Multi‐Step Chemical Solution Deposition‐Annealing Process Toward Wake‐Up Free Ferroelectricity in Y:HfO₂ Films

Abstract

Ferroelectricity in HfO2 thin films can be utilized for fast, power‐efficient, and highly scalable non‐volatile memories. However, the required wake‐up process for inducing ferroelectricity/ achieving higher polarization is one of the major hurdles that hinder HfO2‐based thin films from developing reliable electronic devices. The wake‐up effect is believed to originate from i) phase transformation from non‐ferroelectric to ferroelectric, ii) movement of defect entities (mainly oxygen vacancy defects) near the film‐electrode interface, and iii) heterogeneity of the electrode interfaces. In the present study, an experimental strategy is designed to overcome these sources of the wake‐up process. A multi‐step deposition and annealing process is carried out to induce wake‐up‐free ferroelectricity in Yttrium doped HfO2 (Y:HfO2) thin film directly grown on Si‐substrate. Furnace annealing is utilized instead of the standard rapid thermal annealing process to reduce the oxygen deficiencies and stimulate the direct growth of the polar Y:HfO2. The oxygen‐vacancy‐related defects are found to be the dominating source of wake‐up effect in Y‐doped HfO2 films. The step‐wise deposition and annealing in the oxygen atmosphere facilitate direct growth of the polar phase, reduce the oxygen vacancies, and induce wake‐up‐free ferroelectricity in Y:HfO2.

Large electrocaloric effect with high thermal and electric field cycling stability in solution-processed Y:HfO2 thin films

“…As presented in our previous report, the microstructure observed is very uniform without any cracks, pores, or other kinds of discontinuities. 24 Therefore, a sharp transition is expected – evident from the transition shown in Fig. 2(b).…”

“…The large polarization is the outcome of Y-doping at a suitable concentration. 24 According to the comparative study reported by Starschich et al , polarization strongly depends on the ionic size of the dopants, and an ionic radius of around 85 pm is suitable for achieving a high P r . 34 Thus, rare earth elements such as La, Y, Nd, Sm, and Er are suitable to achieve large polarization.…”

“…In 2019, Park et al suggested that it would be possible to achieve the theoretically estimated ECE Δ S and Δ T in HfO 2 by suitable doping and process optimization. 33 In our present work, this has been achieved through Y-doping and optimized thin film preparation methods (multi-step deposition and step-wise annealing 24 ).…”

“…The details of the preparation can be found in the previous report. 24 Local switching characteristics and piezoelectric responses were investigated by using a commercial piezoresponse force microscopy (PFM) system (Cypher ES AFM, Asylum Research) at several temperatures. The ECE was measured by the indirect method (Maxwell method).…”

“…The preparation of the film and wake-up-free characteristics can be found in our previous report. 24 Fig. 1(a) illustrates the process of reliability tests followed in this study.…”