Investigation on junctionless floating body DRAMs including Trap Assisted Tunneling. (July 2020)

• Record Type: Journal Article
• Authors: Giusi, Gino
• Is Part Of: Solid-state electronics. Volume 169(2020)
• Publication Date: 2020-07
• Subjects: One-transistor dynamic random access memory -- Junctionless -- Trap assisted tunneling -- Band to band tunneling -- Device simulations -- Random dopant fluctuations; Semiconductors -- Periodicals; Semiconducteurs -- Périodiques; 621.38152
• DOI: 10.1016/j.sse.2020.107799
• Languages: English
• ISSNs: 0038-1101

Abstract

Highlights: Physics of operation and performances of a DRAM based on Junctionless transistors and 1T-DRAM concepts. 2D device simulation on a template (independent) double gate junctionless transistor. Statistical variability induced by random dopant fluctuations. Technology (bandgap, lifetime) scaling. Abstract: Junctionless Transistors (JL) and One-Transistor (1T) DRAMs are concepts that come out in order to improve the scalability of logic and volatile memories, respectively. In some recent papers, Floating Body (FB) DRAMs (a class of 1T-DRAM) and JL transistors have been joined in order to propose a solution to overcome the scaling limit of the conventional 1T-1C DRAM cells. In this paper they are discussed in detail the physics of operation and the performances of FB-DRAM cells based on JL transistors including the effect of Trap-Assisted-Tunneling (TAT), neglected in most of previous works. As expected, TAT severely limits the retention time due to the large doping, in particular during HOLD operation. The discussion is supported by 2D device simulation on a double gate junctionless transistor including the effect of statistical variability induced by random dopant fluctuations, and the technology (bandgap, lifetime) scaling. It is found that the cell, at least at the nanoscale, can work only by independent gate operation, having maximum performance when the bottom gate works at the limit of the BBT bias region during READ, and that at a gate length as large as 100 nm and fin width of 10 nm the cell can sustain the high doping induced variability to a retention time in the order of 1 ms, while the use of materials with higher bandgap (~1.3 eV) than Silicon can improve the retention time to the order of 10 ms. However several concerns remain on their actual use related to the necessary bias level and to the impact of the actual technologies on the lifetime, which strongly affects TAT degradation.