Guiding, Localizing and IMaging confined GHz acoustic waves in GaN Elastic waveguides and Resonators for monolithically integrated RF front-ends
Lead Research Organisation:
University of Bristol
Department Name: Electrical and Electronic Engineering
Abstract
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.
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.
Planned Impact
This project fundamentally relies on recognising and exploiting the universality of wave phenomena. By applying methods developed for (silicon) integrated photonics to acoustic waves which share the same wavelength, we can vastly reduce the on-chip footprint of high-frequency acoustic wave resonators and filters and achieve monolithically integrated RF front-ends. As such, we believe the ideas developed as part of this work will serve to underpin future radio frequency (RF) technology and will have a wide impact on societal communications and daily life.
Impact on economy: We foresee our work will impact the UK economy in two complementary ways. In the near term, we will add the novel passive acoustic wave devices developed in this work to the gallium nitride (GaN) RF foundry process development kit (PDK). GaN RF foundry processes are slowly maturing worldwide. With the UK's extensive investments in GaN, including a GaN RF foundry process being developed at the Newport wafer fab in Cardiff, this project provides the necessary toolkit for the UK GaN foundries to differentiate themselves from the competition. This work also builds on the growing industry trend towards 'more than Moore' type systems that are complementary to traditional silicon microelectronics. More specifically, the work will exploit the multifunctional capabilities of the versatile gallium nitride (GaN) platform by showing that its electronic and acoustic properties can be simultaneously harnessed to produce devices with unmatched performance. In the longer term, we will work with our project partners (TI, Qorvo and IQE) to bring such highly integrated GaN chipsets with their inherent size, weight and performance (SWaP) benefits to their future product roadmap.
Impact on knowledge: One of the key pillars of this project is the development of novel visualization tools (in particular the gated Raman microscope) that allow us to map the acoustic energy density at the nanoscale with high spatial and temporal resolution. The development of novel metrological tools has always been a key precursor to scientific progress and we believe the acoustic microscopes developed during this project will open up new avenues of scientific understanding and enquiry beyond the specific project for which they are being developed. More broadly, this project aims to illustrate the power of engineering integrated platforms in materials whose multifunctional properties (in this case electrical and mechanical) can be simultaneously exploited. We believe these paradigms of thinking will broadly influence the academic community, both in the UK and worldwide.
Impact on people: This project combines ideas from integrated photonics, ultrasonics, piezoelectric devices, nanofabrication and RF and microwave device engineering. This interdisciplinary view will greatly benefit the three research associates, as they use this project as a stepping-stone for their future academic careers. We also believe this project will encourage UK academics to take a fresh look at RF systems from the device perspective. While the UK was the world leader in RF device engineering in the 1980s, over time, most of the RF innovation has been occurring at the systems and architecture level with fundamental device innovation being relatively neglected. Going back to the fundamentals of engineering RF devices and rethinking RF systems from the ground up, as this project aims to do, will be a shot in the arm for UK engineering.
Impact on wider society: This project, at its core, is built on the idea of universality of wave phenomena and the similarity of effects that can be observed and exploited across seemingly different experimental engineering platforms. Recognising this similarity will serve the engineers of the future (the high school students and undergraduates of today) in good stead.
Impact on economy: We foresee our work will impact the UK economy in two complementary ways. In the near term, we will add the novel passive acoustic wave devices developed in this work to the gallium nitride (GaN) RF foundry process development kit (PDK). GaN RF foundry processes are slowly maturing worldwide. With the UK's extensive investments in GaN, including a GaN RF foundry process being developed at the Newport wafer fab in Cardiff, this project provides the necessary toolkit for the UK GaN foundries to differentiate themselves from the competition. This work also builds on the growing industry trend towards 'more than Moore' type systems that are complementary to traditional silicon microelectronics. More specifically, the work will exploit the multifunctional capabilities of the versatile gallium nitride (GaN) platform by showing that its electronic and acoustic properties can be simultaneously harnessed to produce devices with unmatched performance. In the longer term, we will work with our project partners (TI, Qorvo and IQE) to bring such highly integrated GaN chipsets with their inherent size, weight and performance (SWaP) benefits to their future product roadmap.
Impact on knowledge: One of the key pillars of this project is the development of novel visualization tools (in particular the gated Raman microscope) that allow us to map the acoustic energy density at the nanoscale with high spatial and temporal resolution. The development of novel metrological tools has always been a key precursor to scientific progress and we believe the acoustic microscopes developed during this project will open up new avenues of scientific understanding and enquiry beyond the specific project for which they are being developed. More broadly, this project aims to illustrate the power of engineering integrated platforms in materials whose multifunctional properties (in this case electrical and mechanical) can be simultaneously exploited. We believe these paradigms of thinking will broadly influence the academic community, both in the UK and worldwide.
Impact on people: This project combines ideas from integrated photonics, ultrasonics, piezoelectric devices, nanofabrication and RF and microwave device engineering. This interdisciplinary view will greatly benefit the three research associates, as they use this project as a stepping-stone for their future academic careers. We also believe this project will encourage UK academics to take a fresh look at RF systems from the device perspective. While the UK was the world leader in RF device engineering in the 1980s, over time, most of the RF innovation has been occurring at the systems and architecture level with fundamental device innovation being relatively neglected. Going back to the fundamentals of engineering RF devices and rethinking RF systems from the ground up, as this project aims to do, will be a shot in the arm for UK engineering.
Impact on wider society: This project, at its core, is built on the idea of universality of wave phenomena and the similarity of effects that can be observed and exploited across seemingly different experimental engineering platforms. Recognising this similarity will serve the engineers of the future (the high school students and undergraduates of today) in good stead.
Publications
Bicer M
(2024)
Low-Loss GHz Frequency Phononic Integrated Circuits in Gallium Nitride for Compact Radio Frequency Acoustic Wave Devices.
in IEEE transactions on ultrasonics, ferroelectrics, and frequency control
Bicer M
(2022)
Gallium nitride phononic integrated circuits platform for GHz frequency acoustic wave devices
in Applied Physics Letters
Description | The main goal of our work was to demonstrate that confining GHz frequency sound waves in wavelength scale waveguides and resonators can open up new avenues for re-thinking RF devices from the ground-up. We have already demonstrated the lowest loss acoustic devices in gallium nitride using whispering gallery modes in microring resonators. In addition, we have shown that spiral waveguides can be used to generate >2 us of on-chip RF signal delay with very compact footprints. |
Exploitation Route | The award is still active, we will update in the next submission. |
Sectors | Digital/Communication/Information Technologies (including Software) Electronics Energy Manufacturing including Industrial Biotechology |
URL | https://ieeexplore.ieee.org/abstract/document/10315160 |
Title | Dataset for Gallium nitride phononic integrated circuits platform for GHz frequency acoustic wave devices |
Description | The datasets underlying the figures in the paper: Bicer et al., "Gallium nitride phononic integrated circuits platform for GHz frequency acoustic wave devices", published in Applied Physics Letters 2022 |
Type Of Material | Database/Collection of data |
Year Produced | 2022 |
Provided To Others? | Yes |
URL | https://data.bris.ac.uk/data/dataset/1lvx706n49chz2g8id14l2oe7c/ |
Description | Article in Compound Semiconductor Magazine on phononic integrated circuits |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Industry/Business |
Results and Impact | We were contacted by the editor of compound semiconductor magazine to write a popular article based on our recent Applied Physics Letters paper (Bicer et al., APL 2023). The audience for the magazine is mainly industry professionals and the hope was to get them excited about the novel research being carried out in Bristol. The article went online end of February. Too early to gauge the impact, but we hope some new industry-academia collaborations develop as a result of this work. |
Year(s) Of Engagement Activity | 2023 |
URL | https://compoundsemiconductor.net/article/116250/Building_phononic_integrated_circuits_with_GaN |
Description | Cardiff University Physics and Astronomy colloquium |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Other audiences |
Results and Impact | I gave a seminar at Cardiff University's Physics and Astronomy colloquium. It was attended by academics from both Physics and EE. It helped strengthen our collaboration with Prof. Oliver Williams' group, which continues through follow on funding from EPSRC standard mode grant NEXTSAW (awarded at the Jan. 2023 ICT panel). |
Year(s) Of Engagement Activity | 2022 |
Description | Conference talk at European Microwave Conference 2023 Yutian Zhang |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | PhD student Yutian Zhang and co-I Martin Cryan presented their efforts towards integrating SAW filters with GaN HEMT amplifiers at the European Microwave Conference (EuMC). The talk was well-received overall and discussions with Win-semiconductor led to the first tapeout of GaN HEMT dies with post-processed SAW filters (currently underway, dies received in Feb.2024). |
Year(s) Of Engagement Activity | 2023 |
URL | https://ieeexplore.ieee.org/abstract/document/10290286 |
Description | Conference talk at IUS2023 - Jacob Brown |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | Student Jacob Brown gave a talk on his work on developing a new kind of acoustic microscope using photoelectric attenuation |
Year(s) Of Engagement Activity | 2023 |
URL | https://ieeexplore.ieee.org/abstract/document/10308317 |
Description | DCMS / Spectrum Policy Forum - Workshop may 26 |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | The PI (Krishna Balram) gave an invited talk at the DCMS / Spectrum Policy forum workshop on novel approaches to RF front-ends using phononic integrated circuits. This was a 6G workshop aimed at new enabling technologies, with an eventual white paper delivered on what technologies can potentially enable the next generation wireless standards. We got some good feedback on our talk from the industry attendees with queries about power handling etc., which we had not fully considered before. |
Year(s) Of Engagement Activity | 2021 |
URL | https://www.techuk.org/resource/slides-6g-technology-enablers-for-spectrum-energy-efficient-wireless... |
Description | Invited talk at International Ultrasonics Symposium -2023 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | The PI gave an invited talk at IUS-2023 talking about phononic integrated circuits and their applications to quantum transducers, spin detection and microwave devices. The prestige of the IUS symposium serves to recognize the ground-breaking work being carried out in our group. Given it was an invited talk and heavily advertised (for instance during the plenary), it was extremely well-attended by folks from both academia and industry. The PI got very valuable feedback on his work from industry and also got some new directions in which this work could be extended. |
Year(s) Of Engagement Activity | 2023 |
URL | https://2023.ieee-ius.org/ |
Description | Lorentz Centre workshop |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Postgraduate students |
Results and Impact | Participated in the Lorentz Centre workshop on quantum optics meets quantum acoustics. |
Year(s) Of Engagement Activity | 2022 |
URL | https://www.lorentzcenter.nl/quantum-optics-meets-acoustics.html |
Description | NIST colloquium |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | I gave a seminar at the NIST Gaithersburg Physical Measurement Laboratory colloquium. The seminar was broadcast to the NIST Boulder campus as well. This visit led to some future collaborations with scientists at both places (Jason Gorman, Veronika Szalai and Kevin Silverman) |
Year(s) Of Engagement Activity | 2022 |
Description | Quantum Engineering CDT open day talk |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | I gave a research talk as part of the QE-CDT visit day at Bristol introducing prospective PhD students to research activities at Bristol. |
Year(s) Of Engagement Activity | 2022 |
URL | https://www.bristol.ac.uk/quantum-engineering/events/open-day/ |
Description | SMART:2021 Future networks research conference |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Industry/Business |
Results and Impact | I gave a presentation on our current progress on the GLIMMER project. The video can be viewed here: https://www.youtube.com/watch?v=jCMHX9xb2vI&ab_channel=SmartInternetLab |
Year(s) Of Engagement Activity | 2021 |
URL | https://www.bristol.ac.uk/engineering/research/smart/smart2021-future-networks-research-conference/s... |
Description | SPIE Photonics West invited talk |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | I gave an invited talk at the SPIE Photonics West conference on piezoelectric routes to microwave to optical signal transduction. I had to give the talk online, due to COVID induced travel restrictions. |
Year(s) Of Engagement Activity | 2022 |
URL | https://spie.org/PWO/conferencedetails/quantum-computing-communication-and-simulation |