Periodic Reporting for period 3 - FRESCO (FeRroElectric control of Spin-charge interCOnversion)
Reporting period: 2023-02-01 to 2024-07-31
After 50 years of exponential increase in computing efficiency through aggressive scaling down to feature sizes smaller than 10 nm, the technology of today’s electronics (complementary metal oxide semiconductor CMOS) is approaching its limits. Most significantly, new schemes must be devised to contain the ever-increasing power consumption of information and communication systems that already amounts to 11% of the world’s electricity and is expected to grow by a factor 2 to 5 by 2030. This requires a paradigm shift, with the introduction of new state variables – physical quantities that store and transmit the logic state – and non-traditional materials, derived from fundamental advances of condensed matter physics. In particular, resorting to ferroic systems with collective switching behavior and non-volatility appears essential to bring memory into logic and alleviate energy-costly on-chip data transfer. One particularly promising approach for information processing is spintronics, a very active field of research that involves the intimate interaction of the magnetic and electronic structure with spin currents. While classical spintronics has traditionally relied on ferromagnetic metals as spin generators and spin detectors, a new approach called spin-orbitronics exploits the interplay between charge and spin currents enabled by the spin-orbit coupling (SOC) in non-magnetic systems. An important advantage of spin-orbitronics is that it allows the generation of pure spin currents from charge currents and vice versa. One family of mechanisms for this purpose is the spin Hall (SHE) and inverse spin Hall effects (ISHE) that exist in bulk materials with SOC. However, SHE and ISHE have an interconversion efficiency (spin Hall angle) rarely exceeding ten percent and do not take full advantage of interfacial and low-dimensional physics otherwise ubiquitous in spintronic hetero- and nanostructures.
The FRESCO project ambitions to exploit another SOC phenomenon – the Rashba effect – occurring at interfaces and able to yield spin-charge interconversion with giant efficiency. The key idea of FRESCO is to combine the Rashba with ferroelectric materials in order to control spin-charge interconversion by electric field, in a non-volatile way. FRESCO proposes beyond-CMOS logic-in-memory device concepts that would operate at ultralow power (in the aJ range), bringing a revolution in microelectronics.
The FRESCO project ambitions to exploit another SOC phenomenon – the Rashba effect – occurring at interfaces and able to yield spin-charge interconversion with giant efficiency. The key idea of FRESCO is to combine the Rashba with ferroelectric materials in order to control spin-charge interconversion by electric field, in a non-volatile way. FRESCO proposes beyond-CMOS logic-in-memory device concepts that would operate at ultralow power (in the aJ range), bringing a revolution in microelectronics.
The ferroelectric control of Rashba SOC and spin-charge interconversion is the goal of FRESCO. Three materials approaches are being explored in parallel: (i) oxide based two-dimensional electron gases (2DEGs) which have large spin-charge interconversion efficiency ; (ii) ferroelectric/SOC material interfaces ; (iii) bulk ferroelectric Rashba oxide systems. Progress has been made in all three routes but the most promising results have been obtained for the oxide 2DEGs. Expanding from our earlier results on non-ferroelectric 2DEGs based on SrTiO3 (STO) we have introduced ferroelectricity in these systems by either inducing a ferroelectric state through the application of a large electric field, or by replacing a few Sr ions by Ca (Ca-STO). With these ferroelectric 2DEGs we could demonstrate a ferroelectric control of spin-charge conversion (Nature 2020). This control was however limited to below the Curie temperature of the ferroelectric 2DEG, about 40 K.
The Nature paper mentioned above is definitely a breakthrough in spin-based electronics. Progress towards room temperature operation is the main result expected until the end of FRESCO. Yet, these results prompted the PI to file several patents together with collaborators from Grenoble with whom he is creating a start up company.