Fig. 4

Optimization of gold microelectrode fabrication. a-d) A ruptured electrode with an "ear pattern" profile fabricated using the conventional AZ monolayer lift-off process and developed for 1 min. a) Top view SEM imaging (the Pt line is deposited for FIB/SEM and is not part of the fabrication process). b) FIB/SEM zoom in the cross section of the area demarcated with a rectangle revealing the continuity of the photoresist. c) Gold electrodes (80 µm diameter, 200 nm height) are broken and disconnected from the substrate. d) The electrodes’ edge cross section profile showing the “ear pattern” edge (arrows). e–h) An intact electrode with a sharp profile fabricated using the bi-layer lift-off process (AZ and LOR) developed for 1 min, 5 min curing at 185 °C and another development phase of 1 min. e–f) SEM imaging of the positive photoresist profile optimization process of a Bi-layer lift-off with LOR10B. e) An SEM image of the top view of a photoresist developed for 1 min. f) An FIB/SEM cross section and a zoom-in on the white rectangular area demarcated in) (e) (where the LOR10B was developed for 1 min, followed by an additional AZ curing step (120ºC). The photoresist has the desired undercut configuration, which is denoted by *. g) Intact gold electrodes (80 µm diameter, 200 nm height) with good attachment to the SU-8 surface. h) An electrode edge cross section profile showing the sharp edge (arrows)