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CMOS/magnetoelectronic Integrated Circuits wil Multifunctional Capabilities

Periodic Reporting for period 4 - MAGICAL (CMOS/magnetoelectronic Integrated Circuits wil Multifunctional Capabilities)

Reporting period: 2020-05-01 to 2021-10-31

The microelectronics industry has heavily invested on Spin Transfer Torque Magnetic Random Access Memory (STT-MRAM) in the past 10 years with the aim of replacing embedded FLASH memory and later address SRAM and other applications at sub-20nm technology nodes.
In this context, this ERC project MAGICAL “CMOS/Magnetoelectronic Integrated Circuits with Multifunctional Capabilities” realized groundbreaking advances in ultra-low power multifunctional systems based on hybrid CMOS/magnetic technology. With the development of portable electronics and of the Internet of Things (IOT), more and more functions must be embedded on chip: logic/memory, sensing, communication, etc. With existing technologies, the hurdles are power consumption, communication bandwidth, processing/ packaging costs. MAGICAL demonstrated that these limitations can be largely overcome through hybrid CMOS/magnetic technology.
The project followed three main goals:
- Firstly, it strengthened the STT-MRAM technology by investigating two novel ideas aiming at solving two remaining difficulties in sub-20nm STT-MRAM development: the nanostructuration of magnetic tunnel junctions at small feature size and narrow pitch and the long-term data retention, opening the path to high density (>Gbit) STT-MRAM. Within MAGICAL, a new method for nanopatterning magnetic tunnel junctions by depositing the magnetic stacks on prepatterned metallic pillars was successfully demonstrated. In addition, a new concept of MRAM relying on the use of a vertically elongated shape of the storage layer was proposed to extend the memory retention in cells of diameter down to 5nm.
-Secondly, we demonstrated that digital, analog (3D orientation sensor) and RF communication functions can be realized using technologies very similar to the one developed for STT-MRAM thus widening the spectrum of applications of this technology.
-Thirdly, through various actions, MAGICAL aimed at narrowing the cultural gap that exists between magnetism and microelectronics communities. Summer schools “Introductory Course on MRAM” were organized four times during the project as well as special events (MRAM special Poster session and MRAM Global Innovation Forums) at each IEDM conferences.
The prime benefits from this project are: ultralow power thanks to STT-MRAM non volatility and on-chip computation capability, improved communication functionalities (in particular intrachip communication), reduced processing costs.
From scientific and technical points of view, several major achievements were realized in the project.
We demonstrated a new approach for the nanopatterning of magnetic tunnel junctions for dense memory applications (e.g.DRAM). Instead of Ion Beam Etching which no longer works at sub-30nm feature size and narrow pitch, we showed that we can obtain functional nanostructured memory dots by directly depositing the magnetic stacks on prepatterned metallic non-magnetic pillars by sputtering. The material is then naturally nanostructured while being deposited thus not requiring any post-deposition etching.
A second major breakthrough is the demonstration of the concept of Perpendicular Shape Anisotropy STT-MRAM. By dramatically increasing the thickness of the storage layer (thickness comparable to diameter), we showed that functional memory dots of diameter down to 5nm can be obtained. Besides, the memory properties (retention, write current) vary much less with operating temperature than in conventional STT-MRAM which is very good for applications such as automotive.
Another breakthrough concerns short distance communication using spin transfer torque oscillators and spin-diodes. We demonstrated signal transmission over tens of meters by using the phase modulation of vortex spin-transfer-torque nano-oscillators. Besides, a new concept of ultrafast spectrum analyzer using these high quality spin transfer oscillators also emerged from the project.
Another important result of the project is the realization of memristive function for neuromorphic computing using magnetic tunnel junctions. We demonstrated that the angular variation of the conductance as a function of the angle between the storage layer and reference layer magnetization can be used to achieve intermediate levels of resistance which can be accessed by pulses of current.
Another important aspect of this project was to foster more relationships between magnetism and microelectronics communities. For that, several events were organized by the PI’s team in particular the Introductory Course on MRAM (sessions in 2017, 2018, 2020, 2021) as well as MRAM special poster sessions and a MRAM Global Innovation Forums gathering 300 attendees at IEDM yearly since 2017. These events contributed reducing the cultural gap between these two communities and easing the penetration of this hybrid CMOS/magnetic technology in microelectronics industry.
The project is now completed but the PI’s team keeps on investigating innovative approaches in the field of magnetic memory, RF components, magnetic field sensors and unconventional computing. Among the last realization, let us cite in particular the proposition and realization of a new concept of STT-MRAM based on double magnetic tunnel junctions comprising a switchable assistance layer. This memory exhibits an increased thermal stability compared to conventional STT-MRAM together with a reduced write current.
Illustration of Perpendicular Shape Anisotropy STT-MRAM concept and examples of properties