INTEGRATED PIEZO-ACOUSTIC CIRCUITS FOR RADIO-FREQUENCY FRONT-ENDSINTEGRATED PIEZO-ACOUSTIC CIRCUITS FOR RADIO-FREQUENCY FRONT-ENDS

氮化镓（GaN）同时是半导体和压电材料。这些特性是非常有价值的，但两者结合的好处仍在研究中。对于GaN的金属氧化物半导体（MOS）应用，例如射频（RF）放大器，已经有很多研究。然而，这些GaN放大器使用的材料和工艺与使用石英或钽酸锂（LiTaO3）制造现代RF滤波器的材料和工艺不兼容。当RF滤波和放大的应用与严格的空间限制相结合时，这会带来重大问题，例如智能手机设计，其中微波和RF滤波和放大一起形成无线数据传输背后的技术。这个问题的理想解决方案是在同一芯片上生产滤波器和放大器。为了促进这一点，滤波器的压电谐振器和MOS放大电路的衬底需要兼容的工艺。来自布里斯托大学的研究表明，GaN是一种合适的材料，可以用来制造表面声波（SAW）RF滤波器。这项研究表明，尽管与钽酸锂相比，GaN的压电性能较差，但可以通过利用材料的特定性能来生产高频滤波器。在GaN层和硬衬底之间的界面处的阻抗阶跃产生有趣的声能反射，这导致受限的兰姆波。该兰姆波的声能由GaN层引导，这使得能够产生小的高Qmech谐振器。根据这项研究，GaN似乎是生产单片射频芯片的理想材料。拟议的研究将继续这种GaN SAW滤波器设计的调查。应制造尺寸逐渐减小的滤波器，并分析其射频性能。理想的器件尺寸来自尺寸和性能的折衷。还应确定性能随尺寸减小而变化的原因，因为这可能表明有机会修改设计。研究还应关注这些滤波器与GaN MOS放大器和其他GaN RF声学元件的集成。该项目福尔斯属于EPSRC量子技术研究领域，并隶属于布里斯托大学的QET实验室研究小组。

Gallium Nitride (GaN) is simultaneously a semiconductor and a piezoelectric material. These properties are singularly valuable but the benefit of both together is still under investigation. There has been much research into metal oxide semiconductor (MOS) applications of GaN such as radio-frequency (RF) amplifiers. However, these GaN amplifiers are made using materials and processes which are incompatible with those used to make modern RF filters, which use quartz or lithium tantalate (LiTaO3). This presents significant problems when the application of RF filtering and amplification is combined with strict space constraints, like smartphone design, where microwave and RF filtering and amplification together form the technology behind wireless data transfer. The ideal solution to this problem is to produce filters and amplifiers on the same chip. To facilitate this the piezoelectric resonator of the filter and the substrate of the MOS amplification circuit need to compatible processes. Research from the University of Bristol illuminates GaN as a suitable material from which to produce surface acoustic wave (SAW) RF filters. This research demonstrates that despite the inferior piezoelectric properties of GaN compared to lithium tantalate, high frequency filters can be produced by exploiting the material's specific properties. The impedance step at the interface between a GaN layer and a hard substrate produces interesting reflections of acoustic energy, which result in a confined Lamb wave. The acoustic energy of this Lamb wave is guided by the GaN layer which enables small, high Qmech resonators to be produced. Following this research, GaN appears to be an ideal material from which to produce monolithic radio-frequency chips. The proposed research would continue the investigation of this design of GaN SAW filters. Filters of decreasing size should be fabricated and their radio-frequency performance analysed. The ideal device size comes from a compromise of size and performance. The reasons for changing performance with decreasing size should also be established as this may indicate opportunities for modification of the design. The research should also concern the integration of these filters with GaN MOS amplifiers and other GaN RF acoustic components. This project falls within the EPSRC Quantum Technologies research area and is affiliated with the QET Labs research group at the University of Bristol.