Impact of asymmetric electrodes on ferroelectricity of sub-10 nm HZO thin films

Hsing-Yang Chen; Yu-Sen Jiang; Chun-Ho Chuang; Chi-Lin Mo; Ting-Yun Wang; Hsin-Chih Lin; Miin-Jang Chen

doi:10.1088/1361-6528/ad0f52

Impact of asymmetric electrodes on ferroelectricity of sub-10 nm HZO thin films

Nanotechnology. 2023 Dec 18;35(10). doi: 10.1088/1361-6528/ad0f52.

Authors

Hsing-Yang Chen¹, Yu-Sen Jiang¹, Chun-Ho Chuang¹, Chi-Lin Mo¹, Ting-Yun Wang¹, Hsin-Chih Lin¹, Miin-Jang Chen^{1

2}

Affiliations

¹ Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan, ROC.
² Graduate Institute of Electronics Engineering, National Taiwan University, Taipei, Taiwan, ROC.

PMID: 37995361
DOI: 10.1088/1361-6528/ad0f52

Abstract

In this study, platinum (Pt) and tungsten (W), two materials with dissimilar coefficients of thermal expansion (CTE) and work functions (WF), are used as the top electrode (TE) and the bottom electrode (BE) in metal/ferroelectric/metal (MFM) structures to explore the ferroelectricity of hafnium zirconium oxide (HZO) with a thickness less than 10 nm. The electrical measurements indicate that a higher CTE mismatch between HZO and TE/BE is beneficial for enhancing the ferroelectric properties of nanoscale HZO thin films. The different WFs of TE and BE generate a built-in electric field in the HZO layer, leading to shifts in the hysteresis loops and the capacitance-voltage characteristics. The structural characterizations reveal that the preferred formation of the orthorhombic phase in HZO is dominated by the W BE. The device in which W is used as the TE and BE (the W/HZO/W MFM structure) presents the optimal ferroelectric performance of a high remanent polarization (2P_r= 55.2μC cm^-2). The presence of tungsten oxide (WO_x) at the W/HZO interfaces, as revealed by high-resolution transmission microscopy, is also responsible for the enhancement of ferroelectric properties. This study demonstrates the significant effects of different CTEs and WFs of TE and BE on the properties of ferroelectric HZO thin films.

Keywords: Ferroelectrics; Hf0.5Zr0.5O2; thermal mismatch; work function.