Towards Room-Temperature Ferroelectric-Spin-Orbit (FESO) Devices Based on Perovskite Ferroelectrics

The power consumption of logic and memory components is one of the key issues faced by the microelectronic industry and the severity of this problem is expected to be further amplified in the near future with the growing use of artificial intelligence and machine learning. This, combined with the impending end of Moore’s law, necessitates new low-power devices and architectures that go beyond CMOS. The separation between memory and logic in the current architectures leads to a significant loss of efficiency and hence a promising approach relies on bringing these elements together (in-memory computing). Ideally, the memory elements should be non-volatile and ferroelectric materials appear as interesting candidates for this purpose, due to their intrinsically low-power switching driven by electric field.
One proposed device architecture is Intel’s magnetoelectric spin-orbit (MESO) device¹ whereby the magnetisation of a ferromagnetic layer encodes information and a voltage applied to a magnetoelectric layer switches the magnetisation. Due to the lack of room temperature multiferroic materials, however, the material choice for this approach is limited. An alternative device proposal that overcomes this limitation is the ferroelectric-spin orbit (FESO) transistor², operating through the ferroelectric control of spin-orbit coupling and spin-charge interconversion. Here, depending on the polarisation direction, electrons are accumulated or depleted at the interface between a ferroelectric and an ultrathin spin-orbit coupling system. This allows control of the interfacial electric field and modulation of the output current through the polarisation.
In this presentation, we will detail our efforts to build room-temperature FESO devices based on Rashba two-dimensional electron gases (2DEGs) formed in perovskite ferroelectrics. We will describe the growth and characterisation of ultra-high-quality epitaxial ferroelectric films. Utilising X-ray photoelectron spectroscopy and magnetotransport we show how 2DEGs can be generated at their surface. We will then demonstrate spin-charge conversion at room temperature with such samples and their integration in nanoscale FESO architectures fabricated by electron beam lithography.
By combining a writing mechanism relying on ferroelectric control of spin-to-charge conversion in 2DEGs and a reading mechanism utilising a fixed ferromagnetic layer, FESO devices provide a direct translation of ferroelectric polarisation into an output signal without switching magnetisation. Hence, this technology holds promise for revolutionising the landscape of electronic devices, paving the way for low ultra-low power in-memory computing with high endurance and magnetic field insensitivity.

[1] S. Manipatruni, et al., Scalable energy-efficient magnetoelectric spin–orbit logic. Nature 565, 35–42 (2019).
[2] P. Noël, et al., Non-volatile electric control of spin–charge conversion in a SrTiO₃ Rashba system. Nature 580, 483-486 (2020).