PEDOT:PSS-Based OECT Common-Source Amplifiers for Electrophysiological Signal Amplification

Stable amplification of weak electrophysiological signals is important for low-voltage bioelectronic interfaces, but the gain and waveform fidelity of organic electrochemical transistor (OECT)-based amplifiers are strongly influenced by device characteristics and bias conditions. Herein, we develop a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) vertical organic electrochemical transistor (vOECT) common-source amplifier using an integrated solid-state electrolyte and investigate its bias-dependent amplification behavior. The fabricated vOECTs exhibits typical p-type depletion-mode operation, effective gate-controlled current modulation, and a maximum transconductance of 22 mS. Transient measurements show reversible current switching with response time constants of 0.909 and 0.635 ms, while repeated gate-voltage modulation over approximately 1000 s confirms stable cycling behavior. Based on the measured transfer and output characteristics, a common-source amplifier model is constructed to analyze the relationship between gate bias, bias resistance, output swing, and voltage gain. By optimizing the voltage-divider bias network, the amplifier achieves a voltage gain of approximately 3.374. The optimized circuit amplifies sinusoidal signals from 1 to 100 Hz and simulated ECG, EEG, and EOG waveforms while preserving their main temporal features and producing the expected phase-inverted output. Distortion and frequency-response analyses further show a 1% total harmonic distortion point at an input peak amplitude of 113 mV and a -3 dB cut-off frequency of 625 Hz. These results demonstrate the importance of bias optimization for achieving stable low-frequency voltage amplification in PEDOT:PSS vOECT common-source amplifiers.