Ge₂Sb₂Te₅ p-Type Thin-Film Transistors on Flexible Plastic Foil

Area of Science:

• Materials Science
• Electronics Engineering
• Semiconductor Physics

Background:

• Prior germanium antimony telluride (Ge2Sb2Te5) thin-film transistors (TFTs) exhibited limited current modulation (ON/OFF ratios ≤20) and non-saturating output characteristics.
• High-performance p-type TFTs are crucial for developing hybrid complementary metal-oxide-semiconductor (CMOS) technologies on flexible substrates.

Purpose of the Study:

• To investigate the performance enhancement of p-type Ge2Sb2Te5 (GST) TFTs on flexible polyimide substrates by downscaling GST layer thickness.
• To evaluate the impact of GST thickness and phase (amorphous vs. crystalline) on TFT characteristics, including ON/OFF ratio, mobility, and saturation.
• To assess the operational stability and mechanical robustness of these flexible TFTs.

Main Methods:

• Fabrication of p-type TFTs utilizing varying thicknesses of Ge2Sb2Te5 (GST) semiconductor layers on flexible polyimide substrates.
• Characterization of TFT performance in both as-deposited (amorphous) and annealed (crystalline at 200°C) states.
• Evaluation of device performance under mechanical bending stress (radius of 6 mm) and bias stress.

Main Results:

• Reducing GST thickness to 5 nm significantly improved performance, achieving ON/OFF ratios up to ≈300 and enabling drain current saturation.
• The highest effective field-effect mobility of 6.7 cm²/Vs was observed in 10-nm-thick crystalline GST TFTs (ON/OFF ratio ≈16).
• Amorphous GST TFTs (5 nm) exhibited a mobility of 0.04 cm²/Vs and were more susceptible to bias stress compared to crystalline counterparts.
• Devices maintained full functionality after bending to a 6 mm radius.

Conclusions:

• Downscaling GST thickness is an effective strategy to enhance the performance of p-type TFTs for flexible electronics.
• Germanium antimony telluride (GST) demonstrates compatibility with flexible electronics, offering a promising material for p-type channel applications in hybrid CMOS technology.
• The study highlights the potential of GST TFTs for applications requiring high-performance, flexible, and robust semiconductor devices.