Strain-induced effects on band-to-band tunnelling and trap-assisted tunnelling in Si examined by experiment and theory

TL;DR

This study combines experimental data and ab-initio calculations to analyze how strain affects leakage currents in silicon, revealing that strain can significantly increase tunnelling-related leakage, impacting device performance.

Contribution

It provides a systematic analysis of strain effects on tunnelling mechanisms in silicon, refining models to predict leakage current changes under various strain conditions.

Findings

Strain can increase leakage current by up to 150 times.

Low uniaxial strains of 0.1% can significantly boost tunnelling leakage.

Tensile strain may reduce or double leakage current.

Abstract

Strain is commonly used in metal-oxide-semiconductor technologies to boost on-state performance. This booster has been in production for at least a decade. Despite this, a systematic study of the impact of strain on off-state leakage current has been lacking. In this work we use experimental data and ab-initio calculations to refine existing models to account for the impact of strain on band-to-band tunnelling and trap-assisted tunnelling in silicon. We observe that the strain may dramatically increase the leakage current, depending on the type of tunnelling involved. For band-to-band and trap-assisted tunnelling, low uniaxial strains of 0.1% (or 180 MPa) can increase the leakage current by 60% and 10% compared to the unstrained case, respectively. Using our models, we predict that compressive strain on the order of 1% (or 2 GPa) can increase the leakage current by 150 times. Conversely, tensile strain may diminish or at most double the leakage current in all observed cases. Though detrimental in conventional inversion-mode MOSFETs, these processes may be used to boost the performance of Tunnel Field Effect Transistors, where on-state current is defined by band-to-band tunnelling.