Observation of Wake-up Effect on Ferroelectric Y:HfO2 Thickness Scaling

Abstract

Ferroelectric HfO2 films have attracted lots of attention because they can be applied to various devices, including memories and logics, with reduced power consumption1. Some of the issues of ferroelectric HfO2 films are the wake-up effect and the thickness scaling to the ferroelectricity. The wake-up effect is the increase in the remnant polarization (Pr ) during the cycling test, and the physical explanation in the film has been reported so far. Also, the crystal structure change after the cycling test has been detected2. The thickness scaling includes both roll-up and off of the Pr on the film thickness. The physical phenomena are still not known, and the combination of the wake-up effect and the thickness scaling may give a clue to understanding the physics. In this study, we investigated the thickness-dependent wake-up effect of Y-doped atomic-layer-deposited (ALD) HfO2 films.Metal-insulator-metal (MIM) capacitors with 5 mol% Y-doped-HfO2 (Y:HfO2) films were sandwiched by W electrodes. A post metallization annealing (PMA) is performed at 600oC (1 min) to crystallize the films. Figure 1 shows the initial Pr of the capacitors on the HfO2 thickness. One can observe a peak in the Pr at a thickness of 8 nm. The existence of a peak in Pr on thickness is in good agreement with references3. The switching cycle dependence on the switching polarization (PSW ), the difference between positive and negative Pr , shown in figure 2, indicates a strong wake-up effect, especially for the 8-nm-thick film. The cross-sectional transmission electron microscope (TEM) image of the 12-nm-thick capacitor, shown in figure 3, indicates the presence of an amorphous interfacial layer at Y:HfO2/W. The magnitude of the wake-up effect might be influenced by the presence of the interface layer.This work is supported by JST-COI (JPMJCE1309).[1] T. S. Boscke, et al., Appl. Phys. Lett., 99, 102903 (2011). [2]Y. Tashiro, et al., The JSAP Autumn Meeting, 20a-C309-5, (2019). [3]X. Tian, et al., Appl. Phys. Lett., 112, 102902 (2018). Figure 1