We might imagine that electric current flows as a smooth, even stream of electrons through our electronics devices, but at the quantum scale the flow of electric current might be more accurately pictured as a bubbling brook containing many tiny ripples. These ripples can be caused by single-electron effects, which arise due to the repulsion among electrons confined in very small spaces, such as trap sites in transistors. Single-electron effects can lead to tiny changes in the current-voltage characteristics of these devices.
Source:
https://phys.org/news/2019-07-transistor-unique-quantum-fingerprintbut-id.html