M.Sc Thesis


M.Sc StudentMiron Dror
SubjectDeveloping Building Blocks for Oxide Electronics
DepartmentDepartment of Electrical and Computers Engineering
Supervisor DR. Lior Kornblum
Full Thesis textFull thesis text - English Version


Abstract

Complex oxides exhibit rich functionalities, such as ferromagnetism, ferroelctricity, superconductivity, memristive effects and metal-insulator transitions. Oxide electronics is an emerging field, aiming to harness these diverse physical phenomena towards practical devices. Implementation of these concepts relies on the development of basic device building blocks such as field-effect transistors (FETs), diodes, capacitors and memory devices which are crucial components of integrated circuits.


A major bottleneck toward implementing such devices is the development of efficient insulators, a critical component of many electronic devices. While in conventional semiconductors such as silicon, proper insulators are a decades-old art, when growing an insulator on top of an oxide conductor or semiconductor, the insulating properties of the junction are not as trivial.


A thorough analysis of currents through Al2O3 deposited on Nb doped SrTiO3 is performed. This combination is not only a useful building block of oxide electronics, but also a clean system for studying the leakage mechanisms of insulators, without interfacial layers that form on most of bottom electrodes used for such studies.

We show that while atomic layer deposited (ALD) Al2O3 is a mature, well-established process for gate insulator applications, optimization of small process details can lead to huge benefits in mitigating leakage. The optimized structures can be useful as gate stacks for oxide electronics, owing to their low leakage which enables significant charge modulation of an underlying channel. We performed conduction analysis and showed that the effect of the assumed flat-band voltage on extracted parameters can be huge, necessitating careful handling of this parameter. We realised that the current conduction in this sample is due to traps inside the Al2O3, most probably oxygen vacancies.


A similar structure composed of Al2O3 grown on reduced undoped SrTiO3 is analyzed. We suggest that in this stack the reduction of the SrTiO3 surface produced oxygen vacancies that acted both as an effective bottom electrode thanks to its high conductivity, but more importantly it served as a reservoir for oxygen vacancies, which enabled the resistive switching properties.

We further implement our leakage current analysis to Ta2O5 grown on Nb doped SrTiO3. This structure produced a rectifying behavior, exhibiting an ideality factor of n≈1.3 over 4 current decades. In this case we utilize the trap-assisted tunneling model to describe the current accurately, while using the energy barrier acquired from X-ray photoelectron spectroscopy and capturing the temperature dependence. This analysis is discussed in the context of pre-forming Ta2O5 resistive switching devices, since it is widely studied for such devices and may explain some recently observed trends in their forming voltage.