CMOS-Compatible Hf_xZr_1-xO₂ Ferroelectrics for Tunable Capacitors and Memristors.

This work focuses on developing Hafnium Zirconium Oxide (Hf_xZr_1-xO₂, HZO) thin films for multifunctional device applications, targeting both tunable microwave electronics and neuromorphic computing. HZO is a CMOS-compatible ferroelectric material that exhibits a stable orthorhombic phase even at nanoscale thicknesses (~10 nm), low dielectric loss, and strong electric-field-dependent dielectric permittivity (ε). These properties enable significant low-voltage tunability (~15% at < 10 V), making HZO highly suitable for compact, energy-efficient RF devices. Using HZO thin films, we have demonstrated coplanar waveguide (CPW) band-pass filters that operate reliably across a broad frequency range from kHz to several GHz, showing low insertion loss and excellent signal integrity, which are essential for applications in satellite communication, radar, and next-generation wireless systems. In addition to their capacitive tuning, HZO films exhibit resistive switching behavior characteristic of memristive devices. Metal/HZO/metal (MIM) structures show robust high-resistance and low-resistance states, a large memory window, excellent retention (>10⁴ s), and high endurance (>10⁴ switching cycles), demonstrating their suitability for non-volatile memory and neuromorphic computing applications. By implementing HZO memristors in a crossbar array architecture, multi-level resistance states can be exploited to emulate synaptic plasticity and facilitate analog-like weight updates in brain-inspired computing circuits. The integration of both ferroelectric capacitive modulation and resistive memristive switching within HZO thin films thus enables a single material platform for multifunctional devices that combine RF signal processing and neuromorphic computation.