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Two orders of magnitude increase in metal piezoresistor sensitivity through nanoscale inhomogenization
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Image of FIG. 1.
FIG. 1.

(a) Schematic representation of different components of the device. (b) Electron micrograph of a 450 nm thick structure with 50 nm gold film, before actuator-sensor isolation. Left inset is a close up image of the notch with pristine gold film. Right inset is a close up image of the coupler beam after actuator-sensor isolation. The gold film is discontinuous while the beam is intact.

Image of FIG. 2.
FIG. 2.

Schematic diagram of the frequency response measurement setup. and are current limiting resistors in the actuation and sensing circuits, respectively. Inset shows the frequency response of DEV12 in pristine condition (). (Different devices are identified with names of the form DEV#.)

Image of FIG. 3.
FIG. 3.

(a) Voltage noise signals at the output of the lock-in amplifier for two different sensor resistances plotted in identical scales. (b) Voltage noise power spectral density of the noise signals in (a). The solid lines indicate the theoretical Johnson noise level.

Image of FIG. 4.
FIG. 4.

(a) and (b) show piezoresistively detected frequency response of two representative devices, DEV12 and DEV14, respectively, at different stages of electromigration. As the resistance of the sensor increases due to electromigration, magnitude of the response becomes larger for the same actuation force. The strain sensitivities of DEV12 and DEV14 increase by a factor of 193 and 230, respectively, from their pristine values. The absolute magnitudes of in different devices vary due to differences in actuation currents and beam stiffnesses.

Image of FIG. 5.
FIG. 5.

Variation of quality factor (left axis, circles) and resonance frequency (right axis, triangles) with sensor resistance.

Image of FIG. 6.
FIG. 6.

Evolution of strain sensitivity as a function of electromigration induced resistance change. Solid lines highlight the logarithmic divergence of the strain sensitivity with R. Insets show the same data on log-log scale with the solid line indicating the power law behaviour during the initial stages.

Image of FIG. 7.
FIG. 7.

SEM image of notch region after the insulating transition () for DEV12 (a) and DEV6 (b). The rectangle in (a) shows the assumed size of the piezoresistor for comparing the SNR performance with silicon.

Image of FIG. 8.
FIG. 8.

Johnson noise limited signal-to-noise ratio as a function of sensor resistance.

Image of FIG. 9.
FIG. 9.

Resistance noise power spectral density at different stages of electromigration.

Image of FIG. 10.
FIG. 10.

Divergence of low frequency resistance noise with electromigration.

Image of FIG. 11.
FIG. 11.

Signal-to-noise ratio for low frequency applications as a function of sensor resistance.

Image of FIG. 12.
FIG. 12.

Closed-loop feedback control system for electromigration.


Generic image for table
Table I.

Material properties for silicon-based piezoresistors.


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Scitation: Two orders of magnitude increase in metal piezoresistor sensitivity through nanoscale inhomogenization