Novel Approach to High κ (∼59) and Low EOT (∼3.8 Å) near the Morphotrophic Phase Boundary with AFE/FE (ZrO₂/HZO) Bilayer Heterostructures and High-Pressure Annealing

Abstract

We present herewith a novel approach of equally thick AFE/FE (ZrO2/HZO) bilayer stack heterostructure films for achieving an equivalent oxide thickness (EOT) of 4.1 Å with a dielectric constant (κ) of 56 in complementary metal-oxide semiconductor (CMOS) compatible metal–ferroelectric–metal (MFM) capacitors using a high-pressure annealing (HPA) technique. The low EOT and high κ values were achieved by careful optimization of AFE/FE film thicknesses and HPA conditions near the morphotropic phase boundary (MPB) after field cycling effects. Stable leakage current density (J < 10–7 A/cm2 at ±0.8 V) was found at 3/3 nm bilayer stack films (κ = 56 and EOT = 4.1 Å) measured at room temperature. In comparison with previous work, our remarkable achievement stems from the interfacial coupling between FE and AFE films as well as a high-quality crystalline structure formed by HPA. Kinetically stabilized hafnia films result in a small grain size in bilayer films, leading to reducing the leakage current density. Further, a higher κ value of 59 and lower EOT of 3.4 Å were found at 333 K. However, stable leakage current density was found at 273 K with a high κ value of 53 and EOT of 3.85 Å with J < 10–7 A/cm2. This is the lowest recorded EOT employing hafnia and TiN electrodes that are compatible with CMOS, and it has important implications for future dynamic random access memory (DRAM) technology.

Emerging Fluorite-Structured Antiferroelectrics and Their Semiconductor Applications

“…Moreover, a leakage current density lower than <10 –7 A/cm 2 was observed at 0.8 V, which is the standard requirement for DRAM cell capacitors. The enhanced electrical properties of the bilayer systems compared with those of the single-layer capacitors likely originated from the small grain size of the ZrO 2 /Hf 0.5 Zr 0.5 O 2 bilayer fabricated by a high-pressure annealing technique . However, several issues must be resolved before realizing practical DRAM applications.…”

“…Copyright 2018 ACS Publications. (b) Reprinted with permission from ref . Copyright 2020 ACS Publications.…”

“…The pioneering report by Park et al was followed by other experimental studies on MPB regions in fluorite-structured FEs. , It has been recently proposed that an AFE/FE (ZrO 2 /Hf 0.5 Zr 0.5 O 2 ) bilayer capacitor could exhibit a high k value and low EOT near the MPB region Figure b shows the capacitance–electric field ( C – E ) plots constructed for single-layer (FE Hf 0.5 Zr 0.5 O 2 and AFE ZrO 2 ) and bilayer (ZrO 2 /Hf 0.5 Zr 0.5 O 2 ) capacitors.…”

Hafnia-Based Ferroelectric Memory: Device Physics Strongly Correlated with Materials Chemistry

“…Another important issue that arises with the decrease in the physical thickness of the ferroelectric HZO film is the increase in the leakage current density. Figure b illustrates the changes in leakage current density as a function of equivalent oxide thickness (EOT) of HfO 2 , ZrO 2 , and HZO thin films . From Figure b, it can be observed that the leakage current density increases as the film thickness decreases, and this trend intensifies, particularly when the EOT falls below 0.8 nm.…”

“…(b) Current density ( J ) at 0.8 V as a function of equivalent oxide thickness (EOT) for ZrO 2 , HZO, and ZrO 2 /HZO bilayer. Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”