A Reconfigurable Sub-Array Multiplexing Microelectrode Array System With 24,320 Electrodes and 380 Readout Channels for Investigating Neural Communication

It is crucial to investigate electrical activities from a single neuron and neuronal synapses in electrophysiology for brain research. Conventional physiological tools such as imaging and labeling are insufficient to cope with neural signals from cells distributed over a large area [1]. Microelectrode array (MEA) systems featuring high-density electrodes and low-noise analog front-ends (AFE) have been representative solutions to acquire intracellular and extracellular potentials from in vitro multiple neurons [2 – 7]. Although the number of electrodes in MEA systems and their spatial resolution are increased thanks to advances in CMOS technology, they still suffer from area constraints in the low - noise AFE and connection complexity from electrodes to corresponding AFE channels. Since neurons are not fully activated and not evenly distributed after being cultivated on an MEA, a full scanning of electrodes in active pixel sensors (APS) is not efficient in terms of power consumption and noise performance [2 – 4]. A switch - matrix (SM) architecture offers high flexibility to select and record electrodes of interest through configuring the switches to randomly connect them to AFE channels, improving efficiency [5,6]. However, a large AFE channel dedicated to an electrode with a small pitch of a few pm limits the scalability in both APS and SM architectures. The more electrodes are integrated into the system, the more complicated the routing connections become, worsening scalability. In this paper, an MEA system with a sub-array multiplexing (SAM) architecture is presented for programmable electrode selection and readout speed to maximize the ratio of the number of recorded electrodes per frame to the total number of electrodes, called an electrode yield. A time-multiplexing scheme allows each AFE channel in a column to record multiple electrodes one-by-one in a given sampling time, alleviating the routing complexity and the number of AFE channels. The reconfigurable SAM provides a pseudo-random connection of electrodes, so that extracellular signals from a single neuron as well as neural synapses can be effectively recorded.