A Study of Operation Performance Promotion for Flash Memory

• Main Authors: Ho, Chia-Huai, 何家淮
• Other Authors: Chang-Liao, Kuei-Shu
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/29657400064356766797

博士 === 國立清華大學 === 工程與系統科學系 === 97 === The programming and erasing operations of flash memory device can be performed by injecting electron through the tunneling dielectric layer while a high voltage is applied. These operations possibly cause damage to the SiO2/Si interface or SiO2 itself if manufacture quality of flash memory is not good, which thereby degrades reliability and eventually causes the failure of flash memory. In this work, a novel operation method, new design of structure, and the high temperature on operation performance of flash memory devices were studied. Regarding novel programming method, experimental results show that the proposed programming method with higher gate current injection efficiency not only increases the operating speed but also improves the reliability. This reliability improvement can be attributed to the reduction of oxide trap charge generation and threshold voltage shift. As for the new flash memory structure, the simulation results show that the employment of a vertical dielectric layer in the depletion region can improve the operation performance of flash memory. The improvement can be attributed to a lower potential in the central region of device channel and the increase of the potential drop in the channel direction near drain junction. Thus, this proposed vertical dielectric layer increases the electrical field of the channel and thus the probability and the momentum of electron injection. The operation characteristics of the flash device with a vertical dielectric layer in the depletion region of source and drain are superior to those of others. In addition, it is found that a vertical dielectric layer with lower dielectric constant can enhance the operation performance of flash device even more. Regarding the high temperature effects, the threshold voltage of flash memory devices is reduced with raising temperature. When the temperature is higher, the operating window (ie threshold voltage shift) of the flash memory are larger for both measurement and simulation results. Although the electron concentration in channel is reduced with increasing temperature, the reduced amount is little in comparison with those at room temperature. The operation performance of flash device at high temperature is better because of the higher electrical field and electron injection probability at channel surface.