Triboelectric Series             

Electrostatic discharge (ESD), which is the rapid transfer of electrostatic charge between two objects that can result in damage to semiconductor devices, arises from charge build-up that occurs as a result of an imbalance of electrons on the surface of a material.  Such a charge build-up develops an electric field that has measurable effects on other objects at a distance. 

The process of electron transfer as a result of two objects coming into contact with each other and then separating is known as 'triboelectric charging'.  The prefix 'tribo' means 'to rub.'  The process of triboelectric charging results in one object gaining electrons on its surface, and therefore becoming negatively charged, and another object losing electrons from its surface, and therefore becoming positively charged.

Which material becomes negative and which becomes positive depend on the relative tendencies of the materials involved to gain or lose electrons.  Some materials have a greater tendency to gain electrons than most others, in the same way that there are others which tend to lose electrons easier than others. 

The triboelectric series is a list that ranks various materials according to their tendency to gain or lose electrons.  It usually lists materials in order of decreasing tendency to charge positively (lose electrons), and increasing tendency to charge negatively (gain electrons).  Somewhere in the middle of the list are materials that do not show strong tendency to behave either way.  Note that the tendency of a material to become positive or negative after triboelectric charging has nothing to do with the level of conductivity (or ability to discharge) of the material.

Due to complexities involved in experiments that involve controlled charging of materials, different researchers sometimes get different results in determining the rank of a material in the triboelectric series.  One of the reasons for this is the multitude of factors and conditions that affect a material's tendency to charge. The triboelectric series shown in Table 1 is a product of the collation of several widely-used triboelectric series published on the web.

Table 1.  The Triboelectric Series