## 6 Functional Properties and Applications of Nanocomposites
### Microelectronic devices  
The addition of conductive nanoparticles to polymers has a strong impact on the resulting composite dielectric properties. With respect to the aspired integration of passive electronic devices, like resistors, capacitors and others, into the printed circuit board (PCB), new composite materials have to be developed to meet the following requirements [172-174]:  
* huge functionality like large capacitance values in case of integrated capacitors
* process compatibility to industrial PCB-fabrication
* abandonment of lead-containing materials
* low overall costs* high reliability and extended life cycle.  
In case of embedded capacitors, suitable materials with high permittivity are needed, achieving, in combination with a further reduction of the capacitor thickness from 100 down to 10 \(\upmu\)m, large capacitance values in the range of some nF/mm\({}^{2}\)[175]. Polymer based-ceramic nanocomposites fulfill the mentioned requirements, if both components possess a high permittivity. Common polymers exhibit only low relative dielectric constant values between 2 and 4 [173]. Epoxies typically used in PCBs shows permittivity values around 3.5 [176]. Ferroelectric polymers like polyvinylidenefluoride (PVDF)-derivatives deliver high-k-values around 60 under ambient conditions, but these polymers cannot be used applying the standard board manufacturing technology [177].  
A very promising way to raise the composites dielectric constant is the addition of suitable ferroelectric ceramics with extreme permittivity values like BaTiO\({}_{3}\) to polymers [173, 178]. As the size effects for dielectric properties are in another size regime as the size effects of magnetic or optical properties (see section 2.1), size effects in the nanocomposites are also expected in another size regime. These perovskite-type ceramics show a pronounced dependence of the permittivity from the crystallite size, decreasing grain sizes down to 1 \(\upmu\)m yielded a significant increase of the relative dielectric constant in the relevant temperature range between -50 \({}^{\circ}\)C and 100 \({}^{\circ}\)C [179]. A further size reduction towards the nanoscale caused a lowering of the permittivity again [180]. It can be expected that an optimized grain size can be found between 100 nm and 1 \(\upmu\)m. First attempts to find a grain size with improved dielectric properties were published 2008 applying a systematic thermal treatment of nanosized BaTiO\({}_{3}\) with an average particle size of 85-128 nm [181, 182]. The thermal treatment at 1000 \({}^{\circ}\)C allowed for a grain size growth and an increase of the dielectric constant from 9 to 25 in a polyester-based composite with a solid load of 60 wt %. The change of the dielectric constant with load in a polyester matrix of different nanosized ceramics like TiO\({}_{2}\), SnO\({}_{2}\), ZnO, BaTiO\({}_{3}\), SrTiO\({}_{3}\) and others, were published quite recently [172]. In all cases poor permittivity values could be measured. Hence, the thermal treatment was extended to nanosized (69-104 nm) SrTiO\({}_{3}\), but only a small improvement was measured due to the cubic phase of the ceramic. In contrast the dielectric loss could be significantly reduced by a factor of 3 [183]. Commercially available BaTiO\({}_{3}\) with different particle size distribution from 100 up to 700 nm (Inframat Advanced Materials) were investigated with respect to their dielectric properties [184]. Composites containing 65 wt % of a 200 nm BaTiO\({}_{3}\) showed a permittivity around 15.  
As a short resume, high-k-ceramics, like BaTiO\({}_{3}\) and others, possess at the nanoscale a non-equilibrium crystal lattice with reduced permittivity values. A controlled grain size growth by thermal treatment towards the microscale helps finding an optimized grain size enabling higher permittivity values [182].