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Nanoelectromechanical Systems (NEMS) for sensing, displays, portable power generation, energy harvesting, drug delivery and imaging

MEMS is a word used for miniaturized devices that are based on Silicon technology or traditional precision engineering, chemical or mechanical. MEMS stands for MicroElectroMechanical Systems denoting man-made mechanical elements, sensors, actuators, and electronics that were produced using microfabrication technology and are integrated on a silicon substrate. The critical structural elements are on the micrometer length scale. These MEMS can be found in several commonly used electromechanical devices, such as accelerometers for airbags, sensors, microphones, LOC’s (lab-on-a-chip), and optical switches.

 

Nanofabrication technology has made significant progress more recently, and it is now possible to further scale MEMS down to nanoelectromechanical systems (NEMS). NEMS is a class of devices integrating electrical and mechanical functionality on the nanoscale ( that have critical structural elements at or below 100 nm.)

 

NEMS & Nanowires are very attractive because of their intrinsic advantages and because they offer the possibility of innovating approaches for the sensors field and the CMOS industry. Their properties include compactness and low cost low power consumption (simplified analog circuit associated with NEMS), good SNR (reduction of parasitics essential for NEMS/Nanowires). However, transitioning nanoscale devices from the realm of one-of-a-kind feats into robust and reproducible nanosystems – that is, useable technology – is a monumental challenge. How

 

NEMS properties

Nanometer range dimensions lead to low mass, high mechanical resonance frequencies, potentially large quantum mechanical effects such as zero-point motion, and a high surface-to-volume ratio useful for surface-based sensing mechanisms.

 

NEMS has several fascinating attributes. It can provide access to fundamental frequencies in the microwave range, force sensitivities at the attonewton level, heat capacities far below a yoctocalorie, active masses in the femtogram range, mass sensitivity at the levels of individual molecules — the list goes on.

 

mems and nems

Due to their low power consumption, fast response time, large dynamic range, high-quality factor, and low mass, NEMS have achieved unprecedented measurement sensitivity. The extremely high fundamental resonance frequencies, diminished active masses, and tolerable force constants; the quality (Q) factors of resonance are in the range Q~10^3–10^5—significantly higher than those of electrical resonant circuits. These attributes collectively make NEMS suitable for a multitude of technological applications such as ultrafast sensors, actuators, and signal processing components.

 

Smaller mass with higher surface area to volume ratio and are therefore most interesting for applications regarding high-frequency resonators and ultrasensitive sensors. Examples for NEMS comprise nanoresonators and nanoaccelerometers, integrated peizoresistive detection devices. NEMS resonators are used for ultrasensitive mass detection through Shift of NEMS resonant frequency caused by mass loading .

 

A generic multiterminal electromechanical device consist of  electromechanical transducers that provide in-put mechanical stimuli to the system, and read out its mechanical response. At additional control terminals, electrical signals—either quasistatic or time varying—can be applied, and subsequently be converted by the control transducers into forces to perturb the properties of the mechanical element .

 

Safety is a key area which will determine the efficiency and usage level of sensors in aerospace and defense. Also, the rising need for sensors that exhibit reliability and resilience under extreme environmental conditions will be a key driving factor for development of rugged sensors in defense and aerospace.

 

Current challenges in NEMS concern the tailored production of metallic or semiconducting Carbon nanotubes as well as stiction and lubrication issues. As the scale of the technologies decreases, devices such as Micro-Mechanical Devices (MMDs) and magnetic hard disk system require an ever decreasing scale of lubrication technology. Monomolecular films, by necessity, are required to provide friction control, wear protection, and system durability. Therefore, film designs are needed to protect such systems.  Monomolecular lubricant films are a hot topic of research.

 

Manufacturing

NEMS typically integrate transistor-like nanoelectronics with mechanical actuators, pumps, or motors, and may thereby form physical, biological, and chemical sensors. Usually, NEMS rely on carbon-based materials, including diamond, carbon nanotubes and graphene.

Nanoelectromechanical Systems (NEMS) | SpringerLink

NEMS can either be produced bottom-up (e.g. chemical self assembly methods, CVD methods, hot plate technique), top-down (e.g. metallic thin films or etched semiconductor layers that are produced with the help of etching, with scanning probe tools or with nanolithography methods) or via combined methods where molecules are integrated into a top-down framework. Carbon (graphene, carbon nanotubes) is a major material used in current NEMS.

 

Top-down approach: It uses conventional microfabrication techniques, such as the electron or optical beam lithography and thermal treatments, to build devices. Although it provides greater control over the resulting structures, it is limited by the resolution of the technique being used. In this approach, starting materials are relatively large structures such as silicon crystals. Generally, etched semiconductors layers or metallic thin films are used to fabricate NEMS devices such as nanorods, nanowires, and patterned nanostructures.

 

In some cases, large materials are crushed to the nanometer scale to increase the surface area to volume ratio, which ultimately enhances the reactivity of nanomaterials. The manufacturing process of carbon nanotubes using graphite in an arc oven is a perfect example top-down approach.

 

Bottom-up approach: It uses the chemical characteristics of molecules to organize or assemble them in the desired conformation. These approaches rely on the concepts of molecular recognition (specific interaction between two or more molecules) or molecular self-assembly (without external direction). While it provides limited control over the fabrication process, one can build much smaller structures without wasting a lot of material as compared to top-down approaches.

 

The bottom-up approach can also be found in nature. For example, biological systems exploit chemical forces to produce cell structures required for life. Researchers try to imitate this behavior of nature to create clusters of certain atoms that can self-assemble into some useful structures. One good example of such approaches is the manufacturing of carbon nanotubes using a metal-catalyzed polymerization technique.

 

Materials Used For Making NEMS

1. Polydimethylsiloxane

Polydimethylsiloxane is the most used silicon-based organic polymer. This silicone elastomer is known for its unique properties. It is thermally stable, chemically inert, mechanically configurable, optically clear, and in general, non-toxic, inert, and non-flammable. Since it can form a tight seal with silicon, it can be integrated into NEMS, configuring both electrical and mechanical characteristics. The adhesive forces of polydimethylsiloxane better perform under varying humid environments and possess a lower coefficient of friction compared to silicon.

 

Polydimethylsiloxane’s low friction coefficient and hydrophobicity make it a perfect material to be incorporated within NEMS research. It is also gaining attention in NEMS technology due to its time-efficient and inexpensive manufacturing. Studies show that the degradation rate of polydimethylsiloxane in light, heat, and radiation can be slowed with appropriate packaging and good aging stability

 

2. Micro and Nano Electromechanical Systems based on Gallium Nitride

MEMS successes are today based on top-down microfabrication and mostly silicon material. NEMS miniaturized mechanical structures offer promising routes for increasing devices sensistivity. However, many sensors markets in industry, exploration, and defense cannot use current MEMS/NEMS technologies because or performance degradation in harsh environments: high temperatures, high vibrations/accelerations, radiations, or corrosive media. In this context, NEMSGAN proposal aims at investigating the use of novel III-N materials and demonstrate the first nitride NEMS integrated inertial sensors.

 

These devices would withstand harsh environments in particular temperatures from 500K to 800K due to epitaxial nitrides robustness and specific refractory technologies developped for the transducers. Nitride NEMS will also take advantage of novel piezo-response phenomena for improved transducers response. They will combine nanostructures to micro-sized moving parts for optimizing the signal-to-noise ratio, having low power consumption and a high measuring bandwidth.

 

3. Carbon-based materials 

Carbon allotropes, specifically graphene and carbon nanotube, are widely used in NEMS technology. Their characteristics directly meet the requirement of NEMS. For example, the semiconductor and metallic conductivities of carbon allotropes enable them to operate as transistors. In addition to the mechanical advantages of carbon allotropes, the electrical properties of graphene and carbon nanotubes allow them to be be used in several components of NEMS. The physical strength of graphene and carbon nanotubes fulfill higher stress demands. Thus, they are majorly used in NEMS technological development. While Graphene NEMS can operate as mass and force sensors, the carbon nanotubes NEMS have been widely utilized in nanomotors (that generate forces on the order of piconewtons), switches, and high-frequency oscillators.

NEMS - NanoElectroMechanical Systems | A Simple Overview - RankRed

3. Biological machines 

Nanorobots

Biological machines, such as myosin (handles muscle contraction), are the most complex macromolecular machines found within cells, typically in the form of multi-protein complexes. Some of them are responsible for energy production and some for gene expression. They might play a crucial role in nanomedicine. For instance, they could be used to detect and destroy tumor cells.

 

Molecular nanotechnology is an emerging field of nanotech that explores the possibility of engineering biological machines, which could rearrange matter at an atomic scale. BioNEMS includes biological and synthetic structural elements (of nanoscale size) for  biomedical /robotic applications. Nanorobots, for example, can be injected into the body to identify and repair infections. While the proposed elements of BioNEMS, such as nanorobots and molecular assemblers, are far beyond current capabilities, several studies have yielded promising results for future applications.

 

 

NEMS Applications

NEMS applications are envisaged in sensing, displays, portable power generation, energy harvesting, drug delivery and imaging. One of their most promising applications is the combination of biology and nanotechnology. Nanoresonators would find application in wireless communication technologies, while nanomotors might be used in nanofluidic pumps for biochips or sensors.

 

Semiconductor Industry: The most widely used semiconductor device is the MOSFET. It accounts for 99.9% of all transistors. Considering the gate length of transistors in CPU or DRAM devices, the critical length scale of integrated circuits is already below 50 nanometers. Recent silicon MOSFETs are based on fin field-effect transistors that utilize 10 nm and 7 nm process.

 

Automotive: Nanomaterials, such as nanosheets, nanofibers nanotubes, nanowires, and nanorods, offers several benefits in the automotive sectors. For example, nano-additives can improve the lifetime of tires significantly, as well as the abrasion resistance, rolling resistance, and wet traction. NEMS is also the key to improving fuel cell performance of future generation of hydrogen-powered cars.

 

Communication: Due to unique mechanical properties (which enables high-resonance frequencies and high-frequency tunability), NEMS resonators, including graphene resonators, provide a promising basis for future ultrafast communication systems. However, most of the developments in this field are currently confined to theoretical models, simulations, and lab experiments.

 

Medical Sector: NEMS sensors detect and monitor patients’ data such as water level, glucose level, and presence of various proteins and ions. These sensors can be configured to identify particular proteins ranging from human albumin to beta-2-microglobulins. In addition to monitoring, they can separate cells of different sizes, preventing clogging in a microfluidic system.

 

Energy Storage and Production: Nanotechnology holds great promise for increasing the lifetimes and performance of lithium-ion batteries. It also has the potential to enhance the power density, shorten the recharge time, as well as reduce the weight and size while improving the stability and safety of the batteries. Furthermore, research is ongoing to use nanoscale electrochemical devices, like galvanic or fuel cells, to produce energy. They are bio-nano generators that draw power from blood glucose in a living body (in the same way the body generates energy from food).

 

The fusion of MEMS/NEMS with nanophotonic elements opens up new possibilities and creates novel, functional photonic devices and systems featuring dynamic tunability, enhanced performance and a higher level of integration.

There is also research into several nanostructured materials, especially nanowires, with the aim to develop more efficient and inexpensive solar cells than are possible with traditional planar silicon solar cells.

 

World’s smallest accelerometer points to new era in wearables, gaming

Researchers at KTH in Sep 2019 reported to have developed the smallest accelerometer yet reported, using the highly conductive nanomaterial, graphene. The tiny accelerometer  was made by an international research team involving KTH Royal Institute of Technology, RWTH Aachen University and Research Institute AMO GmbH, Aachen.

 

“We can scale down components because of the material’s atomic-scale thickness, and it has great electrical and mechanical properties,” Fan says. “We created a piezoresistive NEMS accelerometer that is dramatically smaller than any MEMS accelerometers available today, but retains the sensitivity these systems require.”

 

The future for such small accelerometers is promising, says Fan, who compares advances in nanotechnology to the evolution of smaller and smaller computers. “This could eventually benefit mobile phones for navigation, mobile games and pedometers, as well as monitoring systems for heart disease and motion-capture wearables that can monitor even the slightest movements of the human body,” he says.

 

Other potential uses for these NEMS transducers include ultra-miniaturized NEMS sensors and actuators such as resonators, gyroscopes and microphones. In addition, these NEMS transducers can be used as a system to characterize the mechanical and electromechanical properties of graphene, Fan says.

 

Max Lemme, professor at RWTH, is excited about the results: “Our collaboration with KTH over the years has already shown the potential of graphene membranes for pressure and Hall sensors and microphones. Now we have added accelerometers to the mix. This makes me hopeful to see the material on the market in some years. For this, we are working on industry-compatible manufacturing and integration techniques.”

 

Chinese Researchers develop Si-based super-high frequency nanoelectromechanical resonator reported in Dec 2020

Silicon single-electron/hole transistors (SETs/SHTs) and super-high frequency nanoelectromechanical resonators show great potentials in quantum computation, sensing and many other areas. Recently, a group led by Prof. GUO Guoping from the University of Science and Technology of China of the Chinese Academy of Sciences, collaborating with Prof. ZHANG Zhen’s group from Uppsala University, Sweden, designed and fabricated CMOS-compatible suspended SHT devices which worked as super-high frequency nanoelectromechanical resonators. The work was published in Advanced Materials.

 

The researchers developed the devices using the standard complementary metal-oxide-semiconductor (CMOS) fabrication technology, which is convenient for large-scale integration. The observed Coulomb diamond transport features confirmed the formation of SHT. When suspended, the SHT can also work as a super-high frequency nanoelectromechanical resonator, demonstrating excellent mechanical properties. At ultra-low temperature and under high vacuum, the device showed single-hole tunneling behavior and a mechanical resonance at a record high value of 3 GHz.

 

These properties will be helpful for exploring the interactions between mechanical vibrations and charge carriers, and investigating potential quantum effects. Besides, the researchers found that the electrical readout of the mechanical resonance mainly relied on piezoresistive effect, and was strongly correlated to single-hole tunneling. In the SHT regime, the piezoresistive gauge factor was an order of magnitude larger than that at other different driving powers. This property can be applied to study the piezoresistive effect of silicon in nanoscale and more novel mechanical sensing devices’ design.

 

 

A graphene NEMS switch to protect against electrostatic discharging

One of the most pervasive reliability problems facing the computer chip industry is ESD (electrostatic discharging) failure caused by the rapid, spontaneous transfer of electrostatic charge induced by a high electrostatic field. In order to protect integrated circuits (IC) from being damaged by ESD, chip manufacturers place dedicated ESD protection structures at I/O and power lines on the chip.

 

For decades, conventional on-chip ESD protection structures for ICs has relied on in-Si PN-junction-based device structures (e.g., diodes, bipolar junction transistors, MOSFETs and silicon-controlled rectifiers), which have many inherent disadvantages such as substantial parasitic capacitance, PN junction leakage current, and large Si area consumption, unsuitable for ICs at nanoscale nodes.

 

Recently, a research team led by Professors Albert Wang (University of California at Riverside) and Ya-Hong Xie (University of California at Los Angeles) has devised a novel above-IC graphene based nanoelectromechanical system (NEMS) switch structure (gNEMS) for on-chip ESD protection utilizing the unique properties of graphene.

 

gNEMS ESD switch is a two-terminal device with a vacuum gap between a conducting substrate (Si or metal serving as the anode, A) at the bottom and a suspended graphene membrane on top serving as the discharging path. During normal IC operation, the gNEMS switch is at the OFF state and the graphene ribbon is suspended over the trench. When an ESD surge occurs at I/O, the induced electrostatic force pulls down the suspended graphene membrane to touch the bottom conducting layer, forming a discharging path from graphene to ground.

 

Chen points out that, compared with conventional active ESD devices based on PN junctions, this passive gNEMS switch has several advantages: theoretically, it has zero leakage and minimum parasitic capacitance; it also shows dual-polarity ESD protection features while the conventional counterparts can only work for single-polarity protection, which can largely reduce the ESD device area consumptions. Furthermore, graphene shows superior current and heat handling capability. “Most importantly” he notes, “due to the graphene ESD switch being a passive device, it can be fabricated at the CMOS back end through 3D heterogeneous integration, instead of taking up large chip areas with core IC designs.”

 

“While graphene’s unique properties – atomic layer thickness, electron mobility, thermal conductivity, mechanical strength – make it an ideal material for ESD protection, the main challenge is the quality of the graphene material,” Chen concludes. “Currently, due to graphene quality issues during CVD synthesis, reliability and uniformity is a major challenge for the mass production and real application of graphene for ESD applications.

 

Outlook

Future applications of NEMS are hard to predict. The prototype NEMS that would be economically most interesting are the ones that are most hard to be commercialized. Applications that combine biology and nanotechnology seem to be the most promising ones24. Nanoresonators would have direct consequences for the wireless communication technologies.

 

Possible applications of nanomotors might be nanofluidic pumps for biochips or sensors. According to Alex Zettl from Berkeley University, CA, USA, emerging NEMS might also path the way for novel MicroElectroMechanical Systems (MEMS) that currently have major problems with stiction; integrated systems from NEMS and MEMS might be of high relevance (such as MEMS sensors with NEMS as core components), compared to the natural systems in biology, where cells, true micro-objects, have various nanoparts as integrative components.

 

Recent work by the department of Transducers Science and Technology of the University of Twente, Holland, is concentrated on the construction of truly three-dimensional nanostructures. The fields of applications are not yet fully explored but first studies on cell trapping in 3D nanoconfined objects and self-organizing nanoparticles are underway. Recent studies in 3D sculpturing are on corner lithography for advanced probing (smarticles) and ultimately sharp probe tips. This research might lead to interesting emerging MEMS.

 

Bioinspiration

In MEMS and NEMS technology – comparable to biology – a limited number of base materials is used, providing a wide range of functional and structural properties. The complexity of the approach (in biology as well as in engineering) increases with decreasing number of base materials. Biomimetics, i.e., technology transfer from biology to engineering, is especially promising in MEMS development because of the material constraints in both fields.

 

Diatoms are single celled organisms that have moving parts in relative motion on the nanoscale. Diatoms are algae that live in houses made of glass. They are the only organism on the planet with cell walls composed of transparent, opaline silica. Diatom cell walls are ornamented by intricate and striking patterns of silica. Diatoms have light-absorbing molecules (chlorophylls a and c) that collect energy from the sun and turn it into chemical energy through photosynthesis.

 

They are high-potential biological systems that can inspire emerging NEMS technologies: Diatoms such as Eunotia sudetica, Bacillaria paxillifer and species of Ellerbeckia have hinges and interlocking devices on the several 100 nanometer scale, the diatoms Corethron pennatum and Corethron criophilum exhibit click-stop mechanisms on the micrometer lengthscale and below and the unfolding of cells of these species after cell division is an excellent example on how to obtain 3D structures from fabricated 2D structures. Even springs and micropumps might be realized on the micro- and nanoscale, e.g. in the diatoms Rutilaria grevilleana and Rutilaria philipinnarum.

 

Nanoelectromechanical Systems Market Overview

The current market for NEMS devices is in its infancy. It is segmented into nanotweezers, nanoresonators, gyroscopes, nanosensors, nanorobots, nanotweezers, and other tiny components. The global Nanoelectromechanical Systems (NEMS) market size is projected to reach USD 117.8 million by 2026, from USD 46 million in 2020, at a CAGR of 16.8% during 2021-2026.

 

Applications that have either already reached the market or are available as research prototypes comprise ultrasharp tips for atomic force microscopy (e.g., single-walled carbon nanotubes mounted on the tip of an atomic force microscopy cantilever), a nonvolatile NEMS memory, NEMS sensors, Carbon nanotube single electron transistors, nanoelectrometers, relays and switches with nanotubes, pH sensors, protein concentration detectors, etc. The Nanoelectromechanical Systems (NEMS) market was valued at  Million US$ in 2017 and is projected to reach  Million US$ by 2025, at a CAGR of  during the forecast period.

 

The tremendous growth of the NEMS market is primarily due to the increasing demand for precision microscopes and electronics which offers higher functionality, as well as the rapidly transforming communication industry and a surging demand for BioNEMS. Some of the other factors influencing the swift growth of the market include an emphasis on miniaturization of devices to serve multiple purposes, rising demand for monitoring and detection techniques, and reviving the automotive industry with changing standardizations.

 

Higher functionality for electronic devices and rising demand for precision microscopes are some of the major driving factors of the market. For example, a key application of NEMS is atomic force microscope (AFM) tips. NEMS is expected to find its major applications across semiconductor industry. One of the major restraints of the market is its mass production as the methods available for mass production is costly at present. However, NEMS is expected to play a vital role in the communication technology in the coming years.

 

The key players in the market include Agilent Technologies Inc, Bruker Corporation, Showa Denko K.K., Analog Devices, Inc., Materials And Electrochemical Research Corporation, Vistec Electron Beam GmbH, Graphene Frontiers, Amprius, Inc., Broadcom Corporation, Inframat Corporation, Sun Innovations, Nanoshell LLC, Nanocyl, California Institute Of Technology (Caltech), Korea Institute Of Science And Technology, Robert Bosch, Stmicroelectronics, California Institute Of Technology, Sun Innovation Inc, Asylum Research Corporation, and
Texas Instruments

 

References and resources also include:

https://www.azonano.com/article.aspx?ArticleID=2465

https://www.variantmarketresearch.com/report-categories/semiconductor-electronics/nanoelectromechanical-systems-market

https://www.nanowerk.com/spotlight/spotid=51617.php

https://www.kth.se/en/aktuellt/nyheter/world-s-smallest-accelerometer-points-to-new-era-in-wearables-gaming-1.921647

https://www.rankred.com/nems-nanoelectromechanical-systems/

About Rajesh Uppal

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