Nitrogen Doping Strategy in SiO₂ Insulators for Stable and Hydrogen-Resistant ALD-IGZO TFTs

Area of Science:

• Materials Science
• Semiconductor Physics
• Device Engineering

Background:

• Indium Gallium Zinc Oxide (IGZO) thin-film transistors (TFTs) are crucial for advanced display technologies.
• Current IGZO TFTs fabricated using atomic layer deposition (ALD) suffer from bias instability and hydrogen vulnerability.
• Controlling the interface and bulk properties of the gate insulator is key to overcoming these limitations.

Purpose of the Study:

• To investigate the impact of nitrogen (N) doping in SiO2 gate insulators (GI) on the performance and stability of top-gate bottom-contact (TG-BC) IGZO TFTs.
• To enhance the bias stability and hydrogen resistivity of IGZO TFTs through a novel N doping strategy.
• To explore the correlation between N content, trap densities, and device stability under stress conditions.

Main Methods:

• Fabrication of TG-BC IGZO TFTs with SiO2 GIs.
• Nitrogen doping of SiO2 GIs using nitrous oxide (N2O) plasma with varying power (100-300 W).
• Characterization of N content, trap densities, and device performance under positive bias temperature stress (PBTS) and H2 annealing.

Main Results:

• Increasing N content in SiO2 (0.7-2.2 at.%) led to a 10-fold increase in trap densities.
• PBTS induced a U-shaped threshold voltage (VTH) shift from -4.1 to 4.9 V, linked to H concentration and interface traps.
• Post-H2 annealing significantly improved hydrogen resistivity, reducing VTH shift from -2.1 to 0.0 V.
• A hybrid GI structure further boosted PBTS stability (60%) and H resistivity (71%).

Conclusions:

• N doping of SiO2 GIs effectively controls IGZO TFT interface and bulk properties.
• Nitrogen atoms act as chemical traps for hydrogen, enhancing device stability.
• The proposed N doping strategy, especially with hybrid structures, offers a promising solution for stable and reliable IGZO TFTs in future displays.