Search for: All records

Thin film bulk acoustic wave resonators (FBARs) leveraging sputtered aluminum nitride (AlN) and scandium aluminum nitride (ScAlN) films, are a leading commercial solution for compact radio frequency (RF) filters in mobile devices. However, as 5G/6G bands extend beyond 6 GHz, achieving the required thinner piezoelectric film thicknesses below 500 nm presents a significant challenge to high-quality sputtering, resulting in a moderate quality factor (Q). Additionally, AlN/ScAlN platforms are limited by moderate electromechanical coupling (k2), restricting bandwidth. More recently, ultra-thin transferred single-crystal piezoelectric lithium niobate (LN) has enabled lateral field excited resonators (XBAR) at 10-30 GHz. While these devices boast a high Q and k2, they face challenges with low capacitance density, large footprint, and significant electromagnetic (EM) effects. On the other hand, thickness-field excited LN FBARs face challenges with bottom electrode integration. In this work, we implement a transferred LN on aluminum FBAR platform on sapphire wafers with an intermediate amorphous silicon layer without the need for a patterned bottom electrode. The resonators show first order symmetric mode (S1) at 10.5 GHz with a 3-dB series resonance Q of 38 and k2 of 14.1%, alongside third order symmetric mode (S3) at 27 GHz with a 3-dB series resonance Q of 22 and a high k2 of 11.3%. Further analysis shows that higher Q could be achieved by adjusting the low-loss piezoelectric to lossy metal volume ratio. 

In this work, an Aluminum Scandium Nitride (AlScN) on Diamond Sezawa mode surface acoustic wave (SAW) platform for RF filtering at Ku-band (12-18 GHz) is demonstrated. Thanks to the high acoustic velocity and low-loss diamond substrate, the prototype resonator at 12.9 GHz achieves a high phase velocity (𝑣𝑣p) of 8671 m/s, a maximum Bode-Q of 408, and coupling coefficient (𝑘𝑘eff 2 )of 2.1%, outperforming high-velocity substrates such as SiC and sapphire by more than 20% in velocity. Resonators spanning 8 to 18 GHz are presented. The platform’s high power handling above 12.5 dBm is also experimentally validated. 

This letter presents a versatile design method for achieving precise frequency and bandwidth control of compact acoustic filters monolithically at millimeter wave (mmWave) in transferred thin-film lithium niobate (LiNbO3). Prototypes are implemented with lateral field excited first-order antisymmetric (A1) mode bulk acoustic resonators (XBARs). The design leverages the in-plane anisotropy of the e15 piezoelectric coefficient in 128° Y-cut LiNbO3, enabling monolithic control of electromechanical coupling ( k2 ) by simply rotating the resonator layout. This allows for filters with customizable fractional bandwidths (FBWs). Additionally, fine-tuning of the center frequency ( fc ) is achieved through selective trimming of the film for series and shunt resonators, enabling a single design to be scaled across frequencies with enhanced fabrication tolerance. To validate the approach, we designed and fabricated a filter centered at 18.6GHz, achieving a low insertion loss (IL) of 1.84 dB, and a precise designed FBW of 9.5%. This platform shows a significant promise for enabling a monolithic filter bank with precise band selection, paving the way for the next generation of mmWave acoustic filters. 

Abstract Implementing microelectromechanical system (MEMS) resonators calls for detailed microscopic understanding of the devices, such as energy dissipation channels, spurious modes, and imperfections from microfabrication. Here, we report the nanoscale imaging of a freestanding super-high-frequency (3 – 30 GHz) lateral overtone bulk acoustic resonator with unprecedented spatial resolution and displacement sensitivity. Using transmission-mode microwave impedance microscopy, we have visualized mode profiles of individual overtones and analyzed higher-order transverse spurious modes and anchor loss. The integrated TMIM signals are in good agreement with the stored mechanical energy in the resonator. Quantitative analysis with finite-element modeling shows that the noise floor is equivalent to an in-plane displacement of 10 fm/√Hz at room temperatures, which can be further improved under cryogenic environments. Our work contributes to the design and characterization of MEMS resonators with better performance for telecommunication, sensing, and quantum information science applications. 

This paper presents ISLA, a system that enables low power IoT nodes to self-localize using ambient 5G signals without any coordination with the base stations. ISLA operates by simply overhearing transmitted 5G packets and leverages the large bandwidth used in 5G to compute high-resolution time of flight of the signals. Capturing large 5G bandwidth consumes a lot of power. To address this, ISLA leverages recent advances in MEMS acoustic resonators to design a RF filter that can stretch the effective localization bandwidth to 100 MHz while using 6.25 MHz receivers, improving ranging resolution by 16x. We implement and evaluate ISLA in three large outdoors testbeds and show high localization accuracy that is comparable with having the full 100 MHz bandwidth.