Ultra-fast and high resolution NEMS thermal detector based on a nano-air-gap piezoelectric resonant structure

This paper presents the theoretical modeling and experimental verification of an innovative Nano Electro Mechanical System (NEMS) technology suitable for the implementation of ultra-fast and high resolution un-cooled thermal detectors. Fundamental challenges associated to the implementation of mechanically resonant thermal detectors are overcome with the introduction of an innovative technology platform in which a temperature sensitive Aluminum Nitride (AlN) nano-plate resonator and a monolithically integrated micromachined suspended heat absorbing element are perfectly overlapped but separated by a sub-micron air gap. By placing the absorbing element outside the body of the resonator (but suspended over it) the electromechanical performance of the resonant device is not affected by the absorbing element and the material employed to implement it (quality factor, Q≈1800 and electromechanical coupling coefficient, k_t²≈1%) enabling the use of a compact and low-power self-sustained oscillator circuit as direct frequency readout. At the same time, efficient and quick heat transfer from the absorbing element to the nanomechanical resonant device is achieved by minimizing the air gap between them. The detection capabilities of this first prototype were tested using an integrated resistive heat source in lieu of an absorber. Power level as low as 655 nW was readily detected and a limit of detection of 48 nW was experimentally extracted. In addition a thermal time constant of ~ 60 μs was predicted for this prototype through finite element simulation.