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Defects and piezoresistance

by Rowe Alistair - published on , updated on

Mechanical stress is widely used to improve the performance of commercial, microelectronic semiconductor devices. As device sizes shrink to physical lengths scales coresponding to electrostatic screening lengths, the effect of mechanical on electronic properties can be radically different. In this activity we study these novel physical phenomena.

Contact: Alistair Rowe

The piezoresistance in silicon, and in other bulk semiconductors, is well known. Mechanical stress modifies the position of atoms in space thereby modifying the electronic structure and the electrical properties of the crystal.

Image MEB d’un nanofil de silicium suspendu mécaniquement. Le processus de fabrication dit ’top down’ permet de contacter le nanofil électriquement avec des contacts ohmiques. La piézorésistance est obtenue en mesurant la résistance du nanofil lors d’une sollicitation mécanique en tension parallèle au nanofil.

In silicon nanowires anomalous piezoresistance, whose sign or magnitude can be different from the bulk effect, has been observed, but its cause is not clear. Our research activity targets a better microscopic understanding of the phenomenon which could be important for future silicon nano-devices.

We proposed the first model to link the stress-dependence of the surface Fermi level pinning with giant piezoresistance. Our subsequent experimental studies revealed the difficulty in interpreting apparent giant piezo-resistance. More recent studies have shown that geometric stress concentration in nanostructuresl must be accounted for when interpreting piezo-resistance data. Our latest work reveals explicitly the stress-dependence of the pinned surface Fermi level at an oxidized silicon surface, and demonstrates that electromechanically active atomic defects associated with the oxidized silicon surface are responsible for a piezo-impedance effect consisting of a giant, anomalous piezo-resistance and a novel, giant piezo-capacitance.

This work is undertaken in collaboration with the IEMN in Lille and the University of Melbourne. For more information contact Alistair Rowe.