Characterization Of Graphene And Its Copper Composite And Their Application In Electronic Devices

With 5G communications,portable consumer electronics,and military electronics for the development demand of light and thin,miniaturized,multifunctional,highperformance,and low-cost microelectronic products,the overall integration of microelectronic devices continues to rise.This leads to the fact that the local heat flux density of electronic devices sharply increases.On the other hand,the development of 5G technology has made problems such as electromagnetic interference and electromagnetic interference increasingly serious.High temperature and electromagnetic interference will not only reduce the working stability of electronic devices,but also affect the performance and reliability of electronic devices.Therefore,heat and electromagnetic radiation will be the two major bottlenecks that limit the development of high-frequency and high-power electronic devices in the future.Graphene and its composite materials are considered to be the most promising heat dissipation and electromagnetic shielding materials due to their excellent thermal conductivity,electrical conductivity and electromagnetic shielding properties.Based on this,this thesis focuses on the controllable preparation and characterization of high-performance graphene and graphene/copper composite materials,and explores its application as heat dissipation and electromagnetic interference shielding materials in electronic devices.Firstly,as lateral spreader material,the scalable production of high thermal conductivity thick(?75?m)graphene film(GF)by continuous high-pressure homogenization(HPH)processing was studied.The results have shown that the single-layer sub-micron graphene oxide raw materials prepared after two HPH enable the formation of the thick GF reduced by high-temperature with large grain size,good interlayer alignment,great heat flux carrying capacity,and weak interlayer bonding energy.The conjugation of those structures endows GFs with good flexibility and high in-plane thermal conductivity,which is as high as 1204±35W/mK at 75?m.Compared with commercial thick pyrolytic graphite film(PGF),it is found that GF not only has better thermal conductivity and heat spreading performance than PGF,but also has significantly better flexibility than PGF.Especially,the heat spreading capacity of GF after 5000 bending cycles is not significantly reduced like PGF.In addition,the preparation method used in this research is simple,highly efficient,and offers low energy consumption and low cost,and therefore can realize quasi-industrial production.Secondly,for materials with high thermal conductivity and superior electromagnetic interference shielding effectiveness(EMI SE),the preparation and performance analysis of graphene-copper composite films(GCFs)were carried out based on the sputtering method and the electroplating method.The studies show that GCFs prepared by the two methods can achieve both high thermal conductivity and effective EMI shielding.Here,in the sputtering,the titanium metal layer not only increases the wettability and adhesion of the copper layer on the surface of the graphene film,but also reduces the contact thermal resistance,providing a good ohmic contact.This increases the absorption loss of electromagnetic waves,thereby the thermal conductivity of the GCFs is as high as 1542 W/mK,and the EMI SE is 80.19 d B,which is 20.6% and 24.1% higher than the original graphene film,respectively.In the electroplating,the copper layer could be electroplated directly on the surface of the graphene film through the surface pretreatment of the graphene film and the selection of the electroplating solution additives.It is found that the copper layer structure obtained by the electroplating is more continuous and denser than that obtained by sputtering.The resulting GCFs have a slight decrease in thermal conductivity,but have an obvious increase in electrical conductivity and EMI SE.In addition,the electroplating is simple to operate and can be mass-produced in the future.Finally,in terms of thermal interface materials,the synthesis mechanism of spherical few-layer graphene-encapsulated copper particles(GCPs)in cold-wall CVD was studied,and the synthesis process was optimized by controlling the ratio of hydrogen to methane flow.It was found that the graphene shells synthesized under high flow rate have fewer layers and are more orderly arranged.The obtained GCPs not only maintain an independent spherical shape,but also have a thermal stability of 179°C.The 150°C aging test further shows that the oxidation resistance of the GCPs is significantly improved.Subsequently,GCPs instead of silver particles as the thermally conductive filler were applied in the thermally conductive adhesive,and it was found that the performance of the thermally conductive adhesive can be increased by 74.6% owing to the superior thermal conductivity of graphene and excellent oxidation resistance of GCPs.