Monolithically Integrated Tunable ZnO SAW Chip

本论文主要研究ZnO单片集成可调谐声表面波（MITSAW）芯片的材料生长、器件设计与制作及其应用。这种新颖的芯片在一个材料系统中集成了声、光和电过程。它利用ZnO/MgxZn 1-xO量子阱中的二维电子气（2DEG）与声表面波（SAW）之间的可调谐声-电-声-光相互作用，ZnO是一种具有独特的电学、光学、声学和力学性能的多功能材料。压电ZnO的高机电耦合系数与蓝宝石（Al 2 O3）的低声损耗和高速度相结合，提供了高频和低损耗的RF应用。ZnO与MgO合金化形成三元化合物MgxZn 1-xO，其允许从3.32 eV到4 eV的带隙调谐。ZnO/MgxZn 1-xO异质结构与2DEG的集成可以产生独特的声速调谐机制。2DEG与横向电场相互作用，导致欧姆损耗，这衰减并减慢了表面声波。该机制用于调整声速。ZnO/R-Al_2 O_3系统提供的高耦合系数允许速度调谐达1%。结合宽禁带直接带隙（~3.3eV）半导体ZnO和透明导电ZnO电极的光学特性，MITSAW芯片可用于紫外光信号处理。该MITSAW器件采用MOCVD方法在R面蓝宝石（R-Al 2 O3）衬底上生长ZnO/MgxZn 1-xO量子阱结构。选择R面蓝宝石作为ZnO层的面内各向异性衬底，平行于ZnO薄膜的c轴取向时，可以激发出瑞利型声表面波，垂直于c轴取向时，可以激发出Love型声表面波。瑞利波模式适合于气体环境传感，而勒夫波模式由于没有垂直波分量，适合于液体环境传感。ZnO MITSAW芯片还提供了声光双模传感机制。同样，平行于c轴和垂直于c轴的光学性质也不同，这使得可以制造新型的光学器件，如高对比度调制器。ZnO MITSAW芯片技术的成功开发将为工业提供最先进的新的多功能芯片技术。它不仅将改进现有的器件，而且还将为许多重要的应用领域开发全新的方法，包括可调/自适应通信系统，新型多模可调化学和生物化学传感器，以及延迟线和多路复用器等光学信号处理器。

This proposed research focuses on the materials growth, device design and fabrication, andapplications of a ZnO monolithically integrated tunable surface acoustic wave (MITSAW) chip. Thenovel chip integrates acoustic, optical and electrical process' in one material system. It uses tunableacousto-electric and acousto-optic interaction between surface acoustic waves (SAW) and a twodimensional electron gas (2DEG) in a ZnO/MgxZn1-xO quantum well.ZnO is a multifunctional material possessing unique electrical, optical, acoustical, and mechanicalproperties. The high electromechanical coupling coefficients of piezoelectric ZnO in conjunction with thelow acoustic loss and high velocity of sapphire (Al2O3) offers high frequency and low loss RFapplications. Alloying ZnO with MgO forms the ternary compound MgxZn1-xO, which permits band-gaptuning from 3.32 eV to 4 eV. ZnO/MgxZn1-xO heterostructures with 2DEG can be integrated with SAW tocreate a unique acoustic velocity tuning mechanism. The 2DEG interacts with the lateral electric fieldresulting in ohmic loss, which attenuates and slows the surface acoustic wave. This mechanism is used totune the acoustic velocity. The high coupling coefficients offered by the ZnO/R-Al2O3 systems allowsvelocity tuning up to 1%. Combined with the optical characteristics of the wide and direct band gap(~3.3eV) semiconductor ZnO and transparent conductive ZnO electrodes, the MITSAW chip can be usedfor UV optical signal processing. The proposed MITSAW consists of a ZnO/MgxZn1-xO quantum wellstructure grown on a R-plane sapphire (R-Al2O3) substrate using MOCVD. R-plane sapphire is choseninstead of the popular C-plane substrate, as this substrate provides in-plane anisotropy in the ZnO layer.By aligning the device parallel to the c-axis of the ZnO film, Rayleigh type surface acoustic waves areexcited, while Love type SAWs are excited when the devices are aligned perpendicular to the c-axis. TheRayleigh wave mode is suitable for gaseous environment sensing, while the Love wave mode, which hasno vertical wave component, is ideal for liquid environment sensing. The ZnO MITSAW chip also offersan acoustic-optical dual mode sensing mechanism. Likewise, the optical properties parallel andperpendicular to the c-axis are different, allowing novel optical devices, such as high contrast modulators,to be fabricated.The successful development of the ZnO MITSAW chip technology will provide industry withstate-of-the-art new multifunctional chip technologies. It will not only improve the existing devices butalso develop fundamentally new approaches to many important application areas, includingtunable/adaptive communication systems, novel multi-mode tunable chemical and biochemical sensors,and optical signal processors such as delay lines and multiplexers.