Fabrication of microelectrodes deeply embedded in LiNbO ₃ using a femtosecond laser

We present a novel technique to fabricate deeply embedded microelectrodes in LiNbO ₃ using femtosecond pulsed laser ablation and selective electroless plating. The fabrication process mainly consists of four steps, which are (1) micromachining of microgrooves on the surface of LiNbO ₃ by femtosecond laser ablation; (2) formation of AgNO ₃ films on substrates; (3) scanning the femtosecond laser beam in the fabricated microgrooves for modification of the inner surfaces; and (4) electroless copper plating. The void-free electroless copper plating is obtained with appropriate cross section of microgrooves and uniform initiation of the autocatalytic deposition on the inner surface of grooves. The dimension and shape of the microelectrodes could be accurately controlled by changing the conditions of femtosecond laser ablation, which in turn can control the distribution of electric field inside LiNbO ₃ crystal for various applications, opening up a new approach to fabricate three-dimensional integrated electro-optic devices.