of suspended graphene nanomesh (GNM) can be tuned by systematically changing the porosity with helium ion beam milling (HIBM). The porosity of the GNM is well-controlled by defining the pitch of the periodic nanopores. The defective [...] Read more.

This paper demonstrates that the electrical properties of suspended graphene nanomesh (GNM) can be tuned by systematically changing the porosity with helium ion beam milling (HIBM). The porosity of the GNM is well-controlled by defining the pitch of the periodic nanopores. The defective region surrounding the individual nanopores after HIBM, which limits the minimum pitch achievable between nanopores for a certain dose, is investigated and reported. The exponential relationship between the thermal activation energy (E_A) and the porosity is found in the GNM devices. Good E_A tuneability observed from the GNMs provides a new approach to the transport gap engineering beyond the conventional nanoribbon method. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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Review

Jump to: Research

27 pages, 5433 KiB

Open AccessReview

Carbon Nanomaterials as Versatile Platforms for Biosensing Applications

by Hye Suk Hwang, Jae Won Jeong, Yoong Ahm Kim and Mincheol Chang

Micromachines 2020, 11(9), 814; https://doi.org/10.3390/mi11090814 - 28 Aug 2020

Cited by 71 | Viewed by 5287

Abstract

A biosensor is defined as a measuring system that includes a biological receptor unit with distinctive specificities toward target analytes. Such analytes include a wide range of biological origins such as DNAs of bacteria or viruses, or proteins generated from an immune system [...] Read more.

A biosensor is defined as a measuring system that includes a biological receptor unit with distinctive specificities toward target analytes. Such analytes include a wide range of biological origins such as DNAs of bacteria or viruses, or proteins generated from an immune system of infected or contaminated living organisms. They further include simple molecules such as glucose, ions, and vitamins. One of the major challenges in biosensor development is achieving efficient signal capture of biological recognition-transduction events. Carbon nanomaterials (CNs) are promising candidates to improve the sensitivity of biosensors while attaining low detection limits owing to their capability of immobilizing large quantities of bioreceptor units at a reduced volume, and they can also act as a transduction element. In addition, CNs can be adapted to functionalization and conjugation with organic compounds or metallic nanoparticles; the creation of surface functional groups offers new properties (e.g., physical, chemical, mechanical, electrical, and optical properties) to the nanomaterials. Because of these intriguing features, CNs have been extensively employed in biosensor applications. In particular, carbon nanotubes (CNTs), nanodiamonds, graphene, and fullerenes serve as scaffolds for the immobilization of biomolecules at their surface and are also used as transducers for the conversion of signals associated with the recognition of biological analytes. Herein, we provide a comprehensive review on the synthesis of CNs and their potential application to biosensors. In addition, we discuss the efforts to improve the mechanical and electrical properties of biosensors by combining different CNs. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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