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ZrO2 Ferroelectric Field-Effect Transistors Enabled by the Switchable Oxygen Vacancy Dipoles
Huan Liu1, Yue Peng1, Genquan Han2
1State Key Discipline Laboratory of Wide Band Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi'an, 710071, China.
Nanoscale Research Letters
|May 26, 2020
Summary
This study explores how rapid thermal anneal (RTA) and zirconium dioxide (ZrO2) thickness affect ferroelectric properties in TaN/ZrO2/Ge capacitors and FeFETs. A 4nm ZrO2 film with optimized RTA shows promising long-term data retention for FeFET memory applications.
Area of Science:
- Materials Science
- Electrical Engineering
- Solid State Physics
Background:
- Ferroelectric materials are crucial for non-volatile memory devices.
- Zirconium dioxide (ZrO2) is a promising candidate for gate dielectrics in advanced transistors.
- Understanding the impact of processing parameters on ZrO2's ferroelectric properties is essential for device optimization.
Purpose of the Study:
- To investigate the influence of post-rapid thermal anneal (RTA) temperature and ZrO2 thickness on the polarization (P) and electrical characteristics of TaN/ZrO2/Ge capacitors.
- To evaluate the performance of Ferroelectric Field-Effect Transistors (FeFETs) incorporating varying thicknesses of ZrO2.
- To determine the optimal processing conditions for enhanced memory window (MW), fatigue, and retention in ZrO2-based FeFETs.
Main Methods:
- Fabrication of TaN/ZrO2/Ge capacitors and FeFETs with amorphous ZrO2 films of varying thicknesses (2.5nm, 4nm, 9nm).
- Application of rapid thermal annealing (RTA) at temperatures ranging from 350 to 500 °C.
- Electrical characterization including polarization measurements, memory window (MW) assessment, fatigue testing, and retention analysis using 100ns program/erase pulses.
Main Results:
- TaN/ZrO2/Ge capacitors with 2.5nm and 4nm ZrO2 exhibited stable polarization after RTA.
- FeFETs demonstrated a decent memory window (MW) with 100ns pulses across different ZrO2 thicknesses.
- A 4nm ZrO2 FeFET showed significantly improved fatigue and retention compared to 2.5nm and 9nm devices.
- Increasing RTA temperature enhanced the retention performance of ZrO2 FeFETs.
- Extrapolation indicated a potential for maintaining a ~0.46V MW over 10 years for the 4nm ZrO2 device.
Conclusions:
- The ferroelectric behavior in TaN/ZrO2/Ge structures is attributed to the migration of voltage-driven dipoles, likely involving oxygen vacancies.
- Optimizing ZrO2 thickness to 4nm and controlling RTA temperature are critical for achieving robust ferroelectric properties and reliable memory operation in FeFETs.
- The 4nm ZrO2 FeFET shows significant potential for long-term data retention, making it a viable candidate for future non-volatile memory applications.
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