Mixed Current Model for I-V Characteristic of Nano MOSFETs

• Main Authors: Wei-Lun Wang, 王暐綸
• Other Authors: Heng-Sheng Huang
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/e5udmk

碩士 === 國立臺北科技大學 === 機電整合研究所 === 105 === As IC industries keep making progress, the size of MOSFETs keep scaling down and their electric current become more and more difficult to estimate. Conventionally speaking, the surface drift current of MOSFET is considered only, and it is convinced that as the drain voltage increases, the inversion charge density near drain site is going to decrease and becomes zero in order to generate the pinch-off point which makes the total current stop increasing, remain a constant and the MOSFET becomes saturated. However, why does it go into saturation region instead of completely no electric current? This kind of problem attracts our attention. In order to describe the stable electric current at pinch-off point, some scientists have already proposed some theories such as “velocity saturation” and “velocity overshoot”. However, there are still a lot of problems being unable to solve by these theories. Therefore, we propose a new I-V model based on physics to try to describe the current behavior which couldn’t be described specifically before. We add a concept of gradient of inversion charge density to build our new model because the channel is no longer an even distribution instead of gradient of charge density. That is why we make this assumption to describe the current behavior physically. In our experiments we all use the wafers from UMC which are 28nm High-K metal gate. In this work, the current behavior at saturation region will be focused. The diffusion current dominates close to pinch-off point which is our key assumption. The final result is in our expectation; there is actually apparent diffusion current near the pitch-off point. Nevertheless, as the device is scaling, the channel length also decreases and this phenomenon will induce the larger diffusion current which can’t be ignored anymore due to the larger gradient of inversion charge density. Therefore, a brand new I-V model is strongly needed which is more physical than any others in the past. With our new model, IC designers can design circuits more efficiently and make the power consumption to be much lower. Also, the new model is able to testify the products in the foundry if they all follow the standards or not and to decrease the cost of development. In other words, it is a significant breakthrough for the future CMOS technology.