A system includes a semiconductor device. The semiconductor device includes a first semiconductor layer comprising first transistors, wherein the first transistors are interconnected by at least one metal layer comprising aluminum or copper. The second mono-crystallized semiconductor layer includes second transistors and is overlaying the at least one metal layer, wherein the second mono-crystallized semiconductor layer is less than 150 nm in thickness, and at least one of the second transistors is an N-type transistor and at least one of the second transistors is a P-type transistor.