New microfabrication method to invert micrometric ferroelectric domains on lithium niobate wafers for RF applications

In this paper, we propose a new fabrication method to invert micrometric ferroelectric domains on lithium niobate wafers. Periodically poled lithium niobate (PPLN) is well used for nonlinear-optical applications and recently for radiofrequency applications. The fabrication process of PPLN, based on the application of an electric field on a 500 μm-thick lithium niobate (LiNbO₃) Z-cut wafer is well developed for domains period higher than 10 μm. However, below 10 μm, it is more difficult to fabricate in a repeatable way because it is difficult to control the horizontal growth of inverted domains. An industrial method consists of reducing the thickness of the LiNbO₃ wafer in order to decrease the electrical field applied. This method is however restrictive because the wafer thickness must be high to manipulate it easily. We suggest another method allowing overriding this limit. The LiNbO₃ wafer is bonded on a doped silicon wafer, the ferroelectric substrate is then thinned until a few microns and an electrical field is finally applied on the stack to generate the micrometric domains. A GHz resonator based on a PPLN fabricated with this method is presented.