A micro-electro mechanical system (MEMS) device includes a MEMS substrate, at least one movable element laterally confined within a matrix layer that overlies the MEMS substrate, and a cap substrate bonded to the matrix layer through bonding material portions. A first movable element selected from the at least one movable element is located inside a first chamber that is laterally bounded by the matrix layer and vertically bounded by a first capping surface that overlies the first movable element. The first capping surface includes an array of downward-protruding bumps including respective portions of a dielectric material layer. Each of the downward-protruding bumps has a vertical cross-sectional profile of an inverted hillock. The MEMS device can include, for example, an accelerometer.