Background

Mobile communications from military to commercial applications need to maximize the achievable spectral efficiency to operate simultaneously using the same carrier channel. To this end, electronically programmable self-interference (SI) cancellation networks, including a network of delay lines, are used to suppress the performance degradations due to leakage of the transmitted power into the receiver chain. Current analog delay lines (ADL), which are based on surface acoustic wave (SAW) or lamb wave (LW), are not able to achieve a large enough fractional bandwidth (BW) and a low enough insertion-loss (IL) to be used in the SI-cancellation networks. In recent years, to achieve a wideband and low-loss frequency response, bulk-acoustic-wave filters have been used, which rely on high electromechanical coupling ecoefficiency, attained by piezoelectric materials such as aluminum nitride in film-bulk-acoustic-resonators (FBARs). As the resonance frequency of FBARs is set by their thickness, the integration of multiple FBARs, to form filters, can only be attained through the adoption of frequency tuning fabrication steps, such as mass loading or trimming. However, as the ability to reliably control these steps significantly decays for thinner (or higher frequency) FBARs, manufacturing FBAR-based filters is becoming more and more challenging. Consequently, there is a quest for new acoustic resonant components, simultaneously exhibiting high electromechanical coupling ecoefficiency and a lithographic frequency tunability.

Technology Overview

Researchers at Northeastern University have designed the first ADL relying on the unique acoustic dispersion exhibited by two dimensional resonant rods-based acoustic transducers. This ADL is based on the high piezoelectric coefficients of highly-doped piezoelectric based films, which surpass the fundamental limits in BW and IL of conventional SAW and LW counterparts. The presented ADL relies on wideband input/output terminals separated by a corrugated structure forming an acoustic metamaterial. The corrugated structure creates passbands with BWs exceeding those achievable in conventional counterparts without requiring expensive materials not compatible with conventional CMOS processes, like LiNbO3. Also, this ADL does not need any patterning of the bottom metal plate underneath the required piezoelectric layer of any kind, and this is fundamental as patterning the bottom metal plate is needed for most of the counterparts, even though it significantly degrades the quality of the piezoelectric film. Furthermore, it achieves a group velocity that is exceptionally slow (nearly 1000m/s). The ability to achieve such a slow speed is particularly relevant in applied physics field where classical or quantum wave-matter interaction is of great interest. This unique ADL is an ideal candidate to form the delay lines needed by any self-interference cancellation in full-duplex RF systems.

Benefits

High BW and low IL
No need to patterning the bottom metal plate
Achieving an exceptionally slow group velocity

Applications

Synthesizing any passive RF components
Delay element in self-interference cancellation networks
Synthesizing filtering components with exceptional BW

Opportunity

Research collaboration
Licensing
Partnership
Developmental partner

A Two-Dimensional-Resonant-Rods Delay Line with Record-High Bandwidths and Low Loss

Seeking