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Electrical resistivity is the key parameter in the active regions of many current nanoscale devices, from memristors to resistive random-access memory and phase-change memories. The local resistivity of the materials is engineered on the nanoscale to fit the performance requirements. Phase-change memories, for example, rely on materials whose electrical resistance increases dramatically with a change from a crystalline to an amorphous phase. Electrical characterization methods have been developed to measure the response of individual devices, but they cannot map the local resistance across the active area. Here, we propose a method based on operando electron holography to determine the local resistance within working devices. Upon switching the device, we show that electrical resistance is inhomogeneous on the scale of only a few nanometers.

Ge-rich Ge 2 Sb 2 Te 5 (GGST) is considered as one of the best candidates for industrial phase change memory production. GGST memory cells are generally embedded with Si or Ti nitride layers to prevent oxidation, as it leads to an undesired decrease of the GGST crystallization temperature. Furthermore, GGST films are usually doped with elements such as N, C, O, or Bi, aiming to delay GGST crystallization during the fabrication process as well as during memory cell operation. In this work, ultrahigh vacuum thermal desorption spectroscopy (TDS) was performed during isochronal annealing of a N-doped GGST film covered by a 10 nm-thick TiN x layer. Desorption is observed before GGST crystallization, but the comparison between TDS and in situ x-ray diffraction measurements shows that the main desorption peak, observed between 653 K and 703 K, occurs after GGST full crystallization. The most prominent desorbing species are Ar, N 2 , H 2 , and H. These results show that the TiN x polycrystalline layer cannot prevent N atoms from leaving the GGST layer during annealing, suggesting a progressive change of the N-doped GGST chemical composition during thermal annealing and crystallization., (© 2023 IOP Publishing Ltd.)