Design of neural recording and stimulation IC using time-varying magnetic field

Abstract

In this thesis, I proposed neural recording and stimulation IC for in vitro neuro-research. For stimulation, I brought in magnetic stimulator into CMOS IC. It has several advantages over conventional voltage/current stimulation. In recording part, 16-channel on-chip recording sites are available and readout circuit and SAR ADC are also included in the chip. The distinguish feature of recording system is that we use passivation layer as a capacitor to detect neural signal using capacitive coupling. It leads simple post-processing without define metal electrode and reduce interfacing problem between metal and electrolyte. A 0.18um standard CMOS process is used and post processing for biocompatible passivation is done by manual process. The proposed Micro-Inductor Array(MIA) system has benefits over conventional Micro-Electrode Array(MEA) systems in several points. First of all, a magnetic stimulation is an inherently charge balanced stimulation method. In a conventional metal electrode system, if net injected charges are not zero, the concentration of pH in cell surrounding media will shift. It affects physiology of the cells, and finally drives cell to death. The second standpoint is stimulation artifact. In MEA system, metal electrodes are shared the recording and stimulation functions. This shared electrode causes the stimulation artifact which limits the signal recording right after stimulation. The stimulus by magnetic field is indirect stimulation method which does not irritate the recording path. The third point is spatial resolution of stimulus. The conventional TMS has a large coil and spatial resolution is very low. Hundreds of microns resolution which is achieved by micro-inductor array is lower than conventional MEA, but it is enough to use in implantable stimulator or other in-vitro researches. The proposed system has been tested with cultured neurons. Recording from neurons are successfully done but magnetic stimulation has not been demonstrated at ...