Stress-based resonant volatile gas microsensor operated near the critically buckled state

Abstract

We describe sensing of chemical vapors from the atmosphere using critically buckled polycrystalline silicon doubly clamped mechanical resonators coated on one side with polymethyl methacrylate (PMMA). Our method of sensing is based on stress-induced resonance frequency shifts through volumetric swelling of the 60 nm thick PMMA layer resulting in altered tension in the beams. The stress change produces shifts in the resonance frequency as large as 150% of the baseline frequency. In order to maximize the sensitivity, we tailor residual stress of the polycrystalline silicon resonators to slightly exceed the critical buckling stress. We incorporate a relatively large gap between the bridge and a substrate to provide optical readout and minimize squeezed film effects. We show that the larger gap results in substantial improvements of the quality factor and frequency stability of our resonators under ambient pressure and temperature conditions compared to previous implementations. These lead to resonance frequency shift per concentration change of ethanol vapors of ∼360 Hz/ppm with a response time of a few seconds measured in our gas delivery and readout system.

Size modulated transition in the fluid–structure interaction losses in nano mechanical beam resonators

“…The sensitivity of flexural nanobeam resonators to changes in various physical quantities, such as temperature, pressure, and mass (m), [1][2][3] is most often expressed in terms of the change in resonant frequency (f). The sensitivity to the physical quantities under assay (dm=m) varies as (df =f ) or inversely as the quality factor (Q).…”

Buckled diamond-like carbon nanomechanical resonators

“…[23][24][25] The tuning curves for the DLC resonators can be fitted, assuming that the suspended DLC is buckled upwards, i.e. As the DLC films have built-in compressive stress, the resonators display Euler buckling instabilities upon fabrication.…”

Liquid Mass Sensing Using Resonating Microplates under Harsh Drop and Spray Conditions

“…Since then, resonators based on microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) have been proven as excellent platforms for material spectroscopy in a wide range of sensing applications, including solid [2][3][4][5], gas [6][7][8][9][10], and biochemical fluid composition [11,12], with unprecedented potential for large-scale integration of multiplexed sensors in small monolithic packages [13]. At the ultimate sensitivity limit of inertial mass sensing facilitating such resonating devices [14], recent experiments using NEMS resonators have successfully achieved the power to resolve single molecules [3], atoms [4], and even individual protons in real time [15].…”

“…Typically, NEMS and MEMS resonators (operating in dynamic rather than static mode, in the high-frequency acoustic regime [7]) are driven through closed-gap configuration, and sensing in the gas or liquid phase is limited to clean surface preparation procedures, set by limitations related to stiction, viscous drag, and squeezed-film damping [7,[10][11][12]16]. Durable operation under harsh environmental conditions is an important ongoing goal for realistic integrated MEMS/NEMS sensors.…”