Deboucq Julien, Duquennoy Marc, Ouaftouh Mohammadi, Jenot Frédéric, Carlier Julien, Ourak Mohamed
Université de Valenciennes, Le Mont Houy, F-59313 Valenciennes Cedex 09, France.
Rev Sci Instrum. 2011 Jun;82(6):064905. doi: 10.1063/1.3600797.
In this paper, Rayleigh waves were generated and studied over a broad frequency range (5-50 MHz) and from the dispersion phenomenon, two substrate on layer type-samples with thin layer thicknesses of 1 μm and 500 nm, respectively, were characterized. The originality in this paper is the use of surface acoustic wave interdigital transducers (IDT) to generate surface waves as well as the development of a measuring device enabling an accurate estimation of the phase velocity to be obtained, which is essential in order to characterize such thin layers. Considering the excitation frequencies (5-50 MHz) and therefore the widths necessary on the electrodes for these types of IDT sensors (20-200 μm), a lift-off procedure was chosen to deposit the electrodes on the lithium niobate (LiNbO(3)) piezoelectric substrates. The use of these IDT, first enabled problems of loss and attenuation linked to the high frequency of conventional sensors (wedge sensors) to be overcome and second to carry out quasi-monochromatic measurements in order to obtain an extremely accurate estimation of the phase velocity with rapid post-processing. An inverse method provided a very precise estimation of the thickness of the layers and the elastic constants of the substrate. The estimations of the thicknesses were then confirmed by measurements with a profilometer.
在本文中，在很宽的频率范围（5 - 50 MHz）内产生并研究了瑞利波，并且根据频散现象，对分别具有1μm和500 nm薄层厚度的两种衬底 - 覆盖层型样品进行了表征。本文的创新之处在于使用表面声波叉指换能器（IDT）来产生表面波，以及开发了一种测量装置，能够精确估计相速度，这对于表征此类薄层至关重要。考虑到激励频率（5 - 50 MHz）以及因此这些类型的IDT传感器电极所需的宽度（20 - 200μm），选择了剥离工艺将电极沉积在铌酸锂（LiNbO₃）压电衬底上。使用这些IDT，首先能够克服与传统传感器（楔形传感器）高频相关的损耗和衰减问题，其次能够进行准单色测量，以便通过快速后处理极其精确地估计相速度。一种反演方法能够非常精确地估计层的厚度和衬底的弹性常数。然后通过轮廓仪测量证实了厚度估计值。
