A diode is an electrical circuit component that allows current to flow in only one direction. A diode consists of two electrodes sealed in a vacuum. One electrode, the cathode, is attached to a negative electric potential, the other electrode, the anode, is attached to a positive electrical potential. The word diode is derived from the term di-electrode (i.e., two electrodes).

The diode was first developed by English scientist Sir John Ambrose Fleming. Historically the original diode was an evacuated glass bottle or tube with two metal plates (electrodes) inside, each connected to opposite electrical charges. The negatively charged plate (cathode) was heated to a glowing red temperature and the positively charged electrode (anode) was left cold. Thermionic diode tubes (originally thermionic valves) were the mainstay of the electronics industry until the late 1950s when transistors and, later, integrated circuit (IC) chips became the norm. Today, thermionic...