Sometimes such large shifts in the neutral plane can be partially mitigated by, e.g., increasing the thickness of the more rigid polymer cover layer and or decreasing the thickness of the softening polymer layer. However, these mitigation measures may be insufficient for providing flexible devices that are not too rigid so as to not be able to bend enough, e.g., to form tightly curled structures, and/or, not be too fragile so as to rip, e.g., during surgical implantation, and/or, still have sufficient softening to facilitate long term functionality (e.g., months) after device implantation in living tissue.

As disclosed herein, such large shifts in the neutral plane can be substantially eliminated by manufacturing a device using a polymer cover layer composed of a second softening polymer that can have substantially a same stiffness and/or thickness as the softening polymer layer. Consequently, the electrode layer of such a double softening polymer layer-containing device can be located substantially at or near the mechanical neutral plane of the device.

The ability to use a cover layer composed of a second softening polymer, however, can be problematic. For instance, the use of conventional photolithography materials and methods to define openings in the polymer cover layer to thereby expose interaction pad portions of the electrode layer can damage or dissolve the second softening polymer or etch the metal due to bombardment of plasma on metal electrodes.

As disclosed herein a reactive ion etch process is used to etch through the second softening polymer layer. A patterned hardmask layer is used to define openings to expose portions of the second softening polymer layer to the reactive ion etch process while other portions of the second softening polymer layer are protected by the hardmask from being damaged by the reactive ion etch process.