Study of Cryogenic MOSFET Sub-Threshold Swing Using Ab Initio Calculation

Publication Date

10-1-2023

Document Type

Article

Publication Title

IEEE Electron Device Letters

Volume

44

Issue

10

DOI

10.1109/LED.2023.3310511

First Page

1604

Last Page

1607

Abstract

The abnormal subthreshold swing (SS) in Silicon Metal-Oxide Semiconductor Field Effect Transistor (MOSFET) at cryogenic temperature is commonly attributed to band tail (BT) conduction. The cryogenic SS does not scale with the temperature, T, for T < 50K and it is observed to saturate at 10mV/dec 20mV/dec at low T in most experiments. Hitherto, only analytical studies have been conducted for BT and its properties. It is not clear how much of its effect can be eliminated should there be an ideal manufacturing technology. In this letter, by using robust ab initio calculation with quantum transport, we have successfully calculated the BT in a Si nanowire (NW) and studied its characteristic length. By analyzing the transport properties of the NW with various gate lengths, LG , at various temperatures, it is observed that for LG< 20 nm, the tunneling current dominates, and for LG> 20nm, the BT current dominates at 3K. It is found that, in a perfect nanowire (as a gedanken experimental device), an SS as low as 1.4mV/dec can be achieved at 3K for 15 orders of magnitudes of current change with a minimum of 0.42mV/dec ( LG = 50nm). This also justifies the results in a recent experiment in which a very low SS (3.4mV/dec at 5.5K) was obtained. Moreover, it is also shown that for the 2nm node ( LG∼ 15nm), direct S/D tunneling will set the ultimate limit of SS at 3K.

Funding Number

2046220

Funding Sponsor

National Science Foundation

Keywords

Ab initio calculation, cryogenic, quantum transport, Si nanowire, technology computer-aided design (TCAD)

Department

Electrical Engineering

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