Browsing by Subject "Flash memory"
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Item Floating gate engineering for novel nonvolatile flash memories(2010-05) Liu, Hai, 1977-; Banerjee, Sanjay; Register, Leonard F.; Tutuc, Emanuel; Ekerdt, John G.; Lee, JackThe increasing demands on higher density, lower cost, higher speed, better endurance and longer retention has push flash memory technology, which is predominant and the driving force of the semiconductor nonvolatile memory market in recent years, to the position facing great challenges. However, the conventional flash memory technology using continuous highly doped polysilicon as floating gate, which is the most common in today’s commercial market, can't satisfy these demands, with the transistor size continuously scaling down beyond 32 nm. Nanocrystal floating gate flash memory and SONOS-type flash memory are considered among the most promising approaches to extend scalability and performance improvement for next generation flash memory. This dissertation addresses the issues that have big effects on nanocrystal floating gate flash memory and SONOS-type flash memory performances. New device structures and new material compatible to CMOS flow are proposed and demonstrated as potential solutions for further device performance improvement. First, the effect of nanocrystal-high k dielectric interface quality on nanocrystal flash memory performance is studied. By using germanium-silicon core-shell nanocrystals or ruthenium nanocrystals buried in HfO₂ as charge storage nodes, high interface quality has been achieved, leading to promising memory device performance. Next, another crucial challenge for nanocrystal flash memory on how to deposit uniformly distributed nanocrystal matrix in good shape and size control with high density is discussed. Using protein GroEL to obtain well ordered high density nanocrystal pattern, a flash memory device with Ni nanocrystals buried in HfO₂ is demonstrated. For this technique, the nanocrystal size is restricted to the GroEL's central cavity size and the density is limited by protein template. To overcome this limitation, a novel method using self-assembled Co-SiO₂ nanocrystals as charge storage nodes is demonstrated. Separated by thin SiO₂, these nanocrystals can form close packed form to achieve ultrahigh density. Finally, charge trapping layer band engineering is proposed for SONOS-type memory for better memory performance. By manipulating the pulse ratio of Hf and Al precursor during ALD deposition, the band diagram of Hf[subscript x]Al[subscript y]O charge trapping layer is optimized to have a Hf : Al ratio 3:1 at bottom and 1:3 at the top, leading to better trade-off between programming and retention for the of memory device.Item HyDrive: Enhancing performance and reliability of storage systems(2012-08) Amritkar, Prathamesh; Chen, Yong; Zhuang, YuMost of the data in the world till today has been stored on hard disk drives (HDDs). Though evolution has taken place in HDDs from first IBM’s invention to HDDs till date, in terms of cost, storage size and portability, nothing much development has been seen in its basic internal structure. HDDs still have mechanical components and hence they are power hungry, unreliable, less portable and slower in terms of random performance. Many researchers have started seeing NAND-flash memory as a promising storage media that could revolutionize data storage systems. Replacing HDDs with NAND-flash-based solid state drives (SDDs) is a recently emerging trend for many high-end computing applications. However, due to its high price, low capacity and inability to over-write, a complete replacement of HDDs with SSDs seems to be unreasonable for high-end computing. As new technologies are born, older technologies might take a new role in the process of system evolution. The best results can be achieved in storage systems if both the storage media complement each other in working. We propose a hybrid storage architecture, namely HyDrive, in this research. The HyDrive identifies hot data (data accessed regularly and frequently), and then stores that data on the SSD for faster access. Cold data (less frequently accessed data) will be stored on HDDs, so that the number of write operations issued to SSDs will be controlled and will help to extend SSDs life time. An evaluation of the HyDrive confirms that the HyDrive has a potential to improve present storage architecture. It has potential to improve SSD lifetimes significantly without much affecting the performance. It provides a balance between performance and cost for high-end computing storage systems.