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Micro-Manufacturing Processes for Gas Sensors
Published in Ankur Gupta, Mahesh Kumar, Rajeev Kumar Singh, Shantanu Bhattacharya, Gas Sensors, 2023
Pankaj Singh Chauhan, Shantanu Bhattacharya, Aditya Choudhary, Kanika Saxena
Patterning is performed to fabricate the desired shape with the help of patterned mask and lithography method [42]. The design of the pattern is formed using a computer-aided design (CAD) program on a suitable material surface. The mask for pattern is formed over glass or a transparent polymeric sheet. A thin layer of photoresist is spin-coated over the material on which the pattern is to be made. The photoresist is a photosensitive material which can be structured by exposing it to a light source (ultraviolet light is used for exposing the photoresist). To align the mask and photoresist-coated substrate, a mask aligner can be used. Both negative and positive types of photoresists can be used. In positive type photoresist, the exposed portion is removed by the developer. While in negative photoresist, the unexposed portion of the photoresist is removed by the developer. The remaining portion of the photoresist in both cases is implied as a protective layer for etching. The etchant removes the selected portion of the metallic coating due to masking by the photoresist. After etching, the remaining portion of the photoresist is removed. The patterning steps are sequenced in a schematic representation shown in Figure 4.2.
Photolithography
Published in Eiichi Kondoh, Micro- and Nanofabrication for Beginners, 2021
A photoresist is coated onto a substrate or wafer by the spin-coating method. A liquid photoresist is applied to a spinning wafer that is vacuum-chucked to a pedestal (Fig. 7.3). A photoresist expands due to the centrifugal force while keeping a good thickness uniformity due to the wetness and viscosity of the liquid. The thickness t is known to be determined by the rotation speed ω (Fig. 7.4). () t∝1ω
Laser-Based Semiconductor Fabrication
Published in Leon J. Radziemski, David A. Cremers, Laser-Induced Plasmas and Applications, 2020
For both projection and contact printing, the resolution of the image is fixed by the wavelength of the radiation used to expose the photoresist. This limitation can be overcome with the use of x-ray or electron beam imaging systems. These two experimental techniques can provide image resolutions of better than 0.5 /xm (Voltmer, 1981) and both techniques can be useful for many types of printing operations. In addition to improved resolution, electron beam processing is also unaffected by distortions in the wafer and can be positioned with great accuracy. However, high production costs and low throughputs are limiting features of this technique. X-ray imaging systems are still at an experimental stage and their utilization will depend on solving a number of alignment problems.
Direct growth of patterned graphene based on metal proximity catalytic mechanism
Published in Journal of Experimental Nanoscience, 2023
Zhihao Ye, Kun Xu, Qianqian Li, Siyuan Lu, Hao Wang, Junxian Zhao, Leiming Chen, Fanguang Zeng, Pei Ding, Ximin Tian, Yinxiao Du
The atmospheric pressure chemical vapour deposition single temperature zone tubular furnace was used in this experiment. The patterned metal layer is fabricated by the ‘photolithography-sputtering-stripping’ process. The specific process is as follows: First, a layer of photoresist was spin-coated on the substrate, and a mask was used to locally expose the photoresist. Then the photoresist was developed. The metal layers were sputtered on the patterned photoresist. After sputtering, the sample was ultrasonically exfoliated in acetone solution. The patterned metal layers were completed. The metal layers were Ti/Cu (40 nm/500 nm) and Ti/Co (40 nm/350 nm). The titanium layer is designed to enhance adhesion and prevent shedding of copper or cobalt film. The position of the metal film is complementary to the growth area of the patterned graphene (square graphene film). The SiO2 layer blocks the direct contact between the metal film and the Si substrate to prevent the metal from polluting the Si substrate.
Increasing silicone mold longevity: a review of surface modification techniques for PDMS-PDMS double casting
Published in Soft Materials, 2021
Ali Ansari, Rajiv Trehan, Craig Watson, Samuel Senyo
PDMS is the primary substrate for bioMEMS due to several advantages including being chemically inert, biocompatible, thermally stable properties,[2] and 3D patterning at cell-scale dimensions of microns or smaller.[14] These advantages allow for PDMS to interact with biological tissues and fluids with minimal risks of direct material-induced effects on associating cells. PDMS resolves micron-scale features to mimic complex biological structures.[12,15] Pre-polymerized PDMS is viscous and conformable; it can be cured upon a master mold to generate a negative impression of mold topological features. Typically, these master molds are patterned photoresist on silicon wafers,[16–18] which is an established technique in engineering solid-state devices. While there are many advantages to being able to use photoresist directly for bottom-up fabrication including high spatial resolution and fidelity of feature transfer, there are still significant challenges, namely, photoresist fragility. Deterioration of photoresist masters such as SU8 has been reported in as little as five replication cycles.[19]
Dielectric and electro-optical properties of zinc ferrite nanoparticles dispersed nematic liquid crystal 4’-Heptyl-4-biphenylcarbonnitrile
Published in Liquid Crystals, 2020
Fanindra Pati Pandey, Ayushi Rastogi, Rajiv Manohar, Ravindra Dhar, Shri Singh
Sample cell holder involves the use of indium tin oxide (ITO) coated glass plates (Diamond Coatings Company, UK) having sheet resistance 40 Ω/□. The glass plates were washed with soap solution, for removing any traces of organic impurities, and then cleaned with acetone for removing traces of dust particles. After cleaning the substrate, photoresist was applied onto the cleaned substrate using spin coating method. The etching process was employed to remove the extra ITO from the substrate excluding the patterned photoresist area of 5 × 5 mm2. In order to ensure the removal of extra ITO the conductivity of the substrate was checked by a multimeter. The substrate was then cleaned with the ultrasonification and acetone. Rubbed polyimide technique with nylon 6/6 as aligner has been used to obtain planar alignment of the LC molecules on ITO substrate. In this process, nylon 6/6 spin-coated substrates were dried at 120°C for 1 h. After drying nylon layer, the substrates were rubbed unidirectionally in an anti-parallel manner. The substrates were then placed one over another with mylar spacer (6 µm) to form sample holder of fixed thickness which behaves as a capacitor. The fabricated sample cells were calibrated using non-polar/non-dispersive standard liquid (benzene) as described in ref [1]. Perfect removal of the benzene was ensured by matching capacitance of the cell before and after filling the cell. Now the samples were filled in sample holders by capillary action in their isotropic liquid phase. The sample was slowly cooled to obtain planar alignments. It is important to mention here that empty sample cells (i.e. air between two plates) show a pseudo relaxation around 8–9 MHz which shifts to 4–5 MHz after filling benzene. This is due to the combined effect of lead inductance and ITO resistance [30]. Due to this pseudo relaxation of the cells, any molecular relaxation of the sample above 1 MHz can not be determined precisely.