對最廣為使用的非揮發性記憶體－快閃記憶體而言，通常會遇到兩個瓶頸：一是在元件尺寸繼續微縮下之瓶頸，由於尺寸微縮後穿隧氧化層之厚度亦隨之下降，如此雖可得到較快的讀寫速度，但電荷保存時間亦隨之下降，故須在兩者之間取得平衡點；二是在多次讀寫後在穿隧氧化層品質容易劣化而產生漏電路徑，將使得所有儲存在浮動閘極的電荷都會經由此漏電路徑而全部流失掉。為了克服上述兩個瓶頸，主要有兩種改良的的方法被提出，一是「多晶矽層?氧化層?氮化矽層?氧化層?矽」非揮發性記憶體，另一種是奈米晶體非揮發性記憶體。

For nonvolatile semiconductor memories (NVSM), there are two limitations encountered at the present time. (1) The limited potential for continued scaling of the device structure: this scaling limitation stems from the extreme requirements on the tunnel oxide layer. To balance between program/erase speed and retention time, there is a trade-off between speed and reliability for the optimal tunnel oxide thickness. (2) The quality and strength of tunnel oxide after plenty of program/erase cycles, once a leaky path has been created in tunnel oxide, all charges stored in the floating gate will be lost. Therefore, two approaches, the silicon-oxide-nitride-oxide-silicon (SONOS) and the nanocrystal nonvolatile memory devices, have investigated to overcome this oxide quality limit of the conventional floating gate NVSM.