Abstract
Over the years, piezoresistive nano cantilever sensors have been extensively investigated for various biological sensing applications. Piezoresistive cantilever sensor is a composite structure with different materials constituting its various layers. Design and modeling of such sensors become challenging since their response is governed by the interplay between their geometrical and constituent material parameters. Even though, piezoresistive nano cantilever biosensors have several advantages, they suffer from a limitation in the form of self-heating induced inaccuracy which is seldom considered in design stages. Although, a few simplified mathematical models have been reported which incorporate the self-heating effect, several assumptions made in the modeling stages result in inaccuracy in predicting sensor terminal response. In this paper, we model and investigate the effect of self-heating on the thermo-electro-mechanical response of piezoresistive cantilever sensors as a function of the relative geometries of the piezoresistor and the cantilever platform. Finite element method (FEM) based numerical computations are used to model the target-receptor interactions induced surface stress response in steady state and maximize the electrical sensitivity to thermal sensitivity ratio of the sensor. Simulation results show that the conduction mode of heat transfer is the dominant heat transfer mechanism. Furthermore, the isolation and immobilization layers play a critical role in determining the thermal sensitivity of the sensor. It is found that the shorter and wider cantilever platforms are more suitable to reduce self-heating induced inaccuracies. In addition, results depict that the piezoresistor width plays a more dominant role in determining the thermal drift induced inaccuracies compared to the piezoresistor length. It is found that for surface stress sensors at large piezoresistor width, the electrical sensitivity to thermal sensitivity ratio improves.
Highlights
Nano-electro-mechanical systems (NEMS) based cantilever platform sensors have been utilized as investigation tools for in-situ explorations ranging from measurements at micro gram mass[1] to space applications.[2]
In recent times much focus has been on developing piezoresistive cantilever sensors for biological sensing applications
Compared to conventional clinical diagnostic techniques like lateral flow assays (LFAs) and enzyme-linked immunosorbent assays (ELISAs), cantilever biosensors have the advantage of lower footprint and have an edge due to their capability to perform real time and fast detections with lower detection limits.[3]
Summary
Dynamic mode of operation has numerous advantages, its effectiveness curtails in liquid medium due to fluid damping effect induced reduction in sensitivity and dependence of change in resonant frequency on the position of target-receptor interactions on the cantilever. Piezoresistive nano cantilever sensors have numerous advantages, they suffer from a major limitation in the form of thermal drift in their output characteristics. Joule heating induced self-heating of piezoresistive cantilever biosensors become significant due to (i) the lower thermal mass of the cantilever, and (ii) temperature dependence of the constituent material properties of the sensor. The reported experimental results have mainly considered a fixed piezoresistor and cantilever sensor geometry to investigate its terminal characteristics as a function of either dc-excitation voltage and/or operational ambient.
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