Guiding, Localizing and IMaging confined GHz acoustic waves in GaN Elastic waveguides and Resonators for monolithically integrated RF front-ends

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As smartphones become the dominant mechanism for information transfer and processing in modern society, our expectations on what we hope to achieve with them also increases proportionally. In particular, the smart phone has become our portal to the internet, replaced our television, radio and music devices, and also serves as our credit card and personal guide (GPS). We also expect our mobile phones to work seamlessly as we travel across international borders. All of this is enabled by the separation of the various functions into different wireless (RF) frequency bands, and the development of sophisticated analog and digital circuitry, that enables the phone to simultaneously carry out these communications. As we move towards 5G and other technologies that increase the data throughput available, these channels must increase. While on the digital signal processing side, the steady advance of Moore's law and microelectronic integration has enabled silicon technology to keep up with the demand, this is not the case for the RF front-end circuitry, which is primarily analog. The RF front-end circuit, receives the signal from the antenna and separates it into different channels (based on RF filters), amplifies it with a low noise amplifier (LNA) and then hands it over to the DSP for baseband signal processing. Currently, RF filters and LNAs are primarily discrete devices that are co-packaged together. While this hybrid approach has certain advantages (mainly the choice of piezoelectric materials for the filter), as demand for filters continuously rises, it is known that a co-packaging approach will not scale. The main reason is that the available smartphone footprint (in terms of chip area) for the RF front-end has remained roughly the same across generations, while the filtering demand has continuously increased. As the microelectronics industry has repeatedly taught us, monolithic integration is the only long-term solution to address these problems. In this project, we will demonstrate that gallium nitride (GaN) is the ideal platform for achieving monolithic integration by exploiting a key advantage that GaN provides over traditional solutions: acoustic waveguiding. GaN allows us to guide high-frequency sound on the surface of chip with low acoustic attenuation. By routing sound in nanoscale waveguides and localising it in micron-scale resonators, one can re-design RF system components from the ground up realizing a massive reduction in component footprint, which is key to enabling monolithic integration. By applying ideas from integrated photonics to high-frequency acoustics, we hope to realize for RF systems the same benefits (in terms of size, weight and performance) that silicon photonics has achieved for optical telecommunication systems. We will show that high quality RF passive devices (in particular, piezoelectric resonators and filters) can be built on the same GaN substrate as the active transistor devices. We will implement a process flow and design the associated process development kit to implement these ideas in commercial GaN RF foundries (for ex: the Newport wafer fab) in collaboration with our project partners.