Improved AC Drain Bias Stability in In-Zn-O TFTs with an Hf-Doped Heterobilayer Structure

Area of Science:

• Materials Science
• Electrical Engineering
• Semiconductor Physics

Background:

• Metal oxide semiconductors are crucial for display technologies due to high electron mobility and low leakage.
• Device instability under AC bias stress, particularly due to hot carrier effects (HCE), is a major challenge.
• HCE induce oxygen vacancies (V_O) and defect states, degrading performance.

Purpose of the Study:

• To enhance the AC bias stability and electron mobility of indium-zinc oxide (IZO) based thin-film transistors (TFTs).
• To mitigate hot carrier effects (HCE) and associated defect generation in IZO TFTs.
• To propose a heterobilayer structure for improved device performance under AC stress.

Main Methods:

• Fabrication of a heterobilayer TFT channel using an IZO bottom layer and a Hf-doped IZO top layer.
• Investigation of device characteristics under AC drain bias stress.
• Utilizing TCAD simulations to validate the heterobilayer structure's effectiveness.

Main Results:

• The IZO:Hf/IZO bilayer TFT achieved a mobility of 7.3 cm²/(V s).
• Demonstrated excellent AC stability with only 4% I_on degradation after 1000 s of AC stress.
• Exhibited negligible hysteresis, excellent reproducibility, a threshold voltage shift of 0.11 V, and a high on/off ratio (1.8 × 10⁶).

Conclusions:

• The heterobilayer structure effectively suppresses oxygen vacancies and defect generation, enhancing AC bias stability.
• Hf-doping in the top IZO layer strengthens oxygen bonds, mitigating HCE.
• The proposed IZO:Hf/IZO TFT offers a promising solution for stable and high-performance display applications.