Fabrication capacitance/conductance sensors

Electrochemical sensors can be classified according to their mode of operation, e.g. conductivity/capacitance sensors, potentiometric sensors, and voltammetric sensors. Amperometric sensors can be considered a specific type of voltammetric sensor. The general principles of electrochemical sensors have been extensively described in other chapters of this volume or elsewhere. This chapter will focus on the fabrication of electrochemical sensors of micro or miniature size. 

The team of the Center for Micro-Bio Robotics of Istimto Italiano di Tecnologia (Pisa, Italy) produced a composite capacitive three-axial sensor based entirely on commercial conductive fabrics, demonstrating its high compliance and stability under manipulation (Viry et al., 2014). 

A bolometer is a thermally isolated, temperature-sensitive element that can be used to measure absorbed energy. Either surface micromachining or bulk silicon micromachining can be used to fabricate a structure with low thermal mass that is thermally isolated from the substrate by long, thin suspension arms. Here we consider a bolometer that is fabricated in the Poly2 layer of the PolyMUMPS process, as shown in Figure 5.14. If the device consists of a 100 (pm) platform suspended by four suspension arms that are 5 pm wide, we can calculate the thermal conductance of the arms, the thermal capacitance of the platform, and the thermal time constant for the sensor. 

Examples of successful impedimetric sensors (rather than conductivity or capacitance) are few. One example involved the fabrication of lignin-modified glassy carbon electrodes which are sensitive to ozone. Exposing the sensor electrodes to various ozone concentrations resulted in proportional changes in the charge-transfer resistance in the impedance spectmm. More recently, microelectrochemical sensors were prepared which are suitable for use in marine environments and were tailored to voltammetric and impedimetric or conductivity measurements. ... 

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