Process for making anisotropic resistor for electrical feed throughs

Claim 1

A process for making an anisotropic resistor comprising the process steps of: (a) selecting a body of semiconductor material having two opposed major surfaces substantially parallel to each other, at least one of the major surfaces having a preferred planar orientation which is one selected from the group consisting of (100), (110) and (111), a first selected type conductivity, a first selected level of resistivity, a preferred material crystal structure and a vertical axis substantially aligned with a first crystal axis of the material of the body; (b) selectively etching a selective portion of one of the major surfaces of the body to form at least one depression therein; (c) depositing a mass of a selective metal comprising at least one dopant impurity metal suitable for imparting a second selected type conductivity and a second level of resistivity to the material of the body in the at least one depression in the one major surface of the body of semiconductor material; (d) heating the body and the at least one mass of metal to an elevated temperature to produce a melt of metal-rich semiconductor material in each etched depression; (e) establishing a first thermal gradient aligned substantially parallel with the vertical axis of the body; (f) migrating the at least one melt of metal-rich semiconductor material through the body in the direction of the higher temperature of the thermal gradient from the one major surface to the other of the two major opposed surfaces to form an electrically conductive channel region of recrystallized material of the body having two opposed end surfaces, each end surface being coextensive with a respective one of the two opposed major surfaces, the recrystallized material having the at least one dopant metal impurity therein to impart a second selected type conductivity and a second selected level of resistivity thereto as determined by the level of concentration of that dopant impurity metal in the recrystallized semiconductor material of the channel region; (g) introducing a second thermal gradient into the body while maintaining the first thermal gradient and simultaneously migrating the at least one melt of metal-rich semiconductor material through the body, the second thermal gradient being a radial thermal gradient to change the direction and cross-sectional area of each melt within the body during migration to produce at least one channel region whic has an increasing cross-sectional area with increasing distance from one major surface to the other major surface and a vertical axis which is not parallel with the vertical axis of the body and the first crystal axis of the material of the body, and (h) affixing an ohmic electrical contact to each end surface of each channel region.