Reliability of three-dimensional ferroelectric capacitor memory-like arrays simultaneously submitted to x-rays and electrical stresses

Future development of Ferroelectric Random Access Memories (FeRAM) requires integration of three-dimensional (3D) ferroelectric capacitors in replacement of usual planar capacitors. This innovative geometry enables the fabrication of highly reliable memory devices with improved sensing signal. In order to target space applications, it is of primary interest to analyze the effects of ionizing radiations (x-rays, X-rays...) on capacitors integrated in advanced memory architectures. In this paper, effects of x-rays combined with either bias voltage or bipolar electrical cycling were analyzed on 3D ferroelectric capacitor memory-like arrays. Using an experimental setup enabling measurements under radiations, these arrays were submitted to electrical stresses simulating the various states of the memory. For memory-like arrays in "written" state (no applied bias), high dose of X-rays accelerates both fatigue-like (polarization reduction) and imprint-like (voltage shift) phenomena, which may subsequently alter normal memory operations. Nevertheless, it has been shown that repeated cycling makes the degradation mechanisms reversible. Alternatively, for memory-like arrays in "writing" state, two distinct simulated conditions have been considered. If irradiated capacitors are always being written in the same state, huge and irreversible imprint-like effect may cause memory cell "read" or "write" failures. Moreover, if capacitors are cycled in normal conditions (i e. bipolar pulses), the strong acceleration of fatigue mechanism may cause "read" failures since the two remnant states may be indistinguishable during memory reading.