بررسی نویز فرکانس پایین از تک سلولی های n-MOSFET برای برنامه های کاربردی حافظه
Abstract
1- Introduction
2- Experiment
3- Results and discussion
4- Conclusions
References
Abstract
In this paper, we present a detailed investigation of low frequency noise (LFN) for different n-MOSFET devices dedicated for memory applications. We investigate the impact of the gate oxide thickness (GOX) on LFN. We analyzed how the position, the existence and the composition of Lightly Doped Dopant (LDD) implant in the source/drain region affect the LFN performance of the device. The results demonstrates that the thinner gate oxide and the device without LDD improved the noise performance compared the devices with thick GOX and with LDD implants. On the other hand, the absence of LDD implant on one side of the MOSFET didn’t reveal a global trend for all measured devices. Finally, the different LDD implant composition resulted in different LFN performance which is gate area dependent. These results can be used from both process and design engineers to improve the LFN of n-MOSFET.
Introduction
Today, it is well known that LFN can be used as a characterization tool for the quality and the reliability of the devices [1-2]. It is obvious that the level of noise has a direct impact on the device quality. In addition, LFN can influence the design of an electronic circuit since it can limit the overall performance and operation. Thus, the noise investigation of special architecture devices is of paramount importance for device and design engineers. Single transistors designed for logic NVM of SONOS type memory applications [3] can be used for LFN comprehension analysis due to the special architecture they have. In this experiment five single cell n-MOSFET devices were designed for memory applications and used for noise analysis. In literature exists a number of publications referring to LFN characterization for logic NVM of SONOS type [4-7]. According to our knowledge, we could not find a prior work that used these type of devices for LFN improvement purposes and not for simple characterization. We tried not only to identify the main source of LFN in these devices but also to use this info for the improvement of LFN performance in CMOS technology. In MOSFETs, it is generally accepted that the flicker (1/f-like) noise originates either from carrier number fluctuations (CNF) (Eques 1, 2 Table 1) [1] or from Hooge mobility fluctuations [8]. The CNF noise is due to carrier exchange between the near-interface gate dielectric traps and the channel. The charge fluctuations in the gate dielectric could also induce fluctuations of the carrier mobility, giving rise to the so-called correlated mobility fluctuations (CMF) (Eques 3, 4 Table 1) [9-11].