Resistive switching in nanometric batio3 ferroelectric junctions
- Autores: Mengdi Qian
- Directores de la Tesis: Ignasi Fina Martínez (dir. tes.), Josep Fontcuberta i Griñó (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Francesca Campabadal Segura (presid.), Catherine Dubourdieu (secret.), Stefano Brivio (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia de Materiales por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
Ferroelectric capacitors consisting in two metallic electrodes separated by a ferroelectric layer have great potential for memory and logic devices. The ferroelectric character of the barrier should allow to build multilevel memory with a state (resistance, R) that can be dictated by its previous history (cycling voltage, V). Naturally, the success of this approach relies on the ability to build ferroelectric capacitor displaying large resistance changes (resistive switching, RS) at room temperature.
The goal of the present thesis is the study of the RS behavior of ferroelectric thin (10-100 nm) and ultrathin (<10 nm) films. In particular, I study the different RS response depending on parameters such as ferroelectric layer thickness, writing voltage, amplitude and polarity, writing time, device temperature and contact configuration. For that purpose, epitaxial BaTiO3-based ferroelectric capacitors have been used and a complete characterization set-up has been developed as documented in the present thesis.
In ultrathin BaTiO3-based ferroelectric capacitors, electrons can tunnel across the ferroelectric barrier. In this case, RS results from the different barrier height depending on the ferroelectric polarization state. Although, it is commonly assumed that the UP to DOWN ferroelectric domain switching process is similar to the DOWN to UP, it is found here that these processes occur with very different dynamics. Indeed, fast response is observed for one sign of polarization and slow one for the other. We argue that the presence of imprint electric fields causes the device asymmetry.
When exploring the electroresistance (ER, defined as the relative change of resistance upon reversing the polarization) it is discovered that its magnitude and sign depend on the barrier thickness and writing protocol. Temperature-dependent measurements have been instrumental to obtain evidence of the presence of field-assisted ionic motion contributing to ER. It is argued that the relative balance between purely electronic and ionic diffusion processes, modulate the height of the interfacial Schottky barriers and consequently, are responsible of the observed variations of the magnitude and sign of ER. In ultrathin films these processes are found to be negligible and purely electronic modulation of the tunneling barrier takes place.
Taking benefit of the understanding acquired during the elaboration of the present work, tunneling ferroelectric capacitors have been used to implement a Complementary Resistive Switching (CRS) device. CRS has been developed to overcome the sneak current path problem of passive memory arrays, which reveals opportunities for higher density nanocrossbar arrays. By using a simple anti-serial connection of ferroelectric tunnel junctions, we implemented the CRS functionality that allows effectively writing and reading binary states of identically large resistance state in the unbiased state. Moreover, it is experimentally demonstrated that this arrangement has significant advantages in power saving. We end by discussing the possible bottlenecks that this functionality might show.
