A method for preparing a surface of a YAG crystal for thermal bonding includes performing an ion implantation process to introduce nitrogen into a surface layer of the YAG crystal to replace depleted oxygen therein, to change surface energy of the surface layer of the YAG crystal and to provide desired bonding characteristics for the surface layer; and joining the ion implanted surface layer with a thermal management device configured to dissipate heat from the YAG crystal. Also, a micro-chip device having a YAG crystal whose surface is prepared with the above disclosed method is provided and a device for forming a metallization pattern on a surface of the YAG crystal is provided.