Successor of the Successor of the TransistorTransistor

The Crossbar Latch:The Crossbar Latch:

Presenters:Presenters:

Joseph AdornoJoseph Adorno Brian McSkimmingBrian McSkimming Edward SniezakEdward Sniezak

Current Size of TransistorsCurrent Size of Transistors

Advanced chip Advanced chip manufactures, manufactures, which currently which currently make processors make processors with feature sizes with feature sizes of 90 nanometers, of 90 nanometers, say they could say they could probably reduce probably reduce feature sizes to 32 feature sizes to 32 nanometers.nanometers.

Current Transistor TechnologyCurrent Transistor Technology

To turn the To turn the MOSFET on in MOSFET on in saturation mode saturation mode Vds must be Vds must be greater then or greater then or equal to equal to

Vgs – Vt.Vgs – Vt.

Problems with Current TransistorsProblems with Current Transistors

As transistor sizes decrease, very As transistor sizes decrease, very small gate lengths can cause small gate lengths can cause transistors to leak electricity, transistors to leak electricity, devices to consume large devices to consume large amounts of power, data to amounts of power, data to corrupt, and device performance corrupt, and device performance to vary.to vary.

Heat and Power problemsHeat and Power problems

Power dissipated in this resistance Power dissipated in this resistance causes more heating of the causes more heating of the junction, which further increases junction, which further increases the junction temperature. If the the junction temperature. If the heat produced by the transistor is heat produced by the transistor is more than the heat sink can more than the heat sink can dissipate, the thermal runaway dissipate, the thermal runaway occurs and the transistor will be occurs and the transistor will be destroyed. destroyed.

Technology RoadmapTechnology Roadmap

Hp’s SolutionHp’s Solution

The Crossbar-LatchThe Crossbar-Latch

Crossbar-LatchCrossbar-Latch

Crossbar latches Crossbar latches are not are not transistors, so transistors, so they do not they do not experience the, experience the, size, power, size, power, leakage or heat leakage or heat problems that problems that transistors do.transistors do.

Therefore, chip Therefore, chip makers can use makers can use large numbers of large numbers of small latches, small latches, rather than rather than transistors, to transistors, to make chips more make chips more powerful.powerful.

Crossbar-LatchCrossbar-Latch

Crossbar latches are devices created between Crossbar latches are devices created between the two junctions where one tiny wire – currently the two junctions where one tiny wire – currently 30 nanometers across, but could be decreased to 30 nanometers across, but could be decreased to as small as 2 to 3 nanometers across – crosses as small as 2 to 3 nanometers across – crosses two other parallel wires at right angles. Each two other parallel wires at right angles. Each junction has a switch. 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.

Crossbar-LatchCrossbar-Latch

- The schematic illustrates the basic function of a latch The schematic illustrates the basic function of a latch in a crossbar latchin a crossbar latch

- The schematic of a actual crossbar latch with L being The schematic of a actual crossbar latch with L being the signal line, and Ca and Cb are the two control linesthe signal line, and Ca and Cb are the two control lines

Crossbar-LatchCrossbar-Latch

According to “The crossbar latch: Logic According to “The crossbar latch: Logic value storage, restoration, and value storage, restoration, and inversion in crossbar circuits”, HP lab inversion in crossbar circuits”, HP lab researchers describe and demonstrate researchers describe and demonstrate a microscopic device consisting of a a microscopic device consisting of a single wire acting as a single line, single wire acting as a single line, crossed by two control lines with an crossed by two control lines with an electrically switchable molecular-scale electrically switchable molecular-scale junction where they intersect.junction where they intersect.

Crossbar-LatchCrossbar-Latch

By applying a sequence of voltage By applying a sequence of voltage impulses to the control lines and using impulses to the control lines and using switches of opposite polarities, HP Lab switches of opposite polarities, HP Lab researchers demonstrated that the researchers demonstrated that the crossbar latch can perform the NOT crossbar latch can perform the NOT function which is essential for general function which is essential for general computing operations.computing operations.

Crossbar-LatchCrossbar-Latch

These are experimental demonstrations of a These are experimental demonstrations of a working crossbar latch. (a) The pulse sequence working crossbar latch. (a) The pulse sequence on the two control lines Ca and Cb to achieve the on the two control lines Ca and Cb to achieve the latch function. P1, P4, and P7 are the test pulses, latch function. P1, P4, and P7 are the test pulses, P2 and P3 are open, P5 and P6 are closed. P2 and P3 are open, P5 and P6 are closed.

Crossbar-LatchCrossbar-Latch

These are six trial These are six trial runs varying only runs varying only the input signal the input signal voltage. Input voltage. Input voltages of 0.3 and voltages of 0.3 and 0.4 volts latched 0.4 volts latched correctly and correctly and inverted correctly inverted correctly with signal with signal restoration while restoration while 0.2 volts failed to 0.2 volts failed to latchlatch

Crossbar-LatchCrossbar-Latch

The advantage of using the crossbar latch, The advantage of using the crossbar latch, the two latch control lines may be driven by the two latch control lines may be driven by conventional circuitry outside the nanoscale conventional circuitry outside the nanoscale circuit, which can be connected to a large circuit, which can be connected to a large number of logic signal lines.number of logic signal lines.

The disadvantage of using the crossbar latch The disadvantage of using the crossbar latch is the limited lifetime (of 100 s of cycles) and is the limited lifetime (of 100 s of cycles) and switching speeds (.1kHz), both require switching speeds (.1kHz), both require improvement before reliable applications.improvement before reliable applications.

““Transistors will continue to be used for years Transistors will continue to be used for years to come with conventional silicon circuits, but to come with conventional silicon circuits, but crossbar latches could very well replace crossbar latches could very well replace transistors in computers someday, just as transistors in computers someday, just as transistors replaced vacuum tubes and transistors replaced vacuum tubes and vacuum tubes replaced electromagnetic vacuum tubes replaced electromagnetic relays before them.” relays before them.”

- quote by Phil Kuekes, the holder - quote by Phil Kuekes, the holder of of the patent for the crossbar the patent for the crossbar latch.latch.

BibliographyBibliography

- - Nanotechnology and ScienceNanotechnology and Scienceby: Mitin, Kochelap, and Stroscioby: Mitin, Kochelap, and Stroscio

- The crossbar latch: Logic value storage, - The crossbar latch: Logic value storage, restoration, and inversion in crossbar circuits.restoration, and inversion in crossbar circuits. Journal of Applied Physics, Issue 97, Journal of Applied Physics, Issue 97, Volume 3Volume 3

- Researchers work on Transistor Successor- Researchers work on Transistor SuccessorIEEE article, May 2005IEEE article, May 2005