Dielectric low-k composite films based on PMMA, PVC and methylsiloxane-silica: Synthesis, characterization and electrical properties

This report describes the preparation of low-k inorganic–organic hybrid dielectric films, based on a polymethylmethacrylate–polyvinylchloride (PMMA–PVC) blend and a silica powder functionalized on the surface with methylsiloxane groups (m-SiO2). By dispersing m-SiO2 into a [(PMMA)x(PVC)y] 50/50 (x/y)wt% polymer blend, six [(PMMA)x(PVC)y]/(m-SiO2)z hybrid inorganic–organic materials were obtained, with z ranging from 0 to 38.3wt% and x=y=(100−z)/2. The transparent, homogeneous, crack-free films were obtained by a solvent casting process from a THF solution. The morphology, thermal stability and transitions of hybrid materials were studied by environmental scanning electron microscopy (ESEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). ESEM revealed that hybrid dielectric films are very homogeneous materials. The electrical response of the dielectric films was studied by detailed broadband dielectric spectroscopy (BDS). BDS measurements were performed at frequencies of 40Hz to 10MHz and a temperature range of 0–130°C. In these temperature and frequency ranges the proposed materials have a dielectric constant of <3.5 and a tanδ of <0.05. BDS also revealed molecular relaxation events in [(PMMA)x(PVC)y]/(m-SiO2)z materials as a function of temperature and sample composition. Results showed that these films with z in the range 25–35wt% are very promising low-k dielectrics for applications in organic thin film transistor (OTFT) devices.