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Modern computer microprocessor chips are marvels of engineering complexity. For the current 45 nm technology node, there may be nearly a billion transistors on a chip barely 1 cm2 and more than 10 000 m of wiring connecting and powering these devices distributed over 9-10 wiring levels. This represents quite an advance from the first INTEL 4004B microprocessor chip introduced in 1971 with 10 μm minimum dimensions and 2 300 transistors on the chip! It has been disclosed that advanced microprocessor chips at the 32 nm node will have more than 2 billion transistors. 1 For instance, Figure 1 shows a sectional 3D image of a 90 nm IBM microprocessor, containing several hundred million integrated devices and 10 levels of interconnect wiring, designated as the back-end-of-the-line (BEOL).

Since the invention of microprocessors, the number of active devices on a chip has been exponentially increasing …