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11 pages, 2385 KiB

Open AccessArticle

Frequency Tuning of Graphene Nanoelectromechanical Resonators via Electrostatic Gating

by Tengda Mei, Jaesung Lee, Yuehang Xu and Philip X.-L. Feng

Micromachines 2018, 9(6), 312; https://doi.org/10.3390/mi9060312 - 20 Jun 2018

Cited by 17 | Viewed by 5437

In this article, we report on a comprehensive modeling study of frequency tuning of graphene resonant nanoelectromechanical systems (NEMS) via electrostatic coupling forces induced by controlling the voltage of a capacitive gate. The model applies to both doubly clamped graphene membranes and circumference-clamped [...] Read more.

In this article, we report on a comprehensive modeling study of frequency tuning of graphene resonant nanoelectromechanical systems (NEMS) via electrostatic coupling forces induced by controlling the voltage of a capacitive gate. The model applies to both doubly clamped graphene membranes and circumference-clamped circular drumhead device structures. Frequency tuning of these devices can be predicted by considering both capacitive softening and elastic stiffening. It is shown that the built-in strain in the device strongly dictates the frequency tuning behavior and tuning range. We also find that doubly clamped graphene resonators can have a wider frequency tuning range, while circular drumhead devices have higher initial resonance frequency with same device characteristic parameters. Further, the parametric study in this work clearly shows that a smaller built-in strain, smaller depth of air gap or cavity, and larger device size or characteristic length (e.g., length for doubly clamped devices, and diameter for circular drumheads) help achieve a wider range of electrostatic frequency tunability. This study builds a solid foundation that can offer important device fabrication and design guidelines for achieving radio frequency components (e.g., voltage controlled oscillators and filters) with the desired frequencies and tuning ranges. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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9 pages, 12547 KiB

Open AccessFeature PaperArticle

Effect of Substrate Support on Dynamic Graphene/Metal Electrical Contacts

by Jihyung Lee, Xiaoli Hu, Andrey A. Voevodin, Ashlie Martini and Diana Berman

Micromachines 2018, 9(4), 169; https://doi.org/10.3390/mi9040169 - 07 Apr 2018

Cited by 10 | Viewed by 4488

Abstract

Recent advances in graphene and other two-dimensional (2D) material synthesis and characterization have led to their use in emerging technologies, including flexible electronics. However, a major challenge is electrical contact stability, especially under mechanical straining or dynamic loading, which can be important for [...] Read more.

Recent advances in graphene and other two-dimensional (2D) material synthesis and characterization have led to their use in emerging technologies, including flexible electronics. However, a major challenge is electrical contact stability, especially under mechanical straining or dynamic loading, which can be important for 2D material use in microelectromechanical systems. In this letter, we investigate the stability of dynamic electrical contacts at a graphene/metal interface using atomic force microscopy (AFM), under static conditions with variable normal loads and under sliding conditions with variable speeds. Our results demonstrate that contact resistance depends on the nature of the graphene support, specifically whether the graphene is free-standing or supported by a substrate, as well as on the contact load and sliding velocity. The results of the dynamic AFM experiments are corroborated by simulations, which show that the presence of a stiff substrate, increased load, and reduced sliding velocity lead to a more stable low-resistance contact. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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10 pages, 32376 KiB

Open AccessArticle

A DLC-Punch Array to Fabricate the Micro-Textured Aluminum Sheet for Boiling Heat Transfer Control

by Tatsuhio Aizawa, Kenji Wasa and Hiroshi Tamagaki

Micromachines 2018, 9(4), 147; https://doi.org/10.3390/mi9040147 - 25 Mar 2018

Cited by 11 | Viewed by 4100

Abstract

A diamond-like carbon (DLC) film, coated on an SKD11 (alloy tool steel) substrate, was shaped by plasma oxidation to form an assembly of DLC macro-pillars and to be used as a DLC-punch array that is micro-embossed into aluminum sheets. First, the SKD11 steel [...] Read more.

A diamond-like carbon (DLC) film, coated on an SKD11 (alloy tool steel) substrate, was shaped by plasma oxidation to form an assembly of DLC macro-pillars and to be used as a DLC-punch array that is micro-embossed into aluminum sheets. First, the SKD11 steel die substrate was prepared and DLC-coated to have a film thickness of 10 μm. This DLC coating worked as a punch material. The two-dimensional micro-patterns were printed onto this DLC film by maskless lithography. The unprinted DLC films were selectively removed by plasma oxidation to leave the three-dimensional DLC-punch array on the SKD11 substrate. Each DLC punch had a head of 3.5 μm × 3.5 μm and a height of 8 μm. This DLC-punch array was fixed into the cassette die set for a micro-embossing process using a table-top servo-stamper. Furthermore, through numerically controlled micro-embossing, an alignment of rectangular punches was transcribed into a micro-cavity array in the aluminum sheet. The single micro-cavity had a bottom surface of 3.2 μm × 3.2 μm and an average depth of 7.5 μm. A heat-transfer experiment in boiling water was also performed to investigate the effect of micro-cavity texture on bubbling behavior and the boiling curve. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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10 pages, 4891 KiB

Open AccessArticle

Single-Wall Carbon Nanotube-Coated Cotton Yarn for Electrocardiography Transmission

by Yuliang Zhao, Yuying Cao, Junshan Liu, Zhikun Zhan, Xiaoli Li and Wen Jung Li

Micromachines 2018, 9(3), 132; https://doi.org/10.3390/mi9030132 - 19 Mar 2018

Cited by 22 | Viewed by 6091

Abstract

We fabricated a type of conductive fabric, specifically single-wall carbon nanotube-coated cotton yarns (SWNT-CYs), for electrocardiography (ECG) signal transmission utilizing a “dipping and drying” method. The conductive cotton yarns were prepared by dipping cotton yarns in SWNTs (single-wall carbon nanotubes) solutions and then [...] Read more.

We fabricated a type of conductive fabric, specifically single-wall carbon nanotube-coated cotton yarns (SWNT-CYs), for electrocardiography (ECG) signal transmission utilizing a “dipping and drying” method. The conductive cotton yarns were prepared by dipping cotton yarns in SWNTs (single-wall carbon nanotubes) solutions and then drying them at room temperature—a simple process that shows consistency in successfully coating cotton yarns with conductive carbon nanotubes (CNTs). The influence of fabrication conditions on the conductivity properties of SWNT-CYs was investigated. The results demonstrate that our conductive yarns can transmit weak bio-electrical (i.e., ECG) signals without significant attenuation and distortion. Our conductive cotton yarns, which combine the flexibility of conventional fabrics and the good conductivity of SWNTs, are promising materials for wearable electronics and sensor applications in the future. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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16 pages, 21236 KiB

Open AccessArticle

Fundamental Study for a Graphite-Based Microelectromechanical System

by Junji Sone, Mutsuaki Murakami and Atsushi Tatami

Micromachines 2018, 9(2), 64; https://doi.org/10.3390/mi9020064 - 02 Feb 2018

Cited by 10 | Viewed by 4808

Abstract

We aimed to develop a process for constructing a carbon-based microelectromechanical system (MEMS). First, we prepared a highly oriented pyrolytic graphite (HOPG) crystal microsheet by exfoliation. We fabricated cantilevers and a double-clamped beam by controlling the thickness of the HOPG microsheet using a [...] Read more.

We aimed to develop a process for constructing a carbon-based microelectromechanical system (MEMS). First, we prepared a highly oriented pyrolytic graphite (HOPG) crystal microsheet by exfoliation. We fabricated cantilevers and a double-clamped beam by controlling the thickness of the HOPG microsheet using a MEMS process. Second, we used a graphite sheet with contour line adhesion by metal sputter deposition. Third, we used a highly accurate graphite sheet with face adhesion and laser cutting. The first resonance frequencies were evaluated. We confirmed improvement in Q values to 1/10 level of a quarts vibrator, high performance, and a simple structure. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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12 pages, 8501 KiB

Open AccessArticle

Atomistic and Experimental Investigation of the Effect of Depth of Cut on Diamond Cutting of Cerium

by Junjie Zhang, Maobing Shuai, Haibing Zheng, Yao Li, Ming Jin and Tao Sun

Micromachines 2018, 9(1), 26; https://doi.org/10.3390/mi9010026 - 13 Jan 2018

Cited by 14 | Viewed by 3740

Abstract

The ultra-precision diamond cutting process exhibits strong size effects due to the ultra-small depth of cut that is comparable with the cutting edge radius. In the present work, we elucidate the underlying machining mechanisms of single crystal cerium under diamond cutting by means [...] Read more.

The ultra-precision diamond cutting process exhibits strong size effects due to the ultra-small depth of cut that is comparable with the cutting edge radius. In the present work, we elucidate the underlying machining mechanisms of single crystal cerium under diamond cutting by means of molecular dynamics simulations, with an emphasis on the evaluation of the effect of depth of cut on the cutting process by using different depths of cut. Diamond cutting experiments of cerium with different depths of cut are also conducted. In particular for the smallest depth of cut of 0.2 nm, shallow cutting simulations varying the sharpness of the cutting edge demonstrate that an atomically sharp cutting edge leads to a smaller machining force and better machined surface quality than a blunt one. Simulation results indicate that dislocation slip is the dominant deformation mechanism of cerium under diamond cutting with each depth of cut. Furthermore, the analysis of the defect zone based on atomic radial distribution functions demonstrates that there are trivial phase transformations from γ-Ce to δ-Ce occurred in both the machined surface and the formed chip. It is found that there is a transition of material removal mode from plowing to cutting with the increase of the depth of cut, which is also consistent with the diamond cutting experiments of cerium with different depths of cut. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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2006 KiB

Open AccessArticle

Controlled Solvent-Free Formation of Embedded PDMS-Derived Carbon Nanodomains with Tunable Fluorescence Using Selective Laser Ablation with A Low-Power CD Laser

by María José González-Vázquez and Mathieu Hautefeuille

Micromachines 2017, 8(10), 307; https://doi.org/10.3390/mi8100307 - 17 Oct 2017

Cited by 7 | Viewed by 4799

Abstract

We present a study of the application of a single-step and solvent-free laser-based strategy to control the formation of polymer-derived fluorescent carbon nanodomains embedded in poly-dimethylsiloxane (PDMS) microchannels. A low-power, laser-induced microplasma was used to produce a localised combustion of a PDMS surface [...] Read more.

We present a study of the application of a single-step and solvent-free laser-based strategy to control the formation of polymer-derived fluorescent carbon nanodomains embedded in poly-dimethylsiloxane (PDMS) microchannels. A low-power, laser-induced microplasma was used to produce a localised combustion of a PDMS surface and confine nanocarbon byproducts within the exposed microregions. Patterns with on-demand geometries were achieved under dry environmental conditions thanks to a low-cost 3-axis CD-DVD platform motorised in a selective laser ablation fashion. The high temperature required for combustion of PDMS was achieved locally by strongly focusing the laser spot on the desired areas, and the need for high-power laser was bypassed by coating the surface with an absorbing carbon additive layer, hence making the etching of a transparent material possible. The simple and repeatable fabrication process and the spectroscopic characterisation of resulting fluorescent microregions are reported. In situ Raman and fluorescence spectroscopy were used to identify the nature of the nanoclusters left inside the modified areas and their fluorescence spectra as a function of excitation wavelength. Interestingly, the carbon nanodomains left inside the etched micropatterns showed a strong dependency on the additive materials and laser energy that were used to achieve the incandescence and etch microchannels on the surface of the polymer. This dependence on the lasing conditions indicates that our cost-effective laser ablation technique may be used to tune the nature of the polymer-derived nanocarbons, useful for photonics applications in transparent silicones in a rapid-prototyping fashion. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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1622 KiB

Open AccessFeature PaperArticle

Custom-Designed Glassy Carbon Tips for Atomic Force Microscopy

by Anna Zakhurdaeva, Philipp-Immanuel Dietrich, Hendrik Hölscher, Christian Koos, Jan G. Korvink and Swati Sharma

Micromachines 2017, 8(9), 285; https://doi.org/10.3390/mi8090285 - 20 Sep 2017

Cited by 34 | Viewed by 6897

Abstract

Glassy carbon is a graphenic form of elemental carbon obtained from pyrolysis of carbon-rich precursor polymers that can be patterned using various lithographic techniques. It is electrically and thermally conductive, mechanically strong, light, corrosion resistant and easy to functionalize. These properties render it [...] Read more.

Glassy carbon is a graphenic form of elemental carbon obtained from pyrolysis of carbon-rich precursor polymers that can be patterned using various lithographic techniques. It is electrically and thermally conductive, mechanically strong, light, corrosion resistant and easy to functionalize. These properties render it very suitable for Carbon-microelectromechanical systems (Carbon-MEMS) and nanoelectromechanical systems (Carbon-NEMS) applications. Here we report on the fabrication and characterization of fully operational, microfabricated glassy carbon nano-tips for Atomic Force Microscopy (AFM). These tips are 3D-printed on to micro-machined silicon cantilevers by Two-Photon Polymerization (2PP) of acrylate-based photopolymers (commercially known as IP-series resists), followed by their carbonization employing controlled pyrolysis, which shrinks the patterned structure by ≥98% in volume. Tip performance and robustness during contact and dynamic AFM modes are validated by morphology and wear tests. The design and pyrolysis process optimization performed for this work indicate which parameters require special attention when IP-series polymers are used for the fabrication of Carbon-MEMS and NEMS. Microstructural characterization of the resulting material confirms that it features a frozen percolated network of graphene sheets accompanied by disordered carbon and voids, similar to typical glassy carbons. The presented facile fabrication method can be employed for obtaining a variety of 3D glassy carbon nanostructures starting from the stereolithographic designs provided by the user. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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17823 KiB

Open AccessArticle

Three-Dimensional Finite Element Method Simulation of Perforated Graphene Nano-Electro-Mechanical (NEM) Switches

by Mohd Amir Zulkefli, Mohd Ambri Mohamed, Kim S. Siow, Burhanuddin Yeop Majlis, Jothiramalingam Kulothungan, Manoharan Muruganathan and Hiroshi Mizuta

Micromachines 2017, 8(8), 236; https://doi.org/10.3390/mi8080236 - 31 Jul 2017

Cited by 17 | Viewed by 5144

Abstract

The miniaturization trend leads to the development of a graphene based nanoelectromechanical (NEM) switch to fulfill the high demand in low power device applications. In this article, we highlight the finite element (FEM) simulation of the graphene-based NEM switches of fixed-fixed ends design [...] Read more.

The miniaturization trend leads to the development of a graphene based nanoelectromechanical (NEM) switch to fulfill the high demand in low power device applications. In this article, we highlight the finite element (FEM) simulation of the graphene-based NEM switches of fixed-fixed ends design with beam structures which are perforated and intact. Pull-in and pull-out characteristics are analyzed by using the FEM approach provided by IntelliSuite software, version 8.8.5.1. The FEM results are consistent with the published experimental data. This analysis shows the possibility of achieving a low pull-in voltage that is below 2 V for a ratio below 15:0.03:0.7 value for the graphene beam length, thickness, and air gap thickness, respectively. The introduction of perforation in the graphene beam-based NEM switch further achieved the pull-in voltage as low as 1.5 V for a 250 nm hole length, 100 nm distance between each hole, and 12-number of hole column. Then, a von Mises stress analysis is conducted to investigate the mechanical stability of the intact and perforated graphene-based NEM switch. This analysis shows that a longer and thinner graphene beam reduced the von Mises stress. The introduction of perforation concept further reduced the von Mises stress at the graphene beam end and the beam center by approximately ~20–35% and ~10–20%, respectively. These theoretical results, performed by FEM simulation, are expected to expedite improvements in the working parameter and dimension for low voltage and better mechanical stability operation of graphene-based NEM switch device fabrication. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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8 pages, 4224 KiB

Open AccessLetter

Hard-Baked Photoresist as a Sacrificial Layer for Sub-180 °C Surface Micromachining Processes

by Hani H. Tawfik, Mohannad Y. Elsayed, Frederic Nabki and Mourad N. El-Gamal

Micromachines 2018, 9(5), 231; https://doi.org/10.3390/mi9050231 - 11 May 2018

Cited by 4 | Viewed by 4448

Abstract

This letter proposes a method for utilizing a positive photoresist, Shipley 1805, as a sacrificial layer for sub-180 °C fabrication process flows. In the proposed process, the sacrificial layer is etched at the end to release the structures using a relatively fast wet-etching [...] Read more.

This letter proposes a method for utilizing a positive photoresist, Shipley 1805, as a sacrificial layer for sub-180 °C fabrication process flows. In the proposed process, the sacrificial layer is etched at the end to release the structures using a relatively fast wet-etching technique employing resist remover and a critical point dryer (CPD). This technique allows high etching selectivity over a large number of materials, including silicon-based structural materials such as silicon-carbide, metals such as titanium and aluminum, and cured polymers. This selectivity, as well as the low processing thermal budget, introduces more flexibility in material selection for monolithic integration above complementary metal oxide semiconductor (CMOS) as well as flexible substrates. Full article

(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)

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