Field effect transistor having increased carrier mobility

A FET situated on a substrate, said FET comprising:

• a channel situated in said substrate;
• a gate stack situated over said channel;
• a first gate dielectric situated in said gate stack, said first gate dielectric having a first coefficient of thermal expansion;
• a first gate electrode situated over said first gate dielectric, said first gate electrode having a second coefficient of thermal expansion;
• wherein said second coefficient of thermal expansion is different than said first coefficient of thermal expansion so as to cause a strain in said channel, said strain causing an increase in carrier mobility in said FET;
• a second gate electrode situated between said first gate electrode and said first gate dielectric, said second gate electrode having a third coefficient of thermal expansion, said third coefficient of thermal expansion being greater than said first coefficient of thermal expansion and said third coefficient of thermal expansion being less than said second coefficient of thermal expansion so as to cause a tensile strain in said channel, said tensile strain causing said increase in said carrier mobility.