A structure includes a word-line, a bit-line, and an anti-fuse cell. The anti-fuse cell includes a reading device, which includes a first gate electrode connected to the word-line, a first gate dielectric underlying the first gate electrode, a drain region connected to the bit-line, and a source region. The first gate dielectric has a first thickness. The drain region and the source region are on opposite sides of the first gate electrode. The anti-fuse cell further includes a programming device including a second gate electrode connected to the word-line, and a second gate dielectric underlying the second gate electrode. The second gate dielectric has a second thickness smaller than the first thickness. The programming device further includes a source/drain region connected to the source region of the reading device.