Prof.
Toshishige Yamada, Ph.D. (EE), UC
tyamada@soe.ucsc.edu, t.yamada@ieee.org Lectures 1.
EE135 Electromagnetic fields and
waves in Winter 2006 2.
EE135 Electromagnetic fields and
waves in Winter 2007 3.
EE293 Fundamentals of
semiconductor physics - nanoscale materials and
devices in Winter 2014 4.
EE227 Fundamentals of semiconductor physics in Fall 2014 At Santa
Clara University (SCU), I have taught
ELEN 151 Semiconductor devices, ELEN 152 Semiconductor devices and
technology, ELEN 201 Electromagnetism, ELEN 261 Semiconductor physics and
devices, ELEN 361 Nanoelectronics, and MECH 121 Thermodynamics. |
Toshishige
Yamada Publications
with [PDF] links
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Goals
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Establish
energy band and equivalent circuit methods for nanoscale
devices and materials
Perform bottom up theoretical analysis and compare
with experimental data
Use
thermodynamic ways of thinking in electronic device and material research
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(a) Coulomb blockade for ID-VD
(staircase) interpreted using an energy band diagram (SPIE
2010, UCSC)
Coulomb
staircase is usually described in a highly mathematical way and it is not
easy to visualize it. But using the energy band method, it is possible to visualize
why the I-V characteristics are staircase-like. |
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(b) Carbon nanotube
gas sensing or detection mechanism (PRB
2004, APL
2006, UCSC UARC at NASA)
This is a model of nanotube gas sensing or detection mechanism. Gas
molecules will modify the nanotube-electrode
contact properties (contact theory via Schottky
barrier modulation) rather than change the nanotube
bulk properties (bulk theory via doping). |
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Carbon nanotube FETs
change their channel conductance by orders of magnitude in the gas
atmosphere (the figure in the right column). There have been heated
discussions for the gas detection mechanism. In doping theory, they assume
the nanotube is doped by the gas and thus, there is
a large modification of the channel conductance. I have proposed contact
theory in "Modeling
of Carbon Nanotube Schottky
Barrier Modulation under Oxidizing Conditions," Phys. Rev. B 69 (12), 125408 (2004) and "Equivalent
circuit model for carbon nanotube Schottky barrier: Influence of neutral polarized gas
molecules," Appl. Phys. Lett. 88 (8),
083106 (2006) and considered the gas changes the
electrode-nanotube contact properties while keeping
the nanotube bulk properties unchanged
Recently, scientists at Nanyang have reported an
experiment on the gas detection mechanism in Ning Peng, Hong Li, and Qing Zhang, "Nanoscale
contacts between carbon nanotubes and metallic pads,"
ACS Nano 3
(12), 4117-21 (2009) and scientists at Nanyang and
MIT Ning Peng, Qing
Zhang, Chee Lap Chow, Ooi
Kiang Tan, and Nicola Marzari, "Sensing Mechanisms for
Carbon Nanotube Based NH3 Gas Detection,"
Nano Lett. 9
(4), 1626-30 (2009), and ended this controversy. They have concluded
"Our results are consistent with Yamada's
theoretical prediction that SB (Schottky barrier)
modulation is most significant when CNT is operating in the depletion
mode." The
same work has been reviewed extensively by scientists at Tales and Ecole Polytechnique in Paolo Bondavalli, Pierre Legagneux,
and Didier Pribat, "Carbon nanotubes
based transistors as gas sensors: state of the art and critical review,"
Sensors and Actuators B 140 (1),
304-318 (2009) and scientists at Tales and SKKU, Didier Pribat
and Paolo Bandavalli, "Thin-Film Transistors and
Circuits Based on Carbon Nanotubes," J.
Disp. Tech. 8 (1), 54-60 (2012).
"The IBM works have been analyzed and theoretically modeled by Yamada at
NASA. Yamada has explained simple Schottky model
cannot justify alone the effect of oxygen molecules on the modulation of the Schottky values to obtain a p-type junction in air (Fig.
8)." "Yamada explains that the only way to consistently justify the
effect of oxygen is to take into an account a sort of transition between the
metal and the SWCNTs. This region is characterized
by gold clusters on the electrode surface and charged oxygen molecules."
"We can observe that in this case the Schottky
barriers for holes in air if CNTs are exposed to
air, according to the experimental results obtained by IBM researchers:
Yamada's model seems to be satisfying and suitable to describe the effective
interaction of gases on metal/SWCNT junctions."
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[1] Research activities
in the Electrical Engineering at UC
(a) Study
of InP nanowire devices
in collaboration with Prof. Nobby
P. Kobayashi,
Dr. Andrew J. Lohn (former UCSC Ph.D. student and presently with
Sandia National Labs), and Mr. Hidenori Yamada (presently UCSD Ph.D. student) as
shown in figures in the left column 1. Modeling of staircase-like I-V
characteristics behavior in fused InP
nanowire devices. 2. Staircase period ~ 1 V at room
temperature. 3. Staircase clearly visible in dark,
but disappearing in light illumination. 4. Coulomb island
formed at a location where a pair of nanowires
fuse. The crystalline structure seems continuous there. The staircase I-V
is considered to be due to the partial trap of an electron wave at the fused
segment. The Coulomb island there is so tiny that q2/C >> kBT and the presence or absence of a single
electron will influence transport significantly. Additionally, Rtot >> RQ so that the number
of electrons on the island is quantized. Thus, the Coulomb blockade is
considered to occur (the figure in the left column). Related presentations 1.
T. Yamada, H.
Yamada, A. J. Lohn, and N. P. Kobayashi, "Room-temperature
Coulomb Staircase in Semiconducting InP
Nanowires Modulated with Light Illumination",
Nanotechnology 22 (5), 055201 (2011). [pdf] 2.
T. Yamada, H.
Yamada, A. J. Lohn, and N. P. Kobayashi, (invited)
"Transport
in fused InP nanowire device in dark and under illumination: Coulomb
staircase scenario," Proc. SPIE 8106, 81060I, 3. H. Yamada, T. Yamada, A. J. Lohn, and
N. P. Kobayashi, "Reversible
suppression of Coulomb staircase in InP nanowires with light illumination," pp. 304-305 of the
Proceedings of IEEE
Nanotechnology Materials and Devices Conference 2010 (NMDC 2010), Monterey,
CA, Oct. 12-15, 2010. [pdf] 4.
H. Yamada, T. Yamada, A. J. Lohn, and N. P. Kobayashi, "Coulomb
staircase in fused semiconducting InP nanowires under light illumination," Proc. SPIE 7768, 77680B, San Diego, CA, Aug. 1-5,
2010. [pdf] 5. H. Yamada, T.
Yamada, A. J. Lohn, and N. P. Kobayashi,
"Room-temperature Coulomb Staircase in Semiconducting InP Nanowires Modulated with
Light Illumination," (P3.3) in the Material Research Society Meeting
Spring, San Francisco, CA, Apr. 5-9, 2010. (b) Study of carbon nanotube FET gas sensing
mechanism conducted at 1. T.
Yamada, "Equivalent
Circuit Model for Carbon Nanotube Schottky Barrier: Influence of Neutral Polarized Gas
Molecules," Appl. Phys. Lett. 88
(8), 083106 (2006). [pdf] 2.
T.
Yamada, "Modeling
of Carbon Nanotube Schottky
Barrier Modulation under Oxidizing Conditions," Phys. Rev. B 69 (12), 125408 (2004). [pdf] [2] Research activities at
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