A Flexible and Scalable Neurophysiological Acquisition Array for High-Definition Brain Mapping

For decades, neurophysiologists have relied on electrophysiological recoding arrays to investigate cortical function. Electrocorticography (ECoG) grid arrays are routinely placed on the cortical surface for mapping of functional and diseased cortical tissue and have improved patient outcomes. However, clinically used ECoG arrays have low spatial resolution and have seen little innovation until recently. Owing in part to advances in materials science and semiconductor devices, the field of neural interface technology is now exploding, with different approaches demonstrating improvements in spatiotemporal resolution, coverage, implantability, and scalability towards higher channel counts. Despite these recent strides, many problems in this field remain unsolved. One of these challenges is the scalability of systems towards ultra-high channel counts where wiring within the arrays and toward the outside world remains a major bottleneck. Integrated circuits fabricated using conventional lithographic techniques can significantly simplify routing and reduce the number of connecting wires, but rigid and brittle silicon-based acquisition electronics are incompatible with soft neural tissue.<br/><br/>Toward this end, we have developed a flexible neural interface that incorporates dual-gate indium gallium zinc oxide (IGZO) thin-film transistors (TFT) as active amplifying and multiplexing elements for neurophysiological sensors. These TFTs are optimized for bio-interface applications, generating low heat densities during normal operation while maintaining high sensitivity, with electron mobilities up to 30cm^2/Vs and transconductance per unit drain current comparable to silicon technologies. The TFTs are built with a low-temperature monolithic fabrication process which is compatible with polymer substrates, incorporating a novel multi-layer ceramic-polymer hermetic sealing which acts to protect the system against fluids and charged ions. We have demonstrated that this strategy protects traces from undergoing any electrochemical reaction while immersed in phosphate-buffered saline for 24 hours and driving them with +-6V amplitude square waves, and we plan on conducting accelerated aging tests with single TFT devices under various bias conditions. We have also fabricated 256-channel multiplexed ECoG arrays and have fine-tuned the device characteristics and fabrication flow to be able to conduct benchtop experiments in PBS prior to conducting an in-vivo whisker-barrel stimulation experiment in a rat model.