The unprecedented growth of the computer and the Information technology industry is demanding Very Large Scale Integrated (VLSI) circuits with increasing functionality and performance at minimum cost and power dissipation. VLSI circuits are being aggressively scaled to meet this Demand, which in turn has some serious problems for the semiconductor industry.

Additionally heterogeneous integration of different technologies in one single chip (SoC) is becoming increasingly desirable, for which planar (2-D) ICs may not be suitable. 3-D ICs are an attractive chip architecture that can alleviate the interconnect related problems such as delay and power dissipation and can also facilitate integration of heterogeneous technologies in one chip (SoC). The multi-layer chip industry opens up a whole new world of design. With the Introduction of 3-D ICs, the world of chips may never look the same again.

There is a saying in real estate; when land get expensive, multi-storied buildings are the alternative solution. We have a similar situation in the chip industry. For the past thirty years, chip designers have considered whether building integrated circuits multiple layers might create cheaper, more powerful chips. Performance of deep-sub micrometer very large scale integrated (VLSI) circuits is being increasingly dominated by the interconnects due to increasing wire pitch and increasing die size. Additionally, heterogeneous integration of different technologies on one single chip is becoming increasingly desirable, for which planar (2-D) ICs may not be suitable. The three dimensional (3-D) chip design strategy exploits the vertical dimension to alleviate the interconnect related problems and to facilitate heterogeneous integration of technologies to realize system on a chip (SoC) design. By simply dividing a planar chip into separate blocks, each occupying a separate physical level interconnected by short and vertical interlayer interconnects (VILICs), significant improvement in performance and reduction in wire-limited chip area