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

Rajesh Uppal January 29, 2023 Manufacturing, Material, Nanotech Comments Off on Nanoelectromechanical Systems (NEMS) for sensing, displays, portable power generation, energy harvesting, drug delivery and imaging 2,168 Views

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.

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.

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.

Graphene-Based Nano-Electromechanical Resonators

A resonator measures the target parameters by detecting the frequency signal. It has the advantages of high resolution, good stability, and strong anti-interference ability, which is widely used in various fields. In recent years, efforts have been made to design new generation resonators with high sensitivity, fast response, and high consistency. Importantly, the miniaturization of resonators has a great significance to meet these requirements. The silicon-based microstructure, which has witnessed a mature development in these years, is prone to degrading at the nanometer scale, limiting the further development of resonators in miniaturization and integration

The emergence of graphene and other two-dimensional materials overcomes the limitation in the characteristic size of silicon-based micro-resonators and paved the way in the realization of nano-mechanical resonators. Graphene has a high elasticity modulus, low surface density, and high surface area-to-volume ratio, leading to a significant enhancement in resonant frequency and sensitivity to external parameters, such as force, pressure, and mass. However, the miniaturization also reduces the performance of the graphene devices, which is reflected in the rather low-quality factor and low signal-to-noise ratio at room temperature

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.

Light-Powered Nanomotors Perform as Ultrasmall Energy Converters

Researchers at the University of Texas (UT) reported in July 2022 to have designed a solid-state, optical nanomotor that uses light to power functional devices at the nanoscale — without the challenges that hinder nanomotors operating in liquid environments. According to the research team, its light-driven nanomotor, which is less than 100 nm in width, is the first such device to operate in a solid state.

With their capability to operate on-chip in an ambient environment, the tiny, light-driven motors could have many possible uses. The spinning motion of the motors could pick up dust and other particles, making them useful for air quality measurements. The nanomotors could also serve as the engines that propel nanodevices such as drug delivery mechanisms in the human body, and they could power tiny drones and other miniature vehicles for performing tasks including measurement and surveillance.

The opto-thermocapillary nanomotor rotates on a solid substrate when illuminated with light. The solid state of the nanomotor is possible because of the researchers’ design incorporation of a thin layer of phase change material on the solid substrate.

When the thin film is exposed to light, it undergoes a local, reversible change from a solid to a quasi-liquid phase. This phase change reduces the friction force of the nanomotor and drives the rotation.

Nanomotors in liquid environments must contend with the effects of Brownian motion, a phenomenon that occurs when water molecules push the light-driven nanomotors off their spin. The smaller the motor, the stronger the Brownian motion becomes. When the motor is removed from a liquid solution, Brownian motion is suppressed — and one of the biggest hurdles restricting the application of nanomotors is overcome.

The UT team demonstrated an orbital rotation of 80-nm gold nanoparticles around a laser beam on a solid substrate by optically controlling the nanomotor’s particle-substrate interactions and thermocapillary actuation.

According to the researchers, nanomotors constitute the middle ground in scale between molecular machines at the smaller end and micro-engines at the larger end. It is known that nanomotors mimic biological structures. In nature, biological “motors” drive the division and movement of cells. The combined effort of these bio-motors helps give organisms mobility. Additionally, they are part of the growing field of miniature power sources.

The researchers will continue to improve the optical nanomotors, enhancing their performance by making them more stable and easier to control. These refinements will enable the nanomotors to convert light to mechanical energy at higher rates.

Additionally, the light-driven nanomotors could potentially be used in place of batteries to generate mechanical motion and power. As fuel-free, gear-free engines for converting light into mechanical energy, they could power a range of solid-state micro- and nano-electro-mechanical systems.

The research was published in ACS Nano (www.doi.org/10.1021/acsnano.1c09800).

Nanoelectromechanical Systems Market Overview

The current market for NEMS devices is in its infancy. 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 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. It is poised to grow by $ 216. 53 mn during 2022-2026, accelerating at a CAGR of 29.

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 standardization. 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.

Rising automotive industry as one of the prime reasons driving the nanoelectromechanical systems (NEMS) market growth during the next few years. Also, growing investments on R&D facilities by the vendors and integration of sensors in devices used daily such as mobiles will lead to sizable demand in the market.

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.

It is segmented into nanotweezers, nanoresonators, gyroscopes, nanosensors, nanorobots, nanotweezers, and other tiny components.

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