基于石墨烯电极的AlN声表面波器件的功率耐受性研究

Surface acoustic wave (SAW) device is one of the corner stone components in mobile communication system, and it also holds great promise in the development of Internet of Things. However, the inferior power durability of SAW devices limits their applications as high end duplexers and high frequency devices, due mainly to damaged electrodes under elevated power density by stress induced acoustomigration from the travelling SAW or the electric field caused electromigration. To overcome acousto- and electro-migration, doped Al electrode with metallic atoms such as Cu and multi-layer electrode structure are applied. However, the improved electrodes are still unable to withstand power beyond 1 W, and these measures increase the processing complexity significantly. This project proposes to adopt graphene electrode and single crystalline AlN thin film to improve the power durability of SAW devices. It was proposed based on two premises: (1) the prominent electrical and thermal conductivity, mechanical strength and elasticity of graphene enable it an ideal candidate to overcome the acousto- and electromigration, and (2) the great thermal conductivity and low intrinsic loss of AlN make it a perfect substitute for lithium niobate and tantalite. These two lithium crystals are widely used in commercial SAW devices however exhibiting depressed merit in power durability performance. Lithography and dry etching technique will be utilized to fabricate patterned graphene electrodes. In depth study on interface properties and device failure mode will be performed, and the factors and principals governing the power durability of the devices will be explored, in order to provide both theoretical and technical reference to enhance the power durability of SAW devices.

声表面波(SAW)器件是移动通信的基础元件之一，在物联网中也有广阔的应用前景。然而，由于声、电迁移现象的存在，即功率升高后电极可能在声波传输产生的应力场或电场作用下发生传质，SAW器件的功率耐受能力较弱，影响了其在双工器和高频器件中的应用。目前主要采用在Al中掺入Cu等原子及多层膜结构来缓解声电迁移。但这些措施仍不能使SAW器件在1 W以上的较高功率下工作，且增大了工艺复杂性。本项目拟采用石墨烯电极、AlN单晶薄膜压电材料，利用导电性和弹性好、机械强度高的石墨烯抑制声电迁移，利用热导率高、固有损耗小的AlN，替代相应指标相对低的商业器件用铌(钽)酸锂，改善SAW器件的功率耐受性。拟采用光刻和干法刻蚀工艺制备石墨烯电极，深入研究界面特性和石墨烯电极的失效行为和失效机制，研究器件的功率耐受性的影响规律和机制，为增强SAW器件的功率耐受能力提供理论和技术依据。

作为一种高性能、小尺寸的带通滤波器，声表面波（SAW）器件是移动通信中的核心元件之一，在物联网等多个应用场景中也有广阔前景。在项目经费的支持下，团队在三个方面取得了较大进展，并为后续研究奠定了坚实的基础。主要包括：（i）研究了基于外延AlN薄膜的延迟线型SAW器件的制备及薄膜晶体质量对器件性能的影响，发现与残余应力相比，表面粗糙度对器件性能的影响更为显著。（ii）在延迟线型SAW器件的基础上，初步探索了包括SAW和声体波（BAW）在内的声波传感器的制备及传感系统的集成。在敏感介质材料的探索中发现，用Cu做催化剂、醋酸作助催化剂，在室温下即可得到高结晶度的聚苯胺晶体，该方法绿色高效。集成了基于安卓系统的SAW传感器信号收发及处理系统。（iii）通过理论计算，并结合实验验证，以具有特殊能带结构的化合物半导体CdO和SnTe为例，研究了水蒸气侵蚀下其电学性能的变化。从物理机制上阐明了半导体的稳定性与其导电类型和掺杂浓度的关系，提供了一个判断半导体表面电荷种类的法则，即以∆E=E_F-E_FS为依据，当∆E>0时，表面耗尽电子，带负电；∆E=0时，表面为电中性；∆E<0时，表面富集电子，带正电。该研究结论对于需要与大气环境和液相接触的半导体材料与器件的稳定性控制有重要意义。通过前期探索，确立了近期的重点研究方向为以具有特殊能带结构的半导体为敏感介质的SAW/BAW气体传感器，将半导体电阻型传感器高选择性高灵敏度的优势与声波器件无源无线的优势结合起来，进行高选择性声波气体传感器的应用基础研究。成果发表了6篇学术论文，申请了2个发明专利，登记了1个软件著作权，参加了2次国际学术会议。