## 3 Results
The dielectric properties of two most homogeneous and single phase TiTe\({}_{3}\)O\({}_{8}\) thick films on Al\({}_{2}\)O\({}_{3}\) substrates analysed by SPDR method at 20 GHz are presented in Table 1. 21-\(\upmu\)m-thick TiTe\({}_{3}\)O\({}_{8}\) films sintered at 680 \({}^{\circ}\)C for 5 h display a \(\varepsilon_{\rm r}\) value of 28 and a Q \(\times\) f value of 21,978, while 19-\(\upmu\)m-thick films sintered at 700 \({}^{\circ}\)C for 5 h display \(\varepsilon_{\rm r}\) of 32 and Q \(\times\) f of 21,053. Thus, relative permittivity of TiTe\({}_{3}\)O\({}_{8}\) thick films varies between 28 and 32 and Q \(\times\) f varies approximately between 21,000 and 22,000. This uncertainty reflects the differences in the density, thickness and possibly the residual presence of the interfacial reaction with Al\({}_{2}\)O\({}_{3}\). Indeed, the dielectric permittivity of the Al\({}_{2}\)TeO\({}_{6}\) interface layer present in films sintered at 700 \({}^{\circ}\)C is smaller than that of TiTe\({}_{3}\)O\({}_{8}\)[33]. In a series connection, this should deteriorate the total dielectric properties. However, the negative effect that may be induced by a <200 nm-thick interface layer is apparently compensated by higher density of the films sintered at 700 \({}^{\circ}\)C comparing to that of the films sintered at 680 \({}^{\circ}\)C.  
Figure 3: XRD patterns of TiTe\({}_{3}\)O\({}_{8}\) films deposited on carbon coated alumina substrates and sintered at 680, 700 and 720 \({}^{\circ}\)C for 5 h. The main film’s phase is TiTe\({}_{3}\)O\({}_{8}\). For films sintered above 700 \({}^{\circ}\)C Al\({}_{2}\)TeO\({}_{6}\) is formed due to a reaction between TeO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) substrates. The dielectric performance of TiTe\({}_{3}\)O\({}_{8}\) films on Al\({}_{2}\)O\({}_{3}\) substrates summarized in Table 1 is also compared to that reported for corresponding ceramics at high (GHz) frequencies. It is worthwhile to mention that Q \(\times\) \(f\) for TiTe\({}_{3}\)O\({}_{8}\) thick films have not been reported so far. \(\varepsilon_{\rm r}\) of 50 and Q \(\times\) \(f\) of 30,600 GHz at 5 GHz were reported for TiTe\({}_{3}\)O\({}_{8}\) ceramics sintered at 720 \({}^{\circ}\)C [15]. Besides the lower measurement frequency, the observed differences of the dielectric behaviour between TiTe\({}_{3}\)O\({}_{8}\) thick films and ceramics might also be related to density, residual presence of Al\({}_{2}\)TeO\({}_{6}\) secondary phase and details of the microstructure. For other TiTe\({}_{3}\)O\({}_{8}\) ceramics, sintered at 700 \({}^{\circ}\)C/5 h, \(\varepsilon_{\rm r}\) and Q at 4 GHz were reported to be 36 and 3400, respectively [14]. Comparing these TiTe\({}_{3}\)O\({}_{8}\) ceramics with our films on Al\({}_{2}\)O\({}_{3}\), the results here obtained are rather promising. Moreover, the low losses of polycrystalline alumina (\(\varepsilon_{\rm r}\) = 9, tan\(\delta\) = 9.46 \(\times\) 10\({}^{-5}\), Q = 10570--for \(>\) 99% pure Al\({}_{2}\)O\({}_{3}\)) [34] should improve the dielectric performance of the final device TiTe\({}_{3}\)O\({}_{8}\)/Al\({}_{2}\)O\({}_{3}\) composite structure. Figure 4: SEM micrographs of TiTe\({}_{3}\)O\({}_{8}\) films deposited on carbon coated alumina substrates sintered at 700 \({}^{\circ}\)C for 5 h, surface (**a**), cross section (**b**) and high magnification cross section and energy dispersive spectra for indicated locations (**c**). Under these sintering conditions (700 \({}^{\circ}\)C for 5 h in air) TiTe\({}_{3}\)O\({}_{8}\) films are dense and uniform with the presence of a thin (<200 nm) reaction interlayer of Al\({}_{2}\)TeO\({}_{6}\) confined to the interface between the film and the substrate. Overall and by comparison, EPD TiTe\({}_{3}\)O\({}_{8}\) thick films on Al\({}_{2}\)O\({}_{3}\) reveal a high performance in terms of permittivity and loss tangent (high Q features) making them promising low-sintering-temperature dielectrics for micron sized high-frequency devices.