China
Africa
Explore chapters and articles related to this topic
RF MEMS, FBAR, and CMUT
Published in J. David, N. Cheeke, Fundamentals and Applications of Ultrasonic Waves, 2017
A simple example is shown in Figure 15.4 for the fabrication of a cantilever anchored to a silicon wafer substrate. Silicon dioxide is used for the sacrificial layer as in Figure 15.4a. It is etched out at the anchor point as in Figure 15.4b. Polysilicon is then deposited and patterned to form the cantilever (Figure 15.4c) and finally the rest of the sacrificial layer is etched away to leave the final free standing cantilever. Silicon dioxide is generally used for the sacrificial layer, and it can be dissolved in HF solution without affecting the polysilicon structure. Polysilicon is a very versatile building material as its electrical and mechanical properties can be controlled by doping. Since both polysilicon and SiO2 are fully compatible with IC processing, their use is very appropriate for forming completely integrated structures.
Photovoltaics
Published in Dorothy Gerring, Renewable Energy Systems for Building Designers, 2023
Polycrystalline (sometimes called multicrystalline) solar cells are made from polycrystalline silicon (also called polysilicon, poly-Si). Most polysilicon is created through a chemical distillation process (Siemens process) where large rods which have been broken into chunks are cast into rectangular ingots. These are sized and then sliced into very thin wafers. Because polycrystalline cells are made up of individual crystals that have been melted together, their appearance shows the varying sizes, colors, and angles of the crystalline structure as shown in figure 13.13. The colors vary from medium to darker blues and grays, with an overall blue appearance. The multiple crystalline structure is visible.
Economic and Legal Aspects of Power Generation and the Environment
Published in Anco S. Blazev, Power Generation and the Environment, 2021
Polysilicon is a key material that is needed to manufacture c-Si solar cells, and although it is an abundant material in nature, it has been, and still is, a bottleneck in the solar photovoltaic energy industry explosion. The high initial capital and technical requirements of polysilicon production plants means that only large size (over 1,000 tons per annum) production can be economical, effective and competitive. This also means that only large enterprises with government help (which is the case in Asia) can undertake the huge risks and compete in this area.
Numerical simulation of particle growth process in a polysilicon fluidized bed reactor
Published in Particulate Science and Technology, 2020
Ultrapure polysilicon is the most widely used material in semiconductor and photovoltaic industries due to the superior performance. At present, high quality polysilicon is mainly produced by the SIEMENS method through the bell-jar reactor. However, the costs of this method are high energy consumption and low trichlorosilane conversion (Yadav, Chattopadhyay, and Singh 2017). In comparison, the fluidized bed reactor (FBR) method, using silane as the reactant gas, has attracted much attention due to efficient heat and mass transfer capacities, relatively low energy consumption, and high silane conversion (Filtvedt et al. 2012).
Tribological analysis of tip-cantilever made of SU-8, talc and PFPE composite
Published in Tribology - Materials, Surfaces & Interfaces, 2020
Jitendra K. Katiyar, Sujeet K. Sinha, Tomoko Hirayama, Arvind Kumar
Several materials have been utilized for making micro-electro-mechanical systems (MEMS) structures. Most used material among these is polysilicon (Si). Si is a widely used semiconductor material for which the micro-fabrication process using the wet-etching lithography method is well-established. Though Si has been successfully used for several MEMS, the drawbacks with Si have kept MEMS devices from increasing in number and applications. The micro-fabrication of Si–MEMS is a very energy intensive and expensive process, and fabricating high aspect ratio micro-components remains a challenge [1–3]. Moreover, tribological properties of Si are inferior because of its hydrophilic (high surface energy) and brittle nature which leads to high adhesion, high friction and high abrasive wear when slid against itself or against other similar materials. This has led many researchers to look for alternative materials that could replace Si as the structural material and, at the same time, provide good mechanical and tribological properties. Among polymers, PMMA (poly-methyl methacrylate) [4], SU-8 (an epoxy-based negative photoresist polymer) [5] and a few other polymers [6] have found applications in MEMS. Though these selected polymers are compatible with the micro-fabrication processes, there are serious issues with their mechanical and tribological properties, at least in their pure forms. In particular, SU-8 has shown better mechanical and tribological properties when filled with solid particles and liquid lubricant droplets [7–12]. It has been shown in the literature [13–15] that inclusion of lubricant droplets can reduce the coefficient of friction (CoF) drastically without any negative effect on the mechanical properties of the polymer. Therefore, researchers have proposed that an optimized composition of liquid lubricant with appropriate hard phase particle can enhance both the mechanical and tribological properties [16].