NEMS-based heterodyne self-oscillator

We report a novel NEMS-based heterodyne self-oscillator. By using a downmixing detection scheme, the NEMS motion piezoresistive signal at 20 MHz is shifted down to few tens of kHz, thus avoiding the negative impact of stray capacitances. This technique allows the NEMS self-oscillator to benefit from its major advantages: a high dynamic range and a high signal to background ratio. However in this form, the signal cannot be directly inserted in a standard oscillator feedback loop since the output signal is neither proportional, nor at the same frequency as the NEMS actuation signal. This paper describes a novel heterodyne architecture so that self-oscillation motion of the NEMS builds up with excellent frequency stability. By providing a high dynamic range and high signal to background ratio, this feedback loop architecture represents an efficient way to track NEMS resonance frequency in real time, as required in sensing applications like mass sensors.