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Novel cascadable magnetic majority gate that is based on magnetic tunneling junctions

(Nanowerk News) Researchers at Huazhong University of Science and Technology (HUST) have developed a novel cascadable magnetic majority gate (CMMG) that is based on magnetic tunneling junctions (MTJs).
CMMG utilizes both spin transfer torque (STT) and spin orbit torque (SOT) effects to connects magnetic majority gate units by spin current through a non-ferromagnetic metal wire to design multiple logic-depth circuits.
For the first time, complete logic family have been implemented in very straightforward ways. CMMG paves a pathway for designing complicated logic circuits and realization of process-in-memory.
At HUST, professor Long You and his team have developed a novel CMMG logic which cascades the magnetic majority gate (MMG) units unidirectionally.
A novel MMG logic, utilizing both STT and SOT effects, could implement a logic family including AND/NAND and OR/NOR functions with an easy configuration under a stable operation. Communication between logic units, with non-reciprocity, is realized by spin current injection through a non-ferromagnetic metal wire.
The proposed CMMG can be utilized to design robust and comprehensive logic circuits using full spintronic devices.
This work is presented in IEEE Transactions on Electronic Device ("Novel Cascadable Magnetic Majority Gates for Implementing Comprehensive Logic Functions").
In principle, three vital features are necessary for pragmatic logic circuit implementations, namely the completeness for Boolean operations, cascade-ability and non-reciprocity. There are two conventional spintronic designs could meet these three requirements, spin torque majority gate (STMG) and all spin logic (ASL).
While in practical application, these two designs are not as favorable as CMMG when utilized in pragmatic logic circuit.
Compared with STMG, CMMG mitigates the domain wall reflection issues which hindered the STMG and shows smaller footprint and thus better stability in the scaling process.
While in ASL, the embedded insulating regions in the channel, which is utilized to prevent back current flow from output to input, complicates the fabrication process.
Compared with it, in CMMG logic, we regulate the magnitude of injected current density to confirm the non-reciprocity of the device in the uniquely designed structure.
Furthermore, as is noted in the paper, "with increasing device integration, the much reduced device counts of CMMG are expected to be beneficial for reducing chip footprint."
The authors point out that this newly proposed magnetic device structure is more compatible with CMOS manufacturing process, as compared to existing STMG and ASL structures.
The researchers performed physics-based micro-magnetic simulations on the above designs to estimate switching speed and energy dissipation.
The results indicate that CMMG logic has comparable performance to existing MTJ and spintronic device technology, featuring high energy efficiency, together with the promising device scalability and easy for fabrication, CMMG is an excellent option for CMOS replacement non-volatile logic.
The authors also note that "the fabrication of CMMG is within back-end-of-line (BEOL) technology layers, leaving extra potential for 3-dimensional (3D) monolithic integration schemes."
With the results reported in the paper, the proposed CMMG could overcome the earlier described problems which ASL and STMG faced, including the implementation scheme for inverter and non-reciprocity. It is a promising candidate for fabricating large-scale logic circuits.
Source: Huazhong University of Science and Technology
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