20um x 20um is still a bit impractical -- it gets close to the practical limits of wafer dicing, and you need support circuitry. That said, we've made useful p

20um x 20um is still a bit impractical -- it gets close to the practical limits of wafer dicing, and you need support circuitry. That said, we've made useful payloads in as little as 100um x 100um; here's an example of our (published) work in 200um x 200um: A 200µm x 200µm x 100µm, 63nW, 2.4GHz Injectable Fully-Monolithic Wireless Bio-Sensing System http://www.travisdeyle.com/publications/pdf/2017_rfic_implantable_sensor.pdf http://www.travisdeyle.com/publications/pdf/2017_rfic_implan...