Chapter 1: MEMS

Micro-electromechanical systems, often known as MEMS, are a technology that involves the creation of microscopic devices that contain both electronic and mechanical components. MEMS are composed of components that range in size from 1 to 100 micrometers (i.e., 0.001 to 0.1 mm), and the size of MEMS devices typically ranges from 20 micrometers to a millimeter (i.e., 0.02 to 1.0 mm). However, the size of components that are stacked in arrays (for example, digital micromirror devices) can be greater than 1000 mm2. In most cases, they are made up of a core unit that processes data (an integrated circuit chip such as a microprocessor), as well as multiple components that interact with the environment (such as microsensors).

The forces that are produced by ambient electromagnetism (such as electrostatic charges and magnetic moments) and fluid dynamics (such as surface tension and viscosity) are more essential design issues for MEMS than they are for larger scale mechanical devices. This is because MEMS have a large surface area to volume ratio. In contrast to molecular nanotechnology and molecular electronics, MEMS technology is distinguished by the fact that the latter two technologies are required to take surface chemistry into consideration.

There was an appreciation for the possibilities of very small machines even before the technology that could manufacture them existed (for an example, Richard Feynman's renowned speech from 1959 titled "There's Plenty of Room at the Bottom"). As soon as MEMS were able to be manufactured using modified semiconductor device fabrication procedures, which are typically utilized in the production of electronic devices, they were practically applicable. Molding and plating, wet etching (KOH, TMAH), dry etching (RIE and DRIE), electrical discharge machining (EDM), and other technologies that are capable of making tiny devices are included in this category.

Nanotechnology and nanoelectromechanical systems (NEMS) are the products of their convergence at the nanoscale range.

An early example of a MEMS device is the resonant-gate transistor, which was invented by Robert A. Wickstrom for Harvey C. Nathanson in 1965. This transistor was an adaption of the MOSFET. An further early example is the resonistor, which is an electromechanical monolithic resonator that Raymond J. Wilfinger patented between the years 1966 and 1971. It was during the 1970s and early 1980s that a variety of MOSFET microsensors were developed for the purpose of monitoring various characteristics, including those that are physical, chemical, biological, and environmental.

1986 was the year when the term "MEMS" was first used. The S.C. In addition to Jacobsen, J.E. Through a proposal that was submitted to DARPA on July 15, 1986 and named "Micro Electro-Mechanical Systems (MEMS)," Wood, who was the Co-PI, was the one who first suggested the term "MEMS." The project was awarded to the University of Utah. During a talk that was invited by S.C., the term "MEMS" was introduced to the audience. "Micro Electro-Mechanical Systems (MEMS)" was presented by Jacobsen at the IEEE Micro Robots and Teleoperators Workshop, which took place in Hyannis, Massachusetts, from November 9th to 11th, 1987.A manuscript that was submitted by J.E. was the source of the publication of the term "MEMS." According to Wood, S.C. Jacobsen, and K.W. In the IEEE Proceedings Micro Robots and Teleoperators Workshop, which took place in Hyannis, Massachusetts, from November 9th to 11th, 1987, Grace presented a paper with the title "SCOFSS: A Small Cantilevered Optical Fiber Servo System." On top of MEMS structures, CMOS transistors have been fabricated since their implementation.

Both capacitive and ohmic switch technologies are the two fundamental forms of MEMS switch technology. Changes in capacitance are brought about by the utilization of a moving plate or sensing element in the development of a capacitive MEMS switch. Cantilevers that are controlled by electrostatic forces are used to control ohmic switches. Metal fatigue of the MEMS actuator (cantilever) and contact wear are two factors that can cause ohmic MEMS switches to fail. Cantilevers can bend over time, which allows for contact wear.

MEMS fabrication emerged from the process technology used in the fabrication of semiconductor devices. The fundamental processes used in MEMS fabrication include the deposition of material layers, patterning by photolithography, and etching in order to achieve the desired forms.

When it comes to MEMS processing, one of the fundamental building elements is the capability to deposit thin films of material with a thickness that can range anywhere from one micrometer to around one hundred micromètres. Despite the fact that the measurement of film deposition might range anywhere from a few nanometers to one micrometer, the NEMS process remains the same. In the following, we will discuss the two distinct types of deposition processes.

PVD, which stands for "physical vapor deposition," is a method that involves removing a material from a target and depositing it on a surface by the use of a vapor. The process of sputtering, in which an ion beam releases atoms from a target, allowing them to move through the intervening space and deposit on the desired substrate, and the process of evaporation, in which a material is evaporated from a target using either heat (thermal evaporation) or an electron beam (e-beam evaporation) in a vacuum system, are both examples of techniques that can be utilized to accomplish this.

Chemical vapor deposition (CVD) is one of the techniques that fall under the category of chemical deposition. In this process, a stream of source gas reacts on the substrate in order to build the material that is needed. LPCVD, which stands for low-pressure chemical vapor deposition, and PECVD, which stands for plasma-enhanced chemical vapor deposition, are two examples of the categories that can be further subdivided into depending on the specifics of the technique. There is also the possibility of growing oxide films by the process of thermal oxidation. This method involves exposing the wafer, which is normally made of silicon, to oxygen and/or steam in order to produce a thin coating of silicon dioxide on the surface.

The act of transferring a pattern onto a substance is referred to as patterning.

In the context of MEMS, lithography is often defined as the process of transferring a pattern into a photosensitive material through the selective exposure of the material to a radiation source similar to light. An example of a substance that undergoes a change in its physical properties as a result of being exposed to a radiation source is said to as photographically sensitive. When a photosensitive material is selectively exposed to radiation (for example, by masking some of the radiation), the pattern of the radiation on the material is transferred to the material that is exposed. This is because the characteristics of the regions that are exposed and those that are not exposed are different.

After that, the exposed zone can be removed or treated, which will eventually provide a mask for the substrate that lies beneath it. Photolithography is frequently utilized in conjunction with wet and dry etching, as well as the deposition of metal or other thin films. When it comes to the creation of structures, photolithography is sometimes utilized in place of any form of post-etching. The generation of SU8-based square blocks is an example of a lens that is based on the SU8 algorithm. A semi-sphere that functions as a lens is then formed by melting the photoresist, which is the next step.

The process of scanning a beam of electrons in a patterned manner across a surface that is covered with a film (referred to as the resist) is known as electron beam lithography (often abbreviated as e-beam lithography). This process involves "exposing" the resist and then selectively removing either exposed or non-exposed regions of the resist (referred to as "developing"). In a manner similar to that of photolithography, the objective is to generate extremely minute structures inside the resist, which may then be transferred to the substrate material, typically by the process of etching. It is also utilized for the development of nanoscale structures, in addition to being developed for the purpose of fabricating integrated circuits. The fundamental benefit of electron beam lithography is that it is one of the methods that may be used to surpass the diffraction limit of light and create features that are in the nanoscale range. The manufacture of photomasks for use in photolithography, the low-volume production of semiconductor components, and research and development are all areas that have found widespread application for this type of maskless lithography methodology. The throughput of electron beam lithography is the most significant constraint of this technique. This refers to the extremely lengthy amount of time required to expose a whole silicon wafer or glass substrate. Being exposed for a prolonged period of time leaves the user susceptible to beam drift or instability, both of which may occur during the exposure. Furthermore, if the pattern is not altered the second time around, the turnaround time for reworking or re-designing is stretched considerably more than it would otherwise be.

It is common knowledge that focused-ion beam lithography is capable of printing lines that are exceedingly thin (less than 50 nm line and space has been achieved), and it does so without the presence of proximity effect. On the other hand, because the writing field in ion-beam lithography is rather small, it is necessary to generate big area patterns by sewing together the smaller fields.

Ion track technology features a deep cutting...