Yao Shuai

Bio: Yao Shuai is an academic researcher from University of Electronic Science and Technology of China. The author has contributed to research in topics: Thin film & Pulsed laser deposition. The author has an hindex of 18, co-authored 73 publications receiving 1122 citations. Previous affiliations of Yao Shuai include Helmholtz-Zentrum Dresden-Rossendorf.

Exploiting Memristive BiFeO3 Bilayer Structures for Compact Sequential Logics

Abstract: Resistive switching devices are considered as one of the most promising candidates for the next generation memories and nonvolatile logic applications. In this paper, BiFeO3:Ti/BiFeO3 (BFTO/BFO) bilayer structures with optimized BFTO/BFO thickness ratio which show symmetric, bipolar, and nonvolatile resistive switching with good retention and endurance performance, are presented. The resistive switching mechanism is understood by a model of flexible top and bottom Schottky-like barrier heights in the BFTO/BFO bilayer structures. The resistive switching at both positive and negative bias make it possible to use both polarities of reading bias to simultaneously program and store all 16 Boolean logic functions into a single cell of a BFTO/BFO bilayer structure in three logic cycles.

Nonvolatile bipolar resistive switching in Au/BiFeO3/Pt

Abstract: Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO3/Pt structure, where a Schottky contact and a quasi-Ohmic contact were formed at the Au/BiFeO3 and BiFeO3/Pt interface, respectively. By changing the polarity of the external voltage, the Au/BiFeO3/Pt is switched between two stable resistance states without an electroforming process. The resistance ratio is larger than two orders of magnitude. The resistive switching is understood by the electric field–induced carrier trapping and detrapping, which changes the depletion layer thickness at the Au/BiFeO3 interface.

Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiO3 thin films

Abstract: Single-phase perovskite 5 at. % Mn-doped and undoped polycrystalline BaTiO3 thin films have been grown under different oxygen partial pressures by pulsed laser deposition on platinum-coated sapphire substrates. Ferroelectricity is only observed for the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Compared to undoped BaTiO3, Mn-doped BaTiO3 reveals a low leakage current, increased dielectric loss, and a decreased dielectric constant. Ferromagnetism is seen on Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure and is attributed to the formation of bound magnetic polarons (BMPs). This BMP formation is enhanced by oxygen vacancies. The present work confirms a theoretical work from C. Ederer and N. Spaldin on ferroelectric perovskites [Nature Mat. 3, 849 (2004)] that shows that the existence of ferroelectricity is incompatible with the existence of a spontaneous magnetization in Mn-doped BaTiO3 thin films.

Nonvolatile bipolar resistive switching in Au/BiFeO3/Pt

Abstract: Nonvolatile bipolar resistive switching has been observed in an Au/BiFeO3/Pt structure, where a Schottky contact and a quasi-Ohmic contact were formed at the Au/BiFeO3 and BiFeO3/Pt interface, respectively. By changing the polarity of the external voltage, the Au/BiFeO3/Pt is switched between two stable resistance states without an electroforming process. The resistance ratio is larger than two orders of magnitude. The resistive switching is understood by the electric field - induced carriers trapping and detrapping, which changes the depletion layer thickness at the Au/BiFeO3 interface.

Decisive role of oxygen vacancy in ferroelectric vs. ferromagnetic Mn-doped BaTiO3 thin films

Abstract: Single-phase perovskite 5 at.% Mn-doped and undoped polycrystalline BaTiO3 thin films have been grown under different oxygen partial pressures by pulsed laser deposition on platinum-coated sapphire substrates. Ferroelectricity is only observed for the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Compared to undoped BaTiO3, Mn-doped BaTiO3 reveals a low leakage current, increased dielectric loss, and a decreased dielectric constant. Ferromagnetism is seen on Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure and is attributed to the formation of bound magnetic polarons (BMPs). This BMP formation is enhanced by oxygen vacancies. The present work confirms a theoretical work from C. Ederer and N. Spaldin on ferroelectric perovskites [Nature Mat. 3, 849 (2004)] which shows that the existence of ferroelectricity is incompatible with the existence of a spontaneous magnetization in Mn-doped BaTiO3 thin films.

SLIM: Simultaneous Logic-in-Memory Computing Exploiting Bilayer Analog OxRAM Devices.

Abstract: von Neumann architecture based computers isolate computation and storage (i.e. data is shuttled between computation blocks (processor) and memory blocks). The to-and-fro movement of data leads to a fundamental limitation of modern computers, known as the Memory wall. Logic in-Memory (LIM)/In-Memory Computing (IMC) approaches aim to address this bottleneck by directly computing inside memory units thereby eliminating energy-intensive and time-consuming data movement. Several recent works in literature, propose realization of logic function(s) directly using arrays of emerging resistive memory devices (example- memristors, RRAM/ReRAM, PCM, CBRAM, OxRAM, STT-MRAM etc.), rather than using conventional transistors for computing. The logic/embedded-side of digital systems (like processors, micro-controllers) can greatly benefit from such LIM realizations. However, the pure storage-side of digital systems (example SSDs, enterprise storage etc.) will not benefit much from such LIM approaches as when memory arrays are used for logic they lose their core functionality of storage. Thus, there is the need for an approach complementary to existing LIM techniques, that's more beneficial for the storage-side of digital systems; one that gives compute capability to memory arrays not at the cost of their existing stored states. Fundamentally, this would require memory nanodevice arrays that are capable of storing and computing simultaneously. In this paper, we propose a novel 'Simultaneous Logic in-Memory' (SLIM) methodology which is complementary to existing LIM approaches in literature. Through extensive experiments we demonstrate novel SLIM bitcells (1T-1R/2T-1R) comprising non-filamentary bilayer analog OxRAM devices with NMOS transistors. Proposed bitcells are capable of implementing both Memory and Logic operations simultaneously. Detailed programming scheme, array level implementation, and controller architecture are also proposed. Furthermore, to study the impact of proposed SLIM approach for real-world implementations, we performed analysis for two applications: (i) Sobel Edge Detection, and (ii) Binary Neural Network- Multi layer Perceptron (BNN-MLP). By performing all computations in SLIM bitcell array, huge Energy Delay Product (EDP) savings of ≈75× for 1T-1R (≈40× for 2T-1R) SLIM bitcell were observed for edge-detection application while EDP savings of ≈3.5× for 1T-1R (≈1.6× for 2T-1R) SLIM bitcell were observed for BNN-MLP application respectively, in comparison to conventional computing. EDP savings owing to reduction in data transfer between CPU ↔ memory is observed to be ≈780× (for both SLIM bitcells).

SLIM: Simultaneous Logic-in-Memory Computing Exploiting Bilayer Analog OxRAM Devices

Abstract: Von Neumann architecture based computers isolate/physically separate computation and storage units i.e. data is shuttled between computation unit (processor) and memory unit to realize logic/ arithmetic and storage functions. This to-and-fro movement of data leads to a fundamental limitation of modern computers, known as the memory wall. Logic in-Memory (LIM) approaches aim to address this bottleneck by computing inside the memory units and thereby eliminating the energy-intensive and time-consuming data movement. However, most LIM approaches reported in literature are not truly "simultaneous" as during LIM operation the bitcell can be used only as a Memory cell or only as a Logic cell. The bitcell is not capable of storing both the Memory/Logic outputs simultaneously. Here, we propose a novel 'Simultaneous Logic in-Memory' (SLIM) methodology that allows to implement both Memory and Logic operations simultaneously on the same bitcell in a non-destructive manner without losing the previously stored Memory state. Through extensive experiments we demonstrate the SLIM methodology using non-filamentary bilayer analog OxRAM devices with NMOS transistors (2T-1R bitcell). Detailed programming scheme, array level implementation and controller architecture are also proposed. Furthermore, to study the impact of introducing SLIM array in the memory hierarchy, a simple image processing application (edge detection) is also investigated. It has been estimated that by performing all computations inside the SLIM array, the total Energy Delay Product (EDP) reduces by ~ 40x in comparison to a modern-day computer. EDP saving owing to reduction in data transfer between CPU Memory is observed to be ~ 780x.

Review and perspective on ferroelectric HfO2-based thin films for memory applications

Abstract: The ferroelectricity in fluorite-structure oxides such as hafnia and zirconia has attracted increasing interest since 2011 They have various advantages such as Si-based complementary metal oxide semiconductor-compatibility, matured deposition techniques, a low dielectric constant and the resulting decreased depolarization field, and stronger resistance to hydrogen annealing However, the wake-up effect, imprint, and insufficient endurance are remaining reliability issues Therefore, this paper reviews two major aspects: the advantages of fluorite-structure ferroelectrics for memory applications are reviewed from a material’s point of view, and the critical issues of wake-up effect and insufficient endurance are examined, and potential solutions are subsequently discussed

BiFeO3 epitaxial thin films and devices: past, present and future

Abstract: The celebrated renaissance of the multiferroics family over the past ten years has also been that of its most paradigmatic member, bismuth ferrite (BiFeO3). Known since the 1960s to be a high temperature antiferromagnet and since the 1970s to be ferroelectric, BiFeO3 only had its bulk ferroic properties clarified in the mid-2000s. It is however the fabrication of BiFeO3 thin films and their integration into epitaxial oxide heterostructures that have fully revealed its extraordinarily broad palette of functionalities. Here we review the first decade of research on BiFeO3 films, restricting ourselves to epitaxial structures. We discuss how thickness and epitaxial strain influence not only the unit cell parameters, but also the crystal structure, illustrated for instance by the discovery of the so-called T-like phase of BiFeO3. We then present its ferroelectric and piezoelectric properties and their evolution near morphotropic phase boundaries. Magnetic properties and their modification by thickness and strain effects, as well as optical parameters, are covered. Finally, we highlight various types of devices based on BiFeO3 in electronics, spintronics, and optics, and provide perspectives for the development of further multifunctional devices for information technology and energy harvesting.