Cross-sectional Lame Mode Resonators Research Articles

6-20 GHz 30% ScAlN Lateral Field-Excited Cross-Sectional Lamé Mode Resonators for Future Mobile RF Front Ends.

This article reports on 30% scandium-doped AlN (ScAlN) lateral field-excited (LFE) cross-sectional Lame' mode resonators (CLMRs) with unprecedented performance in the 6-20 GHz range. By combining high-crystallinity 30% ScAlN piezoelectric thin films, a lithographic tunability of the resonance frequency, and a simple three-mask post-CMOS compatible fabrication process, we propose a technology platform that can enable the mass production of low-loss, wideband, and compact microacoustic filtering devices spanning a wide spectrum portion on the same chip for the next-generation radio frequency front ends (RFFEs) of handsets. This article demonstrates a successful scaling of the microacoustic technology well beyond the sub-6-GHz fifth-generation (5G) band, as well as the outstanding capabilities of high-crystallinity 30% ScAlN piezoelectric layers in delivering high-quality factor ( Q ) and high-electromechanical coupling ( kt2 ) resonators, notably exceeding the state of the art in terms of relevant figures of merit (FOMs). Furthermore, we experimentally investigate the impact of geometrical parameters, such as tethering configuration and width-over-length ratio on the devices' 3-dB quality factor ( [Formula: see text]), power linearity (PL), and temperature coefficient of frequency (TCF). By adopting a statistical approach for data analysis, we determine the optimal geometry to maximize the Q value. Moreover, we experimentally demonstrate that a fully tethered device's configuration ensures superior PL, lower TCF, and higher device yield and select that as the best design tradeoff between all the variables under consideration. Finally, we discuss a further scaling of LFE CLMRs, both in terms of higher doping levels in the piezoelectric layer, in order to enhance the performance of microacoustic filters, and in terms of higher operation frequencies, in order to reach and cover the mm-wave spectrum.

Aluminum Nitride Cross-Sectional Lamé Mode Resonators

This paper demonstrates a new class of AlN-based piezoelectric resonators for operation in the microwave frequency range. These novel devices are identified as cross-sectional-Lame-mode resonators (CLMRs) as they rely on the piezoelectric transduction of a Lame mode, in the cross section of an AlN plate. Such a 2-D mechanical mode of vibration, characterized by motion along both the lateral and the thickness directions, is actuated and sensed piezoelectrically through the coherent combination of the $\text{e}_{31 }$ and $\text{e}_{33}$ piezoelectric coefficients of AlN. This special feature enables the implementation of CLMRs with high values of electromechanical coupling coefficient. In particular, we experimentally demonstrated $k_{t}^{2}$ values in excess of 4.6% and 2.5% in CLMRs using, respectively, two or one metallic interdigitated metallic electrodes, and operating around 1 and 2.8 GHz. Furthermore, despite the dependence of the cross-sectional Lame mode on both the thickness and the width of the AlN plate, lithographic tunability of the resonance frequency, by changing only the in-plane dimensions of the device, can be achieved without a substantial degradation of $k_{t}^{2}$ . The capability of achieving high $k_{t}^{2}$ and multiple operating frequencies on the same chip, without additional fabrication costs (lithographic tunability of the resonance frequency), makes this technology one of the best candidates for the implementation of multifrequency and low insertion loss filter banks for reconfigurable radio-frequency front ends. [2015-0244]