Nanoelectromechanical systems
NEMS typically integrate transistor-like nanoelectronics with mechanical actuators, pumps, or motors, and may thereby form physical, biological, and chemical sensors.
The expected benefits include greater efficiencies and reduced size, decreased power consumption and lower costs of production in electromechanical systems.
[8][9][10][11] At UC Berkeley, a group led by Hisamoto and TSMC's Chenming Hu fabricated FinFET devices down to 17 nm channel length in 1998.
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.
[16] 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.
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.
Because carbon based products can be properly controlled and act as interconnects as well as transistors, they serve as a fundamental material in the electrical components of NEMS.
[33] Similarly, other changes to the electronic and mechanical attributes of carbon based materials must fully be explored before their implementation, especially because of their high surface area which can easily react with surrounding environments.
Graphene's mechanical and electronic properties have made it favorable for integration into NEMS accelerometers, such as small sensors and actuators for heart monitoring systems and mobile motion capture.
The spring mass provides greater accuracy, and the piezoresistive properties of graphene converts the strain from acceleration to electrical signals for the accelerometer.
The suspended graphene ribbon simultaneously forms the spring and piezoresistive transducer, making efficient use of space in while improving performance of NEMS accelerometers.
NEMS frequently utilize silicon due to well-characterized micromachining techniques; however, its intrinsic stiffness often hinders the capability of devices with moving parts.
A study conducted by Ohio State researchers compared the adhesion and friction parameters of a single crystal silicon with native oxide layer against PDMS coating.
PDMS is a silicone elastomer that is highly mechanically tunable, chemically inert, thermally stable, permeable to gases, transparent, non-fluorescent, biocompatible, and nontoxic.
PDMS can form a tight seal with silicon and thus be easily integrated into NEMS technology, optimizing both mechanical and electrical properties.
Contact angle measurements and Laplace force calculations support the characterization of PDMS's hydrophobic nature, which expectedly corresponds with its experimentally verified independence to relative humidity.
PDMS’ adhesive forces are also independent of rest time, capable of versatilely performing under varying relative humidity conditions, and possesses a lower coefficient of friction than that of Silicon.
[40] Researchers from the National University of Singapore invented a polydimethylsiloxane (PDMS)-coated nanoelectromechanical system diaphragm embedded with silicon nanowires (SiNWs) to detect chloroform vapor at room temperature.
In addition to its inherent properties discussed in the Materials section, PDMS can be used to absorb chloroform, whose effects are commonly associated with swelling and deformation of the micro-diaphragm; various organic vapors were also gauged in this study.
The constituting elements of bio-nanoelectromechanical systems (BioNEMS) are of nanoscale size, for example DNA, proteins or nanostructured mechanical parts.
Through continuum mechanics and molecular dynamics (MD), important behaviors of NEMS devices can be predicted via computational modeling before engaging in experiments.
[43][44][45][46] Additionally, combining continuum and MD techniques enables engineers to efficiently analyze the stability of NEMS devices without resorting to ultra-fine meshes and time-intensive simulations.
[24] Due to its large surface area to volume ratio and sensitivity, adhesion and friction can impede performance and reliability of NEMS devices.
These tribological issues arise from natural down-scaling of these tools; however, the system can be optimized through the manipulation of the structural material, surface films, and lubricant.
[56] Some mechanical properties, such as hardness, elastic modulus, and bend tests, for nano-materials are determined by using a nano indenter on a material that has undergone fabrication processes.
[58] Effects of residual stresses include but are not limited to fracture, deformation, delamination, and nanosized structural changes, which can result in failure of operation and physical deterioration of the device.
For instance, in various photovoltaic and light emitting diodes (LED) applications, the band gap energy of semiconductors can be tuned accordingly by the effects of residual stress.
[citation needed] Recently, nanowires of chalcogenide glasses have shown to be a key platform to design tunable NEMS owing to the availability of active modulation of Young's modulus.
It is incorporation of electronic displacement transducers based on piezoresistive thin metal film facilitates unambiguous and efficient nanodevice readout.
The functionalization of the device's surface using a thin polymer coating with high partition coefficient for the targeted species enables NEMS-based cantilevers to provide chemisorption measurements at room temperature with mass resolution at less than one attogram.
