Monolithically Integrated Tunable ZnO SAW Chip

本文主要研究了ZnO单片集成可调谐表面声波（MITSAW）芯片的材料生长、器件设计与制造以及应用。该芯片将声学、光学和电学过程集成在一个材料系统中。它利用ZnO/MgxZn1-xO量子阱中表面声波（SAW）和二维电子气（2DEG）之间的可调谐声电和声光相互作用。氧化锌是一种多功能材料，具有独特的电学、光学、声学和力学性能。压电ZnO的高机电耦合系数与蓝宝石（Al2O3）的低声损耗和高速度相结合，提供了高频低损耗的射频应用。ZnO与MgO合金形成了三元化合物MgxZn1-xO，该化合物允许在3.32 eV到4 eV范围内进行带隙调整。具有2DEG的ZnO/MgxZn1-xO异质结构可以与SAW集成，从而创建独特的声速调谐机制。2DEG与侧向电场相互作用，导致欧姆损失，从而衰减和减缓表面声波。这种机制是用来调节声速的。ZnO/R-Al2O3系统提供的高耦合系数允许速度调谐高达1%。结合宽直接带隙（~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。所提出的MITSAW由在r平面蓝宝石（R-Al2O3）衬底上生长的ZnO/MgxZn1-xO量子阱结构组成。选择r平面蓝宝石代替流行的c平面衬底，因为这种衬底提供了ZnO层的平面内各向异性。通过将器件平行于ZnO薄膜的c轴排列，可以激发瑞利型表面声波，而当器件垂直于c轴排列时，则可以激发Love型saw。瑞利波模式适用于气体环境传感，而没有垂直波分量的洛夫波模式适用于液体环境传感。ZnO MITSAW芯片还提供声光双模传感机制。同样，平行和垂直于c轴的光学特性是不同的，这使得新的光学器件，如高对比度调制器，可以被制造出来。ZnO MITSAW芯片技术的成功开发将为工业提供最先进的新型多功能芯片技术。它不仅将改进现有设备，而且还将开发许多重要应用领域的根本新方法，包括可调谐/自适应通信系统，新型多模式可调谐化学和生化传感器，以及延迟线和多路复用器等光信号处理器。

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.