LW - How a chip is designed by YM

The Nonlinear Library: LessWrong

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Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: How a chip is designed, published by YM on June 28, 2024 on LessWrong. Disclaimer: This is highly incomplete. I am not an expert in the field. There might be some unfamiliar terms. While I will try to explain things, explaining every single term would be beyond this post. You will usually be able to get a sufficient understanding by clicking the links or googling it. Introduction I think everyone, if they read about the chip industry long enough, has a moment where they have to put down a book or pause a podcast and simply remain stunned at the fact that it is possible to design and build something that is so incredibly impressive. The Apple A17 chip contains 183 million transistors per square millimeter. All placed in a coherent manner and produced with extremely high reliability. This is exactly why it is so fascinating to learn more about how it is actually done. On top of that, in a universe where compute is arguably the most important input in the AI production function, this knowledge is also crucial to effective AI governance. So what follows is a quick introduction to the processes of getting a chip from a vague idea to sending your files to the manufacturer, also called the tape-out. Background Knowledge One of the most important decisions, a decision that significantly determines all the others, is what manufacturer will build your chip and what process they will use. There are companies that do both design and manufacturing (e.g. Intel), but especially when it comes to the most advanced logic chips, more and more companies are what is called " fabless" - they focus on the design and task a so-called "foundry" (e.g. TSMC) with the manufacturing. Nowadays many fabs and fabless companies work together very closely in what is called Design-Technology Co-Optimization (DTCO). In practice, there are quite significant limitations in chip design, and the fab will check design plans and inform designers what can and can't be manufactured. This collaborative approach ensures that chip designs are optimized for the specific manufacturing process, balancing performance, power, area, and yield considerations. DTCO has become increasingly important as the industry approaches the physical limits of semiconductor scaling, requiring closer integration between design teams and process engineers to continue advancing chip capabilities. The foundry sends the design company what is called the process design kit ( PDK ), which contains all the important specifics to the fab and the manufacturing process (also known as the technology node). One factor that in large part determines the profitability of a chip is the yield of the manufacturing process. The yield is the fraction of chips produced that work flawlessly and can be sold. Compared to other types of products, in the semiconductor industry the yield is quite low, sometimes moving significantly below 50% for periods of time, especially at the beginning of a new technology node. To improve yield, optimal manufacturability is taken into account at many stages of the design process in what is called Design for Manufacturability (DFM). Chips are also designed to be easy to test (Design For Testability, DFT). In this post we are focussing on the design process, not with the actual manufacturing steps or the details of a transistor. But it is important to know that in practice we are working with standard cells that are all equal in height and vary in width. varies to make design and manufacturing easier. Often the IP for the standard cells is licensed from third parties. The Design Process My stages follow the outline given by Prof. Adam Teman in this lecture. Definition and Planning This is the stage where we think about what you even want to build. What bus structure do you want? How many cores should it have? What amount of p...