Search

The design, fabrication and microwave properties of tunable fifth-order combline bandpass filter using etched barium-strontium-titanate (BST) thin films on sapphire (0001) substrates were investiga...

In this paper, a method is introduced to improve the performance of ferroelectric phase shifter. The influences of periodically inserting spiral inductor into ground of coplanar waveguide (CPW) are investigated. Three dimensional electro-magnetic simulation shows that at frequency of 25 GHz, the maximal phase differential will be 449°, which is 97° more than the conventional one with no spiral inductor loaded. The novel ferroelectric phase shifter is also fabricated. Comparing with the conventional phase shifter, additional 49° phase shift is obtained at 18 GHz.

Ba0.6Sr0.4TiO3 (BST) thin films were deposited on Pt/Ti/SiO2/Si (100) substrates by radio-frequency magnetron sputtering. Nanocrystal lines on the BST films surface were obtained by microwave electrical field irradiation annealing. Atomic force microscopy (AFM) results reveal that microwave annealing can give rise to certain self-assembled nanocrystal lines on the BST films surface, and the length and the width of the nanocrystal lines are dependent on annealing time. After the films further annealed for 20 min or more, the nanocrystal lines broke up into spherical nanocrystals of about 25 nm in diameter. The directions of BST nanocrystal lines are determined by microwave electrical field. X-ray diffraction (XRD) shows that the microwave-annealed BST films are (110) preferred orientation. Specular X-ray reflectivity (XRR) measurement shows that the surfaces of the microwave-annealed BST thin films exhibit anisotropy.

Ba0.6Sr0.4TiO3 (BST) thin films were deposited on Pt/Ti/LaAlO3 (100) substrates by radio-frequency magnetron sputtering. Not only the fatigue characteristic of BST thin film but also the temperature and frequency dependences of dielectric constant (e r ), loss tangent (tanδ) and tunability (at 300 kV/cm) were investigated. With the temperature increasing, the dielectric constant of BST thin film increases slowly and the fluctuation range is about 10%. From 20 Hz to 1 MHz, dielectric constant, loss tangent and tunability of BST thin films have a little change. After a hundred million reversals, the tunability of BST thin film slightly decreased, and the dielectric loss increased synchronously. The results reveal that BST thin films have high reliability including temperature, frequency stability and anti-fatigue characteristic.

Dielectric nonlinearity is an important characteristic of ferroelectrics. It is assumed that in ferroelectrics the grains are all uniform, in order and cubic-shaped. Moreover, the dielectric constant of the grain boundary does not vary with direct current bias. And then the grains and the grain boundaries were modeled in terms of capacitors and resistors. Based on these analyses, a model for grain size effect on dielectric nonlinearity of ferroelectrics was established. In this model there are some parameters such as the grain size and the grain boundary width, which intensively influence on the dielectric properties of ferroelectric ceramics and thin films. The accuracy of the model prediction was quantitatively verified by our experimental data. The results proved that the above model can describe the grain size effect on dielectric nonlinearity of ferroelectrics.

Barium strontium titanate (Ba0.6Sr0.4TiO3, short for BST) thin films were prepared by RF-magnetron sputtering. The influences of deposition conditions, such as sputtering power, deposition pressure and sputtering gas, on the microstructures and dielectric non-linearity of BST thin films were investigated. The results show that both dielectric constant and tunability of BST films increase and then decrease as the sputtering power increases. Moreover, the tunability increases as O2:Ar ratio increases from 1:1 to 8:1. Not only the ratios of (Ba+Sr)/Ti and Ba/Sr but also the RMS roughness increases with increasing deposition pressure.

The interface has a crucial influence on the dielectric properties of thin films. A model, including the film thickness and the interfacial layer thickness, for dielectric nonlinearity of ferroelectric films was established. The ferroelectric film and transition layers are modeled by capacitances and resistances, and the Schottky barriers at metal/dielectric interfaces are modeled in terms of diode equivalent circuits. It is found that the increasing tendencies of the remanent polarization, dielectric constant and tunability from model are consistent with those from experiment. The results proved that the above model can describe the interface effect on dielectric nonlinearity of ferroelectric films.

Barium strontium titanate (Ba0.6Sr0.4TiO3, short for BST) thin films were prepared by RF-magnetron sputtering. The influences of deposition conditions, such as substrate temperature and target-substrate distance, on the microstructures and non-linearities of BST thin films were investigated. The non-linearities of Ba0.6Sr0.4TiO3 thin films increase as the substrate temperature increases and/or target-substrate distance decreases.