In a conventional nonvolatile memory, charge is stored in a polysilicon floating gate (FG) surrounded by dielectrics. The scaling limitation stems from the requirement of very thin tunnel oxide layer. For FG, once the tunnel oxide develops a leaky path under repeated write/erase operation, all the stored charge will be lost.Therefore, the thickness of the tunnel oxide can not be scaled down to about 7 nm.
To alleviate the scaling limitation of the conventional FG device while
preserving the fundamental operating principle of the memory, we have studied the distributed charge storage approach such as the nanocrystal nonvolatile memory. Each nanodot will typically store only a handful of electrons; collectively the charges stored in these dots control the channel conductivity of the memory device. Nanocrystal charge storage offers several advantages, the main one being the potential to use thinner tunnel oxide without sacrificing non-volatility. This is a quite attractive proposition since reducing the tunnel oxide thickness is a key to lowering operating voltages and/or increasing operating speeds. The improved scalability results not only from the distributed nature of the charge storage, which makes the storage more robust and fault-tolerant, but also from the beneficial effects of Coulomb blockade. A local leaky path will not cause a fatal loss of information for the nanocrystal non-volatile memory device. Also, the nanocrystal memory device can maintain good
retention characteristics and lower the power consumption.
In recent years, nonvolatile memory with nanocrystals cell have widely applied to overcome the issue of operation and reliability for conventional floating gate memory. The excellent electrical characteristics of memory device need good endurance, long retention time and small operation voltage. Among numerous memory devices with nanocrystals, the memory device with metal nanocrystals was widely researched. It will be a new candidate for flash memory. The advantages of metal nanocrystals has have higher density of states around Fermi level, stronger coupling with conduction channel, wide range of available work functions and smaller energy perturbation due to carrier confinement. So metal nanocrystals can reduce operate voltage, and increase write/erase speed and endurance. Most important of all, we can control the sizes of nanocrystals dot and manufacture at low temperature¡CThis advantage can apply to thin film transistor liquid crystal display; it fabricates driving IC and logical IC on panel for diverseness and adds memory beside switch TFT as image storage to reduce power consumption for portability.
In this thesis, we will discuss metal nanocrystals as memory storage medium. And we can use high temperature oxidation, low temperature annealing with oxygen to form nanocrystals. Most importantly, we analyze the effect of electron storage at metal nanocrystals by means of material and electrical analysis.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0725106-141008 |
| Date | 25 July 2006 |
| Creators | Chang, Chih-Ming |
| Contributors | Cheng-tung Huang, P.T Liu, Ting-Chang Change, Osbert Cheng |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0725106-141008 |
| Rights | withheld, Copyright information available at source archive |
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