Theory of Nanocomposite Network Transistors for Macroelectronics Applications
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the properties of NN-TFTs than the topdown approach of effective mobility modeling, which approximates the random media of the sticks with effective homogenized material.
Theory of Nanocomposite Network Transistors for Macroelectronics Applications M.A. Alam, N. Pimparkar, S. Kumar, and J. Murthy Abstract A new class of nanocomposite network materials based on carbon nanotubes or silicon nanowires for thin-film transistors promises significant improvement in the performance of large-area electronics, or macroelectronics. Evaluation of this novel materials technology requires the development of device models. A multicomponent heterogeneous stick-percolation theory is used to show that the key features of this new transistor technology are the consequences of the percolating spatial geometry of the nanosticks (nanotubes, nanorods, or nanowires) that form the channel. Keywords: microelectronics, nanoscale, nanostructure.
Background Since 2000, there have many reports of a new class of transistors whose channel material is composed of a network of carbon nanotubes (CNTs) or silicon nanowires (SiNWs).1–12 These nanocomposite network thin-film transistors (NN-TFTs) have numerous potential applications, including high-drive-current microelectronics,1,2 large-area electronics (macroelectronics),3–6,11–13 organic electronics,7,14–16 biochemical sensors,8–10 and substrate-neutral technologies for heterogeneous integration. This new class of transistors has the potential to reshape the landscape of classical electronics—which has so far been confined to and dominated by single-crystal Si for high-performance, small-footprint microelectronics17 and by amorphous Si for low-performance macroelectronics14–16,18— by introducing a medium-performance (10–100 MHz) technology suitable for large-area fabrication. In developing a theory of NN-TFTs, one may adopt either a top-down (bulk property)15,19 or a bottom-up (materials struc-
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ture) approach.20,21 The top-down approach assumes that the device obeys square law,22 according to which the effective mobility fits the theoretical expression for the experimental I–V data. In this approach (particularly for network transistors), the mobility might depend on the geometrical parameters of the device such as channel length Lc and “stick” length (nanotube, nanorod, or nanowire length) Ls. On the other hand, the bottom-up approach considers the system as a network of percolating sticks, where current may not always be inversely proportional to Lc.23 If the area density of the sticks is below a percolation threshold (ρ ρc), no conducting path from source to drain exists, while for ρ ρc the carriers can percolate from stick to stick along one or more paths from source to drain. The bottomup approach of “stick-percolation,”24–26 based on percolating electron transport through a collection of nanorod or nanowire “sticks,” provides a more powerful theoretical framework for characterizing
Review of Experimental Results Experiments on NN-TFTs are characterized by several parameters: 1. T
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