Fabrication of a single-crystal giant magnetoresistive device on a polycrystalline film
Technique may promote practical use of high-performance magnetoresistive devices comprising half-metallic heusler alloys

Date:
August 27, 2020
Source:
National Institute for Materials Science, Japan
Summary:
Engineers have succeeded in fabricating a giant magnetoresistive
(GMR) device comprising single-crystal Heusler alloys on an
practical silicon substrate. The team demonstrated for the first
time that a single-crystal magnetoresistive device can be bonded
onto the surface of a polycrystalline electrode using a wafer
bonding technique.



FULL STORY ==========================================================================
NIMS and AIST have jointly succeeded in fabricating a giant
magnetoresistive (GMR) device comprising single-crystal Heusler alloys
on an practical silicon substrate. The team demonstrated for the
first time that a single-crystal magnetoresistive device can be bonded
onto the surface of a polycrystalline electrode using a wafer bonding technique. The fabrication of high-performance single-crystal devices
has proven challenging, and these results may provide new guidance in
the development of larger capacity hard disk drives (HDDs).


==========================================================================
Some Heusler alloys (e.g., Co2MnSi) are known to possess half metallic property?substances that act as conductors to electrons of only one spin orientation when their atoms are in an orderly arrangement. In previous research, a high-quality GMR device was fabricated using half-metallic
Heusler alloys. This device was reported to exhibit an extremely large magnetoresistance ratio, a characteristic vital to the development of
hard disk read heads compatible with HDDs with nearly five times the
recording density of current HDDs. However, the fabrication of this GMR
device required the use of a heat-resistant single-crystal magnesium
oxide (MgO) substrate with an appropriate lattice structure, which is considerably more costly than using the industrially established small
MgO substrate. In addition, HDD read heads need to be fabricated on a polycrystalline magnetic shield, despite the fact that it is impossible to
grow a single-crystal device directly on the surface of a polycrystalline
film with crystal grains having various lattice orientations.

Moreover, Heusler alloys have to be annealed at a temperature of at least 300DEGC to form an orderly atomic ordering. However, this annealing
process also damages the magnetic shield layer. These issues have
prevented practical applications of GMR devices comprising single-crystal Heusler alloys.

This research team deposited a NiAl/CoFe buffer layer on the surface of
a conventional, inexpensive silicon substrate and discovered that the
substrate acquired significantly increased heat resistance and a smoother surface. The team then fabricated a GMR device comprising single-crystal Heusler alloys on the silicon substrate and confirmed that the device
performs comparably to the GMR device grown on the MgO substrate. The
team also grew a polycrystalline electrode film on the surface of another substrate and fabricated a GMR film device comprising single-crystal
Heusler alloys on it. The team subsequently bonded the fabricated GMR
film device onto a wafer using the latest three- dimensional integration technology. Through these processes, the team formed an extremely
smooth, defect-free bonded interface between the polycrystalline and
single crystal films by optimizing wafer bonding conditions. The team
also confirmed that bonding the fabricated GMR film device onto a wafer
did not negatively affect the device's magnetoresistive performance. The techniques the team developed are expected to eliminate the need to grow
a single-crystal magnetoresistive device directly on a polycrystalline electrode film and completely resolve the damage issue caused by high-temperature treatment.

These techniques are applicable not only to the fabrication of
GMR devices comprising single-crystal Heusler alloys but also for
various other purposes, such as the integration of single-crystal
tunneling magnetoresistance devices - - another potentially promising high-performance technology -- onto a heat- susceptible circuit board. The
use of these techniques may promote practical use of high-performance single-crystal spintronic devices, thereby potentially contributing
to the development of larger capacity HDDs and magnetoresistive random
access memory.


========================================================================== Story Source: Materials provided by National_Institute_for_Materials_Science,_Japan. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Jiamin Chen, Yuya Sakuraba, Kay Yakushiji, Yuichi Kurashima, Naoya
Watanabe, Jun Liu, Songtian Li, Akio Fukushima, Hideki
Takagi, Katsuya Kikuchi, Shinji Yuasa, Kazuhiro Hono. Fully
epitaxial giant magnetoresistive devices with half-metallic
Heusler alloy fabricated on poly-crystalline electrode using
three-dimensional integration technology. Acta Materialia, 2020;
DOI: 10.1016/j.actamat.2020.04.002 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200827101828.htm

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