The world's highest performance semiconductor tunnel magnetoresistive element
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Electron micrographs of cross-sections of TMR elements developed this time
Preparation method of single-crystal Ga2O3 film developed this time
The Japan Industrial Technology Research Institute announced on September 20, 2016 that the monocrystalline tunnel magnetoresistance using Ga2O3 as a tunnel barrier has been developed using the single-crystal gallium oxide (Ga2O3) film formation process developed by the institute. (TMR) components. The magnetoresistive change rate, which is the performance index of the memory function, reaches an extremely high 92% at room temperature and is expected to become a basic structure of a vertical spin field-effect transistor (a vertical spin FET) having a memory function, and can achieve zero standby. The power of normally-closed calculations contributes. According to reports, 92% of the magnetoresistance change rate is the world's highest performance at room temperature in a semiconductor TMR device.
Research on spin FETs that use electronic spin to achieve non-volatile memory functions has been successfully promoted globally. However, from the viewpoint of practicality, the MR ratio must reach tens of percent or more, and when using the same lateral element as the current FET, the magnetoresistance change rate at room temperature is only about 0.1%. Recently, the industry has proposed a vertical spin FET scheme based on an all-crystal TMR element, including a single-crystal TMR element with a non-magnetic semiconductor as a barrier layer, exhibiting a magnetic reluctance of 100% or more at extremely low temperatures. Change rate. However, the magnetoresistance change rate of the device at room temperature is almost zero.
The researcher of ZTE developed a trial of a fully monocrystalline TMR device made up of a ferromagnetic electrode and a Ga2O3 tunneling barrier. Molecular beam epitaxy, one of the vapor deposition methods, was used to form the film. Specifically, a very thin (thickness 0.4-0.7 nm) single crystal magnesium oxide (MgO) layer is grown on the single crystal iron as the lower electrode, and then an amorphous Ga2O3 film is formed on the magnesium oxide layer at a temperature near room temperature. (Thickness: 1.5 to 3.0 nm) Then, a suitable high-grade single crystal Ga2O3 film was obtained by performing a heat treatment up to about 500 degrees while blowing an appropriate amount of oxygen to the film. On this single crystal Ga2O3 film, the single crystal iron upper electrode can be grown directly.
Analysis of the single crystal Ga2O3 film revealed that a pure crystal structure called "spinel type" was formed. The reason for the increase in the magnetoresistance change rate is that as the monolayer of the tunnel barrier layer and the upper ferromagnetic electrode is maintained, electrons are transported while maintaining the wave properties. In the future, the company will further improve the magnetoresistance change rate, design a gate structure that controls the output current by applying an electric field to the Ga2O3 film, and conduct work verification. The goal is to develop a vertical type that achieves practical performance after 5 years. Spin FET.
The details of this study were published on the online version of Physical Review Applied, a US scientific journal, on September 20, 2016 (US time). (Special Contributor: Kudosuke)
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