Ahmed Busnaina1
Northeastern University1
Current electronic manufacturing processes have a detrimental impact on the environment and require high operating and capital costs. These processes consist of a complex series of steps using hundreds of high-energy deposition steps (consuming a massive amount of water and electricity). Although conventional silicon-based nanofabrication (top-down approach) has developed into a technique with extremely high precision and integration density, directed assembly-based nanofabrication (bottom-up approach) is attracting more interest because of its low cost and the advantages of additive manufacturing. The directed assembly process is achieved by applying external fields to nanomaterials and driving them toward pre-patterned substrates to form functional nanostructures. Here we introduce sustainable and scalable techniques for additively manufacturing nano and microelectronics. These techniques eliminate high-energy, chemically intense processing by utilizing direct assembly of nanoscale particles or other nanomaterials at room temperature and atmospheric pressure onto a substrate to precisely where the structures are built. Although many of the nanomaterials-based electronics transistors were made using organic materials and/or nanomaterials that do not need to be sintered and annealed such as carbon nanotubes and 2D materials, however, to have the most commercial impact, traditional semiconductors such as silicon, III-V and II-VI semiconductors need to be printed to produce high-performance electronics. Here we show how this technology can print single crystal structures and make transistors using a purely additive (directed assembly enabled) process using inorganic or organic semiconductors, metals, and dielectrics nanoparticles suspended using colloid chemistry, and discuss post assembly crystallization using different annealing conditions.<br/>We will show that II-VI semiconductors could be printed to obtain a high on/off ratio and mobility. Three different assembly techniques will be discussed electrophoretic, convective interfacial, and fast fluidic assembly. The fabrication of ZnO transistors and ZnSe diodes was conducted using a directed assembly of the nanoparticles into micro, and nanopatterned structures. By controlling the concentration of the nanoparticle suspension, void-free patterns can be assembled on silicon/silicon dioxide (Si/SiO2) or sapphire substrates over a four-inch wafer. The assembled patterns are thermally annealed at 100C for one minute prior to the printing of the source/drain electrodes to remove organic stabilizers wrapping around the nanoparticles as well as to sinter the nanoparticles, which leads to a gate voltage-modulated field effect in accumulation mode with Ion/Ioff ratios above 1000,000. The assembly and annealing mechanism will be discussed. We address how these directed assembly processes mechanisms of controlling the nanoparticles or nanoelements and the advantages and drawbacks of utilizing each process.<br/>Results show that at least an order of magnitude savings in embodied energy cost can be realized. This new technology will enable the fabrication of nanoelectronics while reducing the cost by 10-100 times and can print 1000 faster and 1000 smaller (down to 20nm) structures than ink-jet-based printing. The nanoscale printing platform enables the heterogeneous integration of interconnected circuit layers (like CMOS) of printed electronics and sensors at ambient temperature and pressure on rigid or flexible substrates.