- I was studying the silicon die of the Pentium processor and noticed some puzzling structures where signal lines were connected to the silicon substrate for no apparent reason. Two examples are in the photo below, where the metal wiring (orange) connects to small square regions of doped silicon (gray), isolated from the rest of the circuitry. I did some investigation and learned that these structures are “antenna diodes,” special diodes that protect the circuitry from damage during manufacturing. In this blog post, I discuss the construction of the Pentium and explain how these antenna diodes work.