The evolution of technology computer-aided design (TCAD) — the synergistic combination of process, device and circuit simulation and modeling tools — finds its roots in bipolar technology, starting in the late 1960s, and the challenges of junction isolated, double-and triple-diffused transistors. These devices and technology were the basis of the first integrated circuits; nonetheless, many of the scaling issues and underlying physical effects are integral to IC design, even after four decades of IC development. With these early generations of IC, process variability and parametric yield were an issue — a theme that will reemerge as a controlling factor in future IC technology as well.