Isotropic etching technique for three-dimensional microball-bearing raceways

Abstract

A multi-step plasma etching technique is developed to obtain deep-grooved micro-scale ball-bearing raceways and employed in the fabrication of multiple ball-bearing supported microturbines. Deep-groove geometry has been chosen for the microball-bearing systems because of the ability to handle mixed axial and radial loads, allowing for stable, high-speed operation compared to previous iterations of the microball-bearing raceways. The multi-step inductively coupled plasma-based process is optimized to obtain <2% deviation amongst intended raceway depth, width and curvature. Etching non-uniformity is measured to be 0.15% within the raceway of a single device. The bearing dynamics with the new deep-groove geometry have been simulated. The deep-groove raceway packed with off-the-shelf precision ball-bearings provided a stability improvement over previous demonstrations of high-performance rotary micromachines operating at high speeds.

Wet etching of deep trenches on silicon with three-dimensional (3D) controllability

“…Interestingly, upon addition of EtOH, the sidewall and the adjacent region shows nanoporous morphology, indicating the h + density might be essentially different from the vertical etching conditions. Further, we change the type of catalyst and find the etched trenches possessing semi-circular cross section ( Figure 5), which highly resembles the result of acidic wet etching [35]. The istotropic etching profile may be caused by the dissolution and re-deposition of catalyst during etching.…”

Fast ultra-deep silicon cavities: Toward isotropically etched spherical silicon molds using an ICP-DRIE

“…Compared with the microlenses molds 17 and microballbearing mold 19 as is shown in Table III, the smallest opening masks showed much low roughness. The RMS is higher than the respective values reported in 19 due to the higher pressure and larger mask openings used in this work.…”

“…Even though wet silicon etch can have an aspect ratio as high as 600, this deep anistropic etch technique by aqueous solutions is inherently limited to the fabrication of structures such as microlenses mold (see Fig.6) where the isotropic effect is desired. In recent years, much effort has been placed on further improving isotropic wet etching 16,40 and in isotropic dry etching [17][18][19] . Consequently, the spherical cavity size was found to depend mostly on the size of the etch-mask opening, and be independent of the etching time.…”

“…Early works focused on microlenses, which were specifically developed for different MOEMS applications 16,20,41 . Previous reports on isotropic dry etching technology have been documented 17,19 showing that the anisotropic plasma can be optimized, when the mask opening and the process parameter are matched, to produce a sphere shape (Fig.6). Here, we considered different size of circular mask openings ( ranging from 20 µm to 600 µm).…”

“…Indeed, by Deep Reactive Ion Etching (DRIE) technology, the silicon substrate and III-V compound semiconductors can be etched fairly quickly and manufactured at low cost for mass production 6,7 . This plasma technology is becoming increasingly attractive in a very wide set of applications [8][9][10][11] as well as for microfluidic devices [12][13][14] , microprobes 15 , microlens molds [16][17][18] , roll bearing components 19 and micro-optic structures 20 .…”