The Role of Interdigitated Electrodes in Printed and Flexible Electronics

Abstract

Flexible electronics, also referred to as printable electronics, represent an interesting technology for implementing electronic circuits via depositing electronic devices onto flexible substrates, boosting their possible applications. Among all flexible electronics, interdigitated electrodes (IDEs) are currently being used for different sensor applications since they offer significant benefits beyond their functionality as capacitors, like the generation of high output voltage, fewer fabrication steps, convenience of application of sensitive coatings, material imaging capability and a potential of spectroscopy measurements via electrical excitation frequency variation. This review examines the role of IDEs in printed and flexible electronics since they are progressively being incorporated into a myriad of applications, envisaging that the growth pattern will continue in the next generations of flexible circuits to come.

Keywords: combed electrodes; flexible electronics; inkjet printing; interdigitated electronics; planar electrodes; screen printing; sensors.

Figure 1

Configuration of IDE structure wherein (a) geometric parameters of interdigitated sensors; (b) electric current displacement between electrodes; and (c) electrical model of an interdigitated sensor and sample (an ionic solution) (Source: [3]).

Figure 2

Technology schematics of the main (PE) techniques: (a) gravure printing (schemed modified from [31]; (b) screen printing; (c) inkjet printing; (d) 3D printing, (e) flexographic printing (schemed modified from [31] and (f) laser scribbling (reprint with permission from reference [32]).

Figure 2

Technology schematics of the main (PE) techniques: (a) gravure printing (schemed modified from [31]; (b) screen printing; (c) inkjet printing; (d) 3D printing, (e) flexographic printing (schemed modified from [31] and (f) laser scribbling (reprint with permission from reference [32]).

Figure 3

Frequency spectrum for acoustic and electromagnetic digital sensors. OPD: organic photo-diodes, SAW: surface acoustic wave, APM: acoustic plate mode, NDE: node detection emitter, AC: alternating current, FPW: flexural plate-wave, SONAR: sound navigation and ranging.

Figure 4

Design of capacitive devices (1—oscillator, 2—trigger circuit, and 3—output switching device).

Figure 5

Mapping to the unit disk.

Figure 6

(a) Responses of the sensors to 1–10 ppm of NO₂ at room temperature measured under near-infrared light using ZnO/PbS nanocomposites with varying PbS loading. (b) Photoluminescence spectra of ZnO/PbS-2 and PbS excited at 831 nm. Reproduced with permission. (c) Reactions of ZnO/g-C₃N₄ composites to 7 ppm NO₂ under varied light illumination wavelengths with varying g-C₃N₄ content. (d) Dynamic resistance curves for ZnO/g-C₃N₄-10 weight percent to 1%#x2013;6 ppm NO₂ at room temperature under 460 nm light irradiation. Licensed reproduction (reprint with permission from reference [131]).

Figure 7

Resistance vs. temperature at 55%RH for electrodes with a width of 150 μm and spacing of 200 μm was studied, showing the temperature-dependent behavior of the electrode material [97].

Figure 8

Capacitance strain measurement for the capacitive strain gauge shown in Figure 8 undergoing a strain of 125%. The fit was calculated using the equation = + ϵ + C × c c [135].