The electronic feedback used with microcantilevers (&mgr;CLs) to obtain their best performances requires a precise driving
method to exert on them a force proportional to an electrical signal. One of these methods is Electrostatic Driving (ED)
easily achieved on &mgr;CLs placed some mm apart from a conductive surface. This easy appearance of ED is the reason to
find it unexpectedly, coming from electrical fields not properly shielded, in setups designed for other driving as
Magnetic Driving (MD). When feedback loops designed for MD suffers from this ED contamination due to an
unshielded solenoid for example, the tight phase control of the driving is lost. As a result, self-oscillation of the loop
does not take place at f0, the resonance frequency of the &mgr;CL, or an appealing shift in the resonance frequency from f0 without feedback to fFB=f0±&Dgr;f with feedback appears in non-oscillating loops. A feedback force proportional to the displacement (DF) or to the speed (SF) of &mgr;CLs has been studied and it is demonstrated that SF sets an apparent temperature for the thermal motion of a &mgr;CL without changing its native f0 (a desired feature for high stability &mgr;CL-based oscillating sensors) whereas the fFB±f0 produced by DF allows an electrical tuning of fFB very useful for &mgr;CL-based Voltage Controlled Oscillators.
Contrarily to current theories based on hypothetical traps where charge carriers can translocate to, this paper gives an
explanation for 1/f electrical noise in solid-state devices based on well known electrical effects taking place in these
devices. A parasitic capacitor and the backgating effect of its thermal noise, both overlooked in the course of the years,
are the basis of the above explanation. The above effect produces a resistance noise with a Lorentzian spectrum in any
unbiased resistor. As soon as the resistor is biased, this spectrum is scattered into a continuous set of Lorentzian noise
terms that synthesize 1/f noise over a frequency band that is an exponential function of the bias voltage VDS expressed in
thermal units VT. This is due to the exponential dependence of the dynamical resistance in most semiconductor junctions.
A VDS=180mV is thus enough to give 1/f noise over three decades at room temperature. This unexpected and non-linear
feature, where the spectrum of this noise results from the own bias used to measure it, has kept 1/f noise as a puzzling
and enigmatic noise for more than eighty years. The above theory, born in the solid-state field, can also be generalized to
other devices where two orthogonal forces or energy gradients appear while electrical noise is being measured.
The electromechanical response of piezoelectrically-actuated AlN micromachined bridge resonators has been characterized using laser interferometry and electrical admittance measurements. We compare the response of microbridges with different dimensions and buckling (induced by the initial residual stress of the layers). The resonance frequencies are in good agreement with numerical simulations of the electromechanical behavior of the structures. We
show that it is possible to perform a rough tuning of the resonance frequencies by allowing a determined amount of built-in stress in the microbridge during its fabrication. Once the resonator is made, a DC bias added to the AC excitation signal allows to fine-tune the frequency. Our microbridges yield a tuning factor of around 88 Hz/V for a 500 μm-long microbridge.