Fabrication of piezoresistive microcantilever using surface micromachining technique for biosensors

High S/N ratio slotted step piezoresistive microcantilever designs for biosensors

This study proposes new microcantilever designs in slotted step configuration to improve the S/N ratio of surface stress-based sensors used in physical, chemical, biochemical and biosensor applications. The cantilevers are made of silicon dioxide with a u-shaped silicon piezoresistor in p-doped. The cantilever step length and piezoresistor length is varied along with the operating voltage to characterise the surface stress sensitivity and thermal drifting sensitivity of the cantilevers when used as immunosensor. The numerical analysis is performed using ANSYS Multiphysics. Results show the surface stress sensitivity and the S/N ratio of the slotted step cantilevers is improved by more than 32% and 22%, respectively, over its monolithic counterparts.

Comparison between conduction and convection effects on self-heating in doped microcantilevers

The present study investigates the effects of thermal conduction and convection on self-heating temperatures and bimetallic deflections produced in doped microcantilever sensors. These cantilevers are commonly used as sensors and actuators in microsystems. The cantilever is a monolith, multi-layer structure with a thin U-shaped element inside. The cantilever substrate is made of silicon and silicon dioxide, respectively, and the element is p-doped silicon. A numerical analysis package (ANSYS) is used to study the effect of cantilever substrate material, element width, applied voltage and the operating environments on cantilever characteristics. The numerical results for temperature are compared against their analytical models. Results indicate the numerical results are accurate within 6% of analytical, and Si/Si cantilevers are more suitable for biosensors and AFM, whereas, Si/SiO₂ are for hotplates and actuators applications.

An analytical model of joule heating in piezoresistive microcantilevers

The present study investigates Joule heating in piezoresistive microcantilever sensors. Joule heating and thermal deflections are a major source of noise in such sensors. This work uses analytical and numerical techniques to characterise the Joule heating in 4-layer piezoresistive microcantilevers made of silicon and silicon dioxide substrates but with the same U-shaped silicon piezoresistor. A theoretical model for predicting the temperature generated due to Joule heating is developed. The commercial finite element software ANSYS Multiphysics was used to study the effect of electrical potential on temperature and deflection produced in the cantilevers. The effect of piezoresistor width on Joule heating is also studied. Results show that Joule heating strongly depends on the applied potential and width of piezoresistor and that a silicon substrate cantilever has better thermal characteristics than a silicon dioxide cantilever.

Review: Semiconductor Piezoresistance for Microsystems

Piezoresistive sensors are among the earliest micromachined silicon devices. The need for smaller, less expensive, higher performance sensors helped drive early micromachining technology, a precursor to microsystems or microelectromechanical systems (MEMS). The effect of stress on doped silicon and germanium has been known since the work of Smith at Bell Laboratories in 1954. Since then, researchers have extensively reported on microscale, piezoresistive strain gauges, pressure sensors, accelerometers, and cantilever force/displacement sensors, including many commercially successful devices. In this paper, we review the history of piezoresistance, its physics and related fabrication techniques. We also discuss electrical noise in piezoresistors, device examples and design considerations, and alternative materials. This paper provides a comprehensive overview of integrated piezoresistor technology with an introduction to the physics of piezoresistivity, process and material selection and design guidance useful to researchers and device engineers.

Microcantilever sensors

Microfabricated cantilevers have been used in atomic force microscopy for the topography imagingof non-conductive surfaces for more than 20 years. Cantilever beams without tips have proved theirapplicability in recent years as miniaturized, ultrasensitive, and fast-responding sensors for applicationsin chemistry, physics, biochemistry, and medicine. Microcantilever sensors respond by bending dueto the absorption of molecules. A shift in resonance frequency also occurs. They can be operatedin different environments such as gaseous environment, liquids, or vacuum. In gas, microcantileversensors can be operated as an artificial nose, whereby the bending pattern of a microfabricatedarray of eight polymer-coated silicon cantilevers is characteristic of the different vapors from solvents,flavors, and beverages. When operated in a liquid, microcantilever sensors are able to detectbiochemical reactions. Each cantilever is functionalized with a specific biochemical probe receptor,sensitive for detection of the corresponding target molecule. Applications lie in the fields of label-and amplification-free detection of DNA hybridization, the detection of proteins as well as antigen-antibodyreactions, and the detection of larger entities, such as bacteria and fungi.