Sapphire-supported nanopores for low-noise DNA sensing

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

“…Nevertheless, the chip capacitance of only ∼1.5 pF was close to the theoretical calculation of the whole chip (C chip ), taking into account the estimated capacitances from both the 250 μm sapphire substrate (C sub , 1.4 pF) and the sapphire cavity (C slope , 0.2 pF). 16 This also agrees with the fact that the small membrane now contributed only minimal capacitance (C m ). Moreover, it is also worth noting that this measured capacitance is one of the lowest values reported so far (e.g., 1.9−5.8 pF9, 0.69−1.65 pF 12 , 2.2 pF 13 , 2 pF 15 ).…”

“…22 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. 16 Here, within this unique design regime (α from 10 to 35°), the formed triangular membrane sides were parallel to that of the hexagonal etching window instead of staying at a constant crystal plane, yielding a membranewindow angle offset γ ∼ 0°(Figure 2d, shadowed regime, denoted as MPW triangle). This indicates that multiple slowetch-rate sapphire crystal planes were involved and the mask alignment strongly impacts the etched profile within this alignment angle range.…”

“…16 Yet, the membrane geometry and area were rather sensitive to the alignment angle α between the triangular mask and the c-plane sapphire wafer flat [A-plane, (112̅ 0)] (Figure 2a). 16 As a result, an error in α, which is inevitable in practice, would result in a deviation in membrane size and adversely affect the accuracy of controlling the device capacitance. Such an effect makes it challenging to create reproducible small membranes.…”

“…The membrane is outlined and color-coded in (b) (magenta for triangular sides, red for additional sides in ditrigonal geometry) and (c) (blue and green for two different sets of triangular sides, and orange for the additional sides in the nonagonal geometry) for calculating β and γ angles in (d,e), respectively. (c) and part of (a) were reproduced with permission from © 2021 Elsevier 16.…”

In situsolid-state nanopore fabrication

“…147 This may be important for the fabrication of nanopore devices with integrated electrodes. 40,74,148 Given the generalisability of this technique, one might anticipate seeing CBD extended to different dielectric materials such as sapphire 149 and Al 2 O 3 52,53 in the coming years.…”