Patent ID: 7531861

Claim:
A trench capacitor, comprising: a silicon substrate; a first conduction type-doped Si layer on the silicon substrate; an SiGe layer on the first conduction type-doped Si layer; a second conduction type-doped Si layer on the SiGe layer opposite to the first conduction type-doped Si layer; a trench defined in the second conduction type-doped Si layer, the SiGe layer, and the first conduction type-doped Si layer; an undercut region defined in the SiGe layer and extending laterally along the first and second conduction type-doped Si layers; an insulating layer collar in the undercut region that extends laterally along the first and second conduction type-doped Si layers; a buried plate in the first conduction type-doped Si layer along the trench; a dielectric layer in the trench on the buried plate; and a storage electrode on the dielectric layer in the trench opposite to the buried plate.