On the exceptional temperature stability of ferroelectric AlScN thin films
MD Redwanul Islam, Niklas Wolff, Mohammed Yassine, Georg Schönweger, Björn Christian, Hermann Kohlstedt, Oliver Ambacher, Fabian Lofink, Lorenz Kienle, Simon Fichtner
Through its dependence on low symmetry crystal phases, ferroelectricity is inherently a property tied to the lower temperature ranges of the phase diagram for a given material. This paper presents conclusive evidence that in the case of ferroelectric AlScN, low temperature has to be seen as a purely relative term, since its ferroelectric-to-paraelectric transition temperature is confirmed to surpass 1100°C and thus the transition temperature of virtually any other thin film ferroelectric. We arrived at this conclusion through investigating the structural stability of 0.4 - 2 $μ$m thick Al$_{0.73}$Sc$_{0.27}$N films grown on Mo bottom electrodes via in situ high-temperature X-ray diffraction and permittivity measurements. Our studies reveal the wurtzite-type structure of Al$_{0.73}$Sc$_{0.27}$N is conserved during the entire 1100°C annealing cycle, apparent through a constant c over a lattice parameter ratio. In situ permittivity measurements performed up to 1000°C strongly support this conclusion and include what could be the onset of a diverging permittivity only at the very upper end of the measurement interval. Our in situ measurements are well-supported by ex situ (scanning) transmission electron microscopy and polarization and capacity hysteresis measurements. These results confirm the structural stability on the sub-$μ$m scale next to the stability of the inscribed polarization during the complete 1100°C annealing treatment. Thus, AlScN is the first readily available thin film ferroelectric with a temperature stability that surpasses virtually all thermal budgets occurring in microtechnology, be it during fabrication or the lifetime of a device - even in harshest environments.
The discovery of ferroelectricity in AlScN allowed the first clear observation of the effect in the wurtzite crystal structure, resulting in a material with a previously unprecedented combination of very large coercive fields (2-5 MV/cm) and remnant polarizations (70-110 $μ$C/cm$^2$). We obtained initial insight into the switching dynamics of AlScN, which suggests a domain wall motion limited process progressing from the electrode interfaces. Further, imprint was generally observed in AlScN films and can tentatively be traced to the alignment of charged defects with the internal and external p…
Domain-Wall Mediated Polarization Switching in Ferroelectric AlScN: Strain Relief and Field-Dependent Dynamics
Jilin University（吉林大学）；University of Arkansas（阿肯色大学）；Guangdong Technion – Israel Institute of Technology（广东以色列理工学院）；Technion – Israel Institute of Technology（以色列理工学院）
研究铁电AlScN中极化开关机制，发现域壁通过缓解应变导致场依赖的开关动力学，提出通过域工程调控 coercive field 的策略。
Ferroelectric switching is unambigiously demonstrated for the first time in a III-V semiconductor based material: AlScN -- A discovery which could help to satisfy the urgent demand for thin film ferroelectrics with high performance and good technological compatibility with generic semiconductor technology which arises from a multitude of memory, micro/nano-actuator and emerging applications based on controlling electrical polarization. The appearance of ferroelectricity in AlScN can be related to the continuous distortion of the original wurtzite-type crystal structure towards a layered-hexago…
Thickness scaling of ferroelectricity in AlScN is a determining factor for its potential application in neuromorphic computing and memory devices. In this letter, we report on ultrathin (10 nm) Al0.72Sc0.28N films that are ferroelectrically switchable at room temperature. All-epitaxial Al0.72Sc0.28N/Pt heterostructures are grown by magnetron sputtering onto GaN/sapphire substrates followed by an in situ Pt capping approach to avoid oxidation of the Al0.72Sc0.28N film surface. Structural characterization by X-ray diffraction and transmission electron microscopy reveals the established epitaxy. …
We report the first observation of ferroelectric gating in AlScN barrier wide-bandgap nitride transistors. These FerroHEMT devices realized by direct epitaxial growth represent a new class of ferroelectric transistors in which the semiconductor is itself polar, and the crystalline ferroelectric barrier is lattice-matched to the substrate. The FerroHEMTs reported here use the thinnest nitride high K and ferroelectric barriers to date to deliver the highest on currents at 4 A/mm, and highest speed AlScN transistors with fmax larger than 150 GHz observed in any ferroelectric transistor. The Ferro…
In 1963, Moll and Tarui suggested that the field-effect conductance of a semiconductor could be controlled by the remanent polarization of a ferroelectric (FE) material to create a ferroelectric field-effect transistor (FE-FET). However, subsequent efforts to produce a practical, compact FE-FET have been plagued by low retention and incompatibility with Complementary Metal Oxide Semiconductor (CMOS) process integration. These difficulties led to the development of trapped-charge based memory devices (also called floating gate or flash memory), and these are now the mainstream non-volatile memo…
Wafer-Scale Integration of Piezo- and Ferroelectric Al0.64Sc0.36N Thin Films by Reactive Sputtering
Silicon Austria Labs GmbH（硅奥地利实验室有限公司）；Evatec AG（伊瓦泰克股份公司）；STMicroelectronics（意法半导体）；Tandem Laboratory, Uppsala University（乌普萨拉大学双联实验室）；USound GmbH（优声有限公司）
During the last half-decade, a new class of ferroic-fluid, ferroelectric nematic liquid crystals (NFLCs), creates a noise owing to its exceptional properties such as a colossal polarization, high electro-optic activity plus high fluidity. Regardless of recent huge efforts on design and development of new NFLC molecules based on molecular parameters, the control of NF phase transitions and the stabilization of NF phase are still challenging. Here we discuss the impact of mixing of DIO diastereomer [transDIO (1) and cisDIO (2)] to the NF phase transition, in terms of the smectic cybotactic clust…
This paper reports the fatigue and retention behavior for Al1-xBxN thin films, a member of the novel family of wurtzite ferroelectrics, with an emphasis on the role of capacitor architecture. By modifying the capacitor architecture, and thus thermal and electrical boundary conditions, we create insight regarding the relative importance of intrinsic and extrinsic contributors to the degradation tendencies. Our experiments suggest that bipolar cycling of metal (Pt/W)/Al0.93B0.07N/W/Al2O3 film stacks first induced wake-up, then a region of constant switchable polarization. On additional cycling, …
Above Room-Temperature Phase Transition in Helicoidal 2D Halide Perovskite Enables Pyro-Phototronic Control
Institute of Nano Science and Technology（印度纳米科学与技术研究所）；Indian Institute of Technology Bombay（印度孟买理工学院）；Indian Institute of Technology, Kharagpur（印度卡拉格普尔理工学院）
Certain two-dimensional (2D) materials exhibit intriguing properties such as valley polarization, ferroelectricity, superconductivity and charge-density waves. Many of these materials can be manually assembled into atomic-scale multilayer devices under ambient conditions, owing to their exceptional chemical stability. Efforts have been made to add a magnetic degree of freedom to these 2D materials via defects, but only local magnetism has been achieved. Only with the recent discoveries of 2D materials supporting intrinsic ferromagnetism have stacked spintronic devices become realistic. Assembl…
