Credit: AIP

Nanomechanical oscillators can measure masses of less than 10-15 grams and forces of the order of 10-12 Newtons. However, the dynamic range of such devices – the range over which the response of the device to an applied force is linear – is limited. Michael Roukes and colleagues1 at the California Institute of Technology in the US have now shown that electrostatic tuning can be used to both increase the dynamic range and change the resonant frequency of a mechanical oscillator.

Roukes and colleagues constructed a metallized SiC beam – 150 nm wide, 100 nm thick and 15 microns long – that had a resonant frequency of 8.8 MHz when it was clamped at both ends. By applying a voltage to a gate electrode some 400 nm from the beam, it was possible to almost double the dynamic range and shift the resonant frequency by up to 5%.

To model the effect of the gate voltage, the researchers considered both elastic and capacitive contributions to the equation of motion of the oscillator. They showed that the increase in the dynamic range was the result of two nonlinear effects – strain and capacitive attraction to the gate – cancelling one another.

Electrostatic tuning could be used to compensate for any imperfections that result in the manufacturing process, or to push the oscillator into the optimum experimental frequency.