Achyut Bora

Observation of large low-frequency resistance fluctuations in metallic nanowires: Implications on its stability

We have measured the low frequency (1mHz<f<10Hz) resistance fluctuations in metallic nanowires (diameter 15nm to 200nm) in the temperature range 77K to 400K. The nanowires were grown electrochemically in polycarbonate membranes and the measurements were carried out in arrays of nanowires by retaining them in the membrane. A large fluctuation in excess of conventional 1/f noise which peaks beyond a certain temperature was found. The fluctuations with a significant low frequency component (~1/f^{3/2}) arise when the diameter of the wire ~15nm and vanishes rapidly as the diameter is increased. We argue that Rayleigh-Plateau instability is the likely cause of this excess noise.

1/f noise in nanowires

We have measured the low-frequency resistance fluctuations (1 mHz < f < 10 Hz) in Ag nanowires of diameter 15 nm

Evolution of 1∕fα noise during electromigration stressing of metal film: Spectral signature of electromigration process

{\leq}d{\leq}

Experimental study of Rayleigh instability in metallic nanowires using resistance fluctuations measurements from 77K to 375K

200 nm at room temperature. The power spectral density (PSD) of the fluctuations has a

Scanning thermal microscope study of a metal film under current stressing: role of temperature inhomogeneity in the damage process

(1/f{^\alpha})

Study of conductance fluctuations (1/f alpha noise) in metal film with electromigration stressing

character as seen in metallic films and wires of larger dimension.Additionally, the PSD has a significant low-frequency component and the value of α increases from the usual 1 to\simeq 3/2 as the diameter d is reduced.The value of the normalized fluctuations

Temperature dependence of the resistance of metallic nanowires of diameter ≥15nm : Applicability of Bloch-Grüneisen theorem

({\Delta}{R^{2}})/({R^{2}})

Debye Temperature of Metallic Nanowires—An Experimental Determination from the Resistance of Metallic Nanowires in the Temperature Range 4.2 K-300 K

also increases as the diameter d is reduced. We observe that there are new features in the 1/ f noise as the size of the wire is reduced and they become more prominent as the diameter of the wires approaches 15 nm.It is important to investigate the origin of the new behaviour as 1/ f noise may become a limiting factor in the use of metal wires of nanometre dimensions as interconnects.

Low-frequency resistance fluctuations in metal films under current stressing at low temperature (T<0.3Tmelting)

In this paper we report a systematic study of low-frequency 1/fα resistance fluctuation in a metal film at different stages of electromigration. The resistance fluctuation (noise) measurement was carried out in presence of a dc electromigration stressing current. We observe that in addition to the increase in the spectral power SV(f), the frequency dependence of the spectral power changes as the electromigration process progresses and the exponent α starts to change from 1 to higher value closer to 1.5. We interpret this change in α as arising due to an additional contribution to the spectral power with a 1/f3/2 component, which starts to contribute as the electromigration process progresses. This additional component SV(f) ∼ 1/f3/2 has been suggested to originate from long range diffusion that would accompany any electromigration process. The experimental observation finds support in a model simulation, where we also find that the enhancement of noise during electromigration stressing is accompanied by a change in spectral power frequency dependence.

Stability of metal nanowires

Nanowires with high aspect ratio can become unstable due to Rayleigh-Plateau instability. The instability sets in below a certain minimum diameter when the force due to surface tension exceeds the limit that can lead to plastic flow as determined by the yield stress of the material of the wire. This minimum diameter is given dm ≈ 2σS/σY , where σS is the surface tension and σY is the Yield force. For Ag and Cu we estimate that dm ≈ 15nm. The Rayleigh instability (a classical mechanism) is severely modified by electronic shell effect contributions. It has been predicted recently that quantum-size effects arising from the electron confinement within the cross section of the wire can become an important factor as the wire is scaled down to atomic dimensions, in fact the Rayleigh instability could be completely suppressed for certain values of kF r0. Even for the stable wires, there are pockets of temperature where the wires are unstable. Low-frequency resistance fluctuation (noise) measurement is a very sensitive probe of such instabilities, which often may not be seen through other measurements. We have studied the low-frequency resistance fluctuations in the temperature range 77K to 400K in Ag and Cu nanowires of average diameter ≈ 15nm to 200nm. We identify a threshold temperature T* for the nanowires, below which the power spectral density SV(f) ~1/f. As the temperature is raised beyond T* there is onset of a new contribution to the power spectra. We link this observation to onset of Rayleigh instability expected in such long nanowires. T* ~ 220K for the 15nm Ag wire and ~ 260K for the 15nm Cu wire. We compare the results with a simple estimation of the fluctuation based on Rayleigh instability and find good agreement.