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Boosting Performance of Phase Change Devices by Hetero- and Nano-Structure Material Design

Periodic Reporting for period 1 - BeforeHand (Boosting Performance of Phase Change Devices by Hetero- and Nano-Structure Material Design)

Reporting period: 2019-01-01 to 2020-06-30

BeforeHand aims at establishing the foundations of a new technology, suitable for the implementation in networks of Electronic Smart Systems (ESS) exploiting the capability of phase-change materials (PCMs) to process and store data in the very same physical place, with particular focus on automotive applications. The ESS of the future should be able to sense its environment, locally store and process the information, as well as communicate with other objects in a network. Within our project the realization of processing/storage devices will be achieved through the development of new material combinations with the best material trade-off benchmarked for automotive applications. We will make use of a test vehicle to allow the comparison among different materials. After successful evaluation of the best material combination, a demonstrator with processing/storage ability will be implemented. At the end of the project a full evaluation of the demonstrator will be performed. Furthermore, integration in an embedded chip environment for automotive application, as well as scalability and reliability issues, will be evaluated. The results are going to be made public and used to plan the first chip with embedded state of the art technology to be implemented in the automotive sector, with an expected direct impact on the Internet of Things (IoT) market.
IoT refers to a giant network of connections centered on providing distributed intelligence, sensing and connectivity to ESS around us. Such a scenario is no longer the wave of the future; it is here right now and is growing quickly. The IoT is connecting people, places and ESS at a rapid pace. It is a concept that not only has the potential to impact how people live and work, but also how the human society is managing its resources. IoT certainly opens the door to a lot of opportunities, yet bears many challenges. With the surge of connected ESS comes the demand and necessity to implement the exchange and processing, as well as the storage of all the data. The explosion of information that ESS devices within IoT will gather will require huge numbers of low-cost, secure and reliable embedded, non-volatile memory (NVM) for several storage and/or advanced processing purposes. A special societal impact of IoT is given by automotive applications, as related to infotainment, safety and fuel efficiency. For this application an important requirement is that the ESS must be reliably working at a temperature of 165°C. In this respect not all technologies are reliable. One of the most promising NVM is based on PCMs. We aim at solving several of the adverse aspects for PCM technology, focusing on those that strongly affect the implementation for smart automotive applications, by using chalcogenide multilayers. The basic idea is to create multilayers of chalcogenides of different alloy and compound combinations. The PCM cell takes advantage of the merits of the different sorts of materials used for the stack.
A freedom to operate analysis was performed and a time-zero landscape area inside which the activity of BeforeHand will be carried out was identified.
The growth optimization of thin films started with the study of Ge-rich GST (PDI and URTOV) and GaSb (UGRO). The Ge-rich GST composition chosen was from the region highlighted by the black dots in Fig. 2 of P. Zuliani et al., Solid-State Electronics 111 (2015) 27–31. The growth of amorphous samples helps for defining both the crystallization temperature and the alloy composition, thus the growth of both crystalline and amorphous films was carried out in parallel (PDI, UGRO, URTOV). The NW material by MOCVD (CNR-IMM Agrate) was focused on Sb2Te3 or GeSb for the single core and Sb2Te3, InSbTe, GeTe for the shell.
Mempry cell vehicles have gone through the realization process to implement the deposition of PCM multilayers and to allow contact to the active material.
In the meantime the contacting of the NWs is smoothly ongoing with several test of contacts achieved.
The physical characterization activity started in parallel to the deposition of thin films and NWs. we started with investigation by XRD to be combined with Raman vibrational spectroscopy. Due to the fact that the investigated samples with GST composition Ge-rich have not been previously investigated in literature the necessity of a cooperation with the UNIMIB arose. Thus, the acquired spectra were simulated and compared. Some of the samples were also sent to UGRO for detailed TEM investigation. At the same time dedicated samples with Te capping layer were sent to the URTOV unit to be investigated through XPS. The UNIMIB unit modelled also the electronic DOS to compare with the XPS results.
Modulated PhotoThermal Radiometry has been employed in CNRS-I2M to measure the temperature dependent thermal conductivity of Ge-rich GST films from room temperature up to 600°C. The thermal boundary resistance at the interfaces has been also measured within the same temperature range.
The NWs have been investigated with TXRF for composition and subsequently in Catania through TEM for addressing the crystalline quality the composition and possible extended defects.
The activity towards the realization of a demonstrator started with careful planning of the overall structure and 1T-1R wafers realisation already started. The activity was also concerned with the benchmarking issue.
BeforeHand is a project with a strong involvement of material development, device preparation and functionality in terms of memory as well as data processing devices. In the field of basic research, we expect to be able to uncover the switching mechanism behind the improved performances of chalcogenide multilayers. PCM devices feature innovative functionalities and will contribute to data processing advances. PCM provide simultaneous storage and data processing. In the conventional von-Neumann architecture, data are stored in a memory unit and transferred to a dedicated central processor. This is the well-known von-Neumann bottleneck: a program cannot be executed very fast as the instructions are travelling between processor and memory. Devices in which processing and memory functions are performed simultaneously and at the same location promise dramatic improvements in performance along with the new design opportunity.
If we now consider BeforeHand innovation potential in terms of products, the field of embedded memories is the most accessible. Embedded NVM technologies address mainly the MCU market, as this is the most advanced in terms of technology requirements and one of the most interesting from the business point of view. In fact, MCUs are at the heart of several systems within the automotive vehicles, and the number of those systems is increasing year by year, following the increasing “intelligence” requested by modern cars. MCUs are requested not only for engine control, gasoline management, airbag, stability control and Global Positioning System functions, but also for future autonomous driving, electrification and battery control, telematics, inside and for vehicle-to-vehicle communication, etc..