Recent Progress in the Voltage-Controlled Magnetic Anisotropy Effect and the Challenges Faced in Developing Voltage-Torque MRAM

Abstract

The electron spin degree of freedom can provide the functionality of “nonvolatility” in electronic devices. For example, magnetoresistive random access memory (MRAM) is expected as an ideal nonvolatile working memory, with high speed response, high write endurance, and good compatibility with complementary metal-oxide-semiconductor (CMOS) technologies. However, a challenging technical issue is to reduce the operating power. With the present technology, an electrical current is required to control the direction and dynamics of the spin. This consumes high energy when compared with electric-field controlled devices, such as those that are used in the semiconductor industry. A novel approach to overcome this problem is to use the voltage-controlled magnetic anisotropy (VCMA) effect, which draws attention to the development of a new type of MRAM that is controlled by voltage (voltage-torque MRAM). This paper reviews recent progress in experimental demonstrations of the VCMA effect. First, we present an overview of the early experimental observations of the VCMA effect in all-solid state devices, and follow this with an introduction of the concept of the voltage-induced dynamic switching technique. Subsequently, we describe recent progress in understanding of physical origin of the VCMA effect. Finally, new materials research to realize a highly-efficient VCMA effect and the verification of reliable voltage-induced dynamic switching with a low write error rate are introduced, followed by a discussion of the technical challenges that will be encountered in the future development of voltage-torque MRAM.

van der Waals Magnets: Material Family, Detection and Modulation of Magnetism, and Perspective in Spintronics

“…[ 176 ] Particularly, the magnetization of bilayer CrI 3 can also be switched by the gate voltage under a small out‐of‐plane magnetic field, [ 23 ] enabling the electrical switching by voltage and the fabrication of spin tunneling field‐effect transistors (Figure 14g). [ 177 ] Actually, this voltage switching of magnetization, together with aforementioned magnetic anisotropy switching [ 143 ] by ionic gating, offer exciting opportunities for the construction of next‐generation voltage‐torque MRAM (Figure 14f), [ 170,178 ] which is more energy efficient than SOT/STT‐MRAM that relies on current. Moreover, other external stimuli such as strain can also switch the magnetization of vdW magnets, [ 156 ] which provides novel strategies to design the memory devices, e.g., the construction of artificial multiferroic devices with vdW ferroelectrics.…”

Quantum Spin-Wave Materials, Interface Effects and Functional Devices for Information Applications

“…Magnetoresistive random access memory (MRAM) can be directly constructed under electric control based on STT and SOT, instead of using magnetic field generated by current to reverse magnetization in traditional magnetoresistive effect. This provides a significant practical value (Fong et al, 2016;Nozaki et al, 2019). STT-MRAM can achieve the level of integration density similar to the DRAM (Dynamic RAM), while obtain an excellent performance level similar to the SRAM (Static RAM).…”

“…Therefore, barrier breakdown can be almost avoided. The spin-orbit torque also achieves a higher writing speed due to the perpendicular magnetic anisotropic magnetic tunnel junction (Nozaki et al, 2019). Currently, almost all types of memories are faced with the dilemma of stable non-volatility and high working energy.…”

Recent Trends in Microwave Magnetism and Superconductivity

“…The nature of VCMA is the spin-dependent screening of conduction electrons at the interface of a ferromagnetic metal, and their interaction with localized magnetic moments in a metal. As a result, the application of an electric field to the ferromagnetic metal surface (ferromagnetic metal -dielectric interface) leads to a variation of the surface perpendicular anisotropy of a ferromagnet [210,211]. Applications of VCMA benefit from the simplicity of a fabrication of nanoscale structures and ultralow power losses in VCMA transducers due to the zero Joule heating.…”