Low power spintronic ME-MRAM memory

Researchers in Japan have developed a low power magnetic RAM (MRAM) to reduce the energy consumption of memory systems.

MRAM is a popular choice for emerging in-memory computing architectures to reduce the power consumption of AI chips for training and for inference, or example at imec in Belgium. However MRAM devices generally require an electric current to switch the magnetization vectors of magnetic tunnel junctions, similar to the switching capacitor charge states in a DRAM. This needs a large electric current to switch the magnetization vectors during the writing process, resulting in Joule heating and power losses.

• STT-MRAM for fast read and write memory

Instead the researchers at Osaka University uses an electric-field-based writing scheme to change the magnetic state that stores the data, creating a magnetoelectric MRAM (ME-MRAM).

This ME-MRAM uses an iron-based piezo electric structure that can be switched by an electric field. The response of this heterostructure to an electric field is basically characterized in terms of the converse magnetoelectric (CME) coupling coefficient; larger values indicate a stronger magnetization response.

The researchers previously developed a Co2FeSi structure with a large CME coupling coefficient over 10-5 s/m that proved to lack the stability needed for a memory cell. So the researchers added an ultra-thin vanadium layer between the ferromagnetic and piezoelectric layers to control the magnetic anisotropy in the Co2FeSi layer and increased the CME effect.

“As MRAM devices rely on a non-volatile magnetization state rather than a volatile charge state in capacitors, they are a promising alternative to DRAM in terms of their low power consumption in the standby state,” said Takamasa Usami, lead author of the study.

The researchers also demonstrated that two different magnetic state can be reliably realized at zero electric field by changing the sweeping operation of the electric field. This means a non-volatile binary state can be intentionally achieved at zero electric field.

“Through precise control of the multiferroic heterostructures, two key requirements for implementing practical magnetoelectric (ME)-MRAM devices are satisfied, namely a non-volatile binary state with zero electric field, and a giant CME effect,” says Kohei Hamaya, senior author.

This ME-MRAN could be implemented on practical MRAM devices for applications requiring persistent and safe memory, particularly for chips in AI datacentre applications.