Static random access memory and fabrication method thereof

A method for fabricating a static random access memory (SRAM), comprising:

• providing a substrate including a plurality of first substrate regions and a plurality of second substrate regions;
• forming a first doped region in each first substrate region by implanting first doping ions;
• forming a second doped region in each second substrate region by implanting second doping ions;
• forming a plurality of pull-down transistors in the first substrate regions with each pull-down transistor including a first gate structure formed on the first doping region;
• and
• forming a plurality of pass-gate transistors in the second substrate regions with each pass-gate transistor including a second gate structure formed on the second doping region, wherein:
• a concentration of the first doping ions is smaller than a concentration of the second doping ions;
• forming the first gate structure includes forming a first gate dielectric layer on the first doping region, forming a first work function layer on the first gate dielectric layer, and forming a first gate electrode layer on the first work function layer;
• forming the second gate structure includes forming a second gate dielectric layer on the second doping region, forming a second work function layer on the second gate dielectric layer, and forming a second gate electrode layer on the second work function layer;
• and
• a work function of the first work function layer is greater than a work function of the second work function layer.