The control of oscillation mode in silicon microbeams using silicon nitride anchor

Abstract

We designed and fabricated gravimetric sensors composed of silicon (Si) microbeams surrounded by silicon nitride (SiN) anchors. The oscillation properties of the fabricated devices show that a single oscillation mode originating from quasi-one-dimensional microbeams appears at an applied alternating electric field, which motion is well matched to the theoretical predictions and is much different from the dimensionally mixed oscillation modes in normal non-anchored devices. In addition, in order to elucidate the possibilities of the devices for mass sensing applications, we measured the frequency shift as a function of mass loading in a self-assembled monolayer of 3-aminopropyltrimethoxysilane and Au nanoparticles. The resulting limit of detection was 1.05 × 10−18 g/Hz, which is an extremely high value for micro electromechanical system gravimetric sensors relative to the normal ones.

Accurate and Precise Determination of Mechanical Properties of Silicon Nitride Beam Nanoelectromechanical Devices

“…In the case of low stress doubly clamped SiN beams, the frequency variation upon length is seen to follow the tendency of ordinary unstressed beams where the frequency is inversely proportional to the length squared, since the Young's modulus is the dominant factor for determining a beam's elasticity rather than the applied stress. 37 On the other hand, as clearly seen in Figure 2c, highly stressed beams such as the SiN beams studied in this report exhibit stringlike resonance behavior where the resonance frequency is inversely proportional to the length since the tensile stress becomes the dominant factor, 21 which is in good agreement with the resonance frequencies reported by Unterreithmeier et al 27 This confirms that elastic properties of SiN beams with quasi-1-dimensional string-like behavior are more affected by the applied tensile stress than by the Young's modulus. 21,32 For this reason, eq 1 can be simplified to eq 2 by ignoring the Young's modulus term.…”

“…An optical interferometry technique, suitable for detecting resonance behavior of insulating devices, was employed to detect the vibrational motion. 36,37 The intensity of the He-Ne laser used for the interferometry measurements was set to around 80 µW to minimize heating effects or structural deformation of the beams. 27,38 Quasi-static flexural measurement.…”

“…This value is much higher than those observed in conventional silicon devices. 31,35,37 The presence of high stress within these beams, imparted during SiN film growth using PECVD, leads to both high resonance frequencies and high Q factors, both of which are desirable parameters for a high performance NEMS device. Figure 2b shows the Q factor dependence on the beam length.…”

“…When the AC frequency applied to the piezo-ceramic matches the mechanical resonance frequency of the SiN beam, the beam exhibits resonance behavior. An optical interferometry technique, suitable for detecting resonance behavior of insulating devices, was employed to detect the vibrational motion. , The intensity of the He–Ne laser used for the interferometry measurements was set to around 80 μW to minimize heating effects or structural deformation of the beams. , …”

Attogram mass sensing based on silicon microbeam resonators

“…To overcome these limitations, we have recently developed a thin-film based doubly-clamped Si microbeam resonator surrounded by SiN anchors, which significantly improved the performance of the resonator without modifying the geometry of the microbeam 30 . Since the surrounding structure was formed by SiN and silicon dioxide (SiO 2 ) instead of Si, we were able to achieve higher selectivity during fabrication.…”