Fabrication and Characterization of a Polymer/Metal Bimorph Microcantilever for Ultrasensitive Thermal Sensing

In this paper, we demonstrate a novel polymer/metal bimorph microcantilever, which is promising to have an ultrahigh thermal sensitivity. Based on the analysis of the thermoelastic behavior of the bimorph cantilever, polyvinyl chloride (PVC) and aluminum (Al), which have a large mismatch in coefficient of thermal expansion and an appropriate ratio of Young´s modulus, were chosen and the thermal sensitivity was maximized by optimizing the thickness ratio of the two layers. The PVC layer was formed via spin coating and patterned by plasma etching. The fabrication process for the cantilever is compatible with standard micro-fabrication techniques. The thermal responses of the cantilevers were characterized by measuring the thermal deflections during thermal cycles and isothermal holding tests. Experimental results showed that the PVC/Al microcantilevers with a length of 200 μm had an ultrahigh thermal sensitivity above 2044 nm/K. Also, the cantilevers annealed at a temperature above the glass transition point (T_g) of the polymer possessed good linearity and reproducibility of thermal deflection in the temperature range of 28°C-49°C. When heated above room temperature, the cantilevers started to creep, which affected the thermal sensitivity and then introduced inaccuracy.