Simulations of current transport phenomena in ferroelectric tunnel junctions

Sammanfattning

Ferroelectric memories pose as a potential candidate as resistive memory devices that could be used for in-memory computing and artificial synapses. One promising type of ferroelectric memory device is the ferroelectric tunnel junction (FTJ). The basic functionality of a FTJ device is based upon the fact that ferroelectric materials display two distinct polarisation states which could be switched in order to achieve two resistance states in the device. There are several current pathways contributing to the current in a FTJ and the exact mechanisms are not entirely understood. There is a need for a numerical model, where electronic band structure and defect current pathways are considered, that includes physically well grounded fitting parameters. In this thesis two such models for the trap-assisted tunnelling (TAT) current are investigated and fitted to experimental data. The first model is based upon occupational probability in the metal electrodes and transmission probabilities given by the WKB approximation. The second model utilises Fermi's golden rule in order to estimate transition rate. Both models in general display unsatisfactory results in terms of reproducing and fitting to experimental data. The second model displays some promising results once empirical constants are introduced which indicate towards a certain accuracy in the parameters and models used. The main deviations are believed to stem from an overly simplified band structure model and normalisation problems.