RESUMO
Chemical vapor deposition (CVD) of graphene on top of metallic foils is a technologically viable method of graphene production. Fabrication of microelectronic devices with CVD grown graphene is commonly done by using photolithography and deposition of metal contacts on top of the transferred graphene layer. This processing is potentially invasive for graphene, yields large spread in device parameters, and can inhibit up-scaling. Here we demonstrate an alternative process technology in which both lithography and contact deposition on top of graphene are prevented. First a prepatterned substrate is fabricated that contains all the device layouts, electrodes and interconnects. Then CVD graphene is transferred on top. Processing parameters are adjusted to yield a graphene layer that adopts the topography of the prepatterned substrate. The metal-graphene contact shows low contact resistances below 1 kΩ µm for CVD graphene devices. The conformal transfer technique is scaled-up to 150 mm wafers with statistically similar devices and with a device yield close to unity.
RESUMO
A generic process has been developed to grow nearly defect-free arrays of (heterostructured) InP and GaP nanowires. Soft nano-imprint lithography has been used to pattern gold particle arrays on full 2 inch substrates. After lift-off organic residues remain on the surface, which induce the growth of additional undesired nanowires. We show that cleaning of the samples before growth with piranha solution in combination with a thermal anneal at 550 degrees C for InP and 700 degrees C for GaP results in uniform nanowire arrays with 1% variation in nanowire length, and without undesired extra nanowires. Our chemical cleaning procedure is applicable to other lithographic techniques such as e-beam lithography, and therefore represents a generic process.
