Research On Piezoresistive Properties And Sensors Of Diamond-like Carbon Films

Diamond like carbon（DLC）films have excellent mechanical,tribological and optical properties.In addition,DLC has great potential as a piezoresistive material in micro technology applications.Compared with metal films,DLC has higher piezoresistive sensitivity.In this paper,we use magnetron sputtering technology to control the electrical,mechanical,surface friction and affinity properties of DLC thin films by adjusting deposition parameters and element doping composite technology,and systematically combine DLC thin films with different characteristics to build an integrated piezoresistive sensor and surface hard protection carbon based thin film sensor.The main conclusions are as follows（1）Preparation and properties of diamond-like carbon piezoresistive layer:DLC thin films with different carbon structures were obtained by magnetron sputtering technology by adjusting bias voltage and particle energy.The effect of carbon structure on piezoresistive properties of DLC films was studied.The influence of Si content on the piezoresistive properties of DLC films is also discussed.The influence of thickness on the piezoresistive properties of DLC films.The results show that the content of sp³ is the highest,the resistivity is the highest,and the piezoresistive sensitivity coefficient Kp is the highest in the DLC film with bias voltage of 200V.At the same time,the hole defects in the film have a great influence on the piezoresistive sensitivity.With Si doping,the content of sp³ increases,the number of conductive sp² clusters decreases,and the piezoresistive sensitivity Kp decreases,but the Kp value is relatively stable.With the increase of DLC film thickness,sp² content increases,resistance decreases and piezoresistive sensitivity coefficient Kp decreases.After repeated loading for many times,DLC films will graphitize in different degrees according to the load,which is also the reason for the poor repeatability of Kp value of DLC films.（2）Preparation and research of diamond-like carbon insulating layer:the effect of different o content on the structure and properties of SiO_X-DLC insulating layer was studied by magnetron sputtering.The resistant of the insulating layer can reach to 9.42×10^-8Ω·cm,which is mainly due to the solid solution of Si and O in the form of SiO₂in the network structure of C-C,while SiO₂is insulating,thus increasing the resistance of the coating.At the same time,reducing the stress of the coating can be used as a transition layer to improve the adhesion between the conductive layer and the substrate.（3）Preparation and research of wear-resistant and adhesion resistant diamond-like carbon（DLC）coating:the effect of F content on the structure and properties of DLC coating was studied by magnetron sputtering.In the F-DLC coating,the hardness and elastic modulus of the coating decrease due to the local interruption of the C-C network structure.With the increase of F content,the-CF₂ functional group and the contact angle of the surface F-DLC coating increase to 109°.（4）Fabrication and research of carbon based monolithic devices:the insulation layer SiO_X-DLC coating,the conductive layer DLC film and the surface layer F-DLC coating are integrated together,and the Cu electrode is plated between the insulation layer and the conductive layer.After the insulating layer is coated,the electric signal transmission is more stable,so the piezoresistive stability of the whole device is better.