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NATURE: Non-Volatile Nanotube RAM based Field-Programmable Gate Arrays. Wei Zhang † , Niraj K. Jha † and Li Shang ‡ † Dept. of Electrical Engineering Princeton University ‡ Dept. of Electrical and Computer Engineering Queen’s University.

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nature non volatile nanotube ram based field programmable gate arrays

NATURE: Non-Volatile Nanotube RAM based Field-Programmable Gate Arrays

Wei Zhang†, Niraj K. Jha† and Li Shang ‡†Dept. of Electrical EngineeringPrinceton University‡ Dept. of Electrical and Computer EngineeringQueen’s University

a hybrid cmos na no tu be re configurable architecture
A Hybrid CMOS/NAnoTUbe REconfigurable Architecture
  • Motivation
  • Background on CNT and NRAM
  • Architecture of NATURE
  • Logic Folding
  • Experimental Results
  • Conclusions
  • Moore’s Law: What’s Next?
    • Carbon nanotubes (CNTs)
    • Nanowires
    • Single electron devices
    • ...
  • Challenges in nano-circuits/architectures
    • Lack of a mature fabrication process
    • Defects and run-time failures
  • Reconfigurable architectures, such as an FPGA, favored
    • Regular structures ease fabrication
    • Fault tolerance through reconfiguration
motivation contd
Motivation (Contd.)
  • Problems of existing reconfigurable architectures
    • High reconfiguration time overhead
    • Low area efficiency
  • Some recent works on programmable nanofabrics

Molecular logic array (Goldstein et al. [ICCAD 2002])

Nanowire PLA (Dehon et al. [FPGA 2004])

CMOS/nanowire hybrid architecture CMOL (Strukov et al. [Nanotechnology 2005])

  • Fabrication problem not yet solved
advantages of nature
Advantages of NATURE
  • Hybrid design leverages beneficial aspects of both CMOS and CNT technologies
  • NRAMs are distributed in NATURE to store multi-context reconfiguration bits
  • Fine-grain reconfiguration (even cycle-by-cycle)
  • Enables temporal logic folding
    • Flexibility to perform area-performance trade-offs
    • One-to-two orders of magnitude increase in logic density

CMOS fabrication







logic folding





  • Carbon nanotube (CNT)
    • Metallic or semiconducting
    • Single-wall or multi-wall
    • Diameter: 1-100nm
    • Length: up to millimeters
    • Ballistic transport
    • Excellent thermal conductivity
    • Very high current density
    • High chemical stability
    • Robust to environment

Source: Euronanotrade

background contd
Background (Contd.)
  • Non-volatile nanotube random-access memory (NRAM)
    • Mechanically bent or not: determines bistable on/off states
    • Fully CMOS-compatible manufacturing process
    • Prototype chip: 10 Gbit NRAM
    • Will be ready for the market in the near future

Source: Nantero

  • Properties of NRAMs
    • Non-volatile
    • Similar speed to SRAM
    • Similar density to DRAM
    • Chemically and mechanically stable
  • NATURE not tied to NRAMs
    • Phase change RAM
    • Magnetoresistive RAM
    • Ferroelectric RAM
architecture of nature
Architecture of NATURE
  • Island-style logic blocks (LBs) connected by various levels of interconnects
  • An LB contains a super macroblock (SMB) and a local switch matrix
architecture of a super macroblock smb
Architecture of a Super Macroblock (SMB)
  • n1macroblocks (MBs) comprise an SMB, here n1 = 4
architecture of a macroblock mb
Architecture of a Macroblock (MB)
  • n2 logic elements (LEs) comprise an MB, here n2 = 4
logic element and interconnect
Logic Element and Interconnect
  • An LE implements a computation and contains:
    • An m-input look-up table (LUT)
    • A flip-flop
    • A pass transistor
  • Interconnect
    • Mixed wire segment scheme
    • 25%, 50% and 25% distribution for length-1, length-4 and long wires
    • Direct links from one LB to its 4 neighbors
support for reconfiguration
Support for Reconfiguration
  • Reconfiguration time short: 160ps
  • Area overhead of NRAMs
    • k: no. of reconfiguration sets per NRAM, assume k = 16
    • Area overhead: 20.5% per LB, assuming 100nm technology for CMOS logic and nanotube length
    • Logic density = k (conf. copies) x area per configuration = 16*(1-0.205)=12.75
  • Appropriate value for k obtained through design space exploration
temporal logic folding
Temporal Logic Folding
  • Basic idea: one can use NRAM-enabled run-time reconfiguration to realize different Boolean functions in the same logic element (LE) every few cycles

Without logic folding

With logic folding

Num of LEs

= 2

Num of LEs

= 6




= 4 LE delays



Clock period

=LE delay




folding levels
Folding Levels
  • Logic folding can be performed at different levels of granularity, providing flexibility to perform area-performance trade-offs
  • A level-p folding implies reconfiguration of the LE after the execution of p LUT computations

(a) level-1 folding

(b) level-2 folding

choosing the folding level
Choosing the Folding Level
  • Advantages of logic folding
    • Significant flexibility for performing area-performance trade-offs
    • Ability to map much larger circuits using the same number of LEs
    • Significant improvement in the area/circuit delay product
    • Reduction in the need for global routing

Clock period increases:

Routing delay increases

Number of clock cycles decreases

Reconfiguration time decreases

Total delay typically decreases



Area increases

Number of LEs increases

experimental setup
Experimental Setup
  • Instance of architecture: 4 MBs in an SMB, 4 LEs in an MB, and LEs contain a 4-input LUT
  • Number of reconfiguration copies k varied in order to compare implementations corresponding to selected folding levels: level-1, level-2, level-4 and no logic folding
  • Results based on 100nm CMOS technology parameters
experimental results
Experimental Results

Average area-time product advantage = 2X

Maximum area-time product advantage = 3X

experimental results contd
Experimental Results (Contd.)

16-RCA: 16-bit ripple carry adder 16-CLA: 16-bit carry lookahead adder

16-CSA: 16-bit carry select adder 8-MUL: 8-bit multiplier

Average area-time product advantage = 13X

Maximum area-time product advantage = 35X

experimental results contd1
Experimental Results (Contd.)
  • Flexibility in performing area-performance trade-off
  • For area-time (AT) product, larger the circuit depth, more the advantages of level-1 folding relative to no folding
    • For the 64-bit ripple-carry adder, this advantage is about 35X
  • LE utilization and logic density very high, with a reduced need for a deep interconnect hierarchy
  • NATURE: A novel high-performance run-time reconfigurable architecture
  • Introduction of NRAMs into the architecture enables cycle-by-cycle reconfiguration and logic folding
  • Choice of different folding levels allows the flexibility of performing area-performance trade-offs
  • Logic density and area-time product improved significantly
  • Can be very useful for cost-conscious embedded systems and future FPGA improvement