Research and engineering towards the ITFET : graphene heterostructure dielectrics and rhenium based transistors
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As semiconductor device sizes continue to scale downwards, performance degradation associated with quantum mechanical effects become a greater problem. With this, continuing the path along Moore’s Law has become more difficult and paradigm shifting technologies have begun to gain traction in device research communities. One such device is the interlayer tunneling field effect transistor (ITFET) which harnesses quantum mechanical tunneling between two channel materials separated by a thin dielectric. These devices are created from two dimensional Van der Waals crystals stacked into layered heterostructures using advanced semiconductor manufacturing techniques. The pages hereafter represent the research and engineering towards an ITFET focusing on graphene, graphene dielectrics, and Rhenium based transition metal dichalcogenides (TMDs). We begin with a zeroth order investigation of the system by creating backgated devices of two partially overlapped graphene crystals and extracting the interlayer contact resistance. We show that the interlayer contact resistance is small, localized to tunneling ‘hot-spots,’ and that overall device performance is dependent on the characteristics of both graphene layers. To continue we investigate a similar device but with a dielectric deposited between the two via atomic layer deposition (ALD) and physical vapor deposition (PVD). Innovative fabrication techniques were created and allowed for the fabrication of dozens of devices simultaneously. Moving forward, we show that the seed layer in the ALD / PVD process is incompatible with ITFET device physics. The TiO2 seed layer in this process shows Fowler-Nordheim tunneling, Poole-Frenkel tunneling, and thermionic emission through the tunnel barrier at all thicknesses, electric fields, and temperatures. To conclude we investigate the Rhenium based TMDs, ReS2 and ReSe2, as a channel material for an ITFET by analyzing their performance metrics as field effect transistors (FETs). Topgated ReS2 devices were created and showed current saturation, voltage gain, and performance metrics on par with many of the more widely researched TMDs. Backgated ReSe2 devices showed current saturation, low contact resistances, ambipolar conduction, and similar performance capabilities to the ReS2 devices. Both materials may prove an interesting channel material for optoelectronic and novel logic devices.