This innovation is used to connect between synapse and neuron arrays using nanowire in quantum dot and metal in CMOS (complementary metal oxide semi-conductor) technology to enable the density of a brainlike connection in hardware. The hardware implementation combines three technologies:

  1. Quantum dot and nanowire-based compact synaptic cell (50×50 nm2) with inherently low parasitic capacitance (hence, low dynamic power ≈10–11 watts/synapse),
  2. Neuron and learning circuits implemented in 50-nm CMOS technology, to be integrated with quantum dot and nanowire synapse, and
  3. 3D stacking approach to achieve the overall numbers of high density O(1012) synapses and O(108) neurons in the overall system.

In a 1-cm2 of quantum dot layer sitting on a 50-nm CMOS layer, innovators were able to pack a 106-neuron and 1010-synapse array; however, the constraint for the connection scheme is that each neuron will receive a non-identical 104-synapse set, including itself, via its efficacy of the connection.

This is not a fully connected system where the 100×100 synapse array only has a 100-input data bus and 100-output data bus. Due to the data bus sharing, it poses a great challenge to have a complete connected system, and its constraint within the quantum dot and silicon wafer layer.

For an effective connection scheme, there are three conditions to be met:

  1. Local connection.
  2. The nanowire should be connected locally, not globally from which it helps to maximize the data flow by sharing the same wire space location.
  3. Each synapse can have an alternate summation line if needed (this option is doable based on the simple mask creation).

The 103×103-neuron array was partitioned into a 10-block,102×103-neuron array. This building block can be completely mapped within itself (10,000 synapses to a neuron).

This work was done by Tuan A. Duong, Christopher Assad, and Anilkumar P. Thakoor of Caltech for NASA’s Jet Propulsion Laboratory.

This Brief includes a Technical Support Package (TSP).
Optimal and Local Connectivity Between Neuron and Synapse Array in The Quantum Dot/Silicon Brain

(reference NPO-46222) is currently available for download from the TSP library.

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NASA Tech Briefs Magazine

This article first appeared in the October, 2010 issue of NASA Tech Briefs Magazine.

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