Aspects of the technology described herein relate to ultrasound transducer devices including capacitive micromachined ultrasonic transducers (CMUTs) and methods for forming CMUTs in ultrasound transducer devices. Some embodiments include forming a cavity of a CMUT by forming a first layer of insulating material on a first substrate, forming a second layer of insulating material on the first layer of insulating material, and then etching a cavity in the second insulating material. A second substrate may be bonded to the first substrate to seal the cavity. The first layer of insulating material may include, for example, aluminum oxide. The first substrate may include integrated circuitry. Some embodiments include forming through-silicon vias (TSVs) in the first substrate prior to forming the first and second insulating layers (TSV-Middle process) or subsequent to bonding the first and second substrates (TSV-Last process).