A new design of tunable ferroelectric capacitors in RF applications

Tunable Coplanar Waveguide Microwave Devices on MOCVD-SrTiO3Thin Films

“…Concerning dielectric characteristics of the STO films, we obtained low dielectric permittivity values and high loss tangent values as compared to published results, which spread within a very large range of values in other respects. For instance, dielectric permittivity values of 300-450 were given in [15,16] with 38% variation at 12 V/μm, for sputtered STO films and values of 2000 in [12] with 85% variation at 3 V/μm for pulsed laser deposited films. Loss tangent values are also reported in a large range of values but are often less than 0.01.…”

Electrically tunable dielectric materials and strategies to improve their performances

“…Specifically for ferroelectric thin films, besides doping of composites with low loss oxides and doping of elements, many other methods related to the film composition and processing have been employed to either improve or modify the dielectric properties. They include the use of buffer or seeding layers [147][148][149][150][151][152][153][154][155], adoption of compositional gradations [159][160][161][162][163], control of thickness and strain [172][173][174][176][177][178][179][180][181][182][183][184], and so on. The effects and efficiencies of these strategies, in terms of tailoring the dielectric properties of various ferroelectric thin films, are discussed as follows.…”

“…It is therefore expected that using a thin buffer layer could prevent the occurrence of interface diffusion and thus decrease the dielectric loss tangent. Some oxides, such as MgO [147], TiO 2 [149] and LaAlO 3 [151], which have been used to improve the dielectric properties of ferroelectric ceramics and thin films, are employed as buffer layers in deposition of ferroelectric thin films.…”

“…Dielectric properties of the samples were measured at 1 MHz. Ta 2 O 5 has also been considered as a potential candidate for buffer layers used to deposit BST thin films on Si substrates, because it possesses high dielectric constant, low dielectric loss tangent, low leakage current and low defect density [148,151]. Core et al [148] systematically investigated Ta 2 O 5 thin films to evaluate their qualities for buffer layers for the integration of microwave BST thin films with silicon substrates.…”

Novel trimming technique for tunable HTS microstrip filters

“…HTS filters are also suitable for future software-defined radio (SDR) systems. Since SDR systems require a filter with wide-range frequency tunability there has been increasing interest in tunable bandpass filters [1][2][3][4][5][6][7][8][9][10][11]. Center-frequency tuning has been widely researched, and various methods have been devised to increase the frequency range of tunable filters.…”