Convertible multi-function microelectronic logic gate structure and method of fabricating the same

A method of fabricating a logic gate structure on a substrate which normally performs a first logic function and is convertible during said fabrication to perform a selected one of a second, third and fourth logic functions, comprising the steps of:

• (a) partially forming each field effect transistor (FET) of a plurality FETs on the substrate, each partially formed FET having a source, drain and channel region, the plurality of FETs being arranged into series and parallel connected portions;
• (b) doping the channel region of all of the series connected FETs to cause the structure to produce a second logic state which varies for all logical values of applied gate voltage and to convert said structure from performing the first logic function to performing the second logic function;
• (c) doping the channel region of a series connected FET of the plurality of FETs to cause the structure to produce a constant third logic state for all values of applied gate voltage and to convert said structure from performing the first logic function to performing the third logic function;
• (d) doping the channel region of all of the series connected FETs and a parallel connected FET of the plurality of FETs to cause the structure to produce a constant fourth logic state for all values of applied gate voltage and to convert said structure from performing the first logic function to performing the fourth logic function;
• and
• (e) completing fabrication of the plurality of FETs including forming gate electrodes over the channel regions thereof respectively,
• wherein in the steps of doping, the channel region of the respective FETs are implanted with sufficient ions of a predetermined ion species to change the doping level thereof.