US Patent 7948307 Dual dielectric tri-gate field effect transistor

A dual dielectric tri-gate field effect transistor, a method of fabricating a dual dielectric tri-gate field effect transistor, and a method of operating a dual dielectric tri-gate effect transistor are disclosed. In one embodiment, the dual dielectric tri-gate transistor comprises a substrate, an insulating layer on the substrate, and at least one semiconductor fin. A first dielectric having a first dielectric constant extends over sidewalls of the fin, and a metal layer extends over the first dielectric, and a second dielectric having a second dielectric constant is on a top surface of the fin. A gate electrode extends over the fin and the first and second dielectrics. The gate electrode and the first dielectric layer form first and second gates having a threshold voltage Vt1, and the gate electrode and the second dielectric layer form a third gate having a threshold voltage Vt2 different than Vt1.