The space environment exposes electronic systems to harsh conditions where they are subjected to wide temperature variations and, more importantly, to incessant bombardment by high-energy particles. These particles can cause considerable damage to microelectronic components such as semiconductor memories and catastrophically alter data. Magnetic Random Access Memories (MRAM) are known to be almost insensitive to radiation effects. At IRIG, physicists are working on MRAMs whose dimensions can be reduced and which could therefore be interesting candidates for high-density storage and to replace memories currently used by the space industry.

The most common semi-conductor memories work by trapping and untrapping electrical charges. In space (geostationary satellite, distant space missions...) these components are subjected to an intense bombardment of very high energy particles (electrons, protons, gamma rays,…). Some of these particles, often the most energetic, can pass through the shielding devices and damage memories or disrupt their operations. Indeed, a highly energetic particle is capable of "untrapping" a charge, or on the contrary to create one, which has for effect to modify the information in a punctual or definitive way.
MRAMs store information using the relative orientation of the magnetic magnetizations of two ferromagnetic layers. In the absence of a charge, MRAM memories are not susceptible to such a perturbation. IRIG researchers are studying different types of MRAMs. They have studied the robustness to irradiation of Magnetic Tunnel Junctions (MTJ) under radiations for memories that can be used for high-density MRAM memories (over 1 Gb of memory capacity), which involve the most advanced manufacturing processes they have developed. The irradiation experiments were performed in the cyclotron resources at the Université Catholique de Louvain (UCL). The irradiation of the memories with ¹²⁴Xe³⁵⁺ heavy ions of 995 MeV (the most energetic ions available in Leuven, representative of the particle energy that can impact the circuits) shows an insignificant sensitivity of the MTJs to these particles and no modification of their electrical properties. Moreover, the researchers observed that the magnetoresistance properties were slightly improved after irradiation. However, modifications of some magnetic properties can be observed, in particular the reduction of the coercive field and a shift of the hysteresis cycle. These last changes could lead to a degradation of the memory usage, especially in terms of stability. The causes of these degradations seem to be the consequence of heating effects induced by the irradiation (energy deposited by the particles).


The irradiation experiments were performed at the Cyclotron Resource Centre of Université Catholique (UCL). The irradiation of the memories with ¹²⁴Xe³⁵⁺ heavy ions of 995 MeV (the most energetic ions available in Leuven, representative of the energy of the particles that can impact the circuits) shows an insignificant sensitivity of the JTMs to these particles and no modification of their electrical properties. Moreover, the researchers observed that the magnetoresistance properties were slightly improved after irradiation. On the other hand, modifications of some magnetic properties can be observed, in particular the reduction of the coercive field and a shift of the hysteresis cycle. These last changes could lead to a degradation of the memory usage, especially in terms of stability. The causes of these degradations seem to be the consequence of a heating effect induced by the irradiation (energy deposited by the particles).

Hysteresis is the property of a system whose evolution does not follow the same path depending on whether an external cause increases or decreases.