Methodology
Expanding the fundamental understanding of ferroelectrics
In the CONCEPT project, we will systematically investigate the impact of potential ultrasmall ferroelectric (FE) domain structures on the switching dynamics and programming of hafnium zirconium oxide (HZO) synaptic devices. Our primary objective is to examine HZO with single-crystal quality to isolate ferroelectric dynamics from extrinsic effects that are commonly found in polycrystalline ferroelectrics due to grain boundaries and other structural defects. This approach will enable us to assess the scalability potential of HZO devices without the need to manufacture ultra-small devices, which can be costly and challenging. To achieve the CONCEPT project’s objectives, it is essential to deposit films with the required properties. This necessitates expertise in two specialised areas: ferroelectric characterisation and semiconductor physics.
How?
We will leverage state-of-the-art equipment and techniques for macroscopic characterization of ferroelectric capacitors properties:
1) Measurement of the change in surface screening charges due to a change in polarization, using the Virtual Ground method for accurate current measurements.
2) Analysis of ferroelectric memristor devices in the FTJ configuration, measuring resistive loops as a function of pulse width and applying different pulse schemes to study synaptic behaviour.
3) In-situ measurements of cell parameters under perturbation by an electric field using equipment that will help distinguish ferroelectric polarisation from other contributions to the current and increase the chances of beamtime for CONCEPT researchers. Using the Positive-Up Negative-Down (PUND) method to separate ferroelectric polarisation from other contributions, will allow us to obtain a pure and clean ferroelectric hysteresis loop of the remanent polarisation.
Piezo-force microscopy (PFM) will be used to study ferroelectric samples for local characterisation using an atomic force microscope (AFM) in contact mode, taking advantage of the piezoelectric properties of ferroelectrics. PFM is a qualitative technique, but it can provide information on domain size and shape.
Outcomes
The CONCEPT project aims to understand and optimise synaptic behaviour and domain switching dynamics in ferroelectric HZO films for neuromorphic computing applications.
The project aims to investigate whether the plasticity in these epitaxial films is due to mosaicity in the in-plane directions or the small size of the domains. The project also aims to leverage existing work on HZO/WOx ferroelectric synapses to examine the influence of ionic motion between the HZO and the oxide semiconductor.
