In the area of nanoarchitectonics, we are exploring computational architectures that exploit the virtues of nanodevices while mitigating their limitations.
Working at the nanoscale level presents a number of thermodynamics and quantum mechanics challenges. Our research is addressing these issues:
- High defect rates -- Many of the nanoscale devices we fabricate simply do not work as expected, and nanowires occasionally are broken or shorted together. Although improved processes will minimize this, it cannot be eliminated.
- Device variation -- Statistical structural variations due to the small number of atoms composing individual devices leads to unavoidable variation in electrical behavior from one nanodevice to another. Nanowires also exhibit high variation in resistivity due to variability in wire cross-sectional area and grain size.
- Device aging -- Some nanodevices exhibit behavioral changes over time. Although conventional CMOS shows this to some extent (e.g., metal migration), the effect is more pronounced at the nanoscale.
- Noise -- Because fewer electrons are used to convey signals, and nanowires are often physically close, crosstalk and subatomic particle strikes may cause nanocircuits to be much noisier than their conventional counterparts.
- Nonlinearity -- Most nanodevices we've fabricated have shown significant nonlinearity in their transfer functions (probably due to tunneling). Although this is generally a good thing for computation, there are situations (such as routing) where the nonlinearity makes system performance prediction more difficult.
- Dynamical devices -- Many, and perhaps most, of the nanodevices we've fabricated are not simple, two-state devices, but instead exhibit complex, dynamical behaviors. Many are also surprisingly nonvolatile. Because their behavior at any time depends upon their history, simple circuits such as wired-OR gates will not work, at least not for very long. This unusual behavior requires unconventional circuitry.
|
Printable version
