In October 1974, Faggin left Intel to start his first company, Zilog, Inc. He was joined by Ralph
Ungerman, who reported to him at Intel. Faggin conceived and architected the Z80 CPU and the Z80 family of peripheral components. Masatoshi Shima joined Zilog in April
1975 to do the detailed design of the Z80 CPU. The Z80 was introduced in the market in May 1976 and became very successful, supplanting the older generation
8080 in many designs. Faggin was President and CEO of Zilog from inception until December 1980. The reasons that prompted him to leave Intel were many. The most
compelling was discovering that Intel had patented his "buried contact" idea, without his knowledge, under the name of Leslie Vadasz, his former boss at
Fairchild and now at Intel.