Understanding Leakage Currents through $Al_2O_3$ on $SrTiO_3$

TL;DR

This study investigates leakage currents in ALD-grown $Al_2O_3$ on $SrTiO_3$, identifying key mechanisms, effects of processing, and implications for oxide electronics and device modulation.

Contribution

It provides a detailed analysis of leakage mechanisms in $Al_2O_3$ on $SrTiO_3$, highlighting the impact of deposition and annealing on leakage behavior and analysis assumptions.

Findings

Trap-assisted tunneling and Poole-Frenkel are primary leakage mechanisms.

Annealing reduces leakage currents by eliminating traps.

Analysis sensitivity depends critically on flat-band voltage assumptions.

Abstract

Leakage currents through insulators received continuous attention for decades, owing to their importance for a wide range of technologies, and interest in their fundamental mechanisms. This work investigates the leakage currents through atomic layer deposited (ALD) $Al_2O_3$, grown on $SrTiO_3$. This combination is not only a key building block of oxide electronics, but also a clean system for studying the leakage mechanisms without interfacial layers that form on most of the conventional bottom electrodes. We show how tiny differences in the deposition process can have a dramatic effect on the leakage behavior. Detailed analysis of the leakage behavior rules out Fowler-Nordheim tunneling (FNT) and thermionic emission, and leaves the trap-related mechanisms of trap-assisted tunneling (TAT) and Poole-Frenkel as the likely mechanisms. After annealing the sample in air, the currents are reduced, which is ascribed to transition from trap-based mechanism to FNT, due to the elimination of the traps. The dramatic role of the assumptions regarding the flat-band voltage used for analysis is critically discussed, and the sensitivity of the extracted parameters on this magnitude is quantitatively described. We show that field effect devices based on structures similar to those described here, should be able to modulate $>10^{13} cm^{-2}$ electrons. These results provide general guidelines for reducing and analyzing leakage currents in insulators, and highlight some of the possible approaches and pitfalls in their analysis.