1. An apparatus comprising: a memory array; a voltage source coupled to the memory array, the voltage source configured to apply a first voltage to the memory array; a sense amplifier coupled to the memory array, the sense amplifier configured to output a second voltage, based on a comparison of a first read access time of a first bit cell of the memory array and a second read access time of a second bit cell of the memory array, after the voltage source applies the first voltage to the memory array; and a processor coupled to the sense amplifier, the processor configured to determine a physically unclonable function based on the second voltage, the physically unclonable function identifying a circuit, the circuit including the memory array.