An ultrasonic transducer device includes a patterned film stack disposed on first regions of a substrate, the patterned film stack including a metal electrode layer and a bottom cavity layer formed on the metal electrode layer. The ultrasonic transducer device further includes a planarized insulation layer disposed on second regions of the substrate layer, a cavity formed in a membrane support layer and a CMP stop layer, the CMP stop layer including a top layer of the patterned film stack and the membrane support layer formed over the patterned film stack and the planarized insulation layer. The ultrasonic transducer device also includes a membrane bonded to the membrane support layer. The CMP stop layer underlies portions of the membrane support layer but not the cavity.