Nanocrystal Thin films for Applications in Integrated Electronics and Energy Storage
Production of complex metal oxides for high k dielectric applications, either as gate dielectrics or in capacitor technology is commonplace. Requirements for integrated electronics are generally towards miniaturization, higher permittivity (dielectric strength), and lower loss/leakage. New sources of energy production (e.g. generation III solar) will also require advances in energy storage – another place for such technology to have a major sustainable impact. Furthermore, advanced applications for high k dielectric and ferroelectric materials in the electronics industry continues to demand an understanding of the underlying physics in decreasing dimensions into the nanoscale. Assembly of dielectric nanoparticles into thin films is a highly attractive means to produce nanostructured composites with improved performance and tunability as a function of size, composition and structure.
One of the major processing challenges is conversion of the nanoparticle building block9 into a reliable thin film device. Essential to this approach is an understanding of the nanoparticle interface chemistry, combined with an ability to integrate them into thin films that have uniform and characteristic electrical properties.
Our method proves to be a versatile means of preparing micropatterned or continuous BaTiO3 nanocrystal thin films. We have previously demonstrated that nanocrystalline films with grain sizes in the range of 10–30 nm show dielectric constants in the range of 85–90 over the 1 KHz–100 KHz, with low loss.9
More recently we have advanced the principle of using nanocrystals as initial building blocks for the preparation of thin films which exhibit highly uniform nanostructured texture and grain sizes (Fig. 2). Our versatile process allows us to prepare dense or porous capacitor thin films or gate dielectrics (particle/polymer composites) with dielectric constants k in the range of 10-60, with dramatic increases of k in the low frequency range (>300). Such methods circumnavigate the need to develop complex fabrication tools normally associated with semiconductor manufacturing, making the process cheap and scalable.
We are in the stage of developing high k dielectric films based on a range of perovskite materials, in which a mechanically and thermally stable thin film between 10-1000 nm in thickness (or thicker) can be generated on substrates.
Top(a-d) homogeneous solvent suspensions of BaTiO3 nanocrystals are deposited as thin films or incorporated into polymers to make nanocomposites, characterized by SEM/TEM. Bottom(a-b) electrode deposition and frequency dependent dielectric measurement together with loss. (unpublished results10).