Recently, there have been some significant advances in the fabrication and demonstration of individual molecular electronic wires and diode switches. Some novel designs for several such simple molecular electronic digital logic circuits: a complete set of three fundamental logic gates: (AND, OR, and XOR gates), plus and adder function built up from the gates via the well-known combinational logic, was demonstrated. This means in coming future, this technology could be a replacement for VLSI. However, currently, this technology is only available under lab condition. How to mass product moletronics chips is still a big problem.
Currently, integrated circuits by etching silicon wafers using beam of light. It's the VLSI lithography-based technology makes mass production of Pentium III processor possible. But as the size of logic block goes to nano-scale, this technology no long available. As wavelength get too short, they tend to become X-rays and can damage the micro structure of molecules. On the other hand, the mask of lithography of Pentium III is so complex, and the shape and the dimension of its logic block varies so much.
Looking at currently available integrated circuits, the transistor density of memory chip are much higher than processor chip, the reason is that the cell of memory is much more simple than circuit of processor. Because, except the decoding logic, most of the memory bit cell is the same. Could we find a way to fabricate complex logic circuit as Pentium processor using million of same logic units? The PLD(Programmable Logic Devices) is the answer. The paper is organized as following: section II presents some basic of moletronic gate circuit. section III uses PLD technology to build more complex blocks. section IV shows the nanotube can be used for interconnection wires.