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2D MOSFET operation of a fully-depleted bulk MoS<inf>2</inf> at quasi-flatband back-gate
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2015
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Unknown Venue
In this paper, 2D MOSFET operation of a fully-depleted double-gate bulk MoS <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> is studied at a quasi-flatband of the back-gate for the first time. Several key device parameters such as equivalent oxide thickness (EOT), carrier concentration, flatband voltage, dielectric constant and carrier mobility were extracted from I-V and C-V characteristics and at room temperature. In a similar operation to the inversion-mode SOI MOSFETs in [1], the backgate was used to keep a sheet of mobile charges on the flake back-side by its quasi-flatband operation at a fixed voltage (0 V). Afterward, the top-gate was used as the active gate to perform mobile charge accumulation or depletion in the channel. Fig. 1 shows the device architecture together with the high frequency R-C equivalent circuit model for this underlap gate architecture. Fig. 2 represents the top-view microscope picture of the fabricated MoS <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> bulk MOSFET with a flake thickness of 38 nm, measured by AFM. The fabrication steps include mechanical exfoliation of MoS <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> crystals on a 260 nm thick oxidized Si substrate, e-beam lithography to make S/D pads, 50 nm Ni by thermal evaporation and lift-off, gate patterning, high-k/metal-gate stack deposition (1 nm of SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> by thermal evaporation, 11 nm of ZrO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> by ALD deposition at 105 °C, 30 nm of Ni by thermal evaporation) and lift-off. The measurements were done at room temperature using an Agilent B1500A Semiconductor Parameter Analyzer. Fig. 3 shows its I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</inf> -V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</inf> , reporting a subthreshold slope of 110 mV/dec. and I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</inf> /I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</inf> of ∼1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> , both at V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</inf> =100 mV.