Here, a new printing method is proposed: direct printing of metal-oxide patterns with well-defined shapes. This printing utilizes a viscoelastic transformation of precursor gels when imprinted; they soften at a certain temperature during thermal imprinting so that the gels can be rheologically imprinted. The imprinted patterns exhibit very little shrinkage after post-annealing, thereby achieving high shape fidelity to the mold together with metal-oxide condensation at imprinting. The viscoelastic transformation and metal-oxide condensation at imprinting constitute the basis of this printing method, which is closely related to the cluster structure of the precursor gel. This method has worked for patterns with dimensions as small as several tens of nanometers. Because this method utilizes the rheological property of an oxide precursor gel and is good at nano-sized patterning, we named it “nano-rheology printing” (n-RP).
In Sect. 14.1, the features of the n-RP process are introduced, with indium tin oxide, InSnO (ITO), taken as an example. The relationship between the n-RP parameters and the structure of the ITO precursor gel are clarified through multiple analyses. We stress that the ITO precursor gel remains a physical gel consisting of nanoclusters that do not chemically bind to each other. To confirm this fact, a unique analytical method, which can identify the ITO gel as a physical one, is introduced in Sect. 14.2. In Sects. 14.3 and 14.4, n-RP methods using a ZrO gel and an RuLaO gel are described. With respect to device fabrication using the n-RP method, TFTs with a short-channel length and active-matrix devices for displays are reported in Chap. 19.
Direct printing of metal-oxide patterns Nano-rheology printing Indium tin oxide (ITO) Physical gel Viscoelastic properties of gels
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