Resumen de Novel metal insulator metal capacitors based on electrosprayed colloidal nanoparticles
This work develops a novel capacitor device based on the use of nanotechnology. The device starts from the exiting metal-insulator-metal (MIM) concept, but instead of a continuous insulator layer, dielectric nanoparticles are used. Nanoparticles are mainly of silicon oxide (silica) and polystyrene (PS) and the diameter values are 255nm and 295nm respectively. The nanoparticles contribute to a very high surface to volume ratio and are easily available at low cost. The deposition technique developed in this work is the electrospray, which is a bottom-up fabrication technology that allows batch processing and achieves a good compromise between large area and low deposition time. With the objective of increasing the deposit surface, the electrospray set-up has been tuned to allow deposition areas from 1cm2 to 25cm2.
The fabricated devices, the so called nanoparticles metal insulator metal (NP-MIM) capacitors, offer higher capacitance values than a similar conventional capacitor with a continuous insulator layer. In the case of silica NP-MIMs, a factor as high as 1000 of capacitance enhancement is achieved, whereas polystyrene NP-MIMs has capacitance gain of 11. In addition, silica NP-MIMs show capacitive behaviours in a certain frequency range which depends on the humidity and thickness of the nanoparticles layer, while polystyrene MIMs always maintain their capacitive behaviour.
The fabricated devices have been characterized by scanning electron microscopy (SEM) measurements complemented with focusing ion beam (FIB) drilling to characterise the topography of the NP-MIMs. The devices have also been characterized by impedance spectroscopy measurements, at different temperatures and humidifies. The origin of the enhanced capacitance is associated in part to humidity in the nanoparticles interfaces. A circuital model based on distributed elements has been developed to fit and predict the electrical behaviour of the NP-MIMs.
In summary, this thesis shows the design, fabrication, characterization and modelling of a new promising nanoparticles metal-insulator-metal capacitor that may pave the way to the development of a novel MIM-supercapacitor technology.
