In one embodiment, a sensor device includes a bulk silicon layer, a first doped region of the bulk silicon layer of a first dopant type, a second doped region of the bulk silicon layer of a second dopant type, wherein the first dopant type is a type of dopant different from the second dopant type, the second doped region located at an upper surface of the bulk silicon layer and having a first doped portion bounded by the first doped region, a first cavity portion directly above the second doped region, and an upper electrode formed in an epitaxial layer, the upper electrode directly above the first cavity portion.