Heavy ion irradiation induced hard error in MTJ of the MRAM memory array

Abstract

The radiation effects of magnetic tunnel junction (MTJ) in a 180 nm Magnetoresistive Random Access Memory (MRAM) were investigated at the condition of the high heavy ion fluence (up to 1010 ions·cm−2) and high gamma-ray dose (up to 15 Mrad(Si)), respectively. The Hard Bit Error (HBE) was only observed when the energy of 181Ta ions was larger than 95.8 MeV under the ion fluence of 109 ions·cm−2 (~13 ions·bit−1). For gamma-ray exposure, no obvious effects were observed in devices. The HBE counts induced by 181Ta ions have a strong dependence on ion energy and cumulative fluence. In addition, the annealing characteristics of HBE after heavy ion irradiation at room temperature were also observed. It is found that the high ambient temperature is able to accelerate this annealing process. Monte Carlo simulation by using TRIM program revealed that the displacement damages induced by heavy ions were mainly located in the insulating layer of MTJ, which is responsible for the occurrence of HBE.