| As one of the most basic electronic components,dielectric capacitor plays a vital role in various circuit systems and electronic devices.However,with the development of electronic devices towards miniaturization and flexibility,the development of dielectric capacitors is facing a great challenge.Printing electronic technologies,especially inkjet printing has become a facile route to meet these demands.Two-dimensional materials have emerged as promising building blocks for applications in printed electronics due to their remarkable electronic,magnetic,and optical properties.Especially,the characteristics of liquid phase exfoliation enable them to be directly formulated into functional inks,which can be combined with solution processing methods including inkjet printing to achieve the fabrication of high-performance,miniature and flexible two-dimensional material based microelectronic devices.Currently,two-dimensional dielectric materials such as h-BN and BiOCl nanosheets were mainly inkjet-printed into two-dimensional material based microcapacitors,which exhibited low capacitance density owing to the low dielectric constant of h-BN and BiOCl nanosheets.In addition,the structure of these two-dimensional materials has polydispersity,that is,uneven lateral size and thickness,which leads to poor density of the printed film,thus affecting the performance of the printed device.Moreover,these two-dimensional material inks have low concentration and mostly use toxic and high-boiling organic substances,which seriously affects the printing efficiency and post-processing process,and further limits the development of inkjet printing electronic devices.To solve the above problems,perovskite nanosheets with high dielectric constant were prepared by liquid phase exfoliation and were formulated into printable ink by selecting proper solvents and additives and optimizing rheological properties.Finally,perovskite nanosheet-based microcapacitors were prepared by inkjet printing.In addition,dielectric properties of microcapacitors were enhanced by adjusting the structure and composition of perovskite nanosheets,improving the structure of printed microcapacitors,selecting different electrode materials and solvent intercalation.The specific content of our research is listed as follows:(1)Preparation of two-dimensional perovskite nanosheet inks and graphene inks and study on their printability.Ca2Nb3O10,Ca2NaNb4O13,Sr2-xBixNb3O10(x=0.0-0.3)perovskite nanosheets and graphene nanosheets were prepared by liquid phase exfoliation.Perovskite nanosheets were uniform and monolayer with thickness between 2.0-2.5 nm,while the graphene nanosheets were few-layer with thickness between 4-6 nm.These nanosheets all had high crystal quality.And different exfoliation methods and parameters were used to control the lateral size of nanosheets,so that the lateral size of nanosheets was between 200-400 nm,which met the requirements of inkjet printing.Subsequently,water-based,isopropyl alcohol-based and ethanol-based perovskite nanosheet inks were prepared with water as dispersing agent,propylene glycol,Triton X-100,xanthan gum,isopropyl alcohol,2-butanol and ethanol as additives.Graphene ink was prepared with cyclohexanone and terpineol as solvent and ethyl cellulose as additive.The rheological properties of inks were adjusted and optimized by controlling the proportion of ink components,so that these inks can meet the theoretical requirements of inkjet printing.Then,inkjet printing parameters,i.e.,inkjet voltage,frequency,number of holes,droplet spacing and substrate temperature,were optimized,so that prepared inks can realize stable inkjet and print patterns with high resolution and almost no "coffee ring" effect.Finally,the smooth,uniform and dense two-dimensional material functional films can be achieved by inkjet printing.(2)Study on dielectric properties of inkjet-printed Ca2Nam-3NbmO3m+1(m=3,4)and Sr2-xBixNb3O10(x=0.0-0.3)based microcapacitors.Microcapacitors including Ag/Ca2Nam-3NbmO3m+1/Ag,graphene/Ca2Nam-3NbmO3m+1/graphene,Ag/Sr2-xBixNb3O10/Ag and graphene/Sr2-xBixNb3O10/graphene were prepared by inkjet printing isopropyl alcohol-based Ca2Nam-3NbmO3m+1(m=3,4)perovskite nanosheet ink,ethanol-based Sr2-xBixNb3O10 perovskite nanosheet ink,graphene ink and Ag ink,respectively.We found that higher number of perovskite nanosheet layers(m)and more Bi3+ ion doping amount(x)can significantly improve the dielectric properties and the capacitance density of microcapacitors through the dielectric property test.By comparing microcapacitors with different types of electrodes,it can be found that compared with silver electrode,graphene electrode can significantly enhance the dielectric performance of microcapacitors,but it will lead to an increase in dielectric loss.In addition,these microcapacitors showed good electrical insulation,flexibility and thermal stability.However,they were very sensitive to chemical solvents,resulting in a large increase in capacitance value,and their sensitivity to different types of solvents is not the same.(3)Study on dielectric properties of inkjet-printed Ca2NaNb4O13-based multilayer microcapacitors.Two kinds of multilayer microcapacitors including(Ag/Ca2NaNb4O13/Ag)n and(graphene/Ca2NaNb4O13/graphene)n(n=1-3)were fabricated by inkjet printing isopropyl alcohol-based Ca2NaNb4O13 perovskite nanosheet ink,graphene ink and Ag ink,respectively.The dielectric test results showed that with the increase of dielectric layer(n),the dielectric performance of the multilayer microcapacitor was improved,and the capacitance density increased gradually.However,with the increase of dielectric layer(n),the electrical insulation,flexibility and thermal stability of multilayer microcapacitors decreased gradually,but they were more sensitive to chemical solvents.Similar to the results of work(2),we also found that compared with silver electrode,graphene electrode can significantly enhance the dielectric properties of multilayer microcapacitors,but it will lead to an increase in dielectric loss. |
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