A Low-Temperature Poly-Silicon Thin Film Transistor Pixel Circuit for Active-Matrix Simultaneous Neurostimulation

This work reports a novel low-temperature poly-silicon thin-film-transistor-based pixel circuit for active-matrix neurostimulation. The pixel circuit consists of four transistors and one capacitor (4T1C) for programmable current-mode stimulation, which are designed for storing stimulation intensity information, simultaneously stimulating a large number of channels, and discharging stimulation electrodes. Due to the high mobility and low threshold voltages of the devices, the fabricated circuit occupies a pixel area of $200\times 200\,\,\mu \text{m}\,\,^{\mathrm{ 2}}$ , and delivers a stimulation current of $147 ~\mu \text{A}$ , sufficient to stimulate a neuron. The turn-on resistance of the fabricated transistor is below 6 $\text{k}\Omega $ , sufficient to be used as switches for bioelectronic applications. By employing a discharging switch transistor, the accumulated charges on the stimulation electrodes were released, and the electrode voltage was reduced to 0.08 V, thus mitigating corrosion. We demonstrated that two pixel circuits at different rows and columns can output stimuli simultaneously without a noticeable delay. This pixel circuit shows high potential to scale up as an active-matrix neurostimulation system with a high channel count.