Intrinsically Switchable Ferroelectric Filter Banks for Frequency Agile and Reconfigurable Radios

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The next generation of wireless communication systems should be able to intelligently adapt to the environment and reconfigure themselves to exploit available communication channels while maintaining connectivity, quality of service, and a long battery life. Such systems must be able to rapidly switch to different modulation schemes and carrier frequencies to accommodate the required bandwidth, minimize power consumption and interference. The performance and functionality of integrated circuits used in radios has steadily improved mostly as a result of device scaling. In contrast, passive devices such as frequency selective components (like filters) and radiating elements do not follow advances predicted by Moore's law for active devices. Currently, filters, switches and antennas contribute to a large portion of the communications systems size, complexity and cost. The goal of the proposed project is to develop high-performance and compact voltage controlled acoustic resonators and filters operating at radio frequency (RF) and microwave frequencies for the next generation of communications systems. Developing an understanding of acoustic wave generation in electrostrictive thin film ferroelectrics will impact other areas such as acousto-optics and sensors. An important component of this proposal is the research-based education of both undergraduate and graduate students. The research is of particular value for students due to its multidisciplinary nature, involving thin film materials deposition and characterization, RF filter design, microelectromechanical device fabrication, acoustic resonator design, fabrication and characterization. The objective of the proposed project is to develop voltage-controlled bulk acoustic wave resonator (FBAR) filter banks by employing the electrostrictive property of thin-film barium strontium titanate (BST). Ferroelectric BST is a multifunctional material exhibiting many desirable characteristics that can be exploited for the design of intrinsically switched resonators and filters. The application of a DC voltage can be used to change the polarization in ferroelectric material, thereby changing the strength of electrostriction. This effect is unique, and offers a means of controlling the generation of acoustic waves through application of a DC bias. The research approach for the design of novel ferroelectric BST FBAR filter banks will combine thin-film material growth with filter design based on specific properties that are unique to thin-film ferroelectrics. In conjunction with circuit-level design, structural multi-physics simulations will be conducted to optimize the device structure for best performance. The design for switchable RF resonators will utilize the high quality factor, high effective electromechanical coupling coefficient and bias-voltage-dependent piezoelectric response of optimally designed thin-film BST FBARs. The design approach will lead to the development of high-performance switchable resonators, filters, and ultimately filter banks at radio frequencies.