Micro-to-nanometer patterning of solution-based materials for electronics and optoelectronics

Abstract

Technologies for micro-to-nanometer patterns of solution-based materials (SBMs) contribute to a wide range of practical applications in the fields of electronics and optoelectronics. Here, state-of-the-art micro-to-nanometer scale patterning technologies of SBMs are disseminated. The utilisation of patterning for a wide-range of SBMs leads to a high level of control over conventional solution-based film fabrication processes that are not easily accessible for the control and fabrication of ordered micro-to-nanometer patterns. In this review, various patterning procedures of SBMs, including modified photolithography, direct-contact patterning, and inkjet printing, are briefly introduced with several strategies for reducing their pattern size to enhance the electronic and optoelectronic properties of SBMs explained. We then conclude with comments on future research directions in the field.

Fig. 1. Schematic of various printing technology with printing speed and resolution. These figures have been adapted from ref. 5, with permission from the Royal Society of Chemistry.

Fig. 2. (a) Schematics of the nanoscale patterning processes for semiconductor nanocrystals. The patterns (MIT written), which were formed by EBL on PMMA resist film, are positioned on the surface of the substrate with nanoscale precision. Transmission electron micrographs of the nanocrystal films before and after cap exchange. Nanopatterned films of CdS nanocrystals (first and third rows) and Zn_0.5Cd_0.5Se–Zn_0.5Cd_0.5S core–shell nanocrystals (second row). The images of (b) SEM, (c) fluorescence, and (d) AFM. (e) The images of green fluorescence and an electron micrograph indicate that the size of the pattern is only about 30 nm. These figures have been adapted from ref. 30, with permission from the American Chemical Society.

Fig. 3. SEM images of monolayered the nanoscale patterns for QD films. (a) Schematics of the experimental flow of the patterning of QDs. (b) Line and (c) ring patterns with different widths, and the enlarged views of (c) and (e) of some selected widths for the line (b) and ring (d) patterns, respectively. These figures have been adapted from ref. 31, with permission from the American Chemical Society.

Fig. 4. (a) Schematic of basic QD patterning process and photographs of QD-coated substrate during processing. (b) and (c) SEM images of QD film on the substrate before and after OTS treatment and direct patterned QD films by E-beam. Scale bar is 5 (first row) and 2 (second row) μm. (d) SEM images of 30 nm patterned QD film. (e) SEM image of patterned QD lines ranging from 15 to 150 nm thick with the E-beam dose increasing from 7500 to 8500 μC cm⁻². Scale bar is 3 μm. These figures have been adapted from ref. 17, with permission from the American Chemical Society.

Fig. 5. (a) A conventional photolithography procedures such as QDs deposition (spin coating), exposure with a mask, and lift off for patterning of QDs. (b) Optical and SEM images of patterned QDs. These figures have been adapted from ref. 18, with permission from the Wiley-VCH.

Fig. 6. (a) Process flow of SAM-directed cold spin casting. (b) Schematics and SEM images of microdomains of the directed self-assembly of the block-copolymer with the S-CSC procedure. These figures have been adapted from ref. 12, with permission from the American Chemical Society.

Fig. 7. (a) Schematic of the processes of nanopatterned TiO₂ based on embossing TiO₂ sol. SEM images of (b) nanopatterns of Si master template, (c) embossed TiO₂-gel patterns at 200 °C for an hour and (d) nanopatterns of polycrystalline TiO₂ after annealing at 700 °C in atmospheric ambient for an hour. These figures have been adapted from ref. 13, with permission from Elsevier.

Fig. 8. SEM images of ZnO patterns using an h-PDMs mould on the Si substrate. (a) ZnO dot nanopatterns using h-PDMS mould, derived from the Si master mould. (b) 50 nm sized ZnO line nanopatterns on Si substrate (these figures have been adapted from ref. 44, with permission from the Elsevier). (c) Fabrication method for patterned TiO₂ and TiN film. (d) Centimeter-scale PDMS stamps and embossed gratings on silicon. (e) Large-area SEM image of uniform, defect-free, embossed gratings. SEM images before (f–h) and after (i–k) 6 hours nitridation treatment. All scale bars are 3 μm (these figures have been adapted from ref. 46, with permission from IOP Publishing).

Fig. 9. (a) Schematic of ITO patterned, PEDOT:PSS spin-coated, PEDOT:PSS embossed by Si master mould (formation of nanogratings), and P3HT:PCBM spin-coated and thermal evaporation of LiF and Al. SEM images of (b) Si master mould with nanograting pattern and (c) embossed PEDOT:PSS with dehydration (these figures have been adapted from ref. 50, with permission from IOP Publishing). Process flow to form ordered PCPDTBT/C₇₀ heterojunction: (d) schematic and (e) SEM image of embossed PCPDTBT (nanogratings) (these figures have been adapted from ref. 14, with permission from the American Chemical Society).

Fig. 10. (a) Schematic fabrication process of a QD light-emitting diode (QLED) device with grating nanostructures. (b) AFM images of the surface of PDMS mould, PEDOT:PSS, TFB, QDs, and ZnO. (c) Schematic images of the flat and grating device structures of QLEDs and explanation of the mechanism for improving device out-coupling efficiency with grating nanostructures. (d) Current efficiency and external quantum efficiency as a function of current density. (e) Normalised electroluminescence (EL) spectra. The insets are photographs of the fabricated QLED with and without grating nanostructures. These figures have been adapted from ref. 53, with permission from the Royal Society of Chemistry.

Fig. 11. (a) Schematic illustration of the transfer printing procedure, and (b) microscale pixel fabrication by transfer printer with an intaglio stamp. These figures have been adapted from ref. 3, with permission from the Wiley-VCH and ref. 17, with permission from the Nature Publishing Group.

Fig. 12. (a) Schematic of fabrication method of QDs nanoscale pattern using patterned silicon template by stripping. (b) Photo-image and (c) fluorescence image of patterned QD film under an ultraviolet light source. (d) SEM image of the patterned QDs film. (e) The enlarged view of (d). Scale bars of (d) and (e) are 2 μm and 200 nm, respectively. These figures have been adapted from ref. 56, with permission from the American Chemical Society.

Fig. 13. (a) Schematic illustration of LB-nTM and SEM image of the PUA mould and the mould filled with ZTO ink. (b) Schematic diagram of the procedure for fabricating ZTO nanowire FETs using LB-nTM and SEM images of ZTO nanowire FETs. (c) Device performance of the ZTO nanowire FET. These figures have been adapted from ref. 104, with permission from the Nature Publishing Group.

Fig. 14. (a) Schematic illustration of the pattern-formation process. The solution is patterned and pinned by the groove corners during drying. (b) Performances and images of devices and molecule structures. These figures have been adapted from ref. 105, with permission from the Nature Publishing Group.

Fig. 15. (a) Fabrication of polymer nanowires by controlling dewetting on a template with asymmetric wettability. (b) Schematic and SEM image of photodetectors of polymer nanowire arrays (c) I–V curves of polymer photodetectors under dark and light illumination with different irradiances and irradiance-dependent photocurrent and responsivity of a device. These figures have been adapted from ref. 106, with permission from the American Chemical Society.

Fig. 16. (a) Schematic of conducting polymer patterning using selective surface modification. (b) FE-SEM and AFM images of the nanoscale polymer line patterns with a width of 292 nm at 1 μm spacing produced by using the polymer template. These figures have been adapted from ref. 107, with permission from Elsevier.

Fig. 17. (a) Schematic of Principle of the 2D-array generation from solution and Pinning–depinning of a contact line between the substrate and the solution constrained in a wedge-shaped space. (b) Pattern analysis and formation mechanism. AFM image taken from the PMS pattern and surface profile model and variation in lattice parameters with solution viscosity in different systems, and the temperature dependence of the lattice parameters for the PMS pattern from toluene solution and optical image of a quenched growth front of a 2D array of the PMS polymer during growth from its toluene solution. These figures have been adapted from ref. 108, with permission from the Royal Society of Chemistry.

Fig. 18. (a) Phase diagram for printability in a parameter space of Z and the jet Weber number. (b) Conductive copper pattern inkjetted onto polyimide substrate. These figures have been adapted from ref. 116, with permission from the AIP publishing and ref. 117, with permission from the IOP publishing.

Fig. 19. (a) Schematic and SEM image for fabrication of nanoscale circuits using space-confined assembly inkjet printing method. (b) SEM images of well controlled line width of nanoscale circuits by changing concentrations of the Ag nanoparticle solution. (c) Schematic illustration of the process for high-resolution jet printing by the action of electrohydrodynamic forces with block-copolymer. These figures have been adapted from ref. 11 and 107, with permission from the Nature Publishing Group.

Fig. 20. (a) Schematic diagram of ONW printer and NW printing process and optical and SEM image of well-aligned PVK NWs. (b) Electrical characteristics of FET based on ONW and schematic of device fabrication procedures. These figures have been adapted from ref. 76, with permission from the Nature Publishing Group.

Fig. 21. (a) Development roadmap of dip-pen nanolithography. (b) Schematic illustration of dip-pen nanolithography. (c) AFM image of single-dot with dip-pen nanolithography. (d) AFM area, height, and volume of DOPC dot with various dwell times. These figures have been adapted from ref. 121, with permission from the Wiley-VCH and ref. 127, with permission from the Royal Society of Chemistry.