Nonlinear microscopic fluctuators in Ru-based thick film resistors

The paper concerns low-frequency noise of RuO
₂
+glass thick film resistors. Recent experiments performed in liquid helium temperatures indicate that at large bias the noise become nonlinear, that is its power spectral density S
_Vex
does not scale with voltage V like V
²
. In the paper efforts were undertaken to explain this behavior. Data are analyzed in terms of self heating of the resistors by the driving current. It is demonstrated that normalized noise powers S
_Vex
/V
²
, measured at the same electron temperature but various voltages, are different. We conclude that the normalized noise is voltage dependent i.e. nonlinear. The second argument comes from room temperature measurements. Resistors excited by sine waves of various amplitudes and frequencies exhibit both 1/Deltaf and 1/f noises. Arguments are supplied that this is a fingerprint of nonlinear microscopic conduction mechanism, which means the local current (i) is nonlinear function of local voltage (v). General conclusion is that microscopic noise sources responsible for low-frequency noise in RuO
₂
+glass resistors are nonlinear, that is they have nonlinear i(v) and S
_v
(v
²
) dependencies. At room temperature the number of active fluctuators is large. Local voltages take on small values and the overall noise S
_Vex
is linear i.e. ~ V
²
. Nonlinear, asymmetric i(v) curves under ac bias induce a net small DC current and as a result the "ac-induced" 1/f noise. At liquid helium temperatures many fluctuators are frozen. Local voltages take on large values and the overall noise S
_Vex
probes the whole microscopic (nonlinear) S
_v
(v
²
) characteristics