This study demonstrates amplification of electrical signals using a very simple nanomechanical device. It is shown that vibration amplitude amplification using a combination of mechanical resonance and thermal-piezoresistive energy pumping, which was previously demonstrated to drive self-sustained mechanical oscillation, can turn the relatively weak piezoresistivity of silicon into a viable electronic amplification mechanism with power gains of 420 dB. Various functionalities ranging from frequency selection and timing to sensing and actuation have been successfully demonstrated for microscale and nanoscale electromechanical systems. Although such capabilities complement solid-state electronics, enabling state-of-the-art compact and high-performance electronics, the amplification of electronic signals is an area where micro-/nanomechanics has not experienced much progress. In contrast to semiconductor devices, the performance of the proposed nanoelectromechanical amplifier improves significantly as the dimensions are reduced to the nanoscale presenting a potential pathway toward deep-nanoscale electronics. The nanoelectromechanical amplifier can also address the need for ultranarrow-band filtering along with the amplification of lowpower signals in wireless communications and certain sensing applications, which is another need that is not efficiently addressable using semiconductor technology.

This paper demonstrates ultra-high sensitivities for a Lorentz force resonant MEMS magnetometer enabled by internal-thermal piezoresistive vibration amplification. A detailed model of the magneto-thermo-electro-mechanical internal amplification is described and is in good agreement with the experimental results. Internal amplification factors up to ~1620 times have been demonstrated by artificially boosting the effective quality factor of the resonator from 680 to 1.14 × 10 6 by tuning the bias current. The increase in the resonator bias current in addition to the improvement in the quality factor of the device led to a sensitivity enhancement by ~2400 times. For a bias current of 7.245 mA, where the effective quality factor of the device and consequently the sensitivity is maximum (2.107 mV nT −1 ), the noise floor is measured to be as low as 2.8 pT (√Hz) −1 . This is by far the most sensitive Lorentz force MEMS magnetometer demonstrated to date.

Channel-selective filtering and amplification in ultrahigh frequency (UHF) receiver front-ends are crucial for realization of cognitive radio systems and the future of wireless communication. In the past decade, there have been significant advances in the performance of microscale electromechanical resonant devices. However, such devices have not yet been able to meet the requirements for direct channel selection at RF. They also occupy a relatively large area on the chip making implementation of large arrays to cover several frequency bands challenging. On the other hand, electromechanical piezoresistive resonant devices are active devices that have recently shown the possibility of simultaneous signal amplification and channel-select filtering at lower frequencies. It has been theoretically predicted that if scaled down into the nanoscale, they can operate in the UHF range with a very low power consumption. Here, for the first time nanomechanical piezoresistive amplifiers with active element dimensions as small as 50 nm × 200 nm are demonstrated. With a device area of less than 1.5 μm a piezoresistive amplifier operating at 730 MHz shows effective quality factor ( Q) of 89,000 for a 50Ω load and gains as high as 10 dB and Q of 330,000 for a 250Ω load while consuming 189 μW of power. On the basis of the measurement results, it is shown that for piezoresistor dimensions of 30 nm × 100 nm it is possible to get a similar performance at 2.4 GHz with device footprint of less than 0.2 μm.

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