Effect of Ni Doping on Improvement of the Tunability and Dielectric Loss of Ba_0.5Sr_0.5TiO₃ Thin Films for Microwave Tunable Devices

Abstract

The structural, microstructural, and surface morphological properties of Ba 0.5 Sr 0.5 TiO 3 thin films were investigated as a function of Ni dopant concentration. The Ni-dopant concentration in BST films has a strong influence on the material properties including dielectric and tunable properties as well as film growth rate. Ni doped (≤3 mol%) BST films showed denser, smoother, and smaller grain sizes than those with 6 and 12 mol% Ni. Dielectric constant and loss of 3 mol% Ni-doped BST films were about 980 and 0.3%, respectively. In addition, tunability and figure of merit of 3 mol% doped BST films showed maximum values of approximately 39% and 108, respectively. Correlation of the material properties with dielectric and tunable properties suggests the the 3 mol% Ni-doped BST films are the optimal choice for tunable device applications.

Recent progress of (Ba,Sr)TiO3 thin films for tunable microwave devices

“…To date, several group's researches have shown that the additions of some dopants (with small concentrations) such as Fe 2ϩ , Mn 2ϩ , Mg 2ϩ , Ni 2ϩ , and La 3ϩ into pure BST thin films could dramatically reduce the dielectric-loss tangent of BST thin films. [65][66][67][68][69][70][71][72][73][74] The Mg-doping (1 mol.%) has the greatest effect on reducing the dielectric-loss tangent of (Ba 0.6 Sr 0.4 )TiO 3 films at microwave frequencies while retaining useful dielectric tunability and insulating properties compared with the pure (Ba 0.6 Sr 0.4 )TiO 3 thin films. [69][70][71] The mechanism for lowering the dielectric loss by addition of some dopants centers on the thesis that ions with a charge less than 4 ϩ can substitute for Ti 4ϩ and behave as electron acceptors.…”

“…62 dopants must be optimized to obtain the best overall properties for use in tunable devices applications. [72][73][74] It should be kept in mind that good dielectric and insulating properties are not standalone requirements, other material properties, such as film structure, microstructure, surface morphology, and the nature of the film/substrate interface, also affect device performance and long-term reliability. Therefore, to fully evaluate and understand the properties stated previously, the influence of acceptor concentration on the microstructural, surface morphological, and interfacial properties must be assessed and correlated with the films' dielectric and insulating properties.…”

The influence of Mg doping on the dielectric and tunable properties of (Ba0.6Sr0.4)0.925K0.075TiO3 thin films fabricated by sol–gel method

“…Some dopants including Ni 2+ , Fe 2+ , Fe 3+ , Mn 2+ , Mn 3+ , Co 2+ , Co 3+ , Cr 3+ , and Bi 3+ etc. which can occupy the B sites of the (ABO 3 ) perovskite structure and behave as electron acceptors, have been known to lower dielectric loss [3][4][5][6][7][8][9][10][11][12]. At the same time, the dielectric loss of BST also can be dramatically decreased by adding some low-loss and low-K oxides, such as MgO [13,14], Al 2 O 3 [11] and SiO 2 [15,16].…”

“…6 [18]. Chen et al [19] reported the electric properties of La/Mg Co-doped (Ba 0.7 Sr 0.3 )TiO 3 thin films.…”

Lead barium zirconate perovskite films for electrically tunable applications

“…One of the major challenges encountered for realizing the integration of BST thin films into electrically tunable devices is the simultaneous minimization of the dielectric loss and maximization of dielectric tunability. Many attempts to improve the dielectric properties of BST thin films have focused on film texturing, 5 improvement of the dielectric-electrode interface, control of film stress, 6,7 addition of acceptor dopants, [8][9][10] and modification of the film microstructures. 11 Almost no attempt has successfully improved the dielectric tunability and dielectric loss simultaneously.…”