Method of making zener diodes with selectively variable breakdown voltages

Claim 1

A method of making a semiconductor device characterized by a selectively variable breakdown voltage ranging from a few volts to several hundred volts, said method comprising: diffusing into a substrate a first impurity-doped region of a conductivity-type different from that of said substrate, said first region having a surface-adjacent portion of substantially constant impurity concentration and a gradient region of decreasing impurity concentration extending laterally from said surface-adjacent portion; diffusing into said substrate a second region of the same conductivity type as said substrate but of higher impurity concentration, said second region intersecting a surface-adjacent portion of said gradient region to form a P-N junction at the intersection of the edge of said second region with said gradient region; and selecting the location of the intersection between the edge of said second region and the surface-adjacent portion of said gradient region to provide a specific breakdown voltage, V B , which varies with the location of the P-N junction at the surface of the substrate relative to the impurity concentration in the gradient region in accord-with the following equation for linearly graded junctions: V.sub.B ≃ 60(E.sub.g /1.1).sup.6/5 (a/3 × 10.sup.20).sup.-2/5 volts, where E g is the energy bandgap in electron volts and a is the impurity gradient in cm -4 .

Claim 2

A method of making a semiconductor device characterized by a selectively variable breakdown voltage ranging from a few volts to several hundred volts, said method comprising: diffusing into a substrate a first impurity-doped region of a conductivity-type different from that of said substrate, said first region having a surface-adjacent portion of substantially constant impurity concentration and a gradient region of decreasing impurity concentration extending laterally from said surface-adjacent portion; diffusing into said substrate a second region of the same conductivity type as said substrate but of higher impurity concentration, said second region intersecting a surface-adjacent portion of said gradient region to form a P-N junction at the intersection of the edge of said second region with said gradient region; and selecting the location of the intersection between the edge of said second region and the surface-adjacent portion of said gradient region to provide a specific breakdown voltage, V B , which varies with the location of the P-N junction at the surface of the substrate relative to the impurity concentration in the gradient region in accord-with the following equation for linearly graded junctions: V.sub.B ≃ 60(E.sub.g /1.1).sup.6/5 (a/3 × 10.sup.20).sup.-2/5 volts, where E g is the energy bandgap in electron volts and a is the impurity gradient in cm -4 .