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Needs Seminar - Dr. Shaloo Rakheja, Massachusetts Institute of Technology – Birck Nanotechnology Events
Wednesday, March 12, 2014 @ 1:30 pm EDT — Wednesday, March 12, 2014 @ 2:30 pm EDT
BRK 1001

Abstract - With its rich physical properties, the novel 2-D carbon-based material graphene is expected to play an
important role in the advancement of semiconductor technologies. In a recent poll conducted by the International
Technology Roadmap for Semiconductors (ITRS), graphene is named as the material most likely to have the
greatest impact on geometric scaling. As a two-dimensional material, graphene has a limited phase space for
scattering of electrons; hence, the electrons in graphene can have a long mean free path – a property that can be
utilized to build a variety of high frequency analog devices and to implement low-power on-chip interconnects.
Further, the ambipolar characteristics of graphene allow frequency doubler circuits implemented with a single
transistor – something that is not possible with silicon transistors. In my talk, I will examine the requirements and
challenges that must be met for graphene electronics, and discuss possible solutions.


In the first part of the talk, I will describe on-chip interconnect applications with single- and multi-layer graphene
nanoribbons (GNR). I will present physical models for carrier mobility and per-unit-length resistance for
interconnects. The impact of imperfect coupling of contacts with graphene interconnect leads to a non-uniform
distribution of current in the graphene multi-layer interconnect structure. I will quantify the limits imposed on the
maximum benefit of graphene interconnects due to such imperfect contact coupling and interaction of graphene
electrons with the substrate and edge states.


In the second part of the talk, I will present an ambipolar virtual source (AVS) charge-current compact model for
nanoscale graphene transistors applicable in radio frequency (RF) circuits. A self-consistent channel-chargepartitioning
model valid from drift-diffusive to ballistic transport conditions supplements the transport model. The
model has been extensively calibrated with experimental DC I-V and s-parameter measurements of devices with
gate lengths from 650 nm to 40 nm. This has allowed the scaling of mobility and virtual source injection velocity
of carriers in graphene transistors to be studied for the first time.


I will conclude my talk with opportunities for extending graphene technologies to solar cells, optical modulators,
and photo-detectors.

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