Stress Engineering as a Strategy to Achieve High Ferroelectricity in Thick Hafnia Using Interlayer

Abstract

Binary oxides of Hf0.5Zr0.5O2 (HZO) have attracted considerable attentionof the ferroelectricresearch community, owing to their excellent ferroelectric properties and CMOS compatibility. In particular, HZO films of a relatively high thickness (>10 nm) are studied widely for sensor and display applications. However, one of the major constraints of HZO materials is the formation of monoclinic phases (m-phase) with increasing film thickness resulting in the degradation of its remanent polarization ( Pr). Herein, we present a stress engineering method to achieve high ferroelectricity in thick hafnia using an interlayer. In our work, we attempted to address the aforesaid limitation of HZO by inserting a dielectric interlayer and elucidated the influence of interlayer on the relatively thick HZO films. high resolution TEM (HRTEM) analysis revealed that the presence of interlayer allows the growth of the top and bottom HZO layer in an independent direction thereby preventing the loss of ferroelectricity inHZOfilmswith higher thickness by controlling its grain size. Similarly, grain angle incidence X-ray diffraction (GIXRD) and residual stressmeasurements suggest that the interlayer affects the o-phase formation from the t-phase owing to the tensile stress applied to the HZO films because of the coefficient of thermal expansion (CTE) mismatch between the HZO and interlayer. In our study, an improved 2Pr value of 30.2 mu C/cm(2) was achieved by inserting a TiO2 dielectric interlayer in a relatively thicker HZO film. We believe that this approach can be adopted in various applications such as sensors, displays, and memory devices.