The field ring structure is very simple. It is to form a PN junction at an appropriate position around the junction we want to protect, and use the depletion region of this junction to adjust the protected PN junction (main junction). The PN junction depletion region of the original main junction is in the region A, but now it is regulated by the field ring, the depletion region is expanded where the radius of the surface is small, and the new depletion region extends to the B region.

When the designed device requires a withstand voltage of less than 50 V, the width of the depletion layer of the device is not too large, so that a single floating field ring can usually provide a breakdown voltage close to that of a planar junction. However, when the withstand voltage required by the device increases, when designing the device, we will make the width of the depletion layer that withstands the voltage wider to withstand higher voltages.
In principle, the shape of the depletion region can be adjusted by adding a lot of heavy field loops to make it close to a parallel junction. However, as the number of field rings increases, the effect of continuing to increase the field rings will be weakened, and the area and cost of the chip will increase due to occupying more area. Therefore, in applications, only three floating field rings are usually used at most.