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Additive manufacturing at the micron scale
Published in Adedeji B. Badiru, Vhance V. Valencia, David Liu, Additive Manufacturing Handbook, 2017
This chapter presents three micron-scale additive manufacturing techniques based on specialized microelectromechanical systems (MEMS) fabrication processes: bulk micromachining, surface micromachining, and micromolding. Bulk micromachining is a subtractive process where portions of a substrate are patterned and etched resulting in 3D-micromachined features. Surface micromaching is an additive process where thin film layers are deposited, patterned, and etched resulting in planar surface structures. In micromolding, high-aspect ratio devices’ molds (i.e., 100 µm features) are created using thick photosensitive layers that are patterned, developed, and filled using electroplating.
Structuring MEMS: Micromachining
Published in Sunipa Roy, Chandan Kumar Sarkar, MEMS and Nanotechnology for Gas Sensors, 2017
Sunipa Roy, Chandan Kumar Sarkar
Bulk micromachining is a fabrication technique that builds mechanical elements by starting with a silicon wafer, then etching away unwanted parts and being left with useful mechanical devices. Typically, the wafer is photo patterned, leaving a protective layer on the parts of the wafer that you want to keep. The wafer is then submersed into a liquid etchant, like potassium hydroxide, which eats away any exposed silicon. This is a relatively simple and inexpensive fabrication technology and is well suited for applications that do not require much complexity and that are price sensitive.
Transducers
Published in Anton F. P. van Putten, Electronic Measurement Systems, 2019
Bulk micromachining technology is based on single-crystal etching or etching of composite materials deposited or grown on a silicon substrate. Three-dimensional structures can be obtained. The crystallographic orientation determines the etch rate. For instance, the etching effect in the [111] crystal direction is 400 times slower than in other directions and because of this effect it can act as a stopper plane.
Investigation of Various Commonly Associated Imperfections in Radiofrequency Micro-Electro-Mechanical System Devices and its Empirical Modeling
Published in IETE Journal of Research, 2023
A. Karmakar, B. Biswas, A.K. Chauhan
Bulk micromachining is a widely used fabrication process for the realization of multiple kinds of RF devices in MEMS technology. It is achieved either by dry or wet methods of etching process with anisotropic means. DRIE is a well-known dry etching high-aspect-ratio process (HARP). Whereas, anisotropic wet etching method of the silicon wafer is done with the help of TMAH (Tetra Methyl Amino Hydroxide) and KOH (Potassium Hydroxide). Out of these, KOH has become more popular because of its inherent merit of less non-toxic nature and high etch-rate (1.1–1.2 µm/min), as compared to 0.8 µm/min for TMAH solution. The standard process of 40% KOH solution at 800C gives the optimum solution for silicon micromachining. However, it requires a continuous stirring method to maintain the homogeneous property. Etch-stop techniques are implemented for timely terminating this etching process. Although precautions [22-23] are taken during the processing time, there may be a high chance of non-uniformity in case membrane thickness maintaining at the last stage of the whole process, as the whole solution doesn’t remain homogeneous within the entire volume of etch-bath and throughout the whole process duration. This non-uniformity may be of two types: within wafer or wafer-to-wafer. It can be a fatal error in the case of a micro-machined antenna array problem. Though during designing antenna was optimized by assuming uniform membrane thickness for each element, however, due to process variation, each of the array elements gets non-uniform silicon substrate beneath it. Ultimately the resonant frequency will be changed along with its other radiation characteristics. The whole phenomenon can be explained with the help of the proposed electrical model, as shown in Figure 11.
Modeling analysis and fabrication of MEMS capacitive differential pressure sensor for altimeter application
Published in Journal of the Chinese Institute of Engineers, 2018
Eswaran Parthasarathy, S. Malarvizhi
The fabrication of a MEMS highly sensitive CDPS structure is based on bulk and surface micromachining techniques. In bulk micromachining, a portion of the substrate is removed using wet etchant, to create a cavity and via in the sensor structure. The material’s etch rates, and etching profiles are considered based on the literature (Kirt and Richard 1996). Surface micromachining methods are extensively adopted for the development of thin film structure on the silicon wafer.