An extensive deposition work was carried out by the WP2 participants, aiming at the selection of the best performing phase change materials composing the expected heterostructures. The strength of the approach, using in parallel different deposition techniques, allowed the exploration of a common set of phase change materials both in the form of thin films and nanowires. The consortium worked incessantly to improve the control on the deposition of the most promising layers of phase change materials and their combination in multi-layered heterostructures and superlattices. A particularly interesting composition, named as golden Ge-rich GST, was identified and gave rise to a rich and intense stud. WP3 was taking care of the development of several vehicles suitable for electrical testing to allow for the evaluation of different stacks of multilayers. Several materials and heterostructures deposited by different methods within the Consortium were evaluated. The most promising material, among the investigated Ge-rich based alloys, was the golden Ge-rich GST composition, since it exhibits better retention and cyclability, and a very low resistance drift. At the beginning of the project, the primary focus of WP4 was on performing characterization and modeling activities required to optimize the materials development. This was done to check if the desired films were grown each time with the right composition and structure and to guide the growers towards optimized structures. Whereas, in the second half of the project, the characterization was performed with the aim of deep understanding of the various structural, electronic, electrical and thermal properties. Finally we generated an in-depth understanding of the properties and performances of the materials, with strong interlink with the other work packages.
WP5 was mainly devoted to the realization of a demonstrator able to prove the processing/storage concept of a device with the PCM multilayer as active layer. At first we developed multilayered stacks in a 200 mm PVD deposition. The chosen materials were integrated in a demonstrator (1Resistor) single cells, 1 transistor – 1 PCM (1T-1R) single cells and small arrays. The electrical characterization of single cells and arrays was carried out. Benchmarking, between the best PCM materials and GST-225 and Ge-GST:N, was performed to evaluate the possible integration of those materials in an automotive chip for the IoT market. We demonstrated that the golden Ge-rich GST composition used in heterostructures is of great interest, since it combines a good programming window, reduced programming currents, good endurance and data retention, but also could enable multilevel programming.
