An Integrated Circuit device, including: a base wafer including single crystal, the base wafer including a plurality of first transistors; at least one metal layer providing interconnection between the plurality of first transistors; a second layer including a plurality of second transistors, the second layer overlying the at least one metal layer, where the plurality of second transistors include single crystal, and where the second layer includes a through layer via with a diameter of less than 250 nm; a plurality of conductive pads, where at least one of the conductive pads overlays at least one of the second transistors; and at least one I/O circuit, where the at least one I/O circuit is adapted to interface with external devices through at least one of the plurality of conductive pads, where the at least one I/O circuit includes at least one of the first transistors.