Organic Electrochemical Transistor Common‐Source Amplifier for Electrophysiological Measurements

Abstract

The portability of physiological monitoring has necessitated the biocompatibility of components used in circuitry local to biological environments. A key component in processing circuitry is the linear amplifier. Amplifier circuit topologies utilize transistors, and recent advances in bioelectronics have focused on organic electrochemical transistors (OECTs). OECTs have shown the capability to transduce physiological signals at high signal‐to‐noise ratios. In this study high‐performance interdigitated electrode OECTs are implemented in a common source linear amplifier topology. Under the constraints of OECT operation, stable circuit component parameters are found, and OECT geometries are varied to determine the best amplifier performance. An equation is formulated which approximates transistor behavior in the linear, nonlinear, and saturation regimes. This equation is used to simulate the amplifier response of the circuits with the best performing OECT geometries. The amplifier figures of merit, including distortion characterizations, are then calculated using physical and simulation measurements. Based on the figures of merit, prerecorded electrophysiological signals from spreading depolarizations, electrocorticography, and electromyography fasciculations are inputted into an OECT linear amplifier. Using frequency filtering, the primary features of events in the bioelectric signals are resolved and amplified, demonstrating the capability of OECT amplifiers in bioelectronics.

High‐Performance Internal Ion‐Gated Organic Electrochemical Transistors for High‐Frequency Bioimpedance Analysis

“…380 vs 10 kHz). [27] Although IGT was proven feasible to be integrated into solidstate amplification circuits and utilized in medical applications like EEG recordings, its potential in high-frequency applications has yet been fully harnessed. [26] Compared to biopotential measurement on electrogenic cells, monitoring of passive electrical properties of non-electrogenic cells, tissues, or even the human body relies more on high-frequency current to capture physiological changes (e.g.…”

Sub-3 V, MHz-Class Electrolyte-Gated Transistors and Inverters

“…These devices employ gate potentials to modulate the conductivity of conducting polymers in direct contact with electrolytes. Currently, EGTs are again enjoying a resurgence of interest associated with their applications in physiological recording, − neuromorphic computing, − and biosensing, − as well as in fundamental physics, − where the high charge densities achieved in electrolyte-gated semiconductors are leading to exciting discoveries.…”

“…In our view, there are clear reasons why EGTs will not rival the speed of Si MOSFETs (though perhaps not everyone agrees), but for envisioned applications of EGTs, gigahertz speeds do not appear necessary. As EGTs are being developed as physiological recording amplifiers, , and integrated into circuits ,− and neural nets, ,,,, it is nevertheless important to establish the limits of performance that can be obtained by rational design. We note that there are other limitations to EGT performance like high dielectric loss tangents and quasistatic leak currents associated with electrolytes that are important for power consumption, but these are not our focus here.…”

Sub-3V, MHz-Class Electrolyte-Gated Transistors and Inverters

“…These devices employ gate potentials to modulate the conductivity of conducting polymers in direct contact with electrolyte. Currently, EGTs are again enjoying a resurgence of interest associated with their applications in physiological recording [8][9][10] , neuromorphic computing [11][12][13][14][15][16] , and biosensing [17][18][19][20][21][22] , as well as in fundamental physics [23][24][25][26] , where the high charge densities achieved in electrolyte-gated semiconductors are leading to exciting discoveries.…”

“…In our view there are clear reasons why EGTs will not rival the speed of Si MOSFETs 2 (though perhaps not everyone agrees 38 ), but for envisioned applications of EGTs, gigahertz speeds do not appear necessary. As EGTs are being developed as physiological recording amplifiers 9,10 , and integrated into circuits 36,[39][40][41] and neural nets 4,11,13,14,16 , it is nevertheless important to establish the limits of performance that can be obtained by rational design. We note that there are other limitations to EGT performance like high dielectric loss tangents and quasi-static leak currents associated with electrolytes that are important for power consumption 2 , but these are not our focus here.…”