Tesis doctoral de Nekane Martín Arbella
The multifunctionality in ferroelectric materials makes them very useful in applications such as non-volatile memories, infrared sensors or microelectromechanical systems. The constant evolution of the electronic devices towards miniaturization requires the integration of the ferroelectric in the si-technology, and therefore, its manufacture as a thin film onto a semiconductor substrate. the formation of the crystalline phase, responsible for the ferroelectric response, requires high temperatures (up to 600°c). This is a problem when integrating the ferroelectric in the semiconductor circuit, since these devices are not capable of withstanding temperatures over 500°c without degradation. In addition, further investigations are currently being carried out focused on the use of new flexible polymeric substrates, which requires working at temperatures below 450°c. This is the reason why new strategies are investigated to reduce the processing temperature of functional oxide films. this work has successfully used a method called photo-chemical solution deposition (pcsd) as a way to reduce the processing temperature of thin films. This method involves applying uv irradiation of the amorphous films deposited from the precursor solutions in order to promote crystallization of the ferroelectric oxide at low temperature, what requires that such solutions are capable of absorbing uv light. in this thesis ferroelectric thin films of lead titanate (pbtio3, pt) have been prepared at only 400°c by pcsd designing a new synthesis strategy of the precursor solutions, and characterized from a structural, microstructural and electrical point of view. The fabrication of the films has been carried out by spin-coating the solutions onto pt/tio2/sio2/(100) substrates, followed by drying and thermal treatment in a rapid thermal processing oven combined with uv irradiation for the removal of organics and the low temperature crystallization of the oxide. the addition of n-methyldiethanolamine (mdea) to the precursor solutions leads to the formation of complexes with the metals present in the system, which are responsible for a high uv absorption through a charge transference process, a type of electronic transition with molar absorption coefficients much higher than π-π* transitions, the commonly experienced by photoactivated precursor solutions in the pcsd technique. The reduction in the crystallization temperature of the oxide is due both to the increased photosensitivity of the precursor solutions and to a self-combustion process that takes place in the system due to the high content of organics and nitrogen of the mdea, which causes a large amount of energy that the system spends in the crystallization of the oxide, reducing the temperature. Thus, mdea provides results that other photoactivators are not able to provide. in this way, the same effects would be expected for any composition that contains at least one cation with a d0 or d10 configuration, since the complexes formed by the mdea with metal cations are responsible for the increased photosensitivity of precursor solutions through a charge transference process. As the main families of ferroelectrics contain cations of this type, this new synthesis strategy opens the door to the preparation of a wide range of compositions of functional mixed oxides of high interest for applications in electronic devices.
Datos académicos de la tesis doctoral «Fotoactivación de precursores sol-gel para la preparación de láminas delgadas ferroeléctricas de pbtio3 a baja temperatura«
- Título de la tesis: Fotoactivación de precursores sol-gel para la preparación de láminas delgadas ferroeléctricas de pbtio3 a baja temperatura
- Autor: Nekane Martín Arbella
- Universidad: Navarra
- Fecha de lectura de la tesis: 07/03/2012
Dirección y tribunal
- Director de la tesis
- María Lourdes Calzada Coco
- Tribunal
- Presidente del tribunal: José Antonio Navío santos
- José ignacio álvarez galindo (vocal)
- hector Beltran mir (vocal)
- ricardo Jiménez riobóo (vocal)