Sputtering deposition of SrTaO2N films on different types of substrates  Films approach stoichiometry with a bandgap of 2.33 eV when substrate temperature increases to TS = 800°C  Different degrees of film crystallization, from weakly crystallized to fully c-axis oriented, were obtained  Three limiting factors are identified: 1) low absorption coefficient; 2) short lifetimes of excited charge carriers; and 3) permittivity with moderate values  Dual effects of a higher crystallinity and a greater absorbance for the thickest (600 nm) films.

In this paper, ferroelectric ceramics with (Sr 2 Ta 2 O 7 ) 100-x (La 2 Ti 2 O 7 ) x (STLTO) compositions have been investigated and their dielectric properties have been characterized in wide frequency band (from few kHz to few GHz); their integration in Dielectric Resonator Antennas (DRA) was conducted. The dense STLTO ceramics have been obtained by high temperature sintering of powders synthetized by solid state chemistry route. STLTO crystalline cell parameters and volume vary linearly as a function of the chemical composition (x) thus demonstrating an ideal solid solution domain for 0 ≤ x ≤ 3. Dielectric characterizations highlight that the permittivity and the dielectric loss vary according to the composition (x) and that the lowest losses are obtained for x < 1.65 compositions. The latter corresponds to the transition between the ferroelectric and paraelectric compositions of the STLTO material at room temperature. A low profile DRA structure was realized using a cylindrical paraelectric STLTO resonator (with x = 0

This study concerns STLTO compounds of the ferroelectric (Sr2Ta2O7)100-x(La2Ti2O7)x solid solution. The purpose is to produce the STLTO composition x = 1.65 as thin films by thermal oxidation of the corresponding oxynitride composition. Indeed, the combination of an STLTO oxide target with a dioxygen-rich reactive atmosphere during the sputtering deposition leads to Sr-deficient oxide thin films, shifting composition and structure from the perovskite to the tetragonal tungsten bronze type. An alternative synthesis pathway is to first deposit, under nitrogen-rich atmosphere, stoichiometric oxynitride films and produce, by thermal annealing under air, the stoichiometric oxide. For low oxidation temperatures ([550-600°C]), samples remain intact and display an oxide character but still contain a significant amount of nitrogen ; they could be described as intermediate phases containing nitrogen-nitrogen pairs as demonstrated by Raman. Dielectric characteristics of these original film materials are of interest with a tunability value of 26 % at 30 kV/cm (10 kHz).

Structural and dielectric properties of thin films produced by reactive radiofrequency sputtering of a (Sr2Ta2O7)100-x(La2Ti2O7)x target with x = 1.65 were studied. The chemical composition characterization shows Sr/Ta ratios ranging between 0.49 and 0.56, thus pointing out the deposition of strontium deficient films, belonging to the tetragonal tungsten bronze family. The highest permittivities and tunabilities, associated with the lowest dielectric losses, are obtained when films are pure and fully textured. This is achieved for a 900 nm-thick film deposited at TS = 850°C: ' = 116, tan = 0.007 and tunability T = 14.5 % at 340 kV/cm and 100 kHz.