Ferroelectric materials for neuroinspired computing applications

In recent years,the emergence of numerous applications of artificial intelligence(AI)has sparked a new technological revolution.These applications include facial recognition,autonomous driving,intelligent robotics,and image restoration.However,the data processing and storage procedures in the conventional von Neumann architecture are discrete,which leads to the“memory wall”problem.As a result,such architecture is incompatible with AI requirements for efficient and sustainable processing.Exploring new computing architectures and material bases is therefore imperative.Inspired by neurobiological systems,in-memory and in-sensor computing techniques provide a new means of overcoming the limitations inherent in the von Neumann architecture.The basis of neural morphological computation is a crossbar array of high-density,high-efficiency non-volatile memory devices.Among the numerous candidate memory devices,ferroelectric memory devices with non-volatile polarization states,low power consumption and strong endurance are expected to be ideal candidates for neuromorphic computing.Further research on the complementary metal-oxide-semiconductor(CMOS)compatibility for these devices is underway and has yielded favorable results.Herein,we first introduce the development of ferroelectric materials as well as their mechanisms of polarization reversal and detail the applications of ferroelectric synaptic devices in artificial neural networks.Subsequently,we introduce the latest developments in ferroelectrics-based in-memory and in-sensor computing.Finally,we review recent works on hafnium-based ferroelectric memory devices with CMOS process compatibility and give a perspective for future developments.

Observing ferroelastic switching in Hf_(0.5)Zr_(0.5)O_(2) thin film

Hafnium zirconium oxides(HZO),which exhibit ferroelectric properties,are promising materials for nanoscale device fabrication due to their high complementary metal-oxide-semiconductor(CMOS) compatibility.In addition to piezoelectricity,ferroelectricity,and flexoelectricity,this study reports the observation of ferroelasticity using piezoelectric force microscopy(PFM) and scanning transmission electron microscopy(STEM).The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field.Switching of the retentive domains is observed through repeated wake-up measurements.This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.

Highly Weak-light Sensitive and Dual-band Switchable Photodetector Based on CuI/Si Unilateral Heterojunction

In recent years,copper iodide(CuI)is an emerging p-type wide bandgap semiconductor with high intrinsic Hall mobility,high optical absorption and large exciton binding energy.However,the spectral response and the photoelectric conversion efficiency are limited for CuI-based heterostructure devices,which is related to the difficulty in fabrication of high-quality CuI thin films on other semiconductors.In this study,a p-CuI/n-Si photodiode has been fabricated through a facile solid-phase iodination method.Although the CuI thin film is polycrystalline with obvious structural defects,the CuI/Si diode shows a high weak-light sensitivity and a high rectification ratio of 7.6×10^(4),indicating a good defect tolerance.This is because of the unilateral heterojunction behavior of the formation of the p^(+)n diode.In this work,the mechanism of photocurrent of the p^(+)n diode has been studied comprehensively.Different monochromatic lasers with wavelengths of 400,505,635 and 780 nm have been selected for testing the photoresponse.Under zero-bias voltage,the device is a unilateral heterojunction,and only visible light can be absorbed at the Si side.On the other hand,when a bias voltage of-3 V is applied,the photodiode is switched to a broader“UV-visible”band response mode.Therefore,the detection wavelength range can be switched between the“Visible”and“UV-visible”bands by adjusting the bias voltage.Moreover,the obtained CuI/Si diode was very sensitive to weak light illumination.A very high detectivity of 10^(13)-1014 Jones can be achieved with a power density as low as 0.5μW/cm^(2),which is significantly higher than that of other Cu-based diodes.These findings underscore the high application potential of CuI when integrated with the traditional Si industry.

Research progress on 2D ferroelectric and ferrovalley materials and their neuromorphic application

Two-dimensional(2D)ferroelectric and ferrovalley materials have recently received extensive attention due to their significant advantages for modern electronic devices,such as miniaturization,low-dissipation,non-volatility,and multi-functionality.More interestingly,the couplings between the ferroic orders in these materials have enriched the development of intelligent devices,especially in neuromorphic computing.In this paper,the research progress of 2D ferroelectric and ferrovalley materials is introduced and the coupling effects between them are also described.Then,we briefly introduce recent neuromorphic computing reports based on 2D ferroelectric materials and give perspectives on ferrovalley neuromorphic devices.

Ferroelectricity of pristine Hf_(0.5)Zr_(0.5)O_(2) films fabricated by atomic layer deposition

Hafnium-based ferroelectric films,remaining their ferroelectricity down to nanoscale thickness,present a promising application for low-power logic devices and nonvolatile memories.It has been appealing for researchers to reduce the required temperature to obtain the ferroelectric phase in hafnium-based ferroelectric films for applications such as flexible and wearable electronics.This work demonstrates that a remanent polarization(P_(r))value of>5μC/cm^(2)can be obtained in asdeposited Hf_(0.5)Zr_(0.5)O_(2)(HZO)films that are fabricated by thermal atomic layer deposition(TALD)under low temperature of 250℃.The ferroelectric orthorhombic phase(o-phase)in the as-deposited HZO films is detected by scanning transmission electron microscopy(STEM).This low fabrication temperature further extends the compatibility of ferroelectric HZO films to flexible electronics and avoids the cost imposed by following high-temperature annealing treatments.

Multistate circularly polarized luminescence switches based on dual stimuli-responsive chiral[2]rotaxanes

Aiming at the construction of novel multistate circularly polarized luminescence(CPL)switches,dual stimuli-responsive chiral[2]rotaxanes towards anions and light have been designed and constructed.Through the light-controlled on/off F?rster resonance energy transfer(FRET)switching between the emissive stoppers and anion-induced controllable motions of the chiral wheel for the precise regulations of chirality information transfer from the chiral wheel to the emissive stoppers,precisely switching between four CPL emission states with varied emission wavelengths and dissymmetry factors has been successfully realized,making them a promising platform for practical uses such as information storage and encryption.This proof-of-concept study not only provides a novel design strategy for multistate CPL switching but also contributes excellent candidates for the construction of novel smart chiral luminescent materials.

Sequence Engineering in Tuning the Circularly Polarized Luminescence of Aggregation-Induced Emission-Active Hetero[3]rotaxanes

Based on a[2]rotaxane precursor with exchangeable pentafluorophenyl ester stoppers,a new wheelassembling approach has been successfully developed for the precise sequence control of hetero[3]rotaxanes,leading to the facile and efficient synthesis of both sequence isomers of hetero[3]rotaxanes.More importantly,taking advantage of the chirality retention along with the wheel-assembling process,corresponding sequence isomers of chiral AIEgenfunctionalized hetero[3]rotaxanes were further precisely synthesized.Impressively,the resultant hetero[3]rotaxanes revealed remarkable sequencedependent aggregation-induced emission(AIE)behavior and circularly polarized luminescence performance with large dissymmetry factors up to 0.012,highlighting the great power of the newly coined sequence engineering concept in developing novel AIE-active chiroptical materials.This proof-ofconcept study lays the foundation for investigation of the structure-property relationships of heterorotaxanes that can further direct the rational design and precise synthesis of sequence-defined heterorotaxanes with desirable properties for practical applications.

磁有序CoH_(2)SeO_(4)薄片中的室温铁电性

本文通过第一性原理计算和实验表征证明了二维CoH_(2)SeO_(4)薄膜的磁有序和滑移铁电性.首先,实验结果证实了粉末CoH_(2)SeO_(4)样品的反铁磁序.同时,第一性原理计算表明单层CoH_(2)SeO_(4)具有反铁磁(AFM-I)基态(TN≈75 K),且预测了二维CoH_(2)SeO_(4)薄膜具有以不对称的三重势阱态为特征的滑移铁电性,并在实验中测得了180°压电滞回线、可反转铁电畴和二次谐波信号.此外,在基于二维CoH_(2)SeO_(4)薄膜的电容器中获得铁电材料所特有的电滞回线和蝴蝶状的电容曲线.介电温谱测试表明二维CoH_(2)SeO_(4)薄膜的铁电转变温度约为370 K.CoH_(2)SeO_(4)中滑移铁电性和反铁磁性的出现为获得低维多铁材料指出了一条新的途径.

Retinomorphic hardware for in-sensor computing

Rapid developments in the Internet of Things and Artificial Intelligence trigger higher requirements for image perception and learning of external environments through visual systems.However,limited by von Neumann's bottleneck,the physical separation of sense,memory,and processing units in a conventional personal computer-based vision system tend to consume a significant amount of energy,time latency,and additional hardware costs.By integrating computational tasks of multiple functionalities into the sensors themselves,the emerging bio-inspired neuromorphic visual systems provide an opportunity to overcome these limitations.With high speed,ultralow power and strong adaptability,it is highly desirable to develop a neuromorphic vision system that is based on highly precise in-sensor computing devices,namely retinomorphic devices.We here present a timely review of retinomorphic devices for visual in-sensor computing.We begin with several types of physical mechanisms of photoelectric sensors that can be constructed for artificial vision.The potential applications of retinomorphic hardware are,thereafter,thoroughly summarized.We also highlight the possible strategies to existing challenges and give a brief perspective of retinomorphic architecture for in-sensor computing.

Seeing Is Believing:Directly Imaging Contractions of Artificial Molecular Muscles with Platinum Atom Markers

Artificial molecular muscles undergo well-controlled contractile and extensile motions upon external stimulation,leading to remarkable length changes.Evaluating such length changes at the molecular level is essential to the design of integrated artificial molecular muscles that mimic biological muscles.Taking advantage of the strong contrast of platinum(Pt)atoms in high-angle annular dark-field scanning transmission electron microscopy images,we imaged Pt-containing molecular[c2]daisy chains directly by employing metal atom markers.The length changes and associated conformational transformations of these newly developed artificial molecular muscles have been measured experimentally in combination with theoretical calculations.The contraction ratios of these two molecular muscles with the TEMPO or pyrene anchoring group were calculated to be 21.0%or 15.7%respectively,suggesting a substantial anchoring effect.This study demonstrates the experimental measurement of the length changes of artificial molecular muscles and provides a new avenue for investigating the motion of artificial molecular machines.