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

随着智能手机成为现代社会信息传输和处理的主要机制，我们对使用智能手机实现什么目标的期望也成比例增加。特别是，智能手机已经成为我们进入互联网的门户，取代了我们的电视、收音机和音乐设备，还充当了我们的信用卡和个人指南(GPS)。我们还希望我们的手机在我们跨国旅行时能够无缝工作。所有这一切都是通过将各种功能分离到不同的无线(RF)频段，以及开发复杂的模拟和数字电路来实现的，使电话能够同时进行这些通信。随着我们迈向5G和其他增加可用数据吞吐量的技术，这些通道必须增加。而在数字信号处理方面，摩尔定律和微电子集成的稳步发展使硅技术能够跟上需求，而主要是模拟的射频前端电路则不是这样。射频前端电路从天线接收信号，并将其分离到不同的通道(基于射频滤波器)，使用低噪声放大器(LNA)对其进行放大，然后将其移交给DSP进行基带信号处理。目前，RF滤波器和LNA主要是共同封装在一起的分立器件。虽然这种混合方法有一定的优势(主要是选择用于过滤器的压电材料)，但随着对过滤器的需求不断上升，众所周知，共包装方法不会规模化。主要原因是，可用于射频前端的智能手机占地面积(按芯片面积计算)在几代人之间大致保持不变，而过滤需求不断增加。正如微电子行业反复告诉我们的那样，单片集成是解决这些问题的唯一长期解决方案。在这个项目中，我们将展示氮化镓(GaN)是实现单片集成的理想平台，它利用了GaN提供的相对于传统解决方案的关键优势：声波导。GaN使我们能够在声学衰减较小的芯片表面引导高频声音。通过在纳米级波导中路由声音并将其本地化在微米级谐振器中，人们可以从头开始重新设计RF系统组件，实现组件占地面积的大幅减少，这是实现单片集成的关键。通过将集成光子学的想法应用到高频声学中，我们希望为射频系统实现硅光子学在光通信系统中实现的相同好处(在尺寸、重量和性能方面)。我们将展示高质量的射频无源器件(特别是压电谐振器和滤波器)可以与有源晶体管器件建立在相同的GaN衬底上。我们将与我们的项目合作伙伴合作，实施工艺流程并设计相关的工艺开发工具包，以便在商业GaN射频铸造厂(例如：Newport晶圆厂)中实施这些想法。

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.