Simultaneous pulse amplitude and pulse width modulation in a 6T1M2C pixel circuit enabled by the separate timing control for charge injection and transport in the multimodal transistor

Abstract

Emerging micro light-emitting diode (microLED) displays promise high brightness, improved lifetime, and high pixel density. However, to achieve the desired color accuracy, microLEDs require constant current driving, which can result in wavelength shift at higher pixel brightness. This presents a challenge for pixel circuit design. The driving scheme must vary the emission duration (i.e., pulse width modulation, PWM) to prevent wavelength shift, and it must also include an element of current magnitude control (pulse amplitude modulation, PAM) for fine tuning. This results in complex signaling, large footprint, and multiple sources of variability arising from the numerous transistors, which together diminish the implementation's efficacy. Here, we present a 6T1M2C pixel circuit, which takes advantage of the properties of the multimodal thin-film transistor (MMT) to achieve PWM and PAM simultaneously, rather than in a hybrid configuration, while also performing threshold compensation. The MMT is the first transistor that allows for separation of injection (current magnitude) from channel conduction state (timing), allowing a higher degree of freedom for designing pixel circuits with lower complexity. This proof-of-concept TCAD implementation demonstrates the benefits of MMT-based simultaneous PWM and PAM circuits, with compact device footprint, reduced circuit complexity, and power-efficient features.