CMOL: possible hybrid semiconductor/nanodevice circuits

The author reviews the recent work on devices and architectures for possible hybrid semiconductor/nanodevice integrated circuits of "CMOL" variety. Such circuit would combine an advanced CMOS subsystem fabricated by the usual lithographic patterning with a two-layer nanowire crossbar (formed, e.g., by nanoimprinting) with the wires connected, at each crosspoint, by two-terminal nanodevices. The CMOL concept enables a combination of the advantages of its components (e.g., reliability of MOSFET transistors and minuscule footprint of nanodevices), as well as those of patterning techniques: the flexibility of the optical lithography and the potentially low cost of nanoimprinting and nanodevice formation (e.g., the chemically-directed molecular self-assembly). This powerful combination may allow CMOL circuits to reach an unparalleled device density (up to 10¹² functions per cm²) and ultrahigh information processing performance (up to 10²⁰ operations per second per cm²), at acceptable power dissipation (below 100 W/cm²) in several digital and mixed-signal systems including terabit-scale memories, reconfigurable FPGA-like logic circuits, and neuromorphic networks. The main challenges on the way toward practical CMOL systems is the fabrication of highly reproducible nanodevices and the improvement of CMOL circuit architectures.