PDMS residues-free micro/macrostructures on flexible substrates

Transfer printing has been reported recently as a viable route for electronics on flexible substrates. The method involves transferring micro-/macrostructures such as wires or ultra-thin chips from Si (silicon) wafers to the flexible substrates by using elastomeric transfer substrates such as poly(dimethylsiloxane) (PDMS). A major challenge in this process is posed by the residues of PDMS, which are left over on Si surface after the nanostructures have been transferred. As insulator, PDMS residues make it difficult to realize metal connections and hence pose challenge in the way of using nanostructures as the building blocks for active electronics. This paper presents a method for PDMS residues-free transfer of Si micro-/macrostructures to flexible substrates such as polyimide (PI). The PDMS residues are removed from Si surface by immersing the transferred structures in a solution of quaternary ammonium fluoride such as TBAF (Tetrabutylammonium Fluoride) and non-hydroxylic aprotic solvent such as PMA (propylene glycol methyl ether acetate). The residues are removed at a rate (1.5 lm/min) which is about five times faster than the traditional dry etch methods. Unlike traditional alternatives, the presented method removes PDMS without attacking the flexible PI substrates.