Nonlinear Performance of BAW Filters Including BST Capacitors

This paper evaluates the nonlinear effects occurring in a bulk acoustic wave (BAW) filter which includes barium strontium titanate (BST) capacitors to cancel the electrostatic capacitance of the BAW resonators. To do that we consider the nonlinear effects on the BAW resonators by use of a nonlinear Mason model. This model accounts for the distributed nonlinearities inherent in the materials forming the resonator. The whole filter is then implemented by properly connecting the resonators in a balanced configuration. Additional BST capacitors are included in the filter topology. The nonlinear behavior of the BST capacitors is also accounted in the overall nonlinear assessment. The whole circuit is then used to evaluate its nonlinear behavior. It is found that the nonlinear contribution arising from the ferroelectric nature of the BST capacitors makes it impractical to fulfill the linearity requirements of commercial filters

Reconfigurable Bulk Acoustic Wave Resonators and Filters Employing Electric-field-induced Piezoelectricity and Negative Piezoelectricity for 5G

The ever-expanding wireless communications and sensing are influencing every aspect of human life. With the persistent demand for higher data capacity and recent advancements in wireless technologies, the design of current radio frequency front-end circuitry in communication devices calls for transformative changes. Frequency band proliferation is the biggest contributor to the added RF front-ends complexity in the design of future radios. To operate at various frequency bands, a complex combination of switches and filters is used in mobile devices, and the number of these frequency selective components in each device is expected to exceed 100 with the advent of 5th generation (5G) communication networks. Acoustic wave filters based on piezoelectric materials are the primary technologies employed in current communication systems, including mobile phones. Alternatively, the integration of multifunctional ferroelectric materials into reconfigurable frequency selective components promises reduced complexity, diminished size, and high performance for future radios, enabling them to support 5G wireless technologies and beyond. A promising reconfigurable bulk acoustic wave technology, employing electric-field-induced piezoelectricity and negative piezoelectricity in ferroelectrics, is presented in this dissertation. Successful implementation of ferroelectric filters would eliminate the need for external switcheplexers in the RF front-ends and reduce the number of required filters, leading to a significant reduction in size, cost, and complexity. Contributions of this work are categorized into three major parts. In the first part, an intrinsically switchable thin film bulk acoustic wave resonator (FBAR) based on ferroelectric BST with the highest figure of merit (i.e., Q_m×K_t^2) in the literature is presented. The BST FBARs are then employed to design intrinsically switchable filters with the lowest insertion loss to date. Such filters combine filtering and switching functionalities onto a single device, eliminating the need for external switches in RF front-ends. The second part of this work focuses on the development of frequency and bandwidth reconfigurable filters based on BST FBARs. The first switchless acoustic wave filter bank is presented in chapter 3, demonstrating the capability of BST FBARs in simplifying future agile radios. Next, a novel bandwidth reconfigurable filter based on BST FBARs is introduced in chapter 4, where the idea is experimentally validated with multiple design examples. Finally, through rigorous mathematical analysis and experimental validation, it has been demonstrated that a dynamic ‘non-uniform piezoelectric coefficient’ created within a composite structure made up of multi-layers of ferroelectrics allows the selective excitation of different mechanical Eigenmodes with a constant electromechanical coupling coefficient. Such technology overcomes the fundamental limitations associated with the electromechanical coupling coefficient of harmonic resonances in bulk acoustic wave resonators. To create ‘non-uniform piezoelectric coefficients’ in such structures, ferroelectrics’ electric-field-induced piezoelectricity and negative piezoelectricity has been exploited. This innovative technology provides a fundamentally new approach and a framework for synthesizing programmable frequency selective components, which leads to transformative advances in wireless systems’ front-end architecture. As part of the future direction, it is suggested that the multilayer structure presented in this section to be further studies as part of a new acoustic wave resonator design, which: (a) is capable of operation at a wide frequency range up to mm-wave frequencies designated for 5G (b). Such a structure has the potential to overcome the fundamental limitation of acoustic resonator’s ever-decreasing electromechanical coupling factors (Kt2) as their frequency of operation increases.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163011/1/milad_1.pd

Transferred Thin Film Lithium Niobate as Millimeter Wave Acoustic Filter Platforms

This paper reports the first high-performance acoustic filters toward millimeter wave (mmWave) bands using transferred single-crystal thin film lithium niobate (LiNbO3). By transferring LiNbO3 on the top of silicon (Si) and sapphire (Al2O3) substrates with an intermediate amorphous Si (aSi) bonding and sacrificial layer, we demonstrate compact acoustic filters with record-breaking performance beyond 20 GHz. In the LN-aSi-Al2O3 platform, the third-order ladder filter exhibits low insertion loss (IL) of 1.62 dB and 3-dB fractional bandwidth (FBW) of 19.8% at 22.1 GHz, while in the LN-aSi-Si platform, the filter shows low IL of 2.38 dB and FBW of 18.2% at 23.5 GHz. Material analysis validates the great crystalline quality of the stacks. The high-resolution x-ray diffraction (HRXRD) shows full width half maximum (FWHM) of 53 arcsec for Al2O3 and 206 arcsec for Si, both remarkably low compared to piezoelectric thin films of similar thickness. The reported results bring the state-of-the-art (SoA) of compact acoustic filters to much higher frequencies, and highlight transferred LiNbO3 as promising platforms for mmWave filters in future wireless front ends.Comment: 4 pages, 8 figures, accepted by IEEE MEMS 202

38.7 GHz Thin Film Lithium Niobate Acoustic Filter

In this work, a 38.7 GHz acoustic wave ladder filter exhibiting insertion loss (IL) of 5.63 dB and 3-dB fractional bandwidth (FBW) of 17.6% is demonstrated, pushing the frequency limits of thin-film piezoelectric acoustic filter technology. The filter achieves operating frequency up to 5G millimeter wave (mmWave) frequency range 2 (FR2) bands, by thinning thin-film LiNbO3 resonators to sub-50 nm thickness. The high electromechanical coupling (k2) and quality factor (Q) of first-order antisymmetric (A1) mode resonators in 128 Y-cut lithium niobate (LiNbO3) collectively enable the first acoustic filters at mmWave. The key design consideration of electromagnetic (EM) resonances in interdigitated transducers (IDT) is addressed and mitigated. These results indicate that thin-film piezoelectric resonators could be pushed to 5G FR2 bands. Further performance enhancement and frequency scaling calls for better resonator technologies and EM-acoustic filter co-design.Comment: 4 pages, 6 figures, accepted by IEEE MTT-S International Microwave Filter Workshop (IMFW) 202

Piezoelectric Materials in RF Applications

The development of several types of mobile objects requires new devices, such as high‐performance filters, microelectromechanical systems and other components. Piezoelectric materials are crucial to reach the expected performance of mobile objects because they exhibit high quality factors and sharp resonance and some of them are compatible with collective manufacturing technologies. We reviewed the main piezoelectric materials that can be used for radio frequency (RF) applications and herein report data on some devices. The modelling of piezoelectric plates and structures in the context of electronic circuits is presented. Among RF devices, filters are the most critical as the piezoelectric material must operate at RF frequencies. The main filter structures and characterisation methods, in accordance with such operating conditions as high frequencies and high power, are also discussed

Single-Chip Multiple-Frequency ALN MEMS Filters Based on Contour-Mode Piezoelectric Resonators

This paper reports experimental results on a new class of single-chip multiple-frequency (up to 236 MHz) filters that are based on low motional resistance contour-mode aluminum nitride piezoelectric micromechanical resonators. Rectangular plates and rings are made out of an aluminum nitride layer sandwiched between a bottom platinum electrode and a top aluminum electrode. For the first time, these devices have been electrically cascaded to yield high performance, low insertion loss (as low as 4 dB at 93MHz), and large rejection (27 dB at 236 MHz) micromechanical bandpass filters. This novel technology could revolutionize wireless communication systems by allowing cofabrication of multiple frequency filters on the same chip, potentially reducing form factors and manufacturing costs. In addition, these filters require terminations (1 kOmega termination is used at 236 MHz) that can be realized with on-chip inductors and capacitors, enabling their direct interface with standard 50-Omega systems