A report has been released on a new RF acoustic resonant technology that enables the production of integrated silicon chips of low-loss and wideband miniaturized filters for communication systems (cellphones or other wireless devices). The same device can be exploited to attain unique sensors within the Internet-of-Things (IoT). Differently from previously developed technologies, the reported tech uses the unique acoustic properties of profiled piezoelectric layers to achieve much better performance in terms of electromechanical coupling coefficients than that of other devices that use a plate. For this reason, these devices can reach performance levels that are greatly enhanced with respect to the existing counterparts that are used nowadays in modern integrated radio-frequency front-ends.
Technology Overview
Northeastern University researchers have experimentally demonstrated the operation of the first Two-Dimensional-Resonant-Rods resonator (2DRRs). 2DRRs are formed by a profiled AlN‑layer that is sandwiched between one top metal grating and a grounded bottom metal plate. They exploit the excitation of a set of S1 Lamb wave modes in locally resonant AlN-rods. These rods are attained by partially etching the AlN-portions included between adjacent metal strips in the grating. The etching depth is acoustically engineered in order to form steep trenches that exhibit a much higher cut-off frequency than frequencies for the S1‑mode. This feature keeps the vibration of 2DRRs confined in the rods and renders the resonance frequency of 2DRR lithographically controllable through the rod-width (We). In addition, the trenches minimize the lateral coupling between adjacent rods and allow them to suppress any fringing component of the electric field due to the use of the un-patterned bottom metal plate. Also, by adopting un-patterned bottom metal plates, AlN‑films with optimal crystalline orientations can be attained, even when thin films are needed for high-frequency operation.
- The reported devices allow us to simultaneously achieve a higher electromechanical coupling coefficient (kt2) exceeding what currently possible through the other available technologies. This feature permits to build filters with wider fractional bandwidth and enables oscillators capable of dissipating a lower amount of energy to operate.
- The reported devices are the first lithographically defined Aluminum Nitride (AlN) acoustic technologies that have the ability to achieve high kt2 (>7%) while not requiring any patterned bottom-metal structure underneath the AlN-layer. For this reason, they do not suffer from any performance degradation.
- The reported devices use lithographic resolutions that can be much more relaxed than those required by previously developed AlN lithographically defined technologies. This unique feature enables their fabrication through standard lithographic methods, thus opening them to the real change of large-scale production.
Can be used to build low-loss and wideband RF filters for integrated wireless front-ends. 
- The reported devices show a path towards the generation of low-power high-frequency oscillators for timing applications.
- Can open an exciting path towards new sensors directly relying on the topology of the structure to reach higher sensitivity and lower power consumption.
- Allows the construction of other RF passive components, such as hybrid couplers, piezoelectric transformers, and many others.
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Patent Information:
For Information, Contact:
Mark Saulich
Associate Director of Commercialization
Northeastern University
Cristian Cassella
Xuanyi Zhao
RF (Radio Frequency)