Abstract
Anodic HfO2 memristors grown in phosphate, borate, or citrate electrolytes and formed on sputtered Hf with Pt top electrodes are characterized at fundamental and device levels. The incorporation of electrolyte species deep into anodic memristors concomitant with HfO2 crystalline structure conservation is demonstrated by elemental analysis and atomic scale imaging. Upon electroforming, retention and endurance tests are performed on memristors. The use of borate results in the weakest memristive performance while the citrate demonstrates clear superior memristive properties with multilevel switching capabilities and high read/write cycling in the range of 106. Low temperature heating applied to memristors shows a direct influence on their behavior mainly due to surface release of water. Citrate-based memristors show remarkable properties independent on device operation temperatures up to 100 °C. The switching dynamic of anodic HfO2 memristors is discussed by analyzing high resolution transmission electron microscope images. Full and partial conductive filaments are visualized, and apart from their modeling, a concurrency of filaments is additionally observed. This is responsible for the multilevel switching mechanism in HfO2 and is related to device failure mechanisms.
Highlights
Memristive effects in various materials are continuously reported and the interest for memristive devices grows due to their wide range of applications
The presence of O virtually across the entire analyzed structure is due to contamination and additional oxidation occurring during sample preparation and air-exposure before transmission electron microscopy (TEM) analysis
The chemical analysis indicates that all layers are localized as expected from the definition of the metal-insulator-metal systems (MIM) structure with the active medium sandwiched between metallic electrodes
Summary
Memristive effects in various materials are continuously reported and the interest for memristive devices grows due to their wide range of applications. Redox-based random access memories (ReRAMs), as a new generation of memories more progressive than FLASH technology, and dynamic random access memories (DRAM) are some of the most common applications [1,2,3]. Memristors are used as building blocks for neuromorphic architectures [4] such as artificial synapses [5] and logic circuits due to the possibility of multilevel switching to implement a fuzzy behavior [6,7,8]. Due to their reported high stability, memristors are used for various sensing applications [9].
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