An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

The rapid increase in information in the big-data era calls for changes to information-processing paradigms, which, in turn, demand new circuit-building blocks to overcome the decreasing cost-effectiveness of transistor scaling and the intrinsic inefficiency of using transistors in non-von Neumann computing architectures. Accordingly, resistive switching materials (RSMs) based on different physical principles have emerged for memories that could enable energy-efficient and area-efficient in-memory computing. In this Review, we survey the four physical mechanisms that lead to such resistive switching: redox reactions, phase transitions, spin-polarized tunnelling and ferroelectric polarization. We discuss how these mechanisms equip RSMs with desirable properties for representation capability, switching speed and energy, reliability and device density. These properties are the key enablers of processing-in-memory platforms, with applications ranging from neuromorphic computing and general-purpose memcomputing to cybersecurity. Finally, we examine the device requirements for such systems based on RSMs and provide suggestions to address challenges in materials engineering, device optimization, system integration and algorithm design. Resistive switching materials enable novel, in-memory information processing, which may resolve the von Neumann bottleneck. This Review focuses on how the switching mechanisms and the resultant electrical properties lead to various computing applications.

Resistive switching materials for information processing

Ultrathin ferroelectric materials could potentially enable low-power logic and nonvolatile memories1,2. As ferroelectric materials are made thinner, however, the ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides—the archetypal ferroelectric system3. Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes4. Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO2), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems—that is, from perovskite-derived complex oxides to fluorite-structure binary oxides—in which ‘reverse’ size effects counterintuitively stabilize polar symmetry in the ultrathin regime. Enhanced switchable ferroelectric polarization is achieved in doped hafnium oxide films grown directly onto silicon using low-temperature atomic layer deposition, even at thicknesses of just one nanometre.

Enhanced ferroelectricity in ultrathin films grown directly on silicon.

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

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/3DB31D1931EA9955AF5E300BC33891D6/S2159685918001751a.pdf/div-class-title-review-and-perspective-on-ferroelectric-hfo-span-class-sub-2-span-based-thin-films-for-memory-applications-div.pdf

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

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. Using models of ferroelectric domain nucleation we explain the time, field and temperature dependence of polarization reversal. A simple stochastic model is proposed as well, relating nucleation processes to the observed statistical switching behavior. Our results suggest novel opportunities for hafnium oxide based ferroelectrics in nonvolatile memory devices.

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

We developed a stacked horizontal channel type floating gate (HC-FG) NAND memory; a 3-D stacked NAND array composed of conventional FG cells. With this cell structure, a wide program/erase (P/E) window is obtained, accompanied by superior read disturb immunity, P/E endurance, and data retention. In addition, we propose a low-cost layer select transistor (LST) that is easily integrated with the HC-FG cell. Because the 3-D memory composed of the HC-FG cell and the LST has good compatibility with conventional fabrication technology, further bit cost scaling is expected.

Highly Scalable Horizontal Channel 3-D NAND Memory Excellent in Compatibility With Conventional Fabrication Technology

Analogue in-memory computing using memristors could alleviate the performance constraints imposed by digital von Neumann systems in data-intensive tasks. Conventional linear memristors typically operate at high currents, potentially limiting power efficiency and scalability in practical applications. Here, we show that nonlinear ferroelectric tunnel junction memristors can perform linear computation at ultralow currents. Using logarithmic line drivers, we demonstrate that analogue-voltage-amplitude vector–matrix multiplication (VMM) can be performed in selectorless ferroelectric tunnel junction crossbars by exploiting a device nonlinearity factor that remains constant for multiple conductive states. We also show that our ferroelectric tunnel junction crossbars have the attributes required to scale analogue VMM-intensive applications, such as neural inference engines, towards energy efficiencies above 100 tera-operations per second per watt. Nonlinear ferroelectric tunnel junction memristors can be used to perform linear vector–matrix multiplication operations at ultralow currents.

Low-power linear computation using nonlinear ferroelectric tunnel junction memristors

We demonstrate, for the first time, a CMOS compatible ferroelectric HfO 2 -based two-terminal non-volatile resistive switch; HfO 2 ferroelectric tunnel junction (FTJ). The device has characteristics of nA-range operation current, self-compliance, and intrinsic diode properties, as well as good device to device uniformity. Simultaneous achievement of these characteristics, which was not reported in the other two-terminal emerging memories, is significant advantage for future non-volatile applications. Accurate understanding of switching mechanism based on first-principles calculations and material characterization enabled us to establish a solid guideline for performance improvement: scaling of both ferroelectric layer and interfacial layer thickness. As a consequence, reduction of operation voltage while maintaining sufficient ON/OFF ratio was successfully demonstrated.

First demonstration and performance improvement of ferroelectric HfO 2 -based resistive switch with low operation current and intrinsic diode property

According to one embodiment a first variable resistance layer which is arranged between a second electrode and a first electrode and in which a first conductive filament is capable of growing based on metal supplied from the second electrode, and an n-th variable resistance layer which is arranged between an n-th electrode and an (n+1)-th electrode and in which an n-th conductive filament whose growth rate is different from the first conductive filament is capable of growing based on metal supplied from the (n+1)-th electrode are included, a configuration in which a plurality of conductive filaments is electrically connected in series between the first electrode layer and the (n+1)-th electrode layer is included, and a resistance is changed in a stepwise manner.

Nonvolatile resistance change device

According to one embodiment, a nonvolatile memory device includes a first electrode, a second electrode, a variable resistance layer. The variable resistance layer is provided between the first electrode and the second electrode. The variable resistance layer contains impurity of a nonmetallic element. The impurity is at least one selected from the group consisting of S, Se, Te, F, Cl, Br, and I.

Shosuke Fujii

Papers

Highly Scalable Horizontal Channel 3-D NAND Memory Excellent in Compatibility With Conventional Fabrication Technology

Low-power linear computation using nonlinear ferroelectric tunnel junction memristors

First demonstration and performance improvement of ferroelectric HfO 2 -based resistive switch with low operation current and intrinsic diode property

Nonvolatile resistance change device

Nonvolatile memory device