Yongdong Jiang

Epitaxial Growth of Ferroelectric Thin Films by Combustion Chemical Vapor Deposition and Their Electrical Properties

Combustion chemical vapor deposition (CCVD) has been used to grow a wide variety of ferroelectric thin films such as Ba1-xSrxTiO3 (BST) and PbZrxTi1-xO3 (PZT) on single crystal substrates. This paper presents the growth and characterization of epitaxial BST films on sapphire. Surface morphology, phase, and composition of the as -grown films were characterized. Planar gap capacitors were fabricated, and their capacitance, quality factor (Q) and tunability were investigated as a function of film thickness and DC bias. A 2:1 tunability was achieved for BST thin films under a DC bias of 10 V, and low-frequency Q can be as high as 100. Coplanar waveguide (CPW) structures were also designed and fabricated onto BST coated sapphire substrates. S-parameters of the CPW were tested using a vector network analyzer, and dielectric constant and loss tangent were then derived by comparing the measured data with electromagnetic (EM) simulation results. The dielectric constant was found to be in the range of 300-800, and a loss tangent of 0.05 at 40 GHz was achieved for a 300 nm thick BST film. The epitaxial BST films have been used to fabricate low-loss tunable filters and phase shifters with operation frequencies up to 40 GHz.

BST and Other Ferroelectric Thin Films by CCVD and Their Properties and Applications

Ferroelectric materials, such as BaTiO3 (BTO), Pb(Zr,Ti)O3 (PZT), SrBi2Ta2O9 (SBT), and LiNbO3 (LNO), are a category of materials with reorientable spontaneous polarization, a sub-category of pyroelectric materials. Because of their high dielectric constant, large polarization, and high breakdown voltage, ferroelectric materials have a wide range of applications, including infrared (IR) detectors for security systems and navigation, high density capacitors, high-density dynamic random access memory (DRAM), non-volatile ferroelectric random access memory (FRAM), and high frequency devices such as varactors, frequency multipliers, delay lines, filters, oscillators, resonators and tunable microwave devices (Tagantsev, et al., 2003; Cole, et al., 2000; Bao, et al., 2008; Gevorgian, et al., 2001; Dawber, et al., 2005). Among these ferroelectric materials, BTO based films with Sr dopant, namely Ba1-xSrxTiO3 (BST) are the most investigated one for various applications, especially for electric field response (or tunable) components and devices because of its high dielectric constant, reasonable dielectric loss, high tunability, and large breakdown strength. The Curie temperature Tc can be easily adjusted by controlling the Ba to Sr ratio. Studies have revealed that the electrical properties of BST films are influenced by the deposition and postdeposition process, stoichiometry, electrodes, microstructure, thickness, surface roughness, oxygen vacancies in films, and film homogeneity. The composition of the BST film such as the (Ba+Sr)/Ti ratio plays a critical role in determining its electrical properties (Y. H. Xu, 1991; Takeuchi, et al., 1998; Im, et al., 2000). Both the dielectric constant and loss increased with increasing (Ba+Sr)/Ti ratio. The lowest loss tangent (0.0047) and the best figure of merit were achieved with a (Ba+Sr)/Ti ratio of 0.73, but tunability was diminished (Im, et al., 2000). nGimat has also optimized the elemental ratios to achieve some of the highest figures of merit in tunable devices using the enhancements thus optimized. It has also been reported that dopants influence the electrical properties of BST thin films, but all dopants negatively affect at least one of the desired properties of the solicitation (Copel, et al., 1998 and Chung, et al., 2008). Copel and coworkers (Copel, et al., 1998) investigated the effect of Mn on electrical properties of BST thin films and found that leakage current was improved by introducing Mn. This was attributed to the acceptor Mn

Nanomaterials via NanoSpray Combustion Chemical Vapor Condensation, and Their Electronic Applications

NanoSpray Combustion™ processing is a versatile and cost-effective manufacturing method for a wide range of materials, including nanopowders and nanostructured thin films. The NanoSpray process is used in combustion chemical vapor condensation (nCCVC) mode for making metal oxide, metal phosphate, and select metal nanopowders while combustion chemical vapor deposition (nCCVD) is used to make thin films. In this chapter, we will use NanoSpray Combustion process as a benchmark and review its capabilities to that of other nanomaterials’ fabrication processes. Examples will mostly be of nanopowders synthesized using nCCVC. Applications of the nanomaterials in the electronic and energy sectors will be discussed.