256-Channel Flexible Electrode Array Fabricated in Situ on TSV for System-Level Packaging and High-Density Neural Recording

Here report a 256 -channel Flexible Electrode array fabricated in situ on a TSV substrate (FEoT). To break the rigid-soft process barrier during imidization and downstream steps, via-first dielectric-window post-opening and enhanced reverse-sputter pre-clean are tailored for direct TSV-to-flex fan-out. Morphological characterization of the device reveals a connector-less PI-Au-PI array monolithically integrated on a TSV substrate. Probe-station measurements confirm a reliable electrical interconnect between the TSVs and the electrode. Iridium oxide ($\text{IrO}_{\mathrm{x}}$) -modified sites reduce impedance by nearly two orders of magnitude relative to bare Au. Stereotaxic implantation in rats yields stable neural recordings and minimal inflammatory response. This wafer-level route co-integrates flexible neural electrodes with TSV interposers, advancing compact, high-channel-count brain-machine interface (BMI) microsystems packaging.