The potential and realization of multi-layers three-dimensional integrated circuit

3D IC technology with transistors stacked on top of one another in multiple silicon layers has long been a vision for future technology directions to provide a breakthrough towards higher circuit density and functionality. While the idea is simple, techniques to obtain high performance multi-layer transistors are extraordinarily difficult, and it is only recently that such technology has become feasible. In this paper, various techniques to form 3D circuits are reviewed. Recent development of a promising technology to achieve three-dimensional integration using metal-induced-lateral-crystallization is described. Preliminary results for 3D inverters and ring-oscillators have demonstrated the viability of 3D integrated circuits. Finally, the challenges for realization of 3D circuits are discussed.