The polarization switching pathway plays a key role in deciding the magnitudes of the spontaneous polarization and the coercive electric field, which can be used to realize controllable ferroelectric properties. In this paper, by first-principles calculations, we reveal how the spontaneous polarization (P_s) and the switching barrier (E_b) of orthorhombic HfO₂ (o-HfO₂) respond to various lattice strains depending on two kinds of switching pathways, i.e., the shift-across (SA) pathway and the shift-inside pathway. It is revealed that the existence of the two pathways is most likely dependent on the interface termination of o-HfO₂, and the SA pathway exhibits higher critical values of both P_s and E_b. By applying lattice strains on o-HfO₂ (001) and (010) planes, a ferroelectric–paraelectric phase transition from the polar Pca2₁ to the nonpolar Pbcn can be observed. Importantly, the variation trends of P_s and E_b under the same lattice strains are found to be highly different depending on the switching pathways. However, by carefully designing the interfacial tail atoms, strain engineering can efficiently improve E_b and P_s for both pathways in o-HfO₂ films. Our work uncovers the mechanisms of the switching pathways and opens a new avenue for preparing high-performance ferroelectric devices using strain engineering.

Oxygen defect impacts on ferroelectricity in Hf_0.5Zr_0.5O₂ (HZO) are systematically studied on the basis of first-principles calculations. Importantly, the oxygen vacancy and Frenkel pair could enhance the spontaneous polarization (P_s) by an average of 14.5%, while O_i could largely reduce P_s of HZO by 44.8% on the contrary. The altered P_s and, accordingly, the remanent polarization (P_r) agree well with the experimental results of polarization variability. Oxygen vacancy induced P_r enlargement is revealed to be the underlying mechanism responsible for the wake-up effect. Our results provide a guideline to boost the ferroelectricity via defect engineering in ferroelectric HZO.

This paper proposes to apply a newly developed Non-Dispersive Infrared Spectroscopy (NDIR) gas sensing system composed of pyroelectric infrared detectors to monitor the thermal runaway (TR) process of lithium-ion batteries in real time and achieve an early warning system for the battery TR process. The new Electrical Vehicle Safety—Global Technical Regulation (EVS-GTR) requires that a warning be provided to passengers at least five minutes before a serious incident. The experimental results indicate that carbon dioxide and methane gas were detected during the overcharge test of the automotive battery, and the target gas was detected 25 s in advance before the battery TR when the battery vent was closed. In order to further explore the battery TR mechanism, an experiment was carried out using the battery sample with the battery vent opened. The target gas was detected about 580 s before the battery temperature reached the common alarm temperature (60 °C) of the battery management system (BMS). In this study, the beneficial effects of NDIR gas sensors in the field of thermal runaway warnings for automotive batteries were demonstrated and showed great application prospects and commercial value.

Reservoir computing (RC) is a low-cost and temporary-signal friendly computational framework, whose hardware implementation is hindered by integrating huge amounts and various kinds of devices. Benefitted from the logic in memory (LIM) capability, the process compatible Hf _0.5 Zr _0.5 O ₂ (HZO)-based ferroelectric field-effect-transistor (FeFET) is a promising candidate for implementing artificial networks. In this letter, a fully FeFETs RC network is proposed. Multiple functions can be achieved in a single device owing to its intrinsic characteristics, and the richness of virtual nodes is largely enhanced through full-connection structures. Impressively, only 44 FeFETs are required to construct a compact RC network with 100 ns operating speed and high accuracy in classification tasks. This paves the way to develop the high energy-efficiency FeFET RC networks.

3-D NAND flash memory has been attracting much attention owing to its ultrahigh storage density and low bit cost, and it has been widely applied in data centers and mobiles. 3-D triple-level-cell (TLC) NAND flash memory can achieve much larger storage capacity by storing 3 bits in each cell. However, the data reliability issues induced by data retention (DR) and read disturb (RD) greatly limit 3-D TLC NAND applications in hot data storage where the stored data are frequently accessed and RD is more serious. In this article, we first systematically study the retention correlated RD (RCRD) errors in 3-D charge trap (CT) TLC NAND flash memory under various conditions. Error characteristics and underlying mechanisms much different from 2-D NAND flash memory are observed: 1) for RCRD with short retention-after data program, error bits increase due to the negative-shift of program states and 2) for RCRD with long retention-after retention 12 h, error bits can be partially recovered on the contrary due to the charge compensation. We propose schemes of precharge the storage layer (PCSL) and thermally stabilize the storage layer (TSSL) to improve the reliability of 3-D NAND flash memory. By using these two methods, experimental results show that raw bit error rates (RBERs) can be significantly reduced by 30% and 20%, respectively.