Semiconductor varistor embodying a lamellar structure

Claim 1

A varistor comprising a body of semiconductor material having two opposed major surfaces forming respectively the top and bottom surfaces of the body, a predetermined level of resistivity, a predetermined first type conductivity, a preferred crystal structure and a vertical axis substantially perpendicular to the major opposed surfaces aligned substantially parallel with a first crystal axis of the semiconductor material of the body; at least one of the opposed major surfaces having a predetermined crystal planar orientation which is one selected from the group consisting of (100), (110), and (111); a plurality of spaced planar regions formed in the body, each region consisting of recrystallized semiconductor material of the body having a second and opposite type conductivity and a predetermined level of resistivity and so oriented as to be aligned with a second preferred crystal axis of the material of the body; each of the spaced planar regions extending between, and terminating in, the opposed major surfaces of the body and oriented substantially perpendicular thereto and having a vertical axis aligned substantially parallel with the vertical axis of the body and the first preferred crystal axis of the material of the body; the recrystallized material of each spaced planar region is formed in situ by the migration of a melt of metal-rich semiconductor material of the body through the material of the body by thermal gradient zone melting at a predetermined elevated temperature along a thermal gradient aligned substantially parallel with the first preferred crystal axis, and the vertical axis of the body and has a pedetermined level of concentration of the metal of the melt therein as determined by the solid solubility limit of that metal in that semiconductor material at that predetermined elevated temperature of migration; the metal includes at least one dopant impurity material to impart the predetermined type conductivity and predetermined level of resistivity to the recrystallized semiconductor material and the metal is distributed substantially uniformly throughout the material of the region; a P-N junction formed by the abutting, contiguous surfaces of the material of opposite type conductivity of each of the planar regions and that of the body; each P-N junction being substantially perpendicular to, and exposed at, the major opposed surfaces of the body; the spaced planar regions and the material of the body between each pair of planar regions defining a lamellar structure of a plurality of integral diodes arranged in a series electrical circuit relationship, and electrical contact means affixed to selected surface areas of the body to enable a predetermined number of P-N junctions to be biased and cause the integral diode structure defined by the contact means to function as a varistor when electrical potential is applied thereto.