A plug assembly 10 includes a housing 14 and one or more covers 16 coupled to the housing. The SRAM cell has a hybrid SOIbulk structure wherein the sourcedrain diffusions do not penetrate to the underlying insulator layer, resulting in a FET in the surface of an SOI layer with a body or substrate contact formed at a shared contact. The protrusion includes a shank and an engaging portion. The fourth linear segment can be replaced by a sum of one or more polynomials, trigonometric functions or other functions satisfying certain constraints.