Transcript Crossbar

Successor of the Transistor
The Crossbar Latch:
Joseph Adorno
Brian McSkimming
Edward Sniezak
Current Size of Transistors
Advanced chip
which currently
make processors
with feature sizes of
90 nanometers, say
they could probably
reduce feature sizes
to 32 nanometers.
Current Transistor Technology
To turn the MOSFET
on in saturation
mode Vds must be
greater then or
equal to
Vgs – Vt.
Problems with Current Transistors
As transistor sizes decrease, very small
gate lengths can cause transistors to
leak electricity, devices to consume
large amounts of power, data to
corrupt, and device performance to
Heat and Power problems
Power dissipated in this resistance
causes more heating of the junction,
which further increases the junction
temperature. If the heat produced by
the transistor is more than the heat
sink can dissipate, the thermal
runaway occurs and the transistor will
be destroyed.
Technology Roadmap
Hp’s Solution
The Crossbar-Latch
Crossbar latches
are not transistors,
so they do not
experience the,
size, power, leakage
or heat problems
that transistors do.
Therefore, chip
makers can use
large numbers of
small latches,
rather than
transistors, to make
chips more
Crossbar latches are devices created between the two
junctions where one tiny wire – currently 30 nanometers
across, but could be decreased to as small as 2 to 3
nanometers across – crosses two other parallel wires at
right angles. Each junction has a switch. The switch, a
tunnel junction, consists of a single molecular layer
sandwiched between two metal wires. The layer is
normally an insulator. But if it is thin enough, charged
particles can tunnel through the junction. If the
junction’s resistance to such tunneling current is high,
the switch is open; if it is low, the switch is closed.
Applying a high or low voltage across the switch
toggles the barrier between low and high resistance.
The schematic illustrates the basic function of a latch in a
crossbar latch
The schematic of a actual crossbar latch with L being the
signal line, and Ca and Cb are the two control lines
According to “The crossbar latch: Logic
value storage, restoration, and inversion in
crossbar circuits”, HP lab researchers
describe and demonstrate a microscopic
device consisting of a single wire acting as a
single line, crossed by two control lines with
an electrically switchable molecular-scale
junction where they intersect.
By applying a sequence of voltage impulses
to the control lines and using switches of
opposite polarities, HP Lab researchers
demonstrated that the crossbar latch can
perform the NOT function which is essential
for general computing operations.
These are experimental demonstrations of a
working crossbar latch. (a) The pulse sequence on
the two control lines Ca and Cb to achieve the latch
function. P1, P4, and P7 are the test pulses, P2
and P3 are open, P5 and P6 are closed.
These are six trial
runs varying only
the input signal
voltage. Input
voltages of 0.3 and
0.4 volts latched
correctly and
inverted correctly
with signal
restoration while 0.2
volts failed to latch
The advantage of using the crossbar latch, the two
latch control lines may be driven by conventional
circuitry outside the nanoscale circuit, which can be
connected to a large number of logic signal lines.
The disadvantage of using the crossbar latch is the
limited lifetime (of 100 s of cycles) and switching
speeds (.1kHz), both require improvement before
reliable applications.
“Transistors will continue to be used for years to come
with conventional silicon circuits, but crossbar
latches could very well replace transistors in
computers someday, just as transistors replaced
vacuum tubes and vacuum tubes replaced
electromagnetic relays before them.”
- quote by Phil Kuekes, the holder of
the patent for the crossbar latch.
- Nanotechnology and Science
by: Mitin, Kochelap, and Stroscio
- The crossbar latch: Logic value storage, restoration,
and inversion in crossbar circuits.
Journal of Applied Physics, Issue 97, Volume 3
- Researchers work on Transistor Successor
IEEE article, May 2005