Semiconductor structures and methods are provided. An exemplary method includes depositing a first conductive material layer over a substrate, patterning the first conductive material layer to form a first conductor plate over the substrate, forming a first high-K dielectric layer over the first conductor plate, forming a second high-K dielectric layer on the first high-K dielectric layer, forming a third high-K dielectric layer on the second high-K dielectric layer, and forming a second conductor plate over the third high-K dielectric layer and vertically overlapped with the first conductor plate, where a composition of the first high-K dielectric layer is the same as a composition of the third high-K dielectric layer and is different from a composition of the second high-K dielectric layer.