A number of innovations developed by Faggin while working at Fairchild Semiconductor allowed the 4004 to be produced on a single chip. The main concept was the use of the self-aligned gate, made of polysilicon rather than metal, which allowed the components to be much closer together and work at higher speed. To make the 4004 possible, Faggin also developed the "bootstrap load", considered unfeasible with silicon gate, and the "buried contact" that allowed the silicon gates to be connected directly to the source and drain of the transistors without the use of metal. Together, these innovations doubled the circuit density, and thus halved cost, allowing a single chip to contain 2,300 transistors and run five times faster than designs using the previous MOS technology with aluminum gates.