Ferroelectric AlScN and HfZrO Domain Switching Dynamics.

The capability to reliably program partial polarization states with nanosecond programming speed and femtojoule energies per bit in ferroelectrics makes them an ideal candidate to realize multibit memory elements for high-density crossbar arrays, which could enable neural network models with a large number of parameters at the edge. However, a thorough understanding of the domain switching dynamics involved in the polarization reversal is required to achieve full control of the multibit capability. Transient current integration measurements are adopted to investigate the domain dynamics in aluminum scandium nitride (AlScN) and hafnium zirconium oxide (HfZrO).

Influence of Biaxial Strain and Interfacial Layer Growth on Ferroelectric Wake-Up and Phase Transition Fields in ZrO.

Investigations on fluorite-structured ferroelectric HfO/ZrO thin films are aiming to achieve high-performance films required for memory and computing technologies. These films exhibit excellent scalability and compatibility with the complementary metal-oxide semiconductor process used by semiconductor foundries, but stabilizing ferroelectric properties with a low operation voltage in the as-fabricated state of these films is a critical component for technology advancement. After removing the influence of interfacial layers, a linear correlation is observed between the biaxial strain and the electric field for transforming the nonferroelectric tetragonal to the ferroelectric orthorhombic phase in ZrO thin films.

Kinetics of N- to M-Polar Switching in Ferroelectric AlScN Capacitors.

Ferroelectric wurtzite-type aluminum scandium nitride (AlScN) presents unique properties that can enhance the performance of non-volatile memory technologies. The realization of the full potential of AlScN requires a comprehensive understanding of the mechanism of polarization reversal and domain structure dynamics involved in the ferroelectric switching process. In this work, transient current integration measurements performed by a pulse switching method are combined with domain imaging by piezoresponse force microscopy (PFM) to investigate the kinetics of domain nucleation and wall motion during polarization reversal in AlScN capacitors.

Electrically induced cancellation and inversion of piezoelectricity in ferroelectric HfZrO.

HfO-based thin films hold huge promise for integrated devices as they show full compatibility with semiconductor technologies and robust ferroelectric properties at nanometer scale. While their polarization switching behavior has been widely investigated, their electromechanical response received much less attention so far. Here, we demonstrate that piezoelectricity in HfZrO ferroelectric capacitors is not an invariable property but, in fact, can be intrinsically changed by electrical field cycling.

Role of Defects in the Breakdown Phenomenon of AlScN: From Ferroelectric to Filamentary Resistive Switching.

Aluminum scandium nitride (AlScN), with its large remanent polarization, is an attractive material for high-density ferroelectric random-access memories. However, the cycling endurance of AlScN ferroelectric capacitors is far below what can be achieved in other ferroelectric materials. Understanding the nature and dynamics of the breakdown mechanism is of the utmost importance for improving memory reliability.

Thermal Stability of the Ferroelectric Properties in 100 nm-Thick AlScN.

The discovery of ferroelectricity in aluminum scandium nitride (AlScN) opens technological perspectives for harsh environments and space-related memory applications, considering the high-temperature stability of piezoelectricity in aluminum nitride. The ferroelectric and material properties of 100 nm-thick AlScN are studied up to 873 K, combining both electrical and in situ X-ray diffraction measurements as well as transmission electron microscopy and energy-dispersive X-ray spectroscopy. The present work demonstrates that AlScN can achieve high switching polarization and tunable coercive fields in a 375 K temperature range from room temperature up to 673 K.

Reduced fatigue and leakage of ferroelectric TiN/HfZrO/TiN capacitors by thin alumina interlayers at the top or bottom interface.

HfZrO(HZO) thin films are promising candidates for non-volatile memory and other related applications due to their demonstrated ferroelectricity at the nanoscale and compatibility with Si processing. However, one reason that HZO has not been fully scaled into industrial applications is due to its deleterious wake-up and fatigue behavior which leads to an inconsistent remanent polarization during cycling. In this study, we explore an interfacial engineering strategy in which we insert 1 nm AlOinterlayers at either the top or bottom HZO/TiN interface of sequentially deposited metal-ferroelectric-metal capacitors.

Quantification of the Electromechanical Measurements by Piezoresponse Force Microscopy.

Piezoresponse force microscopy (PFM) is widely used for characterization and exploration of the nanoscale properties of ferroelectrics. However, quantification of the PFM signal is challenging due to the convolution of various extrinsic and intrinsic contributions. Although quantification of the PFM amplitude signal has received considerable attention, quantification of the PFM phase signal has not been addressed.

Role of Oxygen Source on Buried Interfaces in Atomic-Layer-Deposited Ferroelectric Hafnia-Zirconia Thin Films.

Hafnia-zirconia (HfO-ZrO) solid solution thin films have emerged as viable candidates for electronic applications due to their compatibility with Si technology and demonstrated ferroelectricity at the nanoscale. The oxygen source in atomic layer deposition (ALD) plays a crucial role in determining the impurity concentration and phase composition of HfO-ZrO within metal-ferroelectric-metal devices, notably at the HfZrO /TiN interface. The interface characteristics of HZO/TiN are fabricated via sequential no-atmosphere processing (SNAP) with either HO or O-plasma to study the influence of oxygen source on buried interfaces.

Local Epitaxial Templating Effects in Ferroelectric and Antiferroelectric ZrO.

Nanoscale polycrystalline thin-film heterostructures are central to microelectronics, for example, metals used as interconnects and high-K oxides used in dynamic random-access memories (DRAMs). The polycrystalline microstructure and overall functional response therein are often dominated by the underlying substrate or layer, which, however, is poorly understood due to the difficulty of characterizing microstructural correlations at a statistically meaningful scale. Here, an automated, high-throughput method, based on the nanobeam electron diffraction technique, is introduced to investigate orientational relations and correlations between crystallinity of materials in polycrystalline heterostructures over a length scale of microns, containing several hundred individual grains.

Piezoelectricity in hafnia.

Because of its compatibility with semiconductor-based technologies, hafnia (HfO) is today's most promising ferroelectric material for applications in electronics. Yet, knowledge on the ferroic and electromechanical response properties of this all-important compound is still lacking. Interestingly, HfO has recently been predicted to display a negative longitudinal piezoelectric effect, which sets it apart from classic ferroelectrics (e.

Stabilizing the ferroelectric phase in HfO-based films sputtered from ceramic targets under ambient oxygen.

Thin film metal-insulator-metal capacitors with undoped hafnium oxide and a mixture of hafnium and zirconium oxides are prepared by sputtering from ceramic targets. The influence of the oxygen concentration while sputtering and of the zirconium concentration on the ferroelectric properties is characterized by electrical and structural methods. Depending on the ambient oxygen, the thin undoped hafnium oxide films show distinct ferroelectric properties.

Fluid Imprint and Inertial Switching in Ferroelectric La:HfO Capacitors.

Ferroelectric (FE) HfO-based thin films, which are considered as one of the most promising material systems for memory device applications, exhibit an adverse tendency for strong imprint. Manifestation of imprint is a shift of the polarization-voltage (-) loops along the voltage axis due to the development of an internal electric bias, which can lead to the failure of the writing and retention functions. Here, to gain insight into the mechanism of the imprint effect in La-doped HfO (La:HfO) capacitors, we combine the pulse switching technique with high-resolution domain imaging by means of piezoresponse force microscopy.

Unveiling the double-well energy landscape in a ferroelectric layer.

The properties of ferroelectric materials, which were discovered almost a century ago, have led to a huge range of applications, such as digital information storage, pyroelectric energy conversion and neuromorphic computing. Recently, it was shown that ferroelectrics can have negative capacitance, which could improve the energy efficiency of conventional electronics beyond fundamental limits. In Landau-Ginzburg-Devonshire theory, this negative capacitance is directly related to the double-well shape of the ferroelectric polarization-energy landscape, which was thought for more than 70 years to be inaccessible to experiments.

Genuinely Ferroelectric Sub-1-Volt-Switchable Nanodomains in Hf ZrO Ultrathin Capacitors.

The new class of fully silicon-compatible hafnia-based ferroelectrics with high switchable polarization and good endurance and thickness scalability shows a strong promise for new generations of logic and memory devices. Among other factors, their competitiveness depends on the power efficiency that requires reliable low-voltage operation. Here, we show genuine ferroelectric switching in Hf ZrO (HZO) layers in the application-relevant capacitor geometry, for driving signals as low as 800 mV and coercive voltage below 500 mV.

On the stabilization of ferroelectric negative capacitance in nanoscale devices.

Recently, the proposal to use voltage amplification from ferroelectric negative capacitance (NC) to reduce the power dissipation in nanoelectronic devices has attracted significant attention. Homogeneous Landau theory predicts, that by connecting a ferroelectric in series with a dielectric capacitor, a hysteresis-free NC state can be stabilized in the ferroelectric below a critical film thickness. However, there is a strong discrepancy between experimental results and the current theory.

Lanthanum-Doped Hafnium Oxide: A Robust Ferroelectric Material.

Recently simulation groups have reported the lanthanide series elements as the dopants that have the strongest effect on the stabilization of the ferroelectric non-centrosymmetric orthorhombic phase in hafnium oxide. This finding confirms experimental results for lanthanum and gadolinium showing the highest remanent polarization values of all hafnia-based ferroelectric films until now. However, no comprehensive overview that links structural properties to the electrical performance of the films in detail is available for lanthanide-doped hafnia.

Understanding the formation of the metastable ferroelectric phase in hafnia-zirconia solid solution thin films.

HfZrO (x ∼ 0.5-0.7) has been the leading candidate of ferroelectric materials with a fluorite crystal structure showing highly promising compatibility with complementary metal oxide semiconductor devices.

Surface and grain boundary energy as the key enabler of ferroelectricity in nanoscale hafnia-zirconia: a comparison of model and experiment.

The unexpected ferroelectric properties of nanoscale hafnia-zirconia are considered to be promising for a wealth of applications including ferroelectric memory, field effect transistors, and energy-related applications. However, the reason why the unexpected ferroelectric Pca2 phase can be stabilized has not been clearly understood although numerous extensive theoretical and experimental results have been reported recently. The ferroelectric orthorhombic phase is not a stable phase under processing conditions from the viewpoint of bulk free energy.

Switching Kinetics in Nanoscale Hafnium Oxide Based Ferroelectric Field-Effect Transistors.

The recent discovery of ferroelectricity in thin hafnium oxide films has led to a resurgence of interest in ferroelectric memory devices. Although both experimental and theoretical studies on this new ferroelectric system have been undertaken, much remains to be unveiled regarding its domain landscape and switching kinetics. Here we demonstrate that the switching of single domains can be directly observed in ultrascaled ferroelectric field effect transistors.

Effect of Zr Content on the Wake-Up Effect in Hf1-xZrxO2 Films.

In this study, the changes in the structural and electrical properties of ferroelectric Hf1-xZrxO2 films with various Zr contents (0.26-0.70) were systematically examined during electric field cycling, resulting in a "wake-up" effect.

Breakdown and Protection of ALD Moisture Barrier Thin Films.

The water vapor barrier properties of low-temperature atomic layer deposited (ALD) AlOx thin-films are observed to be unstable if exposed directly to high or even ambient relative humidities. Upon exposure to humid atmospheres, their apparent barrier breaks down and their water vapor transmission rates (WVTR), measured by electrical calcium tests, deteriorate by several orders of magnitude. These changes are accompanied by surface roughening beyond the original thickness, observed by atomic force microscopy.

Complex Internal Bias Fields in Ferroelectric Hafnium Oxide.

For the rather new hafnia- and zirconia-based ferroelectrics, a lot of questions are still unsettled. Among them is the electric field cycling behavior consisting of (1) wake-up, (2) fatigue, and (3) the recently discovered subcycling-induced split-up/merging effect of transient current peaks in a hysteresis measurement. In the present work, first-order reversal curves (FORCs) are applied to study the evolution of the switching and backswitching field distribution within the frame of the Preisach model for three different phenomena: (1) The pristine film contains two oppositely biased regions.