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The cubic pyrochlore Bi 1.5 MgNb 1.5 O 7 (BMN) thin films were deposited on Pt coated sapphire substrates by rf magnetron sputtering using different pressures. The effects of sputtering pressure on phase structure and dielectric properties of BMN thin films were investigated. The X-ray diffraction results revealed that all the BMN thin films deposited at different sputtering pressures showed a pure cubic pyrochlore phase, but the films sputtered at low pressure have a better crystalline than that sputtered at high pressure. The BMN thin films sputtered at 1 Pa exhibited good crystalline with a strong (222) preferred orientation and excellent dielectric properties, which have a dielectric constant of 80, dielectric loss of ~ 0.007, and dielectric tunability of ~ 38% at bias field of 1.25 MV/cm. The dielectric constant and tunability of BMN thin films were both decreased with increasing sputtering pressure. However, the dielectric loss showed a slightly change with the sputtering pressure. Furthermore, the leakage current density of BMN thin films increased with increasing sputtering pressure, which is suggested to be related with the increasing grain size and surface roughness of thin films sputtered at high pressure.

High temperature operation(HTO) experiments were performed on industrial GaN HEMTs devices. Several degradation failure modes of DC parameters such as transconductance reduction, threshold voltage shift, and gate leakage current increase were identified. The vertical failure localization and analysis of the devices were carried out by electrical method. The results show that the increase of the degradation of the die attach layer is the main reason for the increase of the junction temperature and thermal resistance of the devices. Furthermore, the results are analyzed by three-dimensional X-ray imaging confirming the degradation of the die attach layer. The voids in the die attach layer expanded during the high temperature operation stress experiments, led to a worse heat dissipation performance, which resulting in increased junction temperature, and further accelerate the performance degradation of the devices.

The cubic pyrochlore Bi 1.5 Mg N Nb 2.5 − N O 8.5 − 1.5 N (BMN) thin films with various compositions were deposited on Pt coated sapphire substrates by rf magnetron sputtering. Crystal structures of the BMN thin films by X-ray diffraction exhibited nearly pure cubic pyrochlore phase in a wide range of chemical substituents. The dielectric properties were systematically studied and discussed. The dielectric constant was found to increase with increasing Mg 2+ content, while the dielectric loss changed little with the Mg 2+ concentration and remained in a low level of ∼0.006. The BMN thin films with a composition of Bi 1.5 Mg 1.0 Nb 1.5 O 7 demonstrated a tunability of 20% at applied bias filed of 1.0 MV/cm. The insufficient Mg 2+ content decreased the tunability of the BMN thin films. However, the BMN thin films with excess Mg 2+ content also did not exhibit enhanced tunable performance. These results indicated that the appropriate Mg 2+ content and stoichiometric composition were of significance for improving the tunability of BMN thin films.

The Bi 1.5 MgNb 1.5 O 7 (BMN) thin films were prepared on Pt-coated sapphire substrates by rf magnetron sputter deposition. The as-deposited amorphous films were thermally treated for crystallization and formation of cubic pyrochlore structure. The effects of annealing treatment on microstructures and dielectric properties of BMN thin films have been investigated. X-ray diffraction detected cubic pyrochlore phases in the films annealed at 650 °C and above. The grain size and surface roughness of the films increased with annealing temperature. The as-deposited films and the films annealed up to 600 °C showed a low value of dielectric permittivity and high value of loss tangent. An abrupt increase in dielectric permittivity and a decrease in loss tangent appeared at 650 °C. The thin films annealed above 650 °C showed bias voltage dependence of the dielectric permittivity, and the tunability increased with annealing temperature. However, the leakage current density also increased at high annealing temperatures.

Bi1.5Zn1.0Nb1.5O7 (BZN)/Ba0.5Sr0.5TiO3 (BST) thin films were prepared on Pt/Ti-coated sapphire substrates by radio frequency magnetron sputtering. The specific relationship between the dielectric properties and the thickness ratio of the BZN thickness to the BST thickness was investigated. The presence of BZN films effectively reduced the dielectric loss of the thin films. The thickness-ratio-dependent dielectric constant and dielectric loss behaviors were in good accordance with the simulation results based on the series connection theory. The optimum thickness ratio was determined to be around 0.5, exhibiting a maximum commutation quality factor of about 16,000. The built-in electric field at the region near the BZN–BST interface may be responsible for the asymmetric characteristic of the electric-field-dependent dielectric properties of the BZN/BST thin films.

The Bi1.5MgNb1.5O7 (BMN) thin films were prepared on platinum coated sapphire by rf magnetron sputter deposition. Effects of substrate temperature, sputter pressure and O2/(O2 + Ar) mixing ratio on phase structures and dielectric properties of thin films were investigated. The results indicated that sufficiently high substrate temperature and low sputter pressure would facilitate the formation of cubic pyrochlore in BMN thin films. Meanwhile, the appropriate O2/(O2 + Ar) mixing ratio of sputter atmosphere was required. The deposited Bi1.5MgNb1.5O7 cubic pyrochlore thin films with (222) oriented texture exhibited large tunability of ~ 50% at a maximum applied bias field of 1.5 MV/cm, with low dielectric loss of ~ 0.007. The temperature and frequency dependent dielectric measurements indicated that no noticeable dielectric dispersion was detected in BMN cubic pyrochlore thin films.

Tunable parallel-plate capacitors employing Bi(1.5)Zn(1.0)Nb(1.5)O(7)/Ba(0.5)Sr(0.5)TiO(3) (BZN/BST) thin films for RF applications are reported. The intermediate frequency measurements indicate that the BZN/BST-based varactors demonstrate large tunability of 39% at 40 V and high device quality factor of 300 at 1 MHz. The devices maintain quite low leakage current density even under a high applied bias. The quality factor analysis shows that the device quality factor is highly dependent on conductor loss of electrodes at frequencies above 1 MHz. The phase shifter employing BZN/BST-based varactors exhibits lower insertion loss than does employing semiconductor diodes at a designed frequency of 445 MHz, demonstrating the potential of tunable capacitors employing BZN/BST thin films for RF applications.

Parallel plate capacitors based on Bi1.5Zn1.0Nb1.5O7 (BZN) / Ba0.5Sr0.5TiO3 (BST) bilayered thin films were fabricated on sapphire substrates. The BZN/BST bilayered thin films were deposited by radio frequency magnetron sputtering, from two individual Bi1.5Zn1.0Nb1.5O7 and Ba0.5Sr0.5TiO3 stoichiometric ceramic targets. Dielectric measurements indicated that the capacitors exhibited device quality-factor of up to ∼ 200, with a relative tunability of ∼ 40% at a bias field of 1.6 MV/cm.The figure of merit was about 80. Compared with the parallel plate capacitors with single BST thin film configuration, the leakage current of the BZN/BST capacitors was observed to be much lower. It was also found that the capacitance was frequency independent in the range from 100 kHz to 100 MHz, while the device quality-factor dropped down as frequency increasing. The decrease of device quality-factor accompanied with frequency independent capacitance could be attributed to the conductor loss of electrodes.

The cubic pyrochlore Bi 1.5 MgNb 1.5 O 7 thin films were prepared onto Pt-coated sapphire substrates by rf magnetron sputtering from a stoichiometric target. The phase evolution, morphologies, dielectric properties and voltage tunable properties of thin films with sputtering parameters was investigated. The structure and dielectric properties were dependent on substrate temperature, overall sputter gas pressure and oxygen content. The Bi 1.5 MgNb 1.5 O 7 thin films were found to be electric field tunable and the maximum voltage tunability of 29.2% at bias field 1.2 MV/cm was obtained.

The dielectric loss of parallel-plate Pt/Bi1.5MgNb1.5O7 (BMN)/Pt thin film varactors were investigated. The effects of four extrinsic loss mechanisms were discussed. The results showed that the loss mechanism of conduction electrons, local polar regions, and universal relaxation contributed little to the BMN thin film varactors. However, the losses owing to charged defects were found to be the mainly loss mechanism at low frequency (below 1 MHz). The experimental data were in good agreement with the ω1/3 power law. We studied the effect of charged defects mechanism using BMN thin films annealing in different air conditions. It is clearly seen that the charged defects were associated with oxygen vacancies. In the frequency range 100 MHz-6 GHz, the losses of BMN thin film varactors did no fit the charged defects mechanism very well, which were due to the additional losses induced by electrodes, parasitic capacitances, and test equipments. The study of extrinsic loss mechanisms provided useful information for the deposition, varactor design, and the dielectric properties optimization of the BMN thin films.

The Bi1.5Zn1.0Nb1.5O7 (BZN)/Ba0.5Sr0.5TiO3 (BST) bilayered films and BST thin films were prepared via radio frequency (RF) magnetron sputtering, and the leakage current behaviors of the films were investigated. Lower leakage currents of BZN/BST bilayered films were achieved compared with that of BST thin films, especially in the high field region. The potential barrier height of top contact is increased by insertion of a BZN layer in between BST and top Pt-electrodes, which might be responsible for the current reduction of BZN/BST under negative biases (positive voltage applied to bottom electrodes). For the case of positive biases, BZN/BST showed a significant increase in the threshold electric field of Poole-Frenkel emission compared with that of BST, resulting in a current decrease in BZN/BST than that in BST. For the BZN/BST bilayered films at 300 K, since the Schottky emission, Fowler-Nordheim tunneling and Poole-Frenkel emission occur in an extremely high electric field, the leakage current is gover...

The Bi1.5MgNb1.5O7 thin films with cubic pyrochlore structure were prepared onto Pt-coated sapphire substrates by rf magnetron sputtering deposition from a stoichiometric target. Dielectric measurements indicated that the Bi1.5MgNb1.5O7 thin films exhibited low dielectric loss of ∼0.0018–0.004, medium dielectric constant of ∼86, and superior tunable dielectric properties at room temperature. A bias field of 1.6 MV/cm resulted in the maximum voltage tunability of 39%. A brief discussion is given on the enhanced tunability compared to Bi1.5ZnNb1.5O7 thin films. The low loss and superior tunability make Bi1.5MgNb1.5O7 thin films promising for potential tunable capacitor applications.

The Ba0.5Sr0.5TiO3(BST)/SiN bilayered thin films with a SiN layer serving as a buffer layer between the top electrode and the BST layer have been prepared onto Pt-coated c-plane sapphire substrates. The dielectric measurements show that the loss tangent has been significantly lowered. The dielectric properties of the BST/SiN bilayered thin films are strongly dependent on the SiN thickness. The BST/SiN bilayered thin films at a SiN/BST thickness ratio of 0.2 give the largest figure of merit of 50.1. The thickness effect was discussed as well with a series connection model of multilayered capacitors, and the favorable simulation was obtained.