Micro-LED Microdisplays Driven by Carbon Nanotube Active-Matrix Backplanes

Area of Science:

• Materials Science: Advanced semiconductor materials for display technology.
• Electrical Engineering: Thin-film transistor (TFT) fabrication and circuit design.
• Optoelectronics: Micro-light-emitting-diode (μLED) display systems.

Background:

• Micro-light-emitting-diodes (μLEDs) are crucial for next-generation displays due to their superior brightness, efficiency, and resolution.
• Existing thin-film transistor (TFT) backplanes using silicon CMOS, LTPS, or metal oxides face limitations in scalability, transparency, and performance for high-pixel-density μLED microdisplays.
• Two-dimensional transition metal dichalcogenides (TMDs) show promise but have been hindered by complex integration and scalability issues.

Purpose of the Study:

• To develop and demonstrate an active-matrix (AM) μLED microdisplay utilizing optimized carbon nanotube (CNT) thin-film transistors (TFTs).
• To overcome the limitations of current TFT technologies for high-performance μLED microdisplays.
• To establish CNT TFTs as a viable and scalable backplane solution for advanced microdisplays.

Main Methods:

• Fabrication of CNT TFTs with specific gate dielectric (Al2O3/SiO2) and passivation (Y2O3/SiO2/polyimide) layers.
• Optimization of CNT TFT channel length (Lch) to enhance driving current and mobility.
• Development of a heterogeneous integration process using flip-chip eutectic bonding for μLED array assembly onto CNT TFT backplanes.
• Design of CNT TFT-based 2T1C pixel circuits supporting pulse amplitude modulation (PAM) and pulse width modulation (PWM).

Main Results:

• CNT TFTs with Lch = 3 μm achieved a driving current of ~10 μA/μm and mobility of ~27 cm²/ (V·s).
• Scaling Lch to 0.5 μm boosted driving current to ~80 μA/μm and mobility to ~40 cm²/ (V·s), surpassing previous CNT TFTs for AM displays.
• Enabled AM-μLED microdisplays with up to 3400 PPI.
• Achieved ~100% yield in heterogeneous integration of μLEDs onto CNT TFT backplanes.
• Demonstrated a 32 × 32-pixel AM-μLED prototype microdisplay (357 PPI) capable of dynamic image and video display.

Conclusions:

• Optimized CNT TFTs provide superior driving performance and scalability for high-PPI μLED microdisplays.
• The developed heterogeneous integration method ensures high yield and reliability.
• CNT TFTs represent a promising and scalable solution for next-generation μLED microdisplays, particularly for AR and VR applications.