Evaluating critical metals contained in spintronic memory with a particular focus on Pt substitution for improved sustainability

Abstract

Thanks to their unique combination of properties: non-volatility, speed, density and write endurance, spintronic memory called spin transfer-torque Magnetic Random Access Memory (STT-MRAM) is expected to play a major role in the future development of the Internet of Things (IoT) and more generally in information and communication technologies. This type of spintronic device is usually made of materials, some of which can be classified as critical. Recent studies have evaluated critical materials contained in magnetic random access memory [1,2]. However, in those cases the type of memory analyzed belongs to the first generation of MRAMs developed in the early 2000s. Nowadays, the memory devices are magnetized perpendicularly to the plane of the layers and contain a synthetic antiferromagnet (SAF) that provides a high coercivity to the STT-MRAM reference layer with reduced stray field. This SAF is typically made of cobalt (Co) and platinum (Pt) multilayers antiferromagnetically coupled across a thin ruthenium (Ru) layer. Due to the high-embodied energy of platinum group metals (PGMs), a common concern when evaluating these materials is the environmental risk associated with their production. An evaluation of the environmental and economic risks of using such multilayers is first reported here, followed by a discussion of its supply risk. Substitution of Co/Pt multilayers by Co/Ni multilayers can lead to a reduction by 3-4 orders of magnitude in terms of energy requirements or global warming potential (GWP) associated with the use of these multilayers. An alternative concept based on perpendicular shape anisotropy (PSA) can also yield a reduction by 1-2 orders of magnitude in these quantities. However, for the case of STT-MRAM, tiny quantities of PGM layers are used in comparison with the mass of the silicon wafer on which these type of devices are grown. Therefore, the environmental and economic impact of the silicon wafer fabrication is found to be much higher than that of the PGM materials incorporated in the STT-MRAM stacks. Nonetheless, the high supply risk associated with PGMs remains a reason for awareness. One explored possibility is a SAF structure based on Co/Ni multilayers which can have similar performance. A second more challenging alternative is also proposed based on the aforementioned PSA concept. Finally, we address the case of several other metals identified by the European Commission as critical and used in MRAM such as W or Ta, both recently included in the EU's Conflict Minerals Regulation released in January 2021 [3].

Making supply chains more sustainable through customer and consumer engagement: The case of rare metals

“…In recent years, the literature has extensively discussed the ethical and environmental aspects of rare metals, particularly regarding their technical properties and possible substitution or reduction (Bulai et al, 2015; Kan et al, 2010; Palomino et al, 2021). However, little attention has been paid to managerial aspects, particularly the integration and engagement of downstream actors who are directly involved with the products containing rare metals (Kasulaitis et al, 2021).…”

Thin-Film Heterostructures Based on Co/Ni Synthetic Antiferromagnets on Polymer Tapes: Toward Sustainable Flexible Spintronics

“…43 All of these features, combined with a large PMA (up to 5 MJ/m 3 ) and a moderate saturation magnetization (6−7 MA/m), have made Co/Ni multilayers of great interest for both conventional and next-generation spintronic devices, including GMR-SVs and MTJs, 44,45 domain-wall and skyrmion-based electronics, 19,46,47 spin-wave-based devices, 48 as well as spin transfer and spin−orbit torque components. 28 Besides these technical aspects, the substitution of Co/Pt(Pd) by Co/Ni-based SAFs in spintronic devices was recently demonstrated to lead to a reduction of energy requirements and costs 49 due to the reduced demand of the critical and costly PGMs. Although the economic and environmental gain is low compared with the higher energetic and environmental costs associated with the fabrication of Si wafers, which are commonly used in electronics, the additional benefits related to the low risk of supply of Ni make the replacement of Co/ Pt(Pd) by Co/Ni-based SAFs still convenient to reduce the impact of PGMs and contribute to the general effort to achieve a more sustainable future.…”

Measuring raw-material criticality of product systems through an economic product importance indicator: a case study of battery-electric vehicles

“…for various low-carbon energy technologies: Junne et al 2020;for electric vehicles: Busch et al 2014;Jones et al 2020) as well as down to component level (e.g. for a specific spintronic device used in information and communication technologies: Palomino et al 2021). Due to distinct goals and perspectives of studies, there is no common methodology or harmonized definition that would constitute a standard raw-material criticality assessment procedure for all cases (Dewulf et al 2016;Mancini et al 2018;Schrijvers et al 2020).…”