压电材料中表面声波的波速测量与调制

Wave Velocity Measurement and Modulation of Surface Acoustic Waves in Piezoelectric Materials

三维固体中除了存在人们熟知的体声波传播模式,还存在能量集中在二维界面的表面声波传播模式。我们利用砷化镓衬底的压电和逆压电效应,通过平面叉指实现了射频电磁波和表面声波之间的相互转化,并搭建超外差电路完成了在边长仅4 mm的样品上表面声波波速的测量,结果为(2.9±0.1)km/s。我们还制作了基于压电陶瓷的单轴应力腔,可以对样品施加最大约为10^(-4)的单轴应变,并观测到了应变对表面声波波速的影响。我们还测量了重要半导体砷化镓在应力下的表面声波波速,演示了该波速测量技术原位探测固体内部力学性质的能力。基于平面叉指换能器的波速测量克服了传统的时差法和驻波法对样品宏观尺寸的要求。本文建立的超外差的测量方法代替了使用商用矢量网络分析仪测量表面声波波速,为以后推广到低功率输入、高相位稳定度的应用场景提供了可能。由于测量装置也可以被用于固体物理相关的前沿实验教学,工作提供了表面声波器件和自制应力腔的细节参数和制作过程。

In addition to the well-known conventional acoustic wave propagation mode in three-dimensional solids,there exists the surface acoustic wave propagation mode where energy is only concentrated near the two-dimensional interface.In this work,utilizing the piezoelectric and inverse piezoelectric effects from GaAs substrates,we achieve the conversion between radiofrequency electromagnetic waves and surface acoustic waves with planar interdigital transducers,and successfully measure the surface acoustic wave velocity on a sample with a dimension of only 4 mm using superheterodyne-scheme lock-in technique,yielding a result of(2.9±0.1)km/s.We also fabricate a uniaxial stress cell with piezoelectric ceramics,capable of applying uniaxial strains up to approximately 10^(−4) to the sample,and observe the influence of strain on the surface acoustic wave velocity.We measure the surface acoustic wave velocity of the important semiconductor GaAs under stress,demonstrating the capability of this velocity measurement technique to probe the internal mechanical properties of solids in situ.The wave velocity measurements based on planar interdigital transducers overcome the macroscopic size requirements of traditional time-of-flight and standing wave methods.The superheterodynescheme lock-in technique established in this article has replaced the commercial vector network analyzers for measuring surface acoustic wave velocity,enabling possible future applications with low power input and high phase stability.As the measurement setup can also be used for experimental teaching related to solid-state physics,this work provides detailed parameters and fabrication processes for surface acoustic wave devices and homemade stress cell.