## 4 Patterning towards Devices: Conventional and Unconventional Methods
### Lithographic techniques
#### 4.1.1 Photolithographic techniques
Barium titanate (BT) NPs have been incorporated in SU-8 in order to increase the dielectric constant of the polymer for manufacturing embedded capacitors. A loading of such NPs up to 40 vol% has increased the dielectric constant of SU-8 from 3.5 up to 44-46 ((@10 KHz) [146]. Finally, thick films of a nanocomposite based on SU-8 and carbon black NPs have been processed by X-Ray lithography to fabricate electrically and thermally conductive micro-resistive elements and micro-heat sink arrays with aspect ratio up to 15 [147]. Other papers report the use of colloidal NPs as fillers for epoxy photoresist matrices. The employment of nano-sized fillers surface passivated by organic ligands allows for accessing to loadings in the nanocomposite lower than those used for the powders [148] and nanocomposites relatively more homogeneous can be manufactured. As a result, such a class of nanocomposites can be more easily processed, with a reduced component weight [149, 150] and an enhanced light transmittance. The unique optical properties of luminescent colloidal NCs (tuneable emission from the UV to the infrared spectral range, high fluorescence efficiency and resistance to photobleaching) have been conveyed to epoxy photoresists for sensing, actuation, photonic and optoelectronic applications. In these papers, the NC modified photoresists have been patterned and the overall UV-structuring capability of the final material has been demonstrated, as well as the preservation of the NC distinctive optical properties in the fabricated microstructured patterns. Namely, red emitting cadmium selenide NCs, coated by a shell of zinc sulfide (CdSe(@ZnS) capped by a layer of trioctylphosphine oxide/trioctylphosphine (TOPO/TOP) have been incorporated in epoxy photoresist formulations for surface micromachining components to apply in light sensing and photonic applications [106]. In this work, anisole was selected as common solvent for the NCs and resist formulation, because it possesses good film-forming properties and relative good chemical compatibility with the NC organic surface layer. A successful fabrication of luminescent 3D high-aspect-ratio microstructures with inherent photonic functionalities at the micro-scale was demonstrated (Figure 5). The manufactured features show a resolution down to 6 \(\upmu\)m and exhibit only minor deviations in dimensions, resolution and surface morphology with respect to those of the bare epoxy photoresist [106]. Suspended air bridges on red and green emitting polymer nanocomposites formed of TOPO/TOP-capped CdSe(@ZnS NCs embedded in SU-8 by means of chlorobenzene as common solvent have been fabricated [151]. Here, subsequent steps of spin-coating, alignment and exposition applied at different levels to the red and green luminescent nanocomposites were applied to fabricate suspended bridges based on strips with length and width up to 30 \(\upmu\)m and 10 \(\upmu\)m, respectively. This approach has allowed for reliably localizing bi-luminescent colloidal NCs on the same substrate realizing complex patterns promising for 3D photonic crystal technology and waveguiding applications [151]. In the papers mentioned above, neither the reactivity of the NC surface nor that of the capping molecules have affected the photoresist epoxy group conversion, thus allowing the accomplishment of the structure lithography machining with inherent photonic, optical and magnetic characteristics.