Abstract
We present the first group of GHz broadband SH0 mode acoustic delay lines (ADLs). The implemented ADLs adopt unidirectional transducer designs in a suspended X-cut lithium niobate thin film. The design space of the SH0 mode ADLs at GHz is first theoretically investigated, showing that the large coupling and sufficient spectral clearance to adjacent modes collectively enable the broadband performance of SH0 delay lines. The fabricated devices show 3-dB fractional bandwidth ranging from 4% to 34.3% insertion loss between 3.4 and 11.3 dB. Multiple delay lines have been demonstrated with center frequencies from 0.7 to 1.2 GHz, showing great frequency scalability. The propagation characteristics of SH0 in lithium niobate thin film are experimentally extracted. The demonstrated ADLs can potentially facilitate broadband signal processing applications.
Highlights
T HE emerging enhanced mobile broadband applications for fifth-generation (5G) communication are calling for unprecedented signal processing capabilities [1], [2]
The enhanced performance is collectively enabled by large k2 [35]–[37], the notable reflectivity in the embedded reflectors [31], [34], and the low propagation loss (PL) in single crystal quality (LiNbO3) thin films [32], [34]
The reflected wave propagating toward the forward direction (FWD) constructively interferes with the wave launched toward FWD, while the reflected wave propagating toward the backward direction (BWD) destructively interferes with the wave launched toward BWD [28], [34]
Summary
T HE emerging enhanced mobile broadband (eMBB) applications for fifth-generation (5G) communication are calling for unprecedented signal processing capabilities [1], [2]. Targeting at a thousand-fold increase in the mobile data volume per unit area [3], novel broadband signal processing functions at radio frequency (RF) are highly sought-after. In which RF signals are converted into and processed in the acoustic domain before the conversion back to the electromagnetic (EM) domain, are great candidates for providing such low-loss wideband signal processing capabilities for their three key advantages. Acoustic devices are miniature because of their significantly shorter wavelength (λ) compared to the EM counterparts [4], suitable for handheld and mobile applications. Acoustic devices do not compete with the powerhungry analog-to-digital converters (ADCs) and digital signal
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