Aluminum Nitride Combined Overtone Resonators for the mmWave Spectrum

INV-20023

 

The development of wireless communication systems has been steadily growing, and conventional sub-6 GHz frequency bands are too congested to meet the high data rate requirements of several emerging technologies like a connected vehicle. This game-changing technology requires high-bandwidth, low-latency and high-reliability for short-range wireless links to communicate with compatible systems in vehicles and infrastructures and devices available to pedestrians. The 5G cellular network can be considered the key enabler for such a ubiquitous and pervasive mobile internet connectivity. In particular, the use of the millimeter-wave (mmWave) spectrum represents the major leap forward in the 5G network as it enables improvements in data speed, capacity, quality and latency that are unimaginable in 3G and 4G networks.

These 5G 24 GHz bands are closely located to the 23.8 GHz band which is used for sensitive meteorological and oceanographic measurements. Therefore, the adoption of these 5G bands in communication systems require the use of pass-band filters with a relatively small fractional bandwidth of ~0.42% (i.e.100 MHz) and a high _Q_ > 500 (Quality factor) to achieve the steep roll-off and the large out-of-band rejection needed to enable coexistence with the adjacent band.

 

In this technology, Northeastern University researchers designed a novel solution in which a resonator includes a suspended piezoelectric plate and interdigitated (IDT) electrode(s). The interdigitated electrode includes a plurality of conductive strips disposed over the top surface or the top and the bottom surfaces of the piezoelectric plate. 

A two-dimensional mode of mechanical vibration is excited in a cross-sectional plane of the piezoelectric plate in response to an alternating voltage applied through the interdigitated electrode. 

The two-dimensional mode of mechanical vibration is a combined overtone mode of the 2nd and 3rd order asymmetrical Lamb-wave overtones. 

This combined overtone mode is excited in the structure when the thickness of the piezoelectric layer is approximately equal to the pitch of the employed IDT.

 

- It is a smaller size (500X) than electromagnetic filters

- Significantly improved quality factor and selectivity than any other filters such as electromagnetic filters and aluminum nitride Bulk Acoustic Wave (BAW) resonators, lithium niobate resonators in the same frequency

- Reduced fabrication complexity

- Less sensitive to fabrication variations than BAW resonators

 

- Development of low-cost, low-loss, monolithic integrated miniaturized micro-acoustic filters for 5G cm-mmWave spectrum 6-40 GHz frequency range

- Development of a truly ubiquitous and pervasive Internet-of-Things enabled by high miniaturization and integrated 5G systems

- Development of high-quality factor oscillators for ultra-low jitter clocks for high-speed networks in a 6-40 GHz frequency range

 

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