Resolving Mechanical Properties and Morphology Evolution of Free-Standing Ferroelectric Hf0.5Zr0.5O2

Advances in creating polar structures in atomic-layered hafnia-zirconia (HfxZr1-xO2) films not only augurs extensive growth in studying ferroelectric nanoelectronics and neuromorphic devices, but also spurs opportunities for exploring novel integrated nanoelectromechanical systems (NEMS). Design and implementation of HfxZr1-xO2 NEMS transducers necessitates accurate knowledge of elastic and electromechanical properties. Up to now, all experimental approaches for extraction of morphological content, elastic, and electromechanical properties of HfxZr1-xO2 are based on solidly mounted structures, highly stressed films, and electroded architectures. Unlike HfxZr1-xO2 layers embedded in electronics, NEMS transducers require free-standing structures with highly contrasted mechanical boundaries and stress profiles. Here, a nanoresonator-based approach for simultaneous extraction of Young's modulus and residual stress in free-standing ferroelectric Hf0.5Zr0.5O2 films is presented. High quality factor resonance modes of nanomechanical resonators created in predominantly orthorhombic Hf0.5Zr0.5O2 films are measured using nondestructive optical transduction. Further, the evolution of morphology during creation of free-standing Hf0.5Zr0.5O2 structures is closely mapped using X-ray diffraction measurements, clearly showing transformation of ferroelectric orthorhombic to nonpolar monoclinic phase upon stress relaxation. The extracted Young's modulus of 320.0 +/- 29.4 GPa and residual stress of sigma = 577.4 +/- 24.1 MPa show the closest match with theoretical calculations for orthorhombic Hf0.5Zr0.5O2.