Optical crosstalk reduction in optically controlled microwave circuits on HR-Si using a trap-rich passivation layer

The reduction of Photo-Induced excess carriers of a coplanar waveguide photo-induced RF switch on High Resistivity Silicon substrate is presented. Experimental results from 40 MHz to 40 GHz demonstrate the important reduction of transmission line losses and optical crosstalk obtained by introducing a trap-rich passivation layer (Polysilicon and crystallized amorphous silicon) at the interface between the HR-Si and the field oxide. An optimal design for future photo-induced switches is proposed. By locally removing the passivation layer we can ensure the reduction of the interconnection line losses and optical crosstalk while maintaining an acceptable efficiency for the optical RF switch.