1 Introduction
Microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) are important components of micro/nano technology and are gradually forming a new field of technology. MEMS has been developed on the road to industrialization, and NEMS is still in the basic research stage. This paper analyzes the development characteristics of micro/nano electromechanical systems. After briefly introducing typical MEMS and NEMS devices and systems, it discusses several issues in the development of MEMS and NEMS and the development prospects of MEMS and NEMS.
From the perspective of miniaturization and integration, MEMS (or micro-systems) refers to micro-devices that can be mass-produced, integrating micro-mechanisms, micro-sensors, micro-actuators, and signal processing and control circuits, up to the interface, communication, and power supply. Or system. NEMS (or nanosystem) is a new concept proposed in the late 1990s. It is a kind of ultra-small mechatronic system with nanotechnology characteristics in terms of system feature size and effect after MEMS. Generally speaking, the feature size is in Asia. Devices and systems with nanometers to hundreds of nanometers, with new effects (quantum effects, interfacial effects, and nanoscale effects) produced by nanoscale structures.
MEMS can be seen to some extent as an extension of integrated circuits (ICs). If the IC (microprocessor and signal circuit) can be compared to the human brain and neural network, then MEMS provides the brain with a microsensor to acquire signals and a microactuator to execute commands, such as adding thin films and beams to the circuit. MEMS mechanical components such as springs and gears are capable of sensing, thinking, making decisions and reacting to the environment. NEMS devices based on new effects have higher sensitivity, lower power consumption, and smaller size. Therefore, if the MEMS, NENS and IC are densely integrated into a small volume, the intelligent micro/nano-electromechanical system will improve the system information processing capability and integration, reducing power consumption and volume. For example, the United States is studying the use of MEMS or NEMS resonators to replace the off-chip inductors and capacitors of the RF signal processor, reducing its size by a factor of 100 (from 80 cm2 to less than 0.8 cm2) and reducing power consumption by a factor of 100 (from 300). The mW is reduced to below 0.8 3 mW) and the RF performance (efficiency and bandwidth) is increased by a factor of 10. Future UHF (Ultra High Frequency) communication / GPS reception opportunities such as watch size.
2. Development characteristics of MEMS and NEMS
MEMS and NEMS are multidisciplinary technologies that can be applied and developed in almost all natural and engineering fields, such as OpTIcal-MEMS, RF-MEMS, Bio-MEMS, Power-MEMS, and more. According to the current status and development of MEMS and NEMS, the following characteristics can be roughly seen:
(1) Manufacturing technology is the basis for the development of micro/nano electromechanical systems
After more than a decade of development, a variety of micro-manufacturing technologies have been developed:
a. Silicon micromachining technology based on silicon surface processing and bulk processing; b. LIGA process using X-ray deep lithography and electroforming; c. Development of traditional ultra-precision machining technology, micro EDM processing, EDM, Special micro-machining technology such as ultrasonic processing; in addition, it also includes a combination of various processing technologies.
As micromachining capabilities increase, the characteristic dimensions of micromachining are now extending toward the nanometer. Silicon micromachining systems are also available in nanoscale. The important tools of nanotechnology research in the early 1980s—scanning tunneling microscopy (STM) and atomic force microscopy (AFM)—can be used not only to directly observe the interactions and properties of atoms, molecules, and nanoparticles, but also to characterize nanodevices. The nano-manufacturing technique can move atoms and molecules, construct nanostructures, and study their interactions at the nanoscale.
(2) The mechanism research of microsystems is the basis of its innovative development.
As the scale shrinks to the micron and nanoscale, some of the macroscopic properties of the object will change and some new properties will emerge. As in MEMS, the laws of classical physics are basically applicable. However, in a small space, substances of different nature (solid, liquid, heat, raw, and chemical) are coupled to each other. Some minor influencing factors in the macro world may become important. Under certain conditions, mesoscopic effect. In NEMS, nanoscale structures will produce new effects such as quantum effects, interfacial effects, and nanoscale effects. An in-depth study of these new properties and new effects is the key to the development of MEMS and NEMS technologies.
(3) Demand is the driving force for development.
MEMS and NEMS have the advantages of small size, light weight, low cost, low power consumption, new functions, and mass production, etc. If the developed devices and systems have these advantages, they will have good application prospects. The strong demand traction is the driving force behind the rapid development of MEMS and NEMS research.
MEMS and NEMS are not only a new class of products, but also build a micro-technology development and application platform. On this platform, MEMS and NEMS are combined with different technologies and have a huge impetus to their development. Due to the small scale and multidisciplinary intersection, MEMS and NEMS have also formed a new class of methodology.
3. Examples of MEMS and NEMS devices and systems
Micro-sensor components: There are many types of micro-sensors. The measured parameters include acceleration, pressure, force, touch, flow, magnetic field, temperature, gas composition, humidity, pH, ion concentration and bioconcentration. Typical micromechanical sensor components include pressure sensors, accelerometers, and gyros.
Microfluidic devices: Microfluidic devices are another important class of MEMS devices. It is widely used in systems such as inkjet printing, chip cooling, micro propulsion systems, drug atomization supplies, and biochips. Typical devices such as micropumps and microvalves are microsprayed.
Micro-optics: TI Microsystems developed a DMD (Digital Micromirror Device) using a silicon surface micromachining process. Its display effect exceeds the liquid crystal projection display, and can be used in high-definition television and other fields; in OpTIcal MEMS, optical switches and optical communication have broad development prospects. Figure 6 shows a micro-optical switch array.
Information and bio-MEMS are two important development directions of MEMS, with broad application prospects and market. Such as: RF MEMS switches, RF MEMS filters, RF MEMS oscillators, capacitors, inductors, transmission lines, and micro biosensors, microfluidic chips and more.
Micro-energy devices based on MEMS technology: With the popularization of microelectronic products such as mobile phones, notebook computers, PDAs, and miniature cameras, the miniaturization of energy is urgently required. Micro fuel cells are one of them. The use of MEMS microfluidic technology can greatly improve the fuel cell fuel supply efficiency, and the use of MEMS manufacturing technology can reduce the size of the fuel cell, enabling high-volume, low-cost production.
Microactuators and actuators: Microactuators are an important aspect of today's MEMS development. Micromotors, microjets, microswitches, microspeakers, microresonators, etc. are commonly used. The principles of micro-actuation are: electrostatic, piezoelectric, electromagnetic, thermal, shape memory and other forms.
Some of the above MEMS devices have achieved commercial production, such as pressure sensors, accelerometers, digital micromirrors, micro-jets and biochips, showing good market potential. In addition, MEMS devices are used as components of embedded systems, such as MEMS-based inertial, optical, communication, and energy devices in micro-aircraft.
The NEMS research is still in its infancy. It is estimated that NEMS has significant advantages in terms of high sensitivity, small size, and low power consumption. For example, the sensitivity can be increased by 106, and the power consumption can be reduced by 102.
Nano biodevices: Figure 7, a research team led by Dr. Montemagno of Cornell University in the United States developed a biomolecular motor. The motor consists of an adenosine triphosphatase molecule (ATP), a metal nickel paddle (150 nm in diameter, 750 nm long) and a metallic nickel cylinder (80 nm in diameter, 200 nm high) with an average speed of 4.8 rpm. , running time of up to 40 minutes to 2.5 hours. Biomolecular motors create conditions for the further development of organic or inorganic intelligent nano systems. Another example is Professor Wang Zhonglin from the Georgia Institute of Technology in the United States who used multi-walled carbon nanotubes to develop a nanoresonator. The mass of 30fg (1fg=10-15g) of carbon particles can be weighed by the change of resonance frequency. This type of resonator can be used as a molecular scale to detect the quality of molecules or bacteria.
Nano-sensors: S.Vatannia et al. in the United States have studied the resonant tunneling effect by adding a resonant tunneling displacement converter between the common tunnel gaps to improve the tunnel without reducing the sensitivity and tunneling current. The gap is about 100 angstroms, which not only greatly reduces the difficulty of manufacturing and installing the NEMS system, but also provides a possibility to greatly improve the sensitivity of the tunneling sensor; in addition, one-dimensional or quasi-one-dimensional nanostructures (such as carbon nanotubes and nanometers) With) high toughness, high strength and extremely sensitive conductance. It is made into a nano cantilever beam and used as a sensitive structure of the sensor device to achieve high sensitivity and low power consumption detection.
Information and Interference Devices: Yang, Ekinci, etc. of Caltech in the United States first developed a SiC-NEMS resonant device with a scale of 100 nm, with high frequency (GHZ), high Q (tens of thousands to hundreds of thousands), and low driving power (10- 12W), low thermal noise and high noise-to-noise ratio, etc., can meet the requirements of RF communication systems.
Nanofluidic devices: Nanofluidic systems have feature sizes ranging from a few hundred to a few nanometers. In addition to hydrostatic pressure, electric fields can also be used to control and drive the flow of fluid or the movement of individual molecules in an ionically conductive fluid. Therefore, a nanofluidic system composed of nanofluidic devices can be used for single molecule analysis and detection.
At present, the research fields of MEMS and NEMS are expanding, and new directions such as information (IT), biology (Bio), and energy are gradually formed. And from the research of single MEMS and NEMS devices, the development of MEMS and NEMS devices as components of embedded systems to improve the overall performance and added value of the system, there have been many successful examples.
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