Substrate Thickness
Substrate thickness is the thickness of the silicon or polyimide sheet an electrode array is built on — 15 or 50 µm for NeuroNexus silicon probes and 12 µm for polyimide grids — and it sets the balance between the tissue a shank displaces and the stiffness it needs to reach its target.
It is set on the wafer and is the same for every site on the array; it is not the shank width, which is a design parameter of the layout.
Thinner displaces less. A 15 µm shank parts tissue with less injury and less of the glial response that raises impedance over the weeks of a chronic implant, which is why it is the default for cortex and for most rodent work. Its cost is stiffness: a thin shank bends more easily and can buckle against the dura or in a long trajectory. The 50 µm substrate is for that case: deeper targets, longer shanks, tougher tissue, or an insertion through intact dura — and beyond what 50 µm can reach, the Vector design moves the array onto a stainless-steel support body rather than thickening the silicon further. The choice is made at order: most catalog designs are offered on both.
Polyimide serves the opposite requirement. At 12 µm it is flexible enough to conform to the surface of the cortex, a nerve or the heart, which is why it is the substrate for thin-film grids and for the flexible cable of a Hybrid package; it does not penetrate. Both are laid down in the same thin-film process; what differs is the material and the use of the finished array.
Typical values
| Silicon probes | 15 or 50 µm |
|---|---|
| Polyimide grids | 12 µm |
| Catalog designs offered at 15 µm | 138 of 216 |
| Catalog designs offered at 50 µm | 154 of 216 |