Hot-carrier effects in flash erasable programmable read-only memory devices.

摘要

Design of the high density Flash Erasable Programmable Read-Only-Memory device (Flash EPROMs) requires a good understanding of the physical mechanisms that govern the device operation. The device is a variation of the Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) with an extra polysilicon floating-gate electrode. Its operation relies on hot-electron injection and storage of injected electrons in the floating-gate electrode between two dielectrics. The conductive state of the channel is changed by the stored electrons, which provides the memory information.; Electron trapping in the tunnel oxide associated with the hot-electron transfer through the oxide degrades the performance of the memory cell by retarding the carrier transfer and changing the device parameters. In addition, there is also an unintentional hole injection from the substrate. This imposes even more severe constraints on the design of devices with smaller feature sizes.; This thesis covers a variety of topics in Flash EPROMs, including a summary of the various physical mechanisms that govern the device operation as well as those that cause device degradation, a description of the measurement techniques for characterizing the hot-carrier damage in the memory cells, a comparison of several techniques to determine the floating gate potential, an algorithm for the simulation of the device operation, and an extensive study of the hot-carrier induced effects in Flash memory device and circuits.; The hot-carrier induced effects, being the main focus of this thesis, cover various degradation modes as well as data retention problems. The main source of some random failure modes occurring in the operation of a Flash memory chip has been linked to the hot carriers. One of these random failures is in the form of the erratic/nonuniform erase. The mechanisms responsible for this phenomenon have been elaborated in detail, including hole trapping which may also give rise to various other reliability problems. The damage caused by the write and the erase operations has been investigated with the help of a number of measurement techniques. In addition, several write and erase algorithms have been evaluated for minimizing the hot carrier induced effects.