A device includes a first dielectric layer, a magnetic tunnel junction (MTJ), an oxide layer, a cap layer, and a second dielectric layer. The MTJ is over the first dielectric layer. The oxide layer is over the first dielectric layer. The cap layer is over the first dielectric layer. The cap layer is in contact with a sidewall of the MTJ and a sidewall of the oxide layer. The second dielectric layer is over the cap layer.