Hf_1–xZr_xO₂/ZrO₂ Nanolaminate Thin Films as a High-κ Dielectric

Abstract

Engineering of HfO 2 −ZrO 2 ferroelectric thin films can substantially increase their dielectric constant. Here, we investigate dielectric and structural properties of ∼10 nm thin films consisting of stacked 1 nm thin ferroelectric (FE) Hf 1−x Zr x O 2 (HZO(x)) and antiferroelectric (AFE) ZrO 2 layers. At x < 0.5, the measurements of polarization vs electric field revealed pure FE hysteresis loops, whereas at x > 0.5, pinched hysteresis loops with some remnant polarization were observed, which indicate a coexistence of FE and AFE orderings. Finally, a pure ZrO 2 thin film (x = 1) exhibits only an AFE double hysteresis loop. In this way, we demonstrate that the coexistence of FE and AFE orderings can be controlled by adjusting the composition of HZO(x) layers in the HZO(x)/ZrO 2 nanolaminate films. At x = 0.5, the dielectric constant is ∼60 in nanolaminate films, which is much higher than that of the conventional HZO(x) solid solution thin films. Structural investigations confirm a coexistence of polar orthorhombic and nonpolar tetragonal structures, which is consistent with the observed polarization hysteresis loops. We also show that the strain generated in the nanolaminate structure significantly facilitates a field-induced transition from the AFE to the FE phase. The design does not considerably affect the leakage current in HZO(x)/ZrO 2 nanolaminate films, which makes this system highly promising for complementary metal oxide semiconductor-compatible capacitors.

Sharp Transformation across Morphotropic Phase Boundary in Sub‐6 nm Wake‐Up‐Free Ferroelectric Films by Atomic Layer Technology

“…The ε r taken at 2.5 V of the H 10 Z and H 14 Z samples further decreases to ≈20–21, which can be ascribed to the dominant m‐phase in the thin films. [ 2a,25a ] The dielectric properties of all the samples agree well with the electrical and crystalline phase analyses as revealed by the P–V , J–V , NBD, and XRD measurements.…”

“…The observed remanent polarization in the pinched P–V curves suggests the coexistence of the AFE and FE crystalline phases, that is, the presence of MPB, in the thin films. [ 25 ] It is noticeable that the remanent polarization increases from the H 0 Z to H 4 Z samples, implicating that an increase in the thickness of the HfO 2 seeding layer ( T HfO2 ) results in an increase of the FE phase in the HZ structures.…”

Improvement of endurance and switching speed in Hf1−x Zr x O2 thin films using a nanolaminate structure

“…It was thought that the region of o-phase contributed to these ferroelectric behaviours. HZZ (10-10) yielded a hysteresis loop with mixed ferroelectric and antiferroelectric characteristics, which imply the coexistence of the o-phases and t-phases in the film [14][15][16]. Given the excessive antiferroelectricity inflicted by the 2P r value, it is necessary to suppress the crystallization of the t-phase by reducing the thickness of the ZrO 2 interlayer.…”

Overcoming Size Effects in Ferroelectric Thin Films

“…To improve the retention and endurance of the capacitor, there is a method of inserting the interlayer between HZO and the electrode or changing the doping element of HZO. [132][133][134][135][136][137][138][139][140][141][142]…”