AlScN: A III-V semiconductor based ferroelectric

Abstract

Ferroelectric switching is unambiguously demonstrated for the first time in a III-V semiconductor based material: Al1-xScxN -A discovery which could help to satisfy the urgent demand for thin film ferroelectrics with high performance and good technological compatibility with generic semiconductor technology which arises from a multitude of memory, micro/nano-actuator and emerging applications based on controlling electrical polarization. The appearance of ferroelectricity in Al1-xScxN can be related to the continuous distortion of the original wurtzite-type crystal structure towards a layered-hexagonal structure with increasing Sc content and tensile strain, which is expected to be extendable to other III-nitride based solid solutions. Coercive fields which are systematically adjustable by more than 3 MV/cm, high remnant polarizations in excess of 100 µC/cm² which constitute the first experimental estimate of the previously inaccessible spontaneous polarization in a IIInitride based material, an almost ideally square-like hysteresis resulting in excellent piezoelectric linearity over a wide strain interval from -0.3% to +0.4% as well as a 2 paraelectric transition temperature in excess of 600°C are confirmed. This intriguing combination of properties is to our knowledge as of now unprecedented in the field of polycrystalline ferroelectric thin films and promises to significantly advance the commencing integration of ferroelectric functionality to micro-and nanotechnology, while at the same time providing substantial insight to one of the central open questions of the III-nitride semiconductors -that of their actual spontaneous polarization.

Giant polarization charge density at lattice-matched GaN/ScN interfaces

“…In order to predict this bound charge based on differences between formal polarization values calculated for wz-GaN and rs-ScN, we applied the interface theorem [Eq. (2)]. The application of this theorem requires the interface to be insulating; we verify this by performing explicit superlattice calculations, in which the ScN layer is strained to the in-plane lattice parameters of GaN (but allowing all internal coordinates to relax).…”

A spiking and adapting tactile sensor for neuromorphic applications

“…Although this fundamental working principle is the same for the POSFET and PiezoFET, we would like to emphasise that the here presented PiezoFET based on AlScN exhibits a few distinguishing features. In contrast to the organic copolymer PVDF-TrFE, AlScN is compatible with Si-CMOS technology [38][39][40] . This allows the development of highly compact and integrated tactile sensor units consisting of PiezoFETs and subsequent neuromorphic circuits.…”

“…Therefore, a c-axis oriented AlScN layer containing 27% Sc is deposited in between the control gate and the channel of the MOSFET. AlScN is chosen due to its higher piezoelectric coefficient compared to pure AlN while remaining CMOS compatible paired with lower leakage compared to most perovskite piezoelectrics 38,39,51 . Mechanical stress applied to the AlScN layer induces surface charges which in turn modulate the transistor channel current.…”

Oxygen Incorporation in the Molecular Beam Epitaxy Growth of ScxGa1−xN and ScxAl1−xN

“…have gained attention to increase the functionality of nitride semiconductors through piezoelectric, ferroelectric, superconducting, and magnetic behavior . Sc‐III nitrides in particular have shown promise for extremely large increases in piezoelectric coefficients and spontaneous polarizations and even ferroelectric behavior . These attractive properties have allowed Sc‐III nitrides to find use in applications such as bulk acoustic wave (BAW) resonators and microelectromechanical systems (MEMS) .…”

“…[1] Sc-III nitrides in particular have shown promise for extremely large increases in piezoelectric coefficients and spontaneous polarizations and even ferroelectric behavior. [2][3][4][5][6] These attractive properties have allowed Sc-III nitrides to find use in applications such as bulk acoustic wave (BAW) resonators and microelectromechanical systems (MEMS). [7][8][9][10] Magnetron sputtering has been utilized to deposit thin film Sc x Al 1Àx N, [11][12][13][14] and more recently, molecular beam epitaxy (MBE) to grow Sc-III nitrides films.…”