(Invited) Si-Based Micro-Nanomechanics for Ultimate Sensing
Authors: Ono Takahito , Toda Masaya , Seo Yong-Jun , Inomata Naoki 
Published: February 2020

Recent silicon micro- and nano-fabrication techniques have been well-developed and their application fields are extended. Among them Si micro-nanomechanical systems have been developed for various applications including sensors and actuators. We developed Si micro-nanomechanical resonant sensors for ultimate sensing. One of advantages of silicon material is the compatibility with integrated circuits. Also, Si micro-nanoresonators show a high quality factors by thermal treatment in vacuum [1]. By miniaturization of the resonators, the sensitivity to mass, force, and heat increases due to scaling merit. Therefore, much effort has been made for developing micro/nano-mechanical sensors for such applications.

Magnetic resonance force microscopy is powerful method for visualization of spins in a sample, where a resonant sensor with a magnet is used to detect the flip of magnetic spins due to magnetic resonance [2-4]. From the resonant frequency or vibration amplitude of the resonator, magnetic force between the magnet and spins in a sample can be detected. From scaling low, higher sensitivity is expected using a narrower and longer probe structure, which means that nanowired structure is effective to obtain high sensitivity. Using a silicon insulater wafer, a Si nanowire probe with a micro magnet (Nd-Fe-B) and a Si mirror is fabricated. The nanowire Si structure is fabricated by conventional microfabrication using electron beam lithography. In order to increase the Q factor, the fabricated Si resonator is annealed at H2/N2 atmosphere. The vibration is measured using a fiber-optic interferometer in a vacuum chamber at room temperature [4]. The achieved detectable minimum force was at an order of 10-17 N, which is estimated from thermomechanical noise signal. Mapping of electron resonance is demonstrated on a small particle of PVBPT (Poly-10-(4-vinylbenzyl)-10H-phenothiazine).

Resonant heat sensor are developed and applied to a calorimeter for the detection of heat from a brown fat cell [5]. The measurement principle relies on the resonant frequency tracking of a Si resonator in temperature variation due to heat from a sample, and heat is conducted from the sample in water to the Si resonator in vacuum via a Si heat guide. A heat loss to surrounding and a dumping in water can be reduced by placing the resonant thermal sensor in vacuum. The fabricated resonant thermal sensor shows 1.6 mK of the temperature resolution, and 6.2 pJ of the detectable minimum heat. The heat from the single cell is detected in cases without any stimulation and with stimulation. As the results, pulsed heat production and continuous heat production are observed, respectively.

References

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[5] N. Inomata, M. Toda, M. Sato, A. Ishijima, and T. Ono, Applied Physics Letters 100 (2012) 154104.