Mechanical Design And Analysis Of Stretchable Graphene Electronics

As the dimensions of Si based transistors continue to scale down,the speed and integraton of chips have been boosted over the past 52 years,under the guidance of Moore's Law.However,the traditional electronics devices are basically fabricated on the rigid circuit board,basing on the planar complementary metal-oxide-semiconductor(CMOS)technology,which limits their applications on some non-planar working environment such as in-time healthcare monitoring on human epidermis.Hence,Flexible electronics based inorganic materials,also called "Macroelectronics",have emerged in recent years.But the brittle,thick nature of these the bulk inorganic materials such as Si will lead to the high cost and low efficiency of its flexible devices in industrial applications.Two-dimensional materials(2DMs)are atomically thin,layered crystalline solids with the defining characteristics of intralayer covalent bonding and interlayer van der Waals(vdW)bonding,and represent the ideal conditions for realizing maximum optical transparency,electronstatic control,mechanical flexibility,and chemical sensor sensitivity.Possessing varieties of outstanding properties such as superior transport(charge,spin,light and heat),and no surface dangling bonds,2DMs have inspired tremendous interests for novel flexible nanotechology.Among them,graphene offers the fastest charge transport,highest carrier mobility,and ultrastrong mechanical stiffness,and takes a great advantage over Si in the application of transparent,flexible,and stretchable devices.So We systematically study the growth,transfer and flexible devices fabrication of CVD graphene,and develop the mechanical design and analysis of its stretchable electronics.The main research contents are as follows:1.We grow polycrystalline graphene film with maximum domain of 1.3mm,average domain over 600 ?m,and average surface roughness less than 4nm on copper foil by the chemical vapor deposition(CVD)method,and analyse the electrical properties'difference of CVD graphene transferred on stretchable substrates and rigid substrates like SiO2.Then we come up with the "pouring" method based on PDMS's intrinsic properties to transfer patterned graphene and its flexible devices on highly stretchable PDMS,meanwhile,devices on PDMS will "copy" the surface morphology of CVD copper substrate.Finally,the electrical and mechanical performances of graphene flexible devices tested on PDMS are poor and unstable,and we emphasize the importance of PMMA and other encapsulating materials in flexible devices.2.We fabricate graphene/Au serpentine wire with PMMA back-encapsulated layer by the"pouring" process,and study their elastic stretchability by the deformation diagram and resistance measurement under stretching.First,we test graphene/550 nm PMMA wire,and obtain the elastic stretchability of 35%,which is close to the theoretical simulation value of 41%.We consider that the crumpling of graphene surface induced by the "pouring-copy" process contributes to the degration of mechanical property further,which result in the prematurely elasticity-plasticity transition(cracking)of graphene.As for 1 OOnm Au/550nm PMMA wire,its conductance keeps when stretched for 50%,which is largely over its simulated elastic stretchability at 14%.Because the metal wire in plastic deformation regime cracks after fatigue test with thousands of times' onload-unload strain.But 20nm Au/550nm PMMA wire cracks only when stretched for 25%;with a simulated elastic stretchability of 7.4%,which means fracture strain of graphene has been superior to Au with such thickness.Finally,we design and make a CVD graphene wire with fractal structure,which may be used for E-skin.