Attogram mass sensing based on silicon microbeam resonators

Abstract

Using doubly-clamped silicon (Si) microbeam resonators, we demonstrate sub-attogram per Hertz (ag/Hz) mass sensitivity, which is extremely high sensitivity achieved by micro-scale MEMS mass sensors. We also characterize unusual buckling phenomena of the resonators. The thin-film based resonator is composed of a Si microbeam surrounded by silicon nitride (SiN) anchors, which significantly improve performance by providing fixation on the microbeam and stabilizing oscillating motion. Here, we introduce two fabrication techniques to further improve the mass sensitivity. First, we minimize surface stress by depositing a sacrificial SiN layer, which prevents damage on the Si microbeam. Second, we modify anchor structure to find optimal design that allows the microbeam to oscillate in quasi-one dimensional mode while achieving high quality factor. Mass loading is conducted by depositing Au/Ti thin films on the local area of the microbeam surface. Using sequential mass loading, we test effects of changing beam dimensions, position of mass loading, and distribution of a metal film on the mass sensitivity. In addition, we demonstrate that microbeams suffer local micro-buckling and global buckling by excessive mass loading, which are induced by two different mechanisms. We also find that the critical buckling length is increased by additional support from the anchors.

Nanoelectromechanical Sensors Based on Suspended 2D Materials

“…In comparison, conventional quartz crystal monitors have been shown to be able to measure the mass of a single monolayer of graphene [ 128 ]. The sensitivity of graphene-based mass sensors can reach a value of 10 −27 g/Hz [ 263 ], which greatly outperforms silicon membrane-based sensors, with typical sensitivity values of only 10 −18 g/Hz [ 264 ]. Commercial mass sensors have even lower sensitivity values of around 60 × 10 −9 g/Hz [ 265 ].…”

Ultra-Precise MEMS Based Bio-Sensors

“…With ∆m = 0, Eqs. (17) and (18) take the form ω 2 ip (14) by (15), amplitude ratio (AR) is obtained as…”

“…effective mass/stiffness. Additional features of this method of detection are simple mechanical design, semi-digital nature of the signal (thus using simple frequency measurement system such as frequency counter and not requiring additional analog-todigital (A/D) conversion circuit), ultra-high resolution [8][9][10], (up to 10 À15 grams scale [11][12][13] and up to 10 À18 grams scale [14][15][16][17]). There are however also a challenge associated with the resonant sensor employing only one resonator; firstly, maximum theoretical frequency shift based parametric sensitivity, ∆f/f is limited to 1/2 [18].…”

Simulation of an electrically actuated cantilever as a novel biosensor

“…Recently, stability and frequency analyses of miniature biosensors were the main objectives of numerous studies 1,2,16,43 . In micro and nanoscales, where the ratio of the external surface of the movable electrode to its volume is relatively considerable, the surface energy effect dominates.…”

“…It should be noted that both surface layer parameters can be positive or negative depending on the constitutive materials of the movable arm 59,60 . In addition, it has recently been demonstrated that by minimizing the surface stress we are able to further improve the mass sensitivity of clamped-clamped microresonators 43 . Using the relation of the residual surface, it can be understood that the influence of this parameter will increase by increasing the ratio of beam length to the beam thickness.…”