High Performance Nano-constituent Buffer Layer Thin Films to Enable Low Cost Integrated On-the-move Communications Systems

Successful integration of paraelectric Ba1-xSrxTiO3 (BST) based thin films with affordable Si substrates has a potential significant commercial impact as the demand for high-frequency tunable devices intensifies. Utilizing a coplanar device design we have successfully designed, fabricated, characterized, and optimized a high performance Ta2O5 thin film passive buffer layer on Si substrates, which will allow the integration of BST films with large area affordable Si substrates. This passive buffer layer thin film was fabricated via the industry standard metalorganic solution decomposition technique. The anneal optimized Ta2O5 based thin film possessed excellent material properties. Specifically, these material properties include an enhanced dielectric constant (εr =45.6), low dielectric loss (tan δ=0.006), low leakage current or high film resistivity (ρ=10 Ω-cm at E=1 MV/cm), excellent temperature stability (temperature coefficient of capacitance of 52 ppm/C), and excellent bias stability of capacitance (~1.41% at 1 MV/cm). Additionally, the permittivity and dissipation factor exhibited minimal dielectric dispersion with frequency. The dielectric passive buffer layer film was typified by a uniform dense microstructure with minimal defects, and a smooth, nano-scale fine grain, crack/pinhole free surface morphology. This work also demonstrated that the coefficient of thermal expansion (CTE) mismatch between the Ta2O5 buffer and BST active thin films in the coplanar device design serves to enhance the dielectric tunability of the device. The development of this passive buffer layer thin film materials technology will enable the direct integration of paraelectric active thin films (BST) with silicon substrates. The impact of this materials technology is paramount, as this phase shifter materials technology design will promote broad scale implementation of affordable On The Move (OTM) phased array antenna systems across a variety of DoD platforms.