NANOTECHNOLOGY IN NEW INNOVATION
What is nanotechnology?
These types of technology based in the
experimental process, other than the traditional module, and technology by the
instruments in this era. But, now we are moving towards fundamental technique
like erection and fabrication. This is outdated and not in practice in science
and technology medicine, engineering, space science and so on. That is not in
part of visibility such science and technology is in simple word-nanotechnology.
Minimizing the size of electron devices to
the nanometer scale brings the following quantitative effects. First, greater
manipulation among devices can be achieved. Second, the devices operation
becomes faster, because the distance traveled by the electrons in the devices
is low expedition.
But, what about qualitative effects? Investigating
the qualitative effects of nanotechnology is not so easy, since in many cases
only reducing the structure is not enough to outcome in significant changes.
When dealing with dimensions so small those individual atoms can be counted,
unevenness in the smooth surface of a single atom can obstruct the movement of
electrons, preventing the realization of anticipated physical phenomena. To
obtain perfect qualitative changes, devices must be fabricated with exacting
precision at least single-atom level.
This article describes three qualitative
changes, or effects, that we at the NeRI have observed as we reduce the
dimensions of devices to the nanometer scale. These qualitative effects are
demonstrated for the first time when the structure and surface of the devices
are carefully produced with geometrical precision at the atomic level.
Finding the entire limits of transistor
performance
We are currently conducting research of a
nanoscale metal-oxide-semiconductor field-effect transistor (MOSFET). Showing
the structure of our proposed design for a MOSFET. In this structure, the
semiconductor layer (channel), through which the electrons pass is surrounded
by two gates. The structure is called a double-gate MOSFET, or XMOS, so named
be- cause of the structure's similarity to the Greek letter E (X).
In the planar MOSFETs currently in use,
reducing the distance between source and drain causes leak current, in which
electrons pass from source to drain when they are not supposed to. The XMOS
structure eliminates this problem, as the channel is surrounded by the two
gates. Indeed, performance improves as the size of the device is reduced. The
key here is to produce the larger drain current with the lower gate voltage.
The gate voltage required to change the drain current by a factor of 10 is
called the sub-threshold slope (s-slope). The smaller the s-slope is, the
greater the performance of the device will be.
Recently we succeeded in fabricating a
prototype nanoscale XMOS with an ideal rectangular cross-section as shown in
Figure 1(b): channel thickness of 13nm and width of 82nm. The sides (the
semiconductor surface through which the electrons flow) have a surface that is
smooth at the atomic level. The device's characteristics indicated that, as shown
in Figure 2, performance improves as the thickness of the channel decreases and
the theoretically predicted performance limit is reached at 13nm. This is a
qualitative effect achieved for the first time by accurately and precisely
controlling dimensions, structure, and shape at the atomic level.
Looking Particular electrons
Since electrons are particles carrying an
electrical charge, it should be possible to observe the behavior of individual
electrons. In the ordinary world, this is generally impossible, but when
devices are shrunk to the nanometer level, individual electrons become visible.
The following is an example in which electrons are made visible using a simple
device with silicon rods.
The device used was a rectangular silicon
rod with a cross-section width of 10nm and a height of about 50nm. When a
voltage of (for example) 0.1V is applied between the ends of the rod, a current
is generated. In this state, as the voltage in the silicon substrate shown in
Figure 3(a) is gradually made negative, the current increases or decreases with
a certain step as shown in Figure 3(b). These current steps occur because changes
in the voltage of the substrate cause an electron attached to or released from
the silicon rod surface. When an electron becomes attached to a point anywhere
on the silicon rod surface, a repulsive force is generated between the attached
electron and the electrons flowing through the inside of the rod. This repulsive
force obstructs the flow of the electrons and decreases the current. This
phenomenon occurs only when the rod is extremely and precisely thinned and is
thus a qualitative effect of nanotechnology.
Dominating electron waves
Finally, I present an example of a device
that utilizes the wave properties of electrons. When electrons are constrained
between two walls and the distance between the walls is gradually decreased,
the electrons reflected from the walls begin to behave as waves, reinforcing
each other or canceling each other out. When the distance is integrally
multiplied by the magnitude of the electron wave, the electrons reinforce each
other. When multiplied by a half-integer, however, the electrons cancel each
other out, so that electrons cannot be present.
This phenomenon can be visible at room
temperature by utilizing another property of electrons, called spin, an
ultra-small magnet. Figure 4 shows a cross-section of a prototype spin device
we fabricated. The key feature of this device is that electrons enter a nonmagnetic
layer are reflected by the layers above and below, which are an insulating
layer and a ferromagnetic layer respectively. This device demonstrates the
wave-like overlapping and canceling behavior described above. When the voltage
is applied at a certain level to maintain the wave length constant, the
electrical current through the nonmagnetic layer should change as a function of
the nonmagnetic layer thickness. Under the condition of the thickness where the
waves overlap, the current should increase; otherwise, the current should
decrease.
The results of our experiments will present
in process. When the thickness of the nonmagnetic layer was carefully varied
from 0 to 3 NM, the current changed clearly up and down accordingly to the
thickness variation. This phenomenon was rendered visible for the first time
because the individual layers of metal and insulator are atomically flat and
smooth, testifying once again to the qualitative changes made possible through
nanotechnology.
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