Kim, B. N. | Search bioRxiv

bioRxiv2019

A Wirelessly Powered Implantable CMOS Neural Recording Sensor Array using Pulse-based Neural Amplifier

The most important organ in the human body is unquestionably the brain. Yet, despite its importance, it is one of the least well understood organs. One reason for this lack of understanding of the brain is the lack of data available to researchers from in vivo studies. Historically, collecting measurements from the brain has been difficult due to the high risk to the patient. Recently technology has been developed to allow electrical measurements to be taken from the brain directly, however most systems involve non-permanent sensors because of the requirement for transcranial wiring for power and data. Developments in the field of CMOS circuit design, wireless power transmission, and wireless data transmission have enabled the creation of implantable neural recording devices as a combination of these technologies. The implant designed in this paper is [~]15 mm in diameter and 2 mm at its thickest point on a flexible polyamide PCB. The flexible nature of the implant allows for the implant to conform to the surface of the brain. The implant requires no transcranial orifice since it is powered wirelessly and transmits data wirelessly via Bluetooth low energy. The CMOS neural amplifier chip on the implant utilizes an enhanced form of delta modulation to remove the requirement for large ADCs to be present on the die, saving space and enabling 1024 amplifiers and electrodes to be present on the chip. The implant is capable of measuring, modulating, and wirelessly transmitting a millivolt order signal to a PC for demodulation and analysis.

bioengineering↗

bioRxiv2019

Parallel 1024-ch Cyclic Voltammetry on Monolithic CMOS Electrochemical Detector Array

Large-scale microelectrode arrays offers enhanced spatiotemporal resolution in electrophysiology studies.. In this paper, we discuss the design and performance of an electrochemical detector array which is capable of 1024-ch parallel cyclic voltammetry (CV) as well as other electrochemical measurements. The electrochemical detector is fabricated using a custom-designed CMOS chip which integrates both the circuity and on-chip microelectrode array, to operate and record from electrochemical measurements. For parallel 1024-ch recordings, 1024 capacitor-based integrating transimpedance amplifiers (TIA) are designed and integrated. The TIA design features the bipolar capabilities for measuring both negative and positive electrochemical currents due to reduction and oxidation of molecules. The resulted dynamic range of this TIA is -700 pA - 1968 pA. CV can be used to examine the quality of electrochemical electrodes by measuring the double-layer capacitance. Double-layer capacitance forms at the electrode-electrolyte interface and is a function of the effective area of the electrode. Thus, a contaminated electrode can have smaller effective area resulting in smaller double-layer capacitance. Using the parallel CV capability of the monolithic CMOS device, the double layer capacitance of all 1024 electrodes are simultaneously measured to examine the status of the electrodes surface in real time. The initial measurement of the electrode array showed a mean capacitance of 466 pF. After plasma treatment to remove contamination on the electrodes surface, the increased capacitance was 1.36nF nearly tripling the effective surface area. We have successfully developed of 1024-ch electrochemical detector array using the monolithic CMOS sensor. The CV functionality was validated by measuring the double-layer capacitance of the on-chip electrode array. This method can accelerate the characterization of a massive electrode array before analytical experiments to provide well-controlled electrochemical electrodes, which is crucial in conducting reliable electrochemical measurements.

bioengineering↗