Ferroelectric [HfO₂/ZrO₂] Superlattices with Enhanced Polarization, Tailored Coercive Field, and Improved High Temperature Reliability

Abstract

Modern microelectronic systems and applications demand an every increasing amount of non‐volatile memories that are fast, reliable, and consume little power. Memory concepts based on ferroelectric HfO2 like the ferroelectric field effect transistor (FeFET) and the ferroelectric random access memory (FeRAM) are promising to satisfy these requirements. As a consequence, continuing high attention is given to improve the ferroelectric properties and the reliability characteristics of the ferroelectric HfO2 films –‐ for instance by using different dopant elements, dopant concentrations, and film thicknesses. Superlattices (i.e., a periodic structure of two materials stacked upon each other) are a promising alternative approach. Herein, [HfO2/ZrO2] superlattices of various sublayer thicknesses and a constant total thickness of 10 nm are embedded into metal‐ferroelectric‐metal (MFM) capacitors and then electrically as well as structurally characterized with special focus on remanent polarization, coercive field, endurance, and high temperature reliability. Compared to a 10 nm (Hf,Zr)O2 solid solution reference film, the use of superlattice stacks significantly improves the above mentioned parameters. In addition, most of these parameters depend on the sublayer thickness, which allows, for instance, tailoring the coercive field of the whole device.

HfO2–ZrO2 Ferroelectric Capacitors with Superlattice Structure: Improving Fatigue Stability, Fatigue Recovery, and Switching Speed

“…Compared with HZO, the polarization switching speed of SL structure devices is significantly improved. 12 Similarly, the critical electric field for 80% saturated P sw of HZO, SL 5 , SL 10 , and SL 15 devices was approximately 1.66, 1.57, 1.62, and 1.62 MV/cm, respectively, suggesting that SL structure devices maybe switching more easily under the same condition. 35 The IFM model was employed to further analyze the switching dynamics of the HZO and SL capacitors, which takes into account the nonuniform distribution of the electric field within the polycrystalline HfO 2 -based FE film.…”

“…The 80% saturated P sw of HZO, SL 5 , SL 10 , and SL 15 devices were about 1.13, 0.94, 0.8, and 0.48 μs, respectively, and are marked with the gray dashed line in Figure b–e. Compared with HZO, the polarization switching speed of SL structure devices is significantly improved . Similarly, the critical electric field for 80% saturated P sw of HZO, SL 5 , SL 10 , and SL 15 devices was approximately 1.66, 1.57, 1.62, and 1.62 MV/cm, respectively, suggesting that SL structure devices maybe switching more easily under the same condition …”

“…Recently, researchers have achieved significant progress in the development of ferroelectric (FE) films by realizing a HfO 2 –ZrO 2 superlattice (SL) FE film. − This development has resulted in a remarkable improvement in the endurance performance of the film, exceeding 10 12 cycles, and an improved fatigue recovery capability . Additionally, Liang et al have demonstrated that the SL metal-FE-metal (MFM) capacitors, with 600 °C PMA, exhibited significantly improved endurance performance with almost “wake-up”-free and fatigue-free robust polarization behavior up to 10 11 cycles of field cycling .…”

Toward Energy‐Efficient Ferroelectric Field‐Effect Transistors and Ferroelectric Random Access Memories: Tailoring the Coercive Field of Ferroelectric HfO2 Films

“…As the first three approaches have been discussed in the literature, albeit without a specific emphasis on E c tailoring, electrical data from these publications were utilized. [11][12][13] Additional details regarding these sample sets, including the thickness of the FE stacks, electrode materials, and their deposition processes, as well as annealing treatments, are presented in Table 1. For more comprehensive information, readers are encouraged to refer to the cited references.…”

Improved Polarization‐Retention‐Endurance in Hf0.5Zr0.5O2 Films by ZrO2 Capping via Electrostatic Effects

“…In this regard, nanolaminate periodicity and annealing temperature have an important impact also on endurance and leakage current. [22,23] Nanolaminates based on Al 2 O 3 and ferroelectric doped HfO 2 have demonstrated to be of interest to develop thick (>20 nm) ferroelectric films with sizable polarization, [24,25] of great importance for applications. [26,27] Epitaxial films, of larger crystalline quality than polycrystalline samples, are of significant interest for understanding characteristics and prototyping devices.…”