Micro-LED Pixel Circuit

Micro light-emitting diode (μLED) displays have garnered extensive attention as next-generation displays. Typically, μLEDs refer to ultra-small ≤100-μm LEDs and have many advantages such as low power consumption, excellent efficiency, and long lifetime. In addition, μLEDs can operate even under extreme conditions (below -20 °C and above 100 °C), and they exhibit significantly high brightness without the burn-in phenomenon, which is a severe problem in organic light-emitting diodes (OLEDs). Although μLEDs have many advantages, μLEDs can exhibit wavelength shifts depending on the current density. Therefore, a color shift can occur when grayscale is modulated by using pulse amplitude modulation (PAM), which has been widely used in conventional OLED displays. Pulse width modulation (PWM) is a method used to suppress the color shift of μLEDs.In our lab, we research μLED pixel circuits with PWM based on low-temperature polycrystalline silicon (LTPS) TFTs and amorphous indium–gallium–zinc oxide (a-IGZO) TFTs.

μ-LED Pixel Circuit Structure : (a) Circuit schematic for using the PWM method in the sub-pixel and (b) timing diagram for 1 frame time. (Read More)

(a) The measured and simulated brightness of the red, green, and blue μLEDs and (b) the measured wavelength of the green μLEDs in the fabricated pixel circuits using the PWM and PAM methods. (Read More)

Scan/Emission Driver Circuit

Gate driver circuits consist of scan driver and emission driver circuits. The scan driver circuits are circuits that are necessary to apply data voltage to the driving TFT at the desired timing for light emission from pixel circuits. In addition, the emission driver circuit generates an output controlling ON/OFF states of TFTs required for sequential emission of light-emitting devices. Each circuit plays a role in emitting data by transmitting data to the light-emitting devices as the output waveform of the scan driver circuits and the output waveform of the emission driver circuits are applied to the pixel circuit through the above serial processes.

In our lab, we research scan and emission driver circuits, especially based on amorphous indium–gallium–zinc oxide (a-IGZO) TFTs covering stable operations even in the depletion mode which can cause serious problems in the integrated driver circuit, such as output voltage degradation, ripple voltage generation, and increase in power consumption. We also investigate gate driver circuits using low-temperature polycrystalline silicon (LTPS) TFTs as well as the gate driver circuits using a-IGZO TFTs.

Gate Driver Circuit Structure : (a) circuit schematic, (b) timing diagram, and (c) block diagram. (Read More)

Simulated voltage waveforms of (a) Q[n], (b) A[n], and (c) VOUT[n] nodes for the previously proposed gate driver circuit that exhibit a sufficiently high output voltage and a low ripple voltage in the ON and OFF states, respectively. (Read More)