Characterization of Orientation-Dependent Etching Properties and Surface Morphology of Sapphire Crystal in Wet Etching

Xing, Yan; Guo, Zhiyue; Wu, Guangdong; Gosálvez, Miguel A.

doi:10.1109/transducers.2019.8808344

Cited by 3 publications

(4 citation statements)

References 7 publications

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“…This validated the fact that sapphire etching involves many slow-etch-rate planes. The above analyses presented the complex evolution of sapphire facets, which have been well documented with different etching mask layouts such as cavity and pyramids, , attributed to its trigonal crystal and strong etching selectivity between the sapphire crystal planes …”

Section: Resultsmentioning

confidence: 85%

“…These values are about 20 times smaller compared to the triangular window design [5715 ± 83.9% μm 2 (σ = 6813 μm 2 ) for 6°≤ α ≤ 18°; 5940 ± 81.7% μm 2 (σ = 7275 μm 2 ) for 42°≤ α ≤ 58°], indicating a uniquely wide-range layout design tolerance in crystal alignment where the membrane area remained almost constant. Besides, sapphire etching involves many slow-etch-rate crystal planes, which is very different from conventional silicon alkaline micromachining, where the final etched profile is mainly determined by a single slow-etch-rate (111) plane . This makes the etched profile in sapphire pretty complex and not only associated with the sapphire crystal plane but also significantly affected by the mask alignment .…”

Section: Resultsmentioning

confidence: 99%

“…Accordingly, Miller–Bravais indices { hkil } of the exposed sapphire facets in the cavity were calculated by building a hexagonal coordinate system (Figure S9, Table S2). As expected, the calculated indices cannot be directly linked to any of the typical crystallographic planes of sapphire . This validated the fact that sapphire etching involves many slow-etch-rate planes.…”

Section: Resultsmentioning

confidence: 99%

“…The above analyses presented the complex evolution of sapphire facets, which have been well documented with different etching mask layouts such as cavity 23 and pyramids, 20,24 attributed to its trigonal crystal and strong etching selectivity between the sapphire crystal planes. 21 2.3. Membrane Size Design and Fabrication Reproducibility.…”

Section: Membrane Geometry Control By the Etching Window Layoutmentioning

confidence: 99%

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Wafer-Scale Fabrication of Uniform, Micrometer-Sized, Triangular Membranes on Sapphire for High-Speed Protein Sensing in a Nanopore

Xia

Laskar

Wang

2023

ACS Appl. Mater. Interfaces

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Ultra-low-noise solid-state nanopores are attractive for high-accuracy single-molecule sensing. A conventional silicon platform introduces acute capacitive noise to the system, which seriously limits the recording bandwidth. Recently, we have demonstrated the creation of thin triangular membranes on an insulating crystal sapphire wafer to eliminate the parasitic device capacitance. Uniquely different from the previous triangular etching window designs, here hexagonal windows were explored to produce triangular membranes by aligning to the sapphire crystal within a large tolerance of alignment angles (10–35°). Interestingly, sapphire facet competition serves to suppress the formation of more complex polygons but creates stable triangular membranes with their area insensitive to the facet alignment. Accordingly, a new strategy was successfully established on a 2 in. sapphire wafer to produce chips with an average membrane side length of 4.7 μm, an area of <30 μm2 for 81% chips, or estimated calculated membrane capacitance as low as 0.06 pF. We finally demonstrated <4 μs high-speed and high-fidelity low-noise protein detection under 250 kHz high bandwidth.

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