Flexible a-IGZO TFT-Based Circuit for Active Addressing in Neural Stimulation Electrode Arrays

Neural interfaces have undergone significant advancements in recent decades, aiming for flexible, compact, and high-density electrode arrays with a large number of channels. However, the scalability of these devices is often hindered by the number of wires needed to separately connect each electrode to external electronics. To address this limitation, thin-film transistor (TFT)-based electronic circuits offer a promising solution by enabling active addressing of stimulation electrodes and potentially increasing the channel count with fewer interconnections. This paper presents the integration of a circuit comprising two amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs and a titanium nitride (TiN) electrode on a flexible polymer platform. This circuit precisely controls the electrode's On/Off states and the delivery of current for nerve stimulation. Characterization studies involving frequency and electrochemical analysis demonstrate the TFT-based circuit's capability to operate at high frequencies, deliver biphasic stimulation pulses to the electrode, and store sufficient charge for effective neural stimulation. Moreover, the a-IGZO TFTs exhibit remarkable stability during repeated gate voltage sweeps with minimal changes in electrical performance. This circuit has the potential to be extended to active-matrix devices that enable electrode arrays with a high number of channels and enhanced spatial resolution, which is crucial for selective neural stimulation. Herein, a flexible and softening circuit based on amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFT) designed for active addressing in high-channel-count neural stimulation electrode arrays is presented, exhibiting a high On/Off switching frequency response, electrical stability, and the ability to deliver biphasic stimulation pulses through the electrodes. These characteristics highlight the potential of the circuit in enabling high spatial resolution electrode arrays for neural stimulation.image