The characteristics of silicon voltage-reference diodes

Two theories of breakdown mechanism in silicon junction diodes have at present been advanced, avalanche and field emission, one by Zener and the other by Von Hippel and Fröhlich. At various times physicists have supported one or the other of these theories operating independently, but the development of the low-voltage silicon reference diode has indicated that the two methods of breakdown can occur simultaneously. An explanation of the peculiar behaviour of the voltage/temperature coefficient of such diodes can be made by incorporating both breakdown mechanisms. It is shown that very-close-tolerance devices must be used in experimental work. Comparison of the breakdown theories with experimental results shows that the breakdown of diodes at voltages less than 4.5 volts is due to field emission, greater than 6.5 volts is due to avalanche effects, and between 4.5 and 6.5 volts is due to a combination of both effects. Confirmation of these results is made by noise measurements. A characteristic surface of temperature coefficient of breakdown voltage shows skew properties which suggests that a diode having zero temperature coefficient over a wide range cannot exist for the currents and voltages considered.