One of the most successful long term computer trends is based upon Moore's Law. Moore’s Law is observation that the cost-performance of chip components doubles every 18 months. It is a centerpiece of the evolution of computer technology. While Moore’s Law is not a physical law like Newton’s law of gravitation, it is the result of Moore's empirical observation that the increases in circuit density appeared to double on a regular basis.
However, there are technical and physical obstacles looming ahead for Moore's Law. Just how complex chips can become is subject to the problem of power leakage. Chips with billions of transistor can leak up to 70 Watts which causes serious cooling problems.
In addition, it is possible that circuit dimensions cannot get much smaller than the current 65 nanometer (nm) without increasing production difficulties. In 2004, chips were mass producing the 90 nm integrated circuit (IC), but by 2006, migration began to 65 nm. Changing from 90 nm to 65 nm design rules was quick because the fabrication process required little change. This was because in 1988, IBM fabricated the world's smallest transistor at that time using 70 nm design rules. It used a power supply of one volt instead of five volts and required nitrogen cooling. Today these field effect transistors (FETs) run at room temperature.
Similarly, in late 2003, NEC built a FET with a 5 nm gate length and IBM built one at 6 nm gate. These are n order of magnitude smaller than what's used in production now.
Innovators have also been developing four to eight parallel core microprocessors. By working in parallel, the total throughput of the processor is greatly increased and Quad cores are already being produced commercially.
If we reach a physical limit to Moore's Law, we will require new discoveries in breakthrough phenomena demonstrating new proofs of principle, such as 3D chips and nanotubes.
3D chips uses layers of transistors forming a high rise. New technologies could lead to molecular three-dimensional computing include nanotubes, nanotube molecular computing, and self assembly in nanotube circuits.
Matrix Semiconductor, Inc. is already building three-dimensional circuits using conventional silicon lithography. They are manufacturing memory chips with vertically stacked planes.
Carbon nanotubes and silicon nanowires can be extremely strong materials of metals or semiconductors with good thermal conductivity. They can be used as nano-wires or field-effect transistors. Carbon nanotubes can be 1 to 2 nanometers in length, and substantially reduce energy consumption.
In 1991 the first Nanotubes used a rolled hexagonal network of carbon atoms in a cylinder. In a demonstration at the University of California at Irvine by Peter Burke, nanotube circuits at 2.5 gigahertz (GHz) were operated.
Defense Advanced Research Projects Agency, the National Science Foundation and the Office of Naval Research funded research into a class of molecules called rotaxanes. These were synthetic, dumbbell-shaped compounds for logic operations to provide memory and routing signals. A critical step in making a molecular computer requires that the wire be arranged in one direction as molecular switches and that a second set of wires is aligned opposite. A single layer of molecules, rotaxanes, is at the junction of these wires.
An alternative approach by Fujio Masuoka, the inventor of flash memory, has a memory design that reduces the size and cost-per-bit by a factor of ten.
Major progress has also been made in computing using just a few molecules or single-electron transistors. Avi Aviram of IBM and Mark A. Ratner of Northwestern University first suggested this in 1970.
Using a single electron to turn a transistor on and off would miniaturize as well as reduce power. However, there have been severe problems due to their extreme sensitivity to background noise. Single-electron transistors could store as much as a terabit of data in a square centimeter of silicon. That would be a two order of magnitude improvement over today's technology.
Another interesting new chip technology is crossbar latch. The Quantum Science Research (QSR) group of Hewlett Packard has demonstrated this technology that doesn't use transistors to provide the signal restoration and inversion required for general computing. The experimental latch is a single wire that lies between two control lines at a molecular-scale junction. Voltage to the control lines
allows the latch to perform NOT, AND and OR operations. It allows development of nanometer devices and could improve computing by three orders of magnitude.
While we continue to worry about the longevity of Moore's Law, the prospects for innovations contiues to be very bright.
In Connections: Patterns of Discovery the patterns of discovery are presented that produced Moore’s Law and the book explores the question, “What is the software equivalent of Moore’s Law?”
The patterns challenge the reader to think of the consequences of extrapolating trends, such as, how Moore's Law could reach machine intelligence, or retrench in the face of physical limitations.
REFERENCES:
Connections: Patterns of Discovery
Developing Semantic Web Services
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