Nanofabrication

Nanofabrication

Micro and nanofabrication technology has revolutionized different sectors including computer science. The techniques ensure the production of mass fabrication systems with complex functionalities and geometries like biosensors. Notably, scientists invented micro and nanofabrication methods for use in the semiconductors sector, but their success led to the adoption in medical and biological industries. Nevertheless, both techniques have yielded a wide variety of possibilities, especially in the study of chemical processes at a molecular scale. In addition, nanofabrication is applicable in the design and manufacture of synthetic devices that interact successfully with tecnological systems.

According to Haynes et al. (5607), the integration of nanofabrication and microfabrication technology results in nanodevice design principles for detection of substances, analysis of the environment, and release of specific molecules. In essence, such principles combine micro-electromechanical systems, responsive polymers, nucleotides, and nanoparticles. The advancement in the combination of micro-electromechanical systems with polymers has resulted in the design of controlled release system. For instance, in the latest research on physiologically responsive elements, nanotechnology experts have discovered the design framework for developing environmentally responsive systems. Besides, biological molecular recognition systems are used today to design DNA-fueled molecular machines and other novel nanotech devices.

Microfabrication Techniques

There are several techniques applied in the fabrication of microdevices. Of keen to note is that the process of micro-fabrication utilizes semiconductor techniques sequentially for the desired structure. Thereafter, the designers incorporate substrate material for bulk micro-matching, though they can also apply surface micro-matching for a combination of both in the fabrication of the desired device (Madou17).

            The most important micro-fabrication techniques are film deposition, bonding, photolithography, etching, and soft lithography. Technology experts use photolithography to mount a user-generated device onto a material by exposing it to a photo-sensitive polymer. On the other hand, soft lithography entails three sequential techniques for generating and using dimethylsiloxane poly mold. Further, film disposition leads to the formation of micro-thick films on the substrate surface. In contrast, etching utilizes physical or chemical processes to remove unwanted materials on the surface of a micro-device. Lastly, bonding mixes different substrates without the utilization of intermediary layers.

Photolithography

Figure 1: The Process of Photolithography

Designers employ photolithography to incorporate patterns in a material. Mostly, they apply ultraviolet light in particular steps (as highlighted in figure 1) to generate a pattern on a light-sensitive material. For instance, a mask with opaque region illuminates photoresist’s light-sensitive areas for the best outcome. Depending on the photoresist type used, the outcome can either be cross-linked, or soluble, hence the pattern.

Soft Lithography

Figure 2: The Process of Soft Lithography

Similar to photography, soft lithography transfers an outline onto a surface but utilizes a molding polymer’s micro-structure replica. Often, poly dimethyl siloxane (PDMS) is used in biomedical labs because of its biocompatibility and mechanical properties (Xia and George 158). Soft lithography is relatively inexpensive technique since the mold is reusable. The three soft lithography steps are micro-stamping, microfluidic patterning, and stencil patterning (figure 2).

Film Deposition

Film deposition technique involves the application of films or growth material layers on a microstructure surface. Films act as sacrificial layers to protect the main material from etching. Some of the materials used in film generation are metals, plastics, and silicon.

Etching

Figure 3: Etching

Etching creates topographical features on material’s surface through chemical or physical means. The two Etching mechanisms are isotropism and anisotropy as shown in figure 3.

Bonding

Designers understand that both irreversible and reversible bonds tighten seals in microstructures. For instance, they apply irreversible anodic bonding to impure glass film and silicone substrates to form a stronger micro-structure. In addition, the use of adhesives, pressurization, and extreme heating result in bond formation.

Transformation of Elements to Microdevices

Microfabrication is a compilation of several technologies to make microdevices. Fabrication of a microdevice involves execution and repetition of several processes that include film deposition, patterning, and portion removal. In this way, the film gets the desired features in terms of extinction coefficient, thickness, and refractive index. For instance, in a memory chip, there are 15 doping steps, 20 lithography steps, and 11 oxidation steps for a suitable device behavior. Scientists describe the complexity and uniqueness of microfabrication process via mask count. Essentially the different layers, processes, and steps make up the final device.  In addition, the designers construct microdevices using one or more thin films, although their exact role is dependent on the type of device. In electronic devices, films are insulators or conductors while in optical devices, they reflect or refract light.

Nanofabrication Techniques

            Designers can utilize micro-fabrication techniques such as soft lithography in the formation of 1-100nm nanostructures. However, exclusive miniaturization employs special lithographic techniques such as electron beam lithography, colloid monolayer lithography, and focused ion beam lithography. Other nanofabrication methods are molecular self-assembly, ion projection lithography, x-ray lithography, and electrically-induced nanopatterning.

Electrically-Induced Nanopatterning

Figure 4: Electrically Induced Nanopatterning Process

 In figure 4 (A), there are two electrodes in a system used for electrically-induced micropatterning. An air gap of thickness separates the top and bottom electrodes to allow the movement of electrostatic forces over surface tension forces, hence the development of instability on the polymer. In figure 4 (B), instability columns mimic the format of the top electrode.  Therefore, this technique utilizes the interactions between electric field gradient and dielectric fluid film for the production of lateral patterns.

X-ray lithography

X-ray Lithography technique applies 4nm radiation wavelengths to transfer a pattern to a substrate material from a mask. Usually, silicon carbide from tantalum and tungsten constitute X-ray masks. In addition, parameters like Fresnel diffraction and photoelectron diffusion influence the technique’s resolution.

Ion Projection Lithography

In this lithographic form, the designers expose the wafer to helium or hydrogen ions. However, the use of a mask prevents the exposure specific substrate parts to ions, just like in photolithography (Melngailiset al 14). Still, the ions, in this case, contain an absorbent element to inhibit the projection of ions to the underlying layer.

Rapid Prototyping

Rapid prototyping entails combination of numerous nanofabrication methods to generate complex multi-layered structures, chemical functionality structures, and geometrical structures. Today, designers use CAD (Computer Aided Design) to regulate and monitor the fabrication process.

Molecular Self-Assembly

Molecular self-assembly technique is based on the thermodynamic interaction of protein and DNA molecules. They assemble spontaneously in stable conformations supported by electrostatic and hydrophobic, and hydrogen bonds. As a result, it this technique fabricates 3D structures and material’s molecular control.

            In summary, the utilization of nanofabrication and microfabrication techniques has led to the innovation of novel devices used today in different sectors. Their long-term use guarantees enhanced control feature geometry and feasibility in industrial mass production. Further, these techniques enable the production of devices at a molecular level, hence encouraging further studies on manipulation of atoms, and tissues. Most importantly, this technology eliminates persistent challenges in materials science, chemistry, and physics.

Works Cited

Haynes, Christy L., and Richard P. Van Duyne. "Nanosphere Lithography: A Versatile Nanofabrication Tool for Studies of Size-Dependent Nanoparticle Optics." The Journal of Physical Chemistry B 105.24 (2011): 5599-5611.

Madou, Marc J. Fundamentals of Microfabrication: The Science of Miniaturization. Philadelphia: CRC press, 2012: 1-73. Print.

Melngailis, John, et al. "Ion Projection Lithography." Photomask Japan Symposium on Photomask and X-Ray Mask Technology V. New York: International Society for Optics and Photonics, 2015: 8-42. Print.

Xia, Younan, and George M. Whitesides. "Soft Lithography." Annual Review of Materials Science 28.1 (2013): 153-184.