Femtosecond Laser Fabrication Of Embedded Metal Micro/Nano-Structures

Nowadays,metal micro/nano-structures have been widely used in many important research areas such as photonics,electronics,and biomedical sciences.The metal micro/nano-structures fabricated by most of current micro/nano-processing techniques are usually directly attached to the surfaces of the used substrates.For some dielectric substrates such as glass,and crystals,due to the inherently weak adhesion of the deposited metals on the dielectrics,the stability and reliability of the manufactured devices for long-term operation are largely affected.To solve this issue,fabrication of embedded metal micro/nano-structures by creation of grooves on the substrate surfaces followed by subsequent selective metal deposition has been proposed as an alternative method.For example,the use of femtosecond laser micromachining with combination of electroless metal plating can achieve the preparation of embedded metal microstructures on insulator surfaces.However,it should be pointed out that the preparation of embedded submicron metal structures on the dielectric surfaces and embedded vertical sidewall microelectrodes for electro-optic integration has not yet been reported.In this thesis,femtosecond laser micro/nanofabrication combining with a novel electroless plating technique is carried out the preparation of embedded metal micro/nano-structures.The main research results are concluded as follows.(1)A technique for fabrication of embedded submicron metal wires on the surface of fused silica substrates is proposed,which combines the threshold effect of femtosecond laser ablation and continuous flow electroless plating.Firstly,submicron line width grooves are created on the glass surface by using the femtosecond laser direct ablation with the help of threshold effect.Secondly,metal film is deposited on the surface of the sample by continuous flow chemical plating.Finally,controllable fabrication of highly conductive sub-micron metal structures(minimum linewidth?0.66 ?m)embedded in glass surface can be achieved by thermal treatment and subsequent mechanical polishing.(2)A technique for manufacture of vertical metal microelectrodes embedded in lithium niobate(LN)crystal is proposed by using water-assisted femtosecond laser ablation and electroless plating.Firstly,open micro-grooves with vertical sidewalls are created by the femtosecond laser layer-by-layer ablation of the crystal which is immersed in water.Secondly,silver metal films are deposited on the sample surface including the grooves by continuous flow electroless plating.Next,the films outside the grooves are removed by mechanical polishing.Then,selective metal deposition of copper inside the grooves is carried out for full filling of the grooves using electroless copper plating.Finally,controllable preparation of metal vertical microelectrodes on the LN crystal can be achieved by using additional mechanical polishing for removing extra metal films outside the grooves.The introduction of water during laser ablation enables efficient removal of the debris which in-situ generated on the ablated surface,which greatly promotes the quality and precision for laser structuring.The embedded microelectrodes with vertical configurations provide highly uniform and controllable electric-field control inside the LN substrate.Compared with conventional methods,the proposed techniques for fabrication of submicron metal wires and vertical metal microelectrodes has obvious advantages in term of processing controllability,metal adhesion as well as uniformity control of the electric field in bulk materials,which allows fabrication of embedded metal micro/nanostructures and related devices with flexible configurations and superior field-control capabilities in a facile manner.It is expected to be applied in the fields of electrical interconnection,electro-optic integration,micro-electromechanical systems,and multifunctional microfluidics.