How small can pixels on an image sensor become? We probably don’t know the answer except that they might become very, very small. Semiconductor processing is able to produce features as small as 5 nanometers. And while this extremely small size may not work for pixels on an image sensor, it shows we are not anywhere near the size limit.
In the early days of machine vision, pixels were 17µm. A bit later, with the appearance of VGA resolution sensors in a 2/3 inch format, they became 13µm. From that point on smaller sensors and higher resolution have pushed pixel size downward to 10µm, 7µm, 3.45µ, 2.2µm, and even to 0.8µm today. At least one image sensor company has a roadmap to 0.4µm pixel size.