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Crystalline materials with broken inversion symmetry can exhibit a spontaneous electric polarization, which originates from a microscopic electric dipole moment. Long-range polar or anti-polar order of such permanent dipoles gives rise to ferroelectricity or antiferroelectricity, respectively. However, the recently discovered antiferroelectrics of fluorite structure (HfO2 and ZrO2) are different: A non-polar phase transforms into a polar phase by spontaneous inversion symmetry breaking upon the application of an electric field. Here, we show that this structural transition in antiferroelectric ZrO2 gives rise to a negative capacitance, which is promising for overcoming the fundamental limits of energy efficiency in electronics. Our findings provide insight into the thermodynamically forbidden region of the antiferroelectric transition in ZrO2 and extend the concept of negative capacitance beyond ferroelectricity. This shows that negative capacitance is a more general phenomenon than previously thought and can be expected in a much broader range of materials exhibiting structural phase transitions.

A comprehensive quantitative root cause study of defect evolution leading to memory window closure from a charge balance and charge trapping perspective throughout all phases of a Si channel Hf0.5Zr0.5O2 (HZO) ferroelectric field-effect-transistor (FEFET) is reported. Starting with the first write pulse, an excessive SiO2 interlayer field is revealed that triggers the creation of defect levels Dit in excess of 1015 cm−2 eV−1 at the HZO–SiO2 interface screening ferroelectric (FE) polarization while enabling FE switching. Under subsequent early bipolar fatigue cycling (up to 104 cycles), defect creation commences at the SiO2–Si interface due to the high injected hole fluence (0.39 C/m2) during each stress pulse causing negative bias instability (NBI), which shifts the threshold voltage of the erase state VT,ERS by −0.3 V with accrual of permanently captured charge Nit of up to +5 × 10−3 C/m2 (3 × 1012 cm−2). Subsequently, Nit NBI generation at the SiO2–Si interface accelerates reaching levels of +7 × 10−2 C/m2, locking both FEFET program and erase drain current vs gate–source-voltage (ID–VGS) characteristics in the FEFET on-state inducing memory window closure at 105 cycles while FE switching (switched polarization Psw = 0.34 C/m2) remains essentially intact. These findings guide the down-selection toward suitable semiconductor/FE systems for charge balanced, reliable, and high endurance FEFETs. [ABSTRACT FROM AUTHOR]

Originally based on phenomenological observations, the Janovec–Kay–Dunn (JKD) scaling law has been historically used to describe the dependence of the ferroelectric coercive fields (Ec) on a critical length scale of the material, wherein the film thickness (t) is considered the length scale, and Ec ∝ t−2/3. Here, for the first time, a JKD‐type scaling behavior is reported in an antiferroelectric material, using the ultra‐thin films of prototypical flourite‐structure binary oxide, zirconia. In these films, a decrease in the ZrO2 layer thickness from 20 nm to 5.4 nm leads to an increase in critical fields for both nonpolar‐to‐polar (Ea), and polar‐to‐nonpolar (Ef) transitions, accompanied by a decrease in the average crystallite size, and an increase in the tetragonal distortion of the non‐polar P42/nmc ground state structure. Notably, the ‐2/3 power law as in the JKD law holds when average crystallite size (d), measured from glancing‐incident X‐ray diffraction, is considered as the critical length scale—i.e., Ea, Ef ∝ d−2/3. First principles calculations suggest that the increase of tetragonality in thinner films contributes to an increase of the energy barrier for the transition from the non‐polar tetragonal ground state to the field‐induced polar orthorhombic phase, and in turn, an increase in Ea critical fields. These results suggest a de‐stabilization of the ferroelectric phase with a decreasing thickness in antiferroelectric ZrO2, which is contrary to the observations in its fluorite‐structure ferroelectric counterparts. With the recent interests in utilizing antiferroelectricity for advanced semiconductor applications, our fundamental exposition of the thickness dependence of functional responses therein can accelerate the development of miniaturized, antiferroelectric electronic memory elements for the complementary metal‐oxide‐semiconductor based high‐volume manufacturing platforms. [ABSTRACT FROM AUTHOR]

Since the discovery of ferroelectricity in doped/alloyed HfO2 and ZrO2 thin film, many device engineers have been attracted to its sustainable ferroelectricity at the thickness of a few nanometer. While most of the previous studies have mainly focused on the ferroelectric properties of the thermally atomic layer deposited (THALD) Hf0.5Zr0.5O2 (HZO), the plasma-enhanced ALD (PEALD) HZO has not received much attention. In this work, a direct comparison between the two types of HZO thin films is carried out, where we found that a tradeoff exists between these two fabrication methods. While the THALD HZO was able to maintain a higher cycling endurance, the PEALD HZO showed more stable characteristics over the cycling with reduced wake-up and fatigue effects, in addition to better tolerance against breakdown under high electric field. Furthermore, the PEALD HZO could be crystallized with post deposition annealing at 350 °C, which is of great interest for the back-end-of-line compatibility with silicon fabrication processes. [ABSTRACT FROM AUTHOR]

B Ultra-High Density Memory b Antiferroelectric oxides are a promising candidate for next-generation, ultra-high density memory technologies. In article 2100485, Nazanin Bassiri-Gharb, Asif Islam Khan, and colleagues show that the critical polar - antipolar transition voltages in prototypical fluorite-structured antiferroelectric ZrO SB 2 sb thin films show a -2/3 power law dependence on the average crystallite size, in analogy to the Janovec-Kay-Dunn Law for ferroelectrics. A Janovec-Kay-Dunn-Like Behavior at Thickness Scaling in Ultra-Thin Antiferroelectric ZrO2 Films (Adv. [Extracted from the article]

Since the discovery of ferroelectricity in doped/alloyed HfO 2 and ZrO 2 thin film, many device engineers have been attracted to its sustainable ferroelectricity at the thickness of a few nanometer. While most of the previous studies have mainly focused on the ferroelectric properties of the thermally atomic layer deposited (THALD) Hf 0.5 Zr 0.5 O 2 (HZO), the plasma-enhanced ALD (PEALD) HZO has not received much attention. In this work, a direct comparison between the two types of HZO thin films is carried out, where we found that a tradeoff exists between these two fabrication methods. While the THALD HZO was able to maintain a higher cycling endurance, the PEALD HZO showed more stable characteristics over the cycling with reduced wake-up and fatigue effects, in addition to better tolerance against breakdown under high electric field. Furthermore, the PEALD HZO could be crystallized with post deposition annealing at 350 °C, which is of great interest for the back-end-of-line compatibility with silicon fabrication processes.