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Investigation of HfO2 based Resistive Random Access Memory (RRAM) : characterization and modeling of cell reliability and novel access device

Abstract : The performance gaps in nowadays memory hierarchy on the first hand between processor and main memory, on the other hand between main memory and storage have become a bottleneck for system performances. Due to these limitations, many emerging memories have been proposed as alternative solutions to fill out such concerns. The emerging non-volatile resistive random-access memories (RRAM) are considered as strong candidates for storage class memory (SCM), embedded nonvolatile memories (eNVM), enhanced solid-state disks, and neuromorphic computing. However, reliability challenges such as RRAM thermal stability and resistance variability are still under improvement processes. In addition, to achieve high integration densities the RRAM needs two terminal selector devices in one-selector one-resistor (1S1R) serial cell. The BEOL selector device enables suppression of the parasitic leakage paths, which hinder memory array operation in crossbar and vertical 3D architectures.In this PhD, our main focus is to address and treat the above challenges. Here, the work can be divided into two main parts: i) the investigation of the reliability of HfO2 based RRAM cells and ii) the characterization of the basis memory operations and performances of HfO2 based RRAM cells co-integrated with two different back end of line (BEOL) selector technologies.For the reliability part, we have investigated the effects of aluminum (Al) doping on data retention of HfO2 based RRAM cells. Single and double layer devices with different aluminum concentration were fabricated and tested. From macroscopic electrical characteristics, like time dependent dielectric breakdown (TDDB) and ramped voltage forming, microscopic properties of the materials such as the activation energy to break a bond at zero field and the dipole moment of the bond were extracted. These parameters have been used to shed new light on the mechanisms governing the forming process by means of device level simulations. Second, we have addressed the radiation immunity of HfO2 based RRAM for possible space applications as well. Our RRAM devices were exposed to 266 MeV Iodine heavy ions energy. Pre- and post-exposure analysis were carried out on the memory states and the programming voltages to study the effects of the irradiation on the memory characteristics. Throughout this work, we have performed physics based simulations to understand the dynamics of the forming process as well as the physical mechanisms involved during the memory operations.For the access devices part, we have evaluated two different types of selectors. For accurate reading and low power writing a strong selectivity in the current/voltage characteristics is required. In the first studied device, the selectivity is introduced by adding an oxide tunnel barrier. The main advantage of this strategy is that it is easy to integrate, however it suffers of low selectivity (~10) and low programming current. Second, an OTS based selector co-integrated with HfO2 based RRAM was fully characterized. OTS selector provides higher selectivity compared to the oxide tunnel barrier with the possibilities to strongly increase this selectivity by material engineering. Over 106 read cycles have been achieved on our 1S1R devices using an innovative read strategy that we have suggested to prevent disruptive read and to reduce the power consumption.
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Submitted on : Monday, October 1, 2018 - 9:59:08 AM
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Mouhamad Alayan. Investigation of HfO2 based Resistive Random Access Memory (RRAM) : characterization and modeling of cell reliability and novel access device. Micro and nanotechnologies/Microelectronics. Université Grenoble Alpes, 2018. English. ⟨NNT : 2018GREAT032⟩. ⟨tel-01884491⟩

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