A Review on Surface Stress-Based Miniaturized Piezoresistive SU-8 Polymeric Cantilever Sensors
Ribu Mathew, A. Ravi Sankar⁎
Index: 10.1007/s40820-018-0189-1
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Abstract
In the last decade, micro-electro-mechanical-systems (MEMS) SU-8 polymeric cantilevers with piezoresistive readout combined with the advances in molecular recognition techniques has found versatile applications, especially in the field of chemical and biological sensing. Compared to conventional solid-state semiconductor based piezoresistive cantilever sensors, SU-8 polymeric cantilevers have advantages in terms of better sensitivity along with reduced material and fabrication cost. In recent times, numerous researchers have investigated their potential as a sensing platform due to high performance-to-cost ratio of SU-8 polymer based cantilever sensors. In this article, we critically review the design, fabrication, and performance aspects of surface stress based piezoresistive SU-8 polymeric cantilever sensors. The evolution of surface stress based piezoresistive cantilever sensors from solid-state semiconductor materials to polymers, especially SU-8 polymer is discussed in detail. Theoretical principles of surface stress generation and their application in cantilever sensing technology are also devised. Variants of SU-8 polymeric cantilevers with different composition of materials in cantilever stacks are explained. Furthermore, the interdependence of the material selection, geometrical design parameters and fabrication process of piezoresistive SU-8 polymeric cantilever sensors and their cumulative impact on the sensor response are also explained in detail. In addition to the design, fabrication, and performance related factors; this article also describes various challenges in engineering SU-8 polymeric cantilevers as a universal sensing platform such as temperature and moisture vulnerability. This review article would serve as a guideline for researchers to understand specifics and functionality of surface stress-based piezoresistive SU-8 cantilever sensors. Keywords SU-8 polymer; Surface stress; Biological sensor; Cantilever; Chemical sensor; Piezoresistor; Immobilization