Abstract
We present a new generation of piezoresistive nanomechanical Membrane-type Surface stress Sensor(MSS) chips, which consist of a two dimensional array of MSS on a single chip. The implementation of several optimization techniques in the design and microfabrication improved the piezoresistive sensitivity by 3∼4 times compared to the first generation MSS chip, resulting in a sensitivity about ∼100 times better than a standard cantilever-type sensor and a few times better than optical read-out methods in terms of experimental signal-to-noise ratio. Since the integrated piezoresistive read-out of the MSS can meet practical requirements, such as compactness and not requiring bulky and expensive peripheral devices, the MSS is a promising transducer for nanomechanical sensing in the rapidly growing application fields in medicine, biology, security, and the environment. Specifically, its system compactness due to the integrated piezoresistive sensing makes the MSS concept attractive for the instruments used in mobile applications. In addition, the MSS can operate in opaque liquids, such as blood, where optical read-out techniques cannot be applied.
Highlights
Since all molecules have “volume” and “mass”, transduction of such fundamental parameters into detectable and processable signals can realize label-free and real-time measurements of virtually any kind of target specimen
We found with finite element analysis (FEA) that the stress applied on the sensing beams increases almost linearly by decreasing the thickness of the whole geometry including the membrane and beams
There is a trade-off between the quality of protection and sensitivity; a thicker passivation layer provides better quality of protection, while a thinner layer increases flexibility, leading to higher sensitivity of the piezoresistor. To achieve both the protection quality and sensitivity, we deposited a thin silicon nitride (Si3N4) film by low pressure chemical vapor deposition (LPCVD), as we demonstrated its high protection quality even at rather small thicknesses [14]
Summary
Since all molecules have “volume” and “mass”, transduction of such fundamental parameters into detectable and processable signals can realize label-free and real-time measurements of virtually any kind of target specimen. One of the most promising solutions to these problems is employing lever-integrated piezoresistive sensing [12,13,14,15,16,17,18] as it does not require bulky and complex peripheral devices related with an optical read-out and can be used for measurements in opaque liquids, such as blood. The MSS can detect almost any kind of molecule under various conditions, such as vacuum, gas, and liquid; including opaque liquids like blood It can be miniaturized, integrated, and mass-produced owing to its CMOS compatibility, which fulfill most requirements for realizing a portable sensing device. Note that R1, R3 and R2, R4 in the 2G-MSS and 1G-MSS have the same dimensions, respectively
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