Extended Data Fig. 7: Nanofabrication of soft neural probes.
From: 3D spatiotemporally scalable in vivo neural probes based on fluorinated elastomers
a, Schematics showing the stepwise nanofabrication process of 3D stacked soft electrode arrays encapsulated by PFPE-DMA elastomers. (b, c) Schematic design (b) and photographic image (c) showing the photomask aligner-compatible, 3D-printed Nitrogen diffuser that provides the Nitrogen atmosphere for an oxygen-free photolithography. The Nitrogen diffuser is compatible with the standard 3-inch chuck of a Karl Suss MA6 mask aligner. (d, e) Schematics show the side views of the fabrication substrate inside a photomask aligner without (d) or with (e) a photolithographically defined SU-8 spacer. Without the SU-8 spacer, the direct contact to the photomask damages the soft fluorinated elastomer precursor spin-coated onto the substrate (a). In contrast, with the spacer, the few micrometers gap between the PFPE-DMA surface and the photomask preserves the integrity and smooth surface of PFPE-DMA film, allowing for high-resolution patterning required for the soft brain probes fabrication. (f-h) Enabling photolithographic patterning of metals by plasma treatment of PFPE-DMA films. f, Photograph of DI water (top) and LOR 3 A (bottom) drops on the PFPE-DMA film surfaces in their pristine state, immediately after 6 min plasma treatment, and 1 hr in ambient condition after the plasma treatment. (g, h), DI water (g) and LOR3A (h) drops contact angles as a function of plasma parameters. n = 4 drops for each sample (except ‘DI Water - 2 min, t = 0’, ‘LOR3A - Pristine’ and ‘LOR3A - 6 min, t = 0’ for which n = 3, 5 and 5 drops respectively), value = mean ± S.D. *** p < 0.001, two-tailed, unpaired t-test. The results suggest a significant decrease in LOR 3 A contact angle after 6 min plasma treatment, which, however, can only last for less than 30 min. (i-k) Bonding input/output (I/O) metal pads to flexible cables. i, Schematic of the side view of a brain probe showing that I/O pads are defined on the silica substrate for bonding and connected to interconnects through the smooth edge of the slightly overexposed PFPE-DMA dielectric layer. Flexible cables are bonded through the anisotropic conductive film to I/O pads. j, BF microscopic image of a 250-µm-wide I/O pad. Scale bar, 50 µm. k, Zoom-in view of the red box highlighted region in (j). The focal plane in the images has been adjusted stepwise (indicated by black arrows) to show that the sputtered Al/Au layer deposited on the smooth edge of the PFPE-DMA layer connected with the Cr/Au I/O pads. l, Schematic showing that smooth edges of the overexposed PFPE-DMA dielectric layers are necessary for ensuring the metal interconnects from the PFPE-DMA layers can connect to the I/O regions on the silicon oxide substrate. m, Pseudo-colored SEM images showing the metal interconnects patterned from the PFPE-DMA layers to the I/O pads on the substrate. Pseudo-colors were used to highlight different metal and PFPE-DMA layers.
