A 1024-Channel 10-Bit 36- µW/ch CMOS ROIC for Multiplexed GFET-Only Sensor Arrays in Brain Mapping.

This paper presents a 1024-channel neural read-out integrated circuit (ROIC) for solution-gated GFET sensing probes in massive µECoG brain mapping. The proposed time-domain multiplexing of GFET-only arrays enables low-cost and scalable hybrid headstages. Low-power CMOS circuits are presented for the GFET analog frontend, including a CDS mechanism to improve preamplifier noise figures and 10-bit 10-kS/s A/D conversion. The 1024-channel ROIC has been fabricated in a standard 1.8-V 0.18- µm CMOS technology with 0.012 mm 2 and 36 µ W per channel. An automated methodology for the in-situ calibration of each GFET sensor is also proposed. Experimental ROIC tests are reported using a custom FPGA-based µECoG headstage with 16×32 and 32×32 GFET probes in saline solution and agar substrate. Compared to state-of-art neural ROICs, this work achieves the largest scalability in hybrid platforms and it allows the recording of infra-slow neural signals.

Distortion-Free Sensing of Neural Activity Using Graphene Transistors.

Graphene solution-gated field-effect transistors (g-SGFETs) are promising sensing devices to transduce electrochemical potential signals in an electrolyte bath. However, distortion mechanisms in g-SGFET, which can affect signals of large amplitude or high frequency, have not been evaluated. Here, a detailed characterization and modeling of the harmonic distortion and non-ideal frequency response in g-SGFETs is presented. This accurate description of the input-output relation of the g-SGFETs allows to define the voltage- and frequency-dependent transfer functions, which can be used to correct distortions in the transduced signals. The effect of signal distortion and its subsequent calibration are shown for different types of electrophysiological signals, spanning from large amplitude and low frequency cortical spreading depression events to low amplitude and high frequency action potentials. The thorough description of the distortion mechanisms presented in this article demonstrates that g-SGFETs can be used as distortion-free signal transducers not only for neural sensing, but also for a broader range of applications in which g-SGFET sensors are used.

Integrated electrode and high density feedthrough system for chip-scale implantable devices.

High density feedthroughs have been developed which allow for the integration of chip-scale features and electrode arrays with up to 1141 stimulating sites to be located on a single implantable package. This layered technology displays hermetic properties and can be produced from as little as two laminated 200 µm thick alumina sheets. It can also be expanded to a greater number of layers to allow flexible routing to integrated electronics. The microelectrodes, which are produced from sintered platinum (Pt) particulate, have high charge injection capacity as a result of a porous surface morphology. Despite their inherent porosity the electrodes are electrically stable following more than 1.8 billion stimulation pulses delivered at clinically relevant levels. The ceramic-Pt constructs are also shown to have acceptable biological properties, causing no cell growth inhibition using standard leachant assays and support neural cell survival and differentiation under both passive conditions and active electrical stimulation.