An integrated circuit device includes first and second semiconductor die and a physically unclonable function (PUF). The second semiconductor die is attached, at least partially, to the first semiconductor die using the PUF. The PUF includes a plurality of conductive paths formed between the first semiconductor die and the second semiconductor die. The PUF controller is coupled to the PUF for generating a digital value based on a characteristic of each conductor of the plurality of conductive paths. The digital value logically binds the first semiconductor die to the second semiconductor die. The first semiconductor die may include a nonvolatile memory and the digital value may be an encryption key for encrypting data stored in the nonvolatile memory.