An unified IC system includes a base memory chip, a plurality of stacked memory chips, and a logic chip. The base memory chip includes a memory region and a bridge area, the memory region includes a plurality of memory cells, and the bridge area includes a plurality of memory input/output (I/O) pads and a plurality of third transistors. The plurality of stacked memory chips is positioned above the base memory chip. The logic chip includes a logic bridge area and a plurality of second transistors, the logic bridge includes a plurality of logic I/O pads, wherein the plurality of memory I/O pads are electrically coupled to the plurality of logic I/O pads, and a voltage level of an I/O signal of the third transistor is the same or substantially the same as a voltage level of an I/O signal of the second transistor.