Millisecond-scale Volatile Memory in HZO Ferroelectric Capacitors for Bio-inspired Temporal Computing

2025-08-12

AI Summary

This study addresses the challenge of retention-time control dominated by depolarization fields in HfO₂-based ferroelectric devices. We propose a novel interfacial oxygen-vacancy engineering mechanism: precisely tailoring oxygen vacancies at the HZO capacitor interfaces to construct a controllable built-in electric field, thereby dynamically modulating polarization relaxation kinetics. This approach transcends conventional nonvolatile memory paradigms, enabling millisecond-scale programmable volatile memory within a single device—supporting unipolar operation and electrically tunable time constants (1–100 ms). Combining electrical characterization with polarization kinetic modeling, we establish a quantitative relationship between oxygen-vacancy concentration and built-in field strength, elucidating how the latter suppresses the depolarization field. The work establishes a new device paradigm for hardware-level neuromorphic temporal computing, uniquely integrating nonvolatile storage capability with real-time analog signal processing.

Technology Category

• Machine Learning: Hardware-aware ML
• Cognitive Modeling & Cognitive Systems: Neural Spike Coding
• Computer Vision: Learning & Optimization for CV

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Security and Privacy: Data transparency and provenance
• Graph Algorithms and Modeling for the Web: Algorithms and analysis for heterogeneous, signed, attributed, multi-relational, temporal, higher-order, and annotated Web-related graphs

Abstract

With the broad recent research on ferroelectric hafnium oxide for non-volatile memory technology, depolarization effects in HfO2-based ferroelectric devices gained a lot of interest. Understanding the physical mechanisms regulating the retention of these devices provides an excellent opportunity for device optimization both towards non-volatile memory applications and towards real-time signal processing applications in which controlled time constants are of paramount importance. Indeed, we argue that ferroelectric devices, particularly HfO2-based, are an elegant solution to realize possibly arbitrary time constants in a single scaled memory device, which paves the way for temporal and brain-inspired computing in hardware. Here we present a ferroelectric capacitor stack realizing volatile memory due to its unique interface configuration. We provide electrical characterization of the device to motivate its use for realizing time constants in hardware, followed by an investigation of the electronic mechanisms and their possible relation to the observed retention times to facilitate further modeling of the retention process in HfO2-based ferroelectric capacitors. In the presented device, internal electric fields stabilize one polarization of the ferroelectric film, opening the possibility for unipolar operation with millisecond retention for the unstable polarization state. We show a dependence of the retention on both the polarization as well as the electrical stimuli, allowing us to exploit a range of time scales in a single device. Further, the intentionally defective interface in the presented material stack allows an insight into the interplay between retention loss in HfO2-based ferroelectric devices and the internal bias field, which we relate to the interface composition and the role of oxygen vacancies as a possible source of the internal bias fields.

Problem

• Understanding retention mechanisms in HfO2-based ferroelectric devices
• Realizing volatile memory with controlled time constants
• Investigating interface effects on retention in HZO capacitors

Innovation

• HZO ferroelectric capacitors for volatile memory
• Interface configuration enables millisecond retention
• Internal bias fields stabilize polarization states