Flash Memory Devices

Flash memory devices have represented a breakthrough in storage since their inception in the mid-1980s, and innovation is still ongoing. The peculiarity of such technology is an inherent flexibility in terms of performance and integration density according to the architecture devised for integration. The NOR Flash technology is still the workhorse of many code storage applications in the embedded world, ranging from microcontrollers for automotive environment to IoT smart devices. Their usage is also forecasted to be fundamental in emerging AI edge scenario. On the contrary, when massive data storage is required, NAND Flash memories are necessary to have in a system. You can find NAND Flash in USB sticks, cards, but most of all in Solid-State Drives (SSDs). Since SSDs are extremely demanding in terms of storage capacity, they fueled a new wave of innovation, namely the 3D architecture. Today “3D” means that multiple layers of memory cells are manufactured within the same piece of silicon, easily reaching a terabit capacity. So far, Flash architectures have always been based on "floating gate," where the information is stored by injecting electrons in a piece of polysilicon surrounded by oxide. On the contrary, emerging concepts are based on "charge trap" cells. In summary, flash memory devices represent the largest landscape of storage devices, and we expect more advancements in the coming years. This will require a lot of innovation in process technology, materials, circuit design, flash management algorithms, Error Correction Code and, finally, system co-design for new applications such as AI and security enforcement

Gênese duma sequência de solos da região do planalto médio Riograndense

A toposequense of important soils of the middle plateau region of Rio Grande do Sul were studied with reference to their morphological, geomorphological, chemical and mineralogical properties in order to obtain information concerning their genesis, classification, and agricultural capability. The soils of the plateau are derived from basic igneous rocks as well as from deposits of sandy material, whereas the soils of the back slope and footslopes are derived from the underlying basalt, having also received material eroded from the deeply weathered soils of the undulating uplands. In spite of their steep gradients and stoniness, the soils of the slopes are preferred by farmers because they have clay minerals which have undergone fewer transformations and hence have greater fertility. Although the soils of the older surfaces present undulating relief, they are highly weathered and quite acid, with low reserves of plant nutrients.Foi estudada uma toposseqüência de importantes solos da região do Planalto Médio Riograndense, quanto às suas características morfológicas, geomorfológicas, químicas e mineralógicas, objetivando obter informações quanto à gênese, classificação e utilização dos solos para fins agrícolas. Os solos dos planos elevados foram desenvolvidos a partir de rochas eruptivas básicas e com adição de material arenoso, enquanto que os solos das encostas e declividades inferiores foram originados do basalto subjacente, recebendo contribuição de material erodido dos solos profundamente intemperizados dos planos elevados. Os solos das encostas, apesar de seus fortes declives e pedregosidade, são preferidos pelos agricultores, por apresentarem argilo-minerais menos transformados e elevada fertilidade natural, enquanto que os solos das superfícies mais velhas apresentam relêvo ondulado, mas são fortemente intemperizados, com baixas reservas em elementos nutritivos para as plantas e são francamente ácidos

Understanding the Origin of Metal Gate Work Function Shift and Its Impact on Erase Performance in 3D NAND Flash Memories

We studied the metal gate work function of different metal electrode and high-k dielectric combinations by monitoring the flat band voltage shift with dielectric thicknesses using capacitance–voltage measurements. We investigated the impact of different thermal treatments on the work function and linked any shift in the work function, leading to an effective work function, to the dipole formation at the metal/high-k and/or high-k/SiO2 interface. We corroborated the findings with the erase performance of metal/high-k/ONO/Si (MHONOS) capacitors that are identical to the gate stack in three-dimensional (3D) NAND flash. We demonstrate that though the work function extraction is convoluted by the dipole formation, the erase performance is not significantly affected by it