An integrated circuit including a memory array and a physical unclonable function array is obtained by causing metal back sputtering in specific regions of the integrated circuit during ion beam etch. MRAM pillars within the memory array have larger widths than the underlying bottom electrodes while those within the physical unclonable function array have smaller widths than the underlying bottom electrodes. Metal residue deposited over tunnel barrier layers causes random electrical shorting of some of the MRAM pillars within the physical unclonable function array.