Low-temperature / low-pressure thermo-compressive transfer printing for mechanically robust nanowire integration

Abstract

Recently there are growing interests in reliable and economical processes for one dimensional nanostructure-based fabrication. In this master’s thesis, we developed a novel process for the simultaneous alignment and bonding between nanowires (NWs) and metal electrodes by using thermo-compressive transfer printing on In-based alloy electrodes at low temperature (100 °C) and low pressure (5 bar) for 5min and also room-temperature compressive transfer printing on Au electrodes at low pressure (5 bar) and 23 °C for 5min. In both of these processes, bottom-up synthesized NWs were aligned in parallel by shear loading onto the intermediate substrate and then finally transferred onto the target substrate with low melting temperature (In-based alloy metal electrodes) or high ductility metal electrodes (Au electrodes). In case of multi-layer (eg. Cr/Au/In/Au and Cr/Cu/In/Au) metals, the electrodes are softened at low temperature (below 100 °C) and allow the submergence of aligned NWs into their surfaces at a moderate pressure (5 bar). In case of Au, the electrodes (eg. Cr/Au) are soft even at room temperatures (23 °C) due to their high ductility and malleability, and this facilitates the submergence of aligned NWs into the surface of the electrodes at 5bar and 23 °C. By using this thermo-compressive transfer printing on In-based alloy electrodes, robust bonding strength (>47.7 MPa) and stable ohmic contact between NWs and metal electrodes were realized. This method provided a low contact resistance (ρc=3.04×10-5 Ωocm2). Similarly, by using room-temperature compressive transfer printing on non-alloy (Au) metal electrodes, robust mechanical bonding strength (>576 MPa) was realized and electrical contact exhibited schottky behavior. The electrical characteristic could be converted from schottky to ohmic contact through thermal annealing treatment at 250 °C for 5min due to Cr diffusion and direct Cr-ZnO contact. The devices fabricated by thermo-compressive transfer printing...