Guidelines for one-nanometer magnetic tunnel junction technology

Researchers at Tohoku University have developed guidelines for a single-nanometer magnetic tunnel junction (MTJ), enabling performance to be tailored to meet the requirements of diverse applications, ranging from AI/IoT to automobiles and space technologies.

This advancement will lead to high-performance spintronic non-volatile memory, compatible with cutting-edge semiconductor technologies. Details were published in the journal npj Spintronics on January 4, 2024.

The main characteristic of non-volatile memory is its ability to retain data in the absence of an external power source. Therefore, significant development efforts have been directed toward nonvolatile memory due to its ability to reduce power consumption in semiconductor integrated circuits (ICs). Performance requirements for non-volatile memory vary depending on specific applications. For example, AI/IoT applications demand high-throughput performance, while automotive and space technologies prioritize high retention capabilities.

Spin transfer torque magnetoresistive random access memory (STT-MRAM), a type of nonvolatile memory technology that stores data using the intrinsic angular momentum of electrons, known as spin, has the potential to solve certain limitations associated with existing systems. memory technologies.

The basic element of STT-MRAM is the magnetic tunnel junction (MTJ): two ferromagnetic layers separated by a thin insulating barrier. Scientists have long attempted to address the challenge of reducing the size of MTJs while still meeting performance requirements, but many problems remain.

STT-MRAM, using MTJs with dimensions on the order of tens of nanometers, has been successfully developed for automotive semiconductors using 1X nm technology nodes. However, when it comes to future nodes, there is a need to reduce MTJs to single-digit nanometers, or Xnm, while ensuring the ability to tailor performance based on specific applications.

To do this, the research group devised a way to engineer single-nanometer MTJs with a CoFeB/MgO stack structure, a de facto standard materials system. Varying the thickness of the individual CoFeB layer and the number of stacks (CoFeB/MgO) allowed them to independently control the shape and interfacial anisotropies, which is crucial for achieving high retention and high speed.

As a result, MTJ performance can be tailored to applications ranging from retention-critical to speed-critical applications. At the size of a single nanometer, shape anisotropy-enhanced MTJs demonstrated high retention (>10 years) at 150 °C, while interfacial anisotropy-enhanced MTJs enabled fast switching (10 ns or less) below 1 V.

“Since the proposed structure can be adapted to existing facilities in major semiconductor factories, we believe that our study makes a significant contribution to the future scaling of STT-MRAM,” said Junta Igarashi , one of the main authors of the study.

Lead researcher Shunsuke Fukami added that “semiconductor industries generally tend to be aware of long-term evolution. In this sense, I think this work should send them a strong message that they can count on the future of STT-MRAM to help them usher in a low-carbon society.