| Summary: | 碩士 === 國立交通大學 === 電子工程系 === 91 === SONOS (Silicon Oxide Nitride Oxide Silicon) will become the main stream of nonvolatile memory products because of its simplicity in structure and scalable by comparing with conventional floating gate cells. For the scaling of SONOS memory, the endurance and retention are the two major reliability issues. Also, data retention has been most crucial for the scaling of the cell. For a thin gate oxide SONOS cell in the direct tunneling regime, two leakage current components, i.e., thermionic and direct tunneling (DT), in relating to the data loss, are the two dominant mechanisms.
In this thesis, data retention for various top (blocking) and bottom oxide (tunnel oxide) SONOS cells has been investigated. The direct tunneling through either tunnel or blocking oxide can also be identified experimentally. First of all, it was found that injected charge locates close to the tunnel oxide/nitride interface either during program or erase. This result is then used to identify the charge loss in retention measurement. Results show that the cell with thinner blocking oxide has more charge loss under various baking temperatures, especially when the blocking oxide is thinner than 40A. Thick blocking oxide cell has larger operation window and less charge loss, but needs larger gate voltage during program and erase and has poorer endurance. Finally, A leakage current separation technique has been developed to distinguish the two leakage components via thermionic and direct tunneling. The direct tunneling dominates the short-term leakage while the long-term leakage is dominated by thermionic emission. This will help us to understand the dominant leakage during the scaling of SONOS cells.
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