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Thermal performance and power handling of BAW filters in modern 5G capable handsets is an ever-increasing challenge. Higher integration densities – e. g. more communication bands and other functionality – and smaller form factor PCBs – e. g. slim phones with larger, long-lasting batteries – dictate the trend for smaller BAW filter modules [1]. The higher frequency bands included in 5G with operating frequencies above 3GHz intensify this challenge due to smaller resonators inherent to the BAW technology at these frequencies. As a result, the power density in Tx filters increases, which is unfavorable for power handling and thermal management. Thus, a better understanding of the heat generating mechanism in BAW resonators is of utmost importance to be able to create filter designs that are up to the task. In this paper we will focus on the impact of connection lead geometry on the electrode currents and their distribution in single and cascaded resonator stages. An overview of the mathematical background in means of network theory and the corresponding methodology is presented. To reveal the layout dependent impact on the current distribution, which can drive unwanted localization of joule heating, interferometric surface deflection measurement of BAW resonators on wafer were performed.

In this work we are presenting a method to calculate redistribution currents within the electrodes of a BAW resonator, that are caused by the acoustic deformation of the piezo-electric material. The surface deformation data of the resonators has been recorded with an interferometer capable of measuring the amplitude and phase of surface vibrations in the GHz-range. The local deflection is then fed into a discretized model of the resonator electrodes to calculate the redistribution currents and estimate the accompanying ohmic heating.

For BAW filter structures, the Temperature Coefficient of Frequency (TCF) specifies the frequency shift of the filter skirts over temperature. The lion's share of materials used in BAW filter stacks exhibit negative TCF characteristics, which means as the temperature rises, the filter passband shifts downwards in frequency. At the expense of performance, TCF compensation can be achieved through application of materials with positive TCF characteristics. Therefore, the extent of compensation has to be carefully increased only up to the point where it becomes sufficient for the given application. The intended TCF is usually verified through calculations based on S-parameter measurements on wafer at different temperatures. However, recent performance studies have shown a non-negligible TCF degradation of up to 5 ppm/K, which occurs after flip-chip module assembly. This paper describes the investigations that revealed the main cause for degraded TCF characteristics in a band 7 Tx filter application.

As more LTE bands are squeezed into the crowded global RF spectrum interference becomes a major concern. Some cases require profoundly steep transitions from passband to the tightly packed neighboring bands. The most demanding high frequency LTE bands may only be served with high-performance BAW resonators that have been temperature compensated to have essentially zero temperature drift. There is a variety of known challenges associated with the traditional temperature compensation techniques applied to BAW devices. This work will address those challenges and present a novel no-drift BAW-SMR using over-moded acoustic reflector layers. A solution for Band 30 utilizing the over-moded reflector will be presented.

We report a new type of nanomechanical resonator system based on one-dimensional chains of only 4 to 7 weakly coupled small molecules. Experimental characterization of the truly nanoscopic resonators is achieved by means of a novel radio-frequency scanning tunneling microscopy detection technique at cryogenic temperatures. Above 20 K we observe concerted oscillations of the individual molecules in chains, reminiscent of the first and second eigenmodes of a one-dimensional harmonic resonator. Radio-frequency scanning tunneling microscopy based frequency measurement reveals a characteristic length dependence of the oscillation frequency (between 51 and 127 MHz) in reasonable agreement with one-dimensional oscillator models. Our study demonstrates a new strategy for investigating and controlling the resonance properties of nanomechanical oscillators.

Stable hydrocarbon radicals are utilized as spin standards and prototype metal-free molecular magnets able to withstand ambient conditions. Our study presents experimental results obtained with submolecular resolution by scanning tunneling microscopy and spectroscopy from monomers and dimers of stable hydrocarbon π radicals adsorbed on the Au(111) surface at 7–50 K. We provide conclusive evidence of the preservation of the radical spin-1/2 state, aiming to establish α,γ-bisdiphenylene-β-phenylallyl (BDPA) on Au(111) as a novel Kondo system, where the impurity spin is localized in a metal-free π molecular orbital of a neutral radical state in gas phase preserved on a metal support.

Stable hydrocarbon radicals are able to withstand ambient conditions. Their combination with a supporting surface is a promising route toward novel functionalities or carbon-based magnetic systems. This will remain elusive until the interplay of radical–radical interactions and interface effects is fundamentally explored. We employ the tip of a low-temperature scanning tunneling microscope as a local probe in combination with density functional theory calculations to investigate with atomic precision the electronic and geometric effects of a weakly interacting metal support on an archetypal hydrocarbon radical model system, i.e., the exceptionally stable spin-1/2 radical α,γ-bisdiphenylene-β-phenylallyl (BDPA). Our study demonstrates the self-assembly of stable and regular one- and two-dimensional radical clusters on the Au(111) surface. Different types of geometric configurations are found to result from the interplay between the highly anisotropic radical–radical interactions and interface effects. We investigate the interaction mechanisms underlying the self-assembly processes and utilize the different configurations as a geometric design parameter to demonstrate energy shifts of up to 0.6 eV of the radicals’ frontier molecular orbitals responsible for their electronic, magnetic, and chemical properties.