Low-voltage punch-through bi-directional transient-voltage suppression devices

A bi-directional transient voltage suppression device comprising:

• a lower semiconductor layer of a first conductivity type;
• an upper semiconductor layer of said first conductivity type;
• and
• a middle semiconductor layer adjacent to and disposed between said lower and upper layers, said middle layer having a second conductivity type opposite said first conductivity type such that upper and lower p-n junctions are formed,
• wherein said middle layer has a net doping concentration that is highest at a midpoint between said junctions,
• wherein a doping profile along a line normal to said lower, middle and upper layers is such that the doping profile on one side of a centerplane of said middle layer mirrors the doping profile on an opposite side of said centerplane within said middle layer, and
• wherein an integral of the net doping concentration of the middle layer taken over the distance between the junctions is such that breakdown, when it occurs, is punch through breakdown, rather than avalanche breakdown,
• wherein said first conductivity type is p-type conductivity and said second conductivity type is n-type conductivity,
• and further comprising a p++ semiconductor substrate, wherein said lower layer is a first epitaxial p+ layer deposited on said p++ substrate, wherein said middle layer is an epitaxial n layer deposited on said first epitaxial p+ layer, wherein said upper layer is a second epitaxial p+ layer deposited on said epitaxial n layer and wherein the peak net doping concentration of each of the first and second epitaxial p+ layers ranges from 5 to 20 times the peak net doping concentration of the epitaxial n layer.