Intregrating metallic wiring with three-dimensional polystyrene colloidal crystals using electron-beam lithography and three-dimensional laser lithography

Abstract

Abstract. We demonstrate a method to fabricate narrow, down to a few micron wide metallic leads on top of a three-dimensional colloidal crystal self-assembled from polystyrene (PS) nanospheres of diameter 260 nm, using electron-beam lithography. This fabrication is not straightforward due to the fact that PS nanospheres cannot usually survive the harsh chemical treatments required in the development and lift-off steps of electron-beam lithography. We solve this problem by increasing the chemical resistance of the PS nanospheres using an additional electron-beam irradiation step, which allows the spheres to retain their shape and their self-assembled structure, even after baking to a temperature of 160 degrees C, the exposure to the resist developer and the exposure to acetone, all of which are required for the electron-beam lithography step. Moreover, we show that by depositing an aluminum oxide capping layer on top of the colloidal crystal after the e-beam irradiation, the surface is smooth enough so that continuous metal wiring can be deposited by the electron-beam lithography. Finally, we also demonstrate a way to self-assemble PS colloidal crystals into a microscale container, which was fabricated using direct-write three-dimensional laser-lithography. Metallic wiring was also successfully integrated with the combination of a container structure and a PS colloidal crystal. Our goal is to make a device for studies of thermal transport in 3D phononic crystals, but other phononic or photonic crystal applications could also be envisioned.

Fundamentals, progress and perspectives on high-frequency phononic crystals

“…3D PnCs resemble classical natural crystals but their fabrication is more complicated as compared to the lower dimensionality PnCs fabricated by microlithography. Generally speaking, the latter builds the 3D structure in a lay-by-lay process [87,88], e.g. stacking the 2D patterns creates the stacked-stripe layer structures (figure 1(f)) [66].…”

Controlling thermal conductance using three-dimensional phononic crystals

“…However, there is no easy way to integrate any measurement devices and circuitry with such crystals. There have been efforts to allow fabrication of metallic wires on these crystals by hardening the spheres with an electron beam [28], but issues still exist with the continuity of the wiring due to the cracking of the crystals and separation at the substrate interface during drying. In this study, in contrast, 3D laser lithography is used for the direct crystal fabrication.…”

Controlling thermal conductance using three-dimensional phononic crystals

“…7,12,19,20,[29][30][31] However, there is no easy way to integrate sophisticated measurement devices and circuitry with such crystals. There have been efforts to allow the fabrication of metallic wires on these crystals by hardening the spheres with an electron beam, 32 but issues still exist with the continuity of the wiring due to the cracking of the crystals and separation at the substrate interface during drying.…”