Ferroelectric Transistors for Memory and Neuromorphic Device Applications

Abstract

Because a non-centrosymmetric crystal structure is mandatory for ferroelectric properties, very few materials are classified as ferroelectric. Historically, materials with complex crystal structures, such as BaTiO 3 (BTO), Pb[Zr x Ti 1−x ]O 3 (PZT), and Sr 2 Bi 2 TaO 9 (SBT), have been found to exhibit ferroelectricity. [5][6][7][8][9] Due to their spontaneous polarization, ferroelectric materials are diversely applied in memory devices, actuators, sensors, and energy storage. [1,2,[10][11][12][13] As the polarization state of ferroelectric materials can be regulated by an external electric field and the polarization is retained after the removal of the external electric field, such materials have the potential for applications involving high-performance non volatile memories. [9,14] However, some issues of conventional ferroelectric materials, such as high annealing temperatures, the requirement of noble electrode materials, and the diffusion of elements such as Pb complicate the integration of the previously reported ferroelectric materials into complementary metal-oxide semiconductors (CMOSs). [15][16][17][18] Furthermore, the large dielectric constants of perovskite-based ferroelectrics lead to high depolarization fields; [9,16] thus, the materials have short retention time and exhibit unstable polarization. [9] Additionally, the limited thickness scalability, complex etching process, and fatigue behaviors of perovskite-based ferroelectrics hinder the development of highly scaled ferroelectric devices. [9,18] Thus, semiconductor devices based on ferroelectric materials have limited commercial applications. Since the development of hafnia-based ferroelectrics, ferroelectric hafnia has attracted immense attention toward the development of semiconductor devices. [19][20][21] Compared to perovskite-based ferroelectric materials, hafnia-based ferroelectrics exhibit high scalability, and have high coercive electric fields (E c ) and low dielectric permittivity values, making them suitable for the fabrication of high-performance memory devices. [2,16,20,22] Additionally, hafnia is compatible with Si-based CMOS processes. Due to these advantages, hafnia-based ferroelectrics have been used in next-generation memory devices (such as ferroelectric capacitors, transistors, and tunnel junctions [FTJs]). [22][23][24][25][26] This paper reviews the recent findings and applications of hafnia-based ferroelectrics, highlighting the recent advances in ferroelectric transistors for next-generation memory and neuromorphic Ferroelectric materials have been intensively investigated for highperformance nonvolatile memory devices in the past decades, owing to their nonvolatile polarization characteristics. Ferroelectric memory devices are expected to exhibit lower power consumption and higher speed than conventional memory devices. However, non-complementary metal-oxidesemiconductor (CMOS) compatibility and degradation due to fatigue of traditional perovskite-based ferroelectric materials have hindered the development of high-density...

Recent Advances and Future Prospects for Memristive Materials, Devices, and Systems

“…Recently, memristive devices using ferroelectricity and their array structure have been actively studied to achieve high-performance, high-density neural networks. − Using partial polarization characteristics of ferroelectric gate insulators, precise control of carriers inside the channel layer can be achieved, which can lead to conductance modulation in the channel layer. − Among diverse ferroelectric materials, hafnia-based ferroelectric materials have been widely investigated for neuromorphic applications due to their CMOS compatibility, fast switching speeds, and high scalability. − At the erased state (i.e., downward polarization), the electrons inside the channel are depleted, which leads to low channel conductance (Figure a). , When a programming pulse with increasing amplitude is applied to the gate, the direction of polarization gradually changes to an upward direction and electrons are accumulated at the interface between the ferroelectric layer and the channel layer. This gradual switching of polarization under incremental pulses results in a gradual increase in channel conductance. , Thus, voltage pulses with incremental pulse amplitude or width are usually used to achieve linear and symmetric conductance change in ferroelectric transistors. , With incremental pulse schemes, classification accuracy as high as 91% is expected for handwritten digits, which is similar to that of ideal synapses .…”

Controlling the optical properties of hafnium dioxide thin films deposited with electron cyclotron resonance ion beam deposition

“…They are also commonly used in multilayer optical coatings as the high index material, alongside low index material like silica, where it can be utilized in interference filters, anti-reflective coatings, metal-oxide-semiconductor transistors, and cameras that can be utilized for space applications [2][3][4]. Other applications that HfO 2 films has been utilized aside for optical coatings are memory applications [1,5,6], ferroelectrics transistors which can be used for in-memory computing devices, as well as neuromorphic devices [7][8][9] and as HfO 2 based nanoagent in clinical trials for radiosensitized tumor therapy [10]. HfO 2 has optical transparency over a wide spectral range, from ultraviolet (UV) to mid-infrared (mid-IR) region, due to its wide bandgap of 5.3 -5.7 eV [11,12], alongside high laser induced damage threshold (LIDT), allowing it to often be utilized as the coating for optics in high power laser systems.…”

Memory and Synaptic Devices Based on Emerging 2D Ferroelectricity

“…In addition to traditional random access memory (RAM) devices, neuromorphic technology demands highly integrated and low-energy-operational devices, which could most probably be developed with 2D ferroelectric materials. [63,64] Various retention time constants and continuous non-volatile memory states have been successfully demonstrated with 2D ferroelectric materials. [65][66][67] Accordingly, we encourage researchers to investigate and exploit emerging 2D ferroelectric materials for next-generation memory and synaptic devices.…”