Sub-10 nm Fully Atomic-Layer-Deposited MFM Stack with Enhanced Reliability: Record-low Ileakage and Record-high EBD in 3 nm Ferroelectric HZO

The article titled "Sub-10 nm Fully Atomic-Layer-Deposited MFM Stack with Enhanced Reliability: Record-low Leakage and Record-high EBD in 3 nm Ferroelectric HZO" focuses on the development and performance enhancement of ultra-thin metal-ferroelectric-metal (MFM) capacitors with a 3 nm ferroelectric HfZrOₓ (HZO) layer. These capacitors are key for future high-density, low-voltage ferroelectric memories, including 3D-integrated non-volatile memory (NVM) technologies. Here’s a summary of the main findings:

Key Findings:

1. Ultra-thin MFM Stack Development:

• The paper presents a fully atomic-layer-deposited (ALD) MFM stack consisting of 3 nm TiN / 3 nm HZO / 3 nm TiN, achieving a record-low coercive voltage (2Vc < 0.65V) and significant improvements in key reliability metrics, including a very low leakage current density (<10⁻³ A/cm² at 3 MV/cm) and an exceptionally high breakdown electric field (EBD > 9.5 MV/cm).

• The ultra-thin MFM capacitors exhibited endurance greater than 10¹¹ cycles without failure, with stable ferroelectric polarization (2Pr > 18 μC/μm²) and no dielectric breakdown.

2. Thinning TiN Electrodes for Enhanced Performance:

• A key discovery is the enhancement of ferroelectricity and reliability in HZO when TiN electrodes are thinned below 8 nm. Specifically, thinner TiN electrodes help promote the formation of the "o-phase" in HZO, a crucial phase for strong ferroelectric properties.

• Thinning the TiN electrodes also leads to smoother surfaces, which suppresses oxygen vacancies, reduces leakage current, and improves breakdown strength.

3. Material Transition and Benefits:

• A structural transition from polycrystalline to amorphous TiN occurs as the electrode thickness is reduced. This transition significantly improves the interface with HZO, allowing for better ferroelectric properties. Amorphous TiN is found to promote o-phase formation in HZO more effectively than polycrystalline TiN, thus enhancing the ferroelectric properties.

• The study combines experimental data with first-principles calculations to explain that the lattice mismatch between TiN and HZO plays a significant role in promoting the desired phase in HZO, further supporting the benefits of thinner TiN.

4. Improved Reliability and Breakdown Tolerance:

• With thinner TiN, the MFM capacitors showed an order of magnitude reduction in leakage current and significant improvements in breakdown strength. The 3 nm HZO with 3 nm TiN exhibited a record-high EBD, exceeding 9.5 MV/cm, and a remarkably low leakage current.

• The improved reliability is attributed to the smoother TiN surfaces and reduced oxygen scavenging at the TiN/HZO interface, which minimizes defect formation and leakage paths.

5. Endurance and Long-term Stability:

• The endurance tests demonstrated that the 3 nm HZO capacitors with 3 nm TiN electrodes had minimal degradation in 2Pr after 10¹¹ cycles, highlighting their potential for long-term stable performance.

• Retention tests further confirmed stable behavior with a lower leakage current, positioning these capacitors as ideal candidates for high-performance ferroelectric memory technologies.

Conclusion:

The work introduces the thinnest fully ALD-deposited MFM capacitor with 3 nm HZO and 3 nm TiN electrodes, setting new records for ferroelectric performance and reliability. The combination of thinner TiN electrodes and the optimized HZO layer enables improved ferroelectricity, significantly reduced leakage, enhanced breakdown tolerance, and exceptional endurance. These findings pave the way for the development of ultra-high-density, low-voltage ferroelectric memories and 3D integration in future memory technologies. The study provides insights into the potential for scaling down ferroelectric devices while maintaining reliability, offering a promising path for next-generation memory applications.