3 research outputs found
Improved Contacts to MoS<sub>2</sub> Transistors by Ultra-High Vacuum Metal Deposition
The scaling of transistors to sub-10
nm dimensions is strongly
limited by their contact resistance (<i>R</i><sub>C</sub>). Here we present a systematic study of scaling MoS<sub>2</sub> devices
and contacts with varying electrode metals and controlled deposition
conditions, over a wide range of temperatures (80 to 500 K), carrier
densities (10<sup>12</sup> to 10<sup>13</sup> cm<sup>ā2</sup>), and contact dimensions (20 to 500 nm). We uncover that Au deposited
in ultra-high vacuum (ā¼10<sup>ā9</sup> Torr) yields
three times lower <i>R</i><sub>C</sub> than under normal
conditions, reaching 740 Ī©Ā·Ī¼m and specific contact
resistivity 3 Ć 10<sup>ā7</sup> Ī©Ā·cm<sup>2</sup>, stable for over four months. Modeling reveals separate <i>R</i><sub>C</sub> contributions from the Schottky barrier and
the series access resistance, providing key insights on how to further
improve scaling of MoS<sub>2</sub> contacts and transistor dimensions.
The contact transfer length is ā¼35 nm at 300 K, which is verified
experimentally using devices with 20 nm contacts and 70 nm contact
pitch (CP), equivalent to the ā14 nmā technology node
Role of Remote Interfacial Phonon (RIP) Scattering in Heat Transport Across Graphene/SiO<sub>2</sub> Interfaces
Heat
transfer across interfaces of graphene and polar dielectrics
(e.g., SiO<sub>2</sub>) could be mediated by direct phonon coupling,
as well as electronic coupling with remote interfacial phonons (RIPs).
To understand the relative contribution of each component, we develop
a new pumpāprobe technique called voltage-modulated thermoreflectance
(VMTR) to accurately measure the change of interfacial thermal conductance
under an electrostatic field. We employed VMTR on top gates of graphene
field-effect transistors and find that the thermal conductance of
SiO<sub>2</sub>/graphene/SiO<sub>2</sub> interfaces increases by up
to Ī<i>G</i> ā 0.8 MW m<sup>ā2</sup> K<sup>ā1</sup> under electrostatic fields of <0.2 V nm<sup>ā1</sup>. We propose two possible explanations for the small
observed Ī<i>G</i>. First, because the applied electrostatic
field induces charge carriers in graphene, our VMTR measurements could
originate from heat transfer between the charge carriers in graphene
and RIPs in SiO<sub>2</sub>. Second, the increase in heat conduction
could be caused by better conformity of graphene interfaces under
electrostatic pressure exerted by the induced charge carriers. Regardless
of the origins of the observed Ī<i>G</i>, our VMTR
measurements establish an upper limit for heat transfer from unbiased
graphene to SiO<sub>2</sub> substrates via RIP scattering; for example,
only <2% of the interfacial heat transport is facilitated by RIP
scattering even at a carrier concentration of ā¼4 Ć 10<sup>12</sup> cm<sup>ā2</sup>
Stacked Graphene-Al<sub>2</sub>O<sub>3</sub> Nanopore Sensors for Sensitive Detection of DNA and DNAāProtein Complexes
We report the development of a multilayered graphene-Al<sub>2</sub>O<sub>3</sub> nanopore platform for the sensitive detection of DNA and DNAāprotein complexes. Graphene-Al<sub>2</sub>O<sub>3</sub> nanolaminate membranes are formed by sequentially depositing layers of graphene and Al<sub>2</sub>O<sub>3</sub>, with nanopores being formed in these membranes using an electron-beam sculpting process. The resulting nanopores are highly robust, exhibit low electrical noise (significantly lower than nanopores in pure graphene), are highly sensitive to electrolyte pH at low KCl concentrations (attributed to the high buffer capacity of Al<sub>2</sub>O<sub>3</sub>), and permit the electrical biasing of the embedded graphene electrode, thereby allowing for three terminal nanopore measurements. In proof-of-principle biomolecule sensing experiments, the folded and unfolded transport of single DNA molecules and RecA-coated DNA complexes could be discerned with high temporal resolution. The process described here also enables nanopore integration with new graphene-based structures, including nanoribbons and nanogaps, for single-molecule DNA sequencing and medical diagnostic applications