Title: Microsystem Based on CMOS Multielectrode Array for Extracellular Neural Stimulation and Recording
Description: Neurobiology is constantly in search of new tools and techniques to extract structural and functional information from neural circuitry. Conventional electrophysiological stimulation and measurement technique such as patch clamping have become the standard techniques for accurate stimulation and recording of electrical activities in neurons. Nevertheless, the number of electrodes that can be introduced into the working chamber is severely limited by the electrode dimension and head stages. Integrating electrodes on chip with complementary metal-oxide-semiconductor (CMOS) technologies enables significantly higher throughput, making analysis on large neural networks possible. This thesis presents the design, characterization, verification, and post-fabrication steps of a microsystem based on a fully integrated high-density multielectrode array (MEA) chip for extracellular stimulation of neural activity. The active MEA is implemented in a standard 0.25 μm CMOS technology with 65,536 non-Faradaic electrodes in an array area of 9 mm2.

Each electrode can be configured to produce unique stimulus waveform, delivering a spatial resolution exceeding 12 μm and a temporal resolution exceeding 125 nsec. The array is integrated with neurons in both dispersed culture and acute thalamocortical slices. Experimental results verify the array functionality by attaining high-resolution stimulation of dispersed primary hippocampal neuronal cultures. Neuronal activity induced from stimulation is detected through changes in real-time calcium fluorescence calibrated with cell-attached patching. Precise electrical stimulation of individual neurons is achieved by optimizing stimulation waveforms, culture preparation, and interface design. The design of a second MEA CMOS chip that integrates extracellular recording with on-chip stimulation is also presented. The chip contains 256x256 non-Faradaic circular electrodes with 14 μm diameter and 20 μm pitch. The active area of the array at 32 mm2 is designed to accommodate entire mouse thalamocortical acute slice with an electrode density of 2000 electrodes per square milimeter.

Each electrode integrates with a stimulation pulse generator and a single-transistor transconductance amplifier. The new configuration does not require optical recording and reduces the mechanical setup of the microsystem.