Quantum-Dot Cellular Automata SPICE Macro Model

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Quantum-Dot Cellular Automata SPICE Macro Model
Electrical and Computer Engr. Department
Rui Tang, Fengming Zhang, Yong-Bin Kim
Electrical and Computer Engineering Department,
Northeastern University

• Why QCA
• CMOS technology has reached physical limits
• Technology Goal
• The cell size of QCA is about
• several nanometers _at_ room temperature
• Alternative Nano technology
• Quantum Cellular Automata (QCA)
• New method of information transformation
• Why SPICE Model
• CAD tools are essential for real application
• QCADesigner is a good bottom-up design
  tool.

QCA Cell and Two-Junction Realization
Majority Voter (MV) FABACBC
device cell

• 4 dots and 2 electrons
• Electrons tend to occupy antipodal dots
• (a) shows two-junction realization of the
  quantum cellular automata
• (b) shows a schematic diagram of the half-QCA
  cell

• AND/OR functions obtained by setting one input of
  MV to
• 0 for AND
• 1 for OR

The Schematic and Function of One-bit QCA
Full-Adder
Graph Representation of QCA SPICE Model
QCA SPICE Model

• The electrostatic energy to move an electron from
  one island i to another island j is given by
• In a simple case, there is only one extra
  electron in one pair of quantum dots.
• Therefore, only two states of the transition
  exist, one state is the extra electron trapped in
  island i and the other state is island j holding
  the extra electron. Therefore, the following
  expression can be obtained
• The tunnel rate is formulated based on the
  orthodox theory and given by
• The changes in energy when an electron tunnels
  from node i to j or an electron tunnels from node
  j to i are
• Once we know the tunnel rate, we can deduce the
  probabilities of the different states in the QCA
  cell

• Cin is the capacitance between the QCA cells
• Ci is the capacitance between the two pairs of
  QCA dots
• RT1 is the junction resistor

Simulation Results
The Traditional CMOS Circuits Design Process and
the Proposed QCA Circuits Design Flow

Truth Table of Full Adder
a b c Sum Cout
0 0 0 0 0
0 1 0 1 0
1 0 0 1 0
1 1 0 0 1
0 0 1 1 0
0 1 1 0 1
1 0 1 0 1
1 1 1 1 1


Conclusions and Future Research
Conclusions
Future Researches

• SPICE model for QCA cell is proposed
• Based on the orthodox theory and single electron
  tunneling
• First effort to develop SPICE macro modeling of
  QCA cells
• Based on experimental demonstrations of QCA cells
• The functions of full-adder and majority voter
  are verified in SPICE

• Develop QCA Synthesis Methodology
• Timing Characterization Across QCA Modules
• Cell Placement/Routing for Room
• Temperature Operation
• Pipeline Design for High Performance