Oxygen Defect-Induced Metastability in Oxide Semiconductors Probed by Gate Pulse Spectroscopy

Area of Science:

• Materials Science
• Semiconductor Physics
• Device Engineering

Background:

• Amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) transistors are crucial for display technologies.
• Understanding instability mechanisms is key to improving device reliability.
• Metastable oxygen defects are implicated in the threshold voltage shifts observed in these devices.

Purpose of the Study:

• To investigate the underlying mechanisms of instability in a-IGZO transistors.
• To characterize the distribution of activation energies associated with oxygen defects.
• To differentiate between oxygen defect-related instability and charge trapping/detrapping phenomena.

Main Methods:

• Bias and illumination stress-recovery experiments were performed.
• Analysis employed stretched exponential functions and inverse Laplace transforms.
• A novel gate-pulse spectroscopy technique was utilized to probe post-stress defect profiles.

Main Results:

• The recovery process after illumination stress exhibits persistent slowness.
• A broad distribution of activation energies (0.85–1.38 eV) was retrieved, indicative of ionized oxygen vacancies and interstitials.
• Charge trapping/detrapping events, requiring lower activation energies (~0.53 eV), were ruled out.

Conclusions:

• The primary source of instability in a-IGZO transistors under stress is attributed to metastable oxygen defects.
• Ionized oxygen vacancies and interstitials are the dominant defect types responsible for slow recovery.
• The findings provide insights into the electronic structure, including anti-bonding states, of these defects.