Ultrahigh Dielectric Permittivity of a Micron-Sized Hf0.5Zr0.5O2 Thin-Film Capacitor After Missing of a Mixed Tetragonal Phase

Abstract

Innovative use of HfO₂-based high-dielectric-permittivity materials could enable their integration into few-nanometre-scale devices for storing substantial quantities of electrical charges, which have received widespread applications in high-storage-density dynamic random access memory and energy-efficient complementary metal-oxide-semiconductor devices. During bipolar high electric-field cycling in numbers close to dielectric breakdown, the dielectric permittivity suddenly increases by 30 times after oxygen-vacancy ordering and ferroelectric-to-nonferroelectric phase transition of near-edge plasma-treated Hf_0.5Zr_0.5O₂ thin-film capacitors. Here we report a much higher dielectric permittivity of 1466 during downscaling of the capacitor into the diameter of 3.85 μm when the ferroelectricity suddenly disappears without high-field cycling. The stored charge density is as high as 183 μC cm^-2 at an operating voltage/time of 1.2 V/50 ns at cycle numbers of more than 10¹² without inducing dielectric breakdown. The study of synchrotron X-ray micro-diffraction patterns show missing of a mixed tetragonal phase. The image of electron energy loss spectroscopy shows the preferred oxygen-vacancy accumulation at the regions near top/bottom electrodes as well as grain boundaries. The ultrahigh dielectric-permittivity material enables high-density integration of extremely scaled logic and memory devices in the future.

Keywords: Charge storage; Hf0.5Zr0.5O2 thin film; Near-edge plasma treatment; Oxygen vacancy; Ultrahigh dielectric permittivity.

Fig. 1

Size-scaling effect on dielectric permittivity. a, b Frequency dependences of ε′ and tanδ for the HZO capacitors of various diameters. The solid lines represent data fittings according to Eqs. (4) − (6). c ε′-l dependence at 1 MHz. The solid line represents the best fit for the data according to Eq. (1) when considering the edging-area contribution under the top electrodes in the geometries illustrated in the inset. d D-E hysteresis loops for the capacitors of various diameters when characterized at 1 MHz. e D-E hysteresis loops at different periodicities for the capacitor in the diameter of 3.85 μm when ferroelectricity disappears. The inset figure shows the high frequency dependence of dielectric permittivity calculated from the slopes of the loops. f Cycling number dependences of maximum charge densities at 1.2 V for the size-scaled capacitors when using square fatigue pulses of ± 1.2 V/50 ns at a repetition frequency of 10 MHz. The inset figure shows D-E hysteresis loops after fatigue

Fig. 2

C − V loops in ferroelectric and nonferroelectric capacitors. a Typical C-V loops at 1 MHz for ferroelectric capacitors of various diameters. b C-V loops at different frequencies for a nonferroelectric capacitor in the diameter of 3.85 μm. c log|J|− E curves for the capacitors of various diameters. d Leakage current density (1 MV cm⁻¹) dependences of dielectric permittivities at different frequencies fitted by two solid lines

Fig. 3

XRD patterns. a Synchrotron in-plane grazing-incidence diffraction pattern for a large-area TiN/HZO/TiN capacitor using a synchrotron radiation source at a wavelength of 0.6887 Å. b, c Synchrotron X-ray micro-diffraction patterns of small capacitors in diameters of 4.07 μm and 3.85 μm with/without ferroelectricity, respectively, using a synchrotron radiation source at a wavelength of 0.6209 Å. From solid and dashed line fits of the peaks using the Gaussian function, we calculated area ratios of 0.76:0.24, 0.87:0.13, and 1:0 for O (111) and T (011) reflections with increasing dielectric permittivities from 24 to 1466, respectively. All patterns were corrected using W (110) reflections of top electrodes

Fig. 4

Phase structure and oxygen vacancy distribution. a Low-magnification HAADF-STEM cross-sectional image of a 300 nm-sized TiN/HZO capacitor. b Typical O K EELS spectra within areas 1 and 2 in a. c HAADF-STEM image near the phase boundary below the TiN top electrode. d EELS mapping of the B/A distribution in c