Earlier this year, Tim Ansell of Google announced a collaboration between Google and SkyWater to provide a fully open-source PDK, which can be used to create manufacturable designs in the 130 nm at SkyWater’s facility. This enables the complete design of a chip to be open-source, from the HDL (hardware description language) source code describing the digital logic, to the lithographic masks used to etch millions of transistors onto a silicon wafer.
One reason that there are so few open-source chip projects, as compared to open-source circuit boards, is that the cost starts in the thousands even for decade-old technology like SkyWater 130 nm. However, there will soon be manufacturing runs you can be part of for absolutely zero cost, thanks to Google and efabless. The first run will take place in November 2020, with several more to come starting in early 2021. As long as your design is totally open-source, you can get your own chip manufactured – what an achievement for Open Source Hardware!