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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Nanoelectromechanical systems | 1/4 | https://en.wikipedia.org/wiki/Nanoelectromechanical_systems | reference | science, encyclopedia | 2026-05-05T03:55:36.112304+00:00 | kb-cron |
Nanoelectromechanical systems (NEMS) are a class of devices integrating electrical and mechanical functionality on the nanoscale. NEMS form the next logical miniaturization step from so-called microelectromechanical systems, or MEMS devices. NEMS typically integrate transistor-like nanoelectronics with mechanical actuators, pumps, or motors, and may thereby form physical, biological, and chemical sensors. The name derives from typical device dimensions in the nanometer range, leading 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. Applications include accelerometers and sensors to detect chemical substances in the air.
== History ==
=== Background ===
As noted by Richard Feynman in his famous talk in 1959, "There's Plenty of Room at the Bottom," there are many potential applications of machines at smaller and smaller sizes; by building and controlling devices at smaller scales, all technology benefits. The expected benefits include greater efficiencies and reduced size, decreased power consumption and lower costs of production in electromechanical systems. The first silicon dioxide field effect transistors were built by Frosch and Derick in 1957 at Bell Labs. In 1960, Atalla and Kahng at Bell Labs fabricated a MOSFET with a gate oxide thickness of 100 nm. In 1962, Atalla and Kahng fabricated a nanolayer-base metal–semiconductor junction (M–S junction) transistor that used gold (Au) thin films with a thickness of 10 nm. In 1987, Bijan Davari led an IBM research team that demonstrated the first MOSFET with a 10 nm oxide thickness. Multi-gate MOSFETs enabled scaling below 20 nm channel length, starting with the FinFET. The FinFET originates from the research of Digh Hisamoto at Hitachi Central Research Laboratory in 1989. At UC Berkeley, a group led by Hisamoto and TSMC's Chenming Hu fabricated FinFET devices down to 17 nm channel length in 1998.
=== NEMS === In 2000, the first very-large-scale integration (VLSI) NEMS device was demonstrated by researchers at IBM. Its premise was an array of AFM tips which can heat/sense a deformable substrate in order to function as a memory device (Millipede memory). Further devices have been described by Stefan de Haan. In 2007, the International Technical Roadmap for Semiconductors (ITRS) contains NEMS memory as a new entry for the Emerging Research Devices section.
== Atomic force microscopy == A key application of NEMS is atomic force microscope tips. The increased sensitivity achieved by NEMS leads to smaller and more efficient sensors to detect stresses, vibrations, forces at the atomic level, and chemical signals. AFM tips and other detection at the nanoscale rely heavily on NEMS.
== Approaches to miniaturization == Two complementary approaches to fabrication of NEMS can be found, the top-down approach and the bottom-up approach. The top-down approach uses the traditional microfabrication methods, i.e. optical, electron-beam lithography and thermal treatments, to manufacture devices. While being limited by the resolution of these methods, it allows a large degree of control over the resulting structures. In this manner devices such as nanowires, nanorods, and patterned nanostructures are fabricated from metallic thin films or etched semiconductor layers. For top-down approaches, increasing surface area to volume ratio enhances the reactivity of nanomaterials. Bottom-up approaches, in contrast, use the chemical properties of single molecules to cause single-molecule components to self-organize or self-assemble into some useful conformation, or rely on positional assembly. These approaches utilize the concepts of molecular self-assembly and/or molecular recognition. This allows fabrication of much smaller structures, albeit often at the cost of limited control of the fabrication process. Furthermore, while there are residue materials removed from the original structure for the top-down approach, minimal material is removed or wasted for the bottom-up approach. A combination of these approaches may also be used, in which nanoscale molecules are integrated into a top-down framework. One such example is the carbon nanotube nanomotor.
== Materials ==
=== Carbon allotropes === Many of the commonly used materials for NEMS technology have been carbon based, specifically diamond, carbon nanotubes and graphene. This is mainly because of the useful properties of carbon based materials which directly meet the needs of NEMS. The mechanical properties of carbon (such as large Young's modulus) are fundamental to the stability of NEMS while the metallic and semiconductor conductivities of carbon based materials allow them to function as transistors. Both graphene and diamond exhibit high Young's modulus, low density, low friction, exceedingly low mechanical dissipation, and large surface area. The low friction of CNTs, allow practically frictionless bearings and has thus been a huge motivation towards practical applications of CNTs as constitutive elements in NEMS, such as nanomotors, switches, and high-frequency oscillators. Carbon nanotubes and graphene's physical strength allows carbon based materials to meet higher stress demands, when common materials would normally fail and thus further support their use as a major materials in NEMS technological development. Along with the mechanical benefits of carbon based materials, the electrical properties of carbon nanotubes and graphene allow it to be used in many electrical components of NEMS. Nanotransistors have been developed for both carbon nanotubes as well as graphene. Transistors are one of the basic building blocks for all electronic devices, so by effectively developing usable transistors, carbon nanotubes and graphene are both very crucial to NEMS. Nanomechanical resonators are frequently made of graphene. As NEMS resonators are scaled down in size, there is a general trend for a decrease in quality factor in inverse proportion to surface area to volume ratio. However, despite this challenge, it has been experimentally proven to reach a quality factor as high as 2400. The quality factor describes the purity of tone of the resonator's vibrations. Furthermore, it has been theoretically predicted that clamping graphene membranes on all sides yields increased quality numbers. Graphene NEMS can also function as mass, force, and position sensors.
==== Metallic carbon nanotubes ====