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。这些属性非常有价值，但两者结合的好处仍在调查中。氮化镓在金属氧化物半导体（MOS）中的应用，如射频（RF）放大器，已经得到了很多研究。然而，这些GaN放大器使用的材料和工艺与用于制造使用石英或钽酸锂（LiTaO3）的现代RF滤波器的材料和工艺不兼容。当射频滤波和放大的应用与严格的空间限制相结合时，就会出现严重的问题，比如智能手机设计，其中微波和射频滤波和放大一起构成了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。为了实现这一点，滤波器的压电谐振器和MOS放大电路的衬底需要兼容工艺。布里斯托尔大学的研究表明，氮化镓是制造表面声波（SAW）射频滤波器的合适材料。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了有趣的声波能量反射，这导致了受限的兰姆波。这种兰姆波的声能由氮化镓层引导，这使得小的、高Qmech谐振器得以产生。根据这项研究，氮化镓似乎是生产单片射频芯片的理想材料。提出的研究将继续研究这种GaN SAW滤波器的设计。应制作尺寸越来越小的滤波器，并对其射频性能进行分析。理想的设备尺寸来自于尺寸和性能的折衷。还应确定随着尺寸减小而改变性能的原因，因为这可能表明修改设计的机会。研究还应关注这些滤波器与GaN MOS放大器和其他GaN射频声学元件的集成。该项目属于EPSRC量子技术研究领域，隶属于布里斯托尔大学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.