Surface effects on the electro-mechanical properties of silicon nano-ribbons and nano-wires
(2013)
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- Abstract
- (en) The need for developing simple and generic characterization tools to deform freestanding silicon beams down to the nanometre scale, sufficiently equipped to investigate both the mechanical properties and the carrier transport under large strains, has been met in this research through the design of a versatile lab-on-chip. The Young’s modulus was observed to unexpectedly decrease from a bulk value of 169 GPa down to 96 GPa when varying the thickness of silicon from 200 down to 30 nm. The fracture strain increases when decreasing the volume of the test specimen starting from 0.2 % for a bulk silicon wafer, to reach 5% in the smallest SiNWs. In order to proceed with characterizing its electro-mechanical properties, it is necessary to understand the influence of surface state charge distributions on SiNW transport characteristics. The removal of the oxide at the surface of SiNWs by a HF treatment results in a drop in conductance up to six orders of magnitude. This effect is from a surface depletion of holes in the SiNW induced by positive surface charges deposited from the HF treatment. However, it is observed that this charge density is transient and is dissipated with the re-growth of an oxide layer. Additionally, atomic layer deposited Al203 can be used to control the surface potential of p-type SiNWs from depletion to accumulation. In summary, the SiNW conductance can be reproducibly controlled up to several orders of magnitude, while playing with four common surface conditions: with a native oxide, deposited Al203, thermal oxide and HF induced H-terminations. Finally, the piezo-resistance of SiNWs has been investigated under large uniaxial tension up to fracture using an original on-chip tensile testing technique. The piezo-resistance coefficient (π) was found to increase by a factor of 6, when decreasing the dopant concentration from Na ~ 1 x 1019 cm-3 down to ~ Na ~ 5 x 1017 cm-3. Reduction of resistance up to a factor of 5.8, higher than theoretical prediction of 4.5 is reported for Na ~ 5 x 1017 cm-3 under a stress of 1.7 GPa, without any sign of saturation.
- Affiliations
UCLouvain SST/ICTM/ICTM - Institute of Information and Communication Technologies, Electronics and Applied Mathematics
Citations
Bhaskar, U. K. (2013). Surface effects on the electro-mechanical properties of silicon nano-ribbons and nano-wires. https://hdl.handle.net/2078.5/204524