Silicone-Based Soft Electronics

Lately, the marriage of elastic silicone rubbers and electronics has given birth to a radically new class of electronic devices and systems, so-called silicone-based soft electronics. Based on this new concept, electronics can nowadays be built in soft, rubbery, biological formats, for enabling numerous new applications, in which conventional rigid electronics are impossible to use. 

This chapter briefly reviews recent research advances in the emerging field of soft electronics. Various strategies for realizing elastic electronics are addressed, and the focus of this chapter lies in microfluidic approaches. Recently reported elastomeric soft electronic devices using microfluidic techniques, e.g., elastic passive antennas, a soft RF radiation sensor, as well as a reversibly stretchable, body-worn wireless strain sensor, are presented and analyzed in detail. Lastly, future perspectives and outlook for silicone-based soft electronics are discussed. 

Keywords Antennas, elastomers, galinstan, integrated circuits (ICs), liquid alloy, microfluidics, planar inverted cone antenna (PICA), polydimethylsiloxane (PDMS), radiofrequency (RF), sensors, silicones, stretchable electronics, ultrawideband (UWB), voltage-controlled oscillators (VCOs) 

Silicones, a category of polymers, are widely used in sealants, adhesives, medical applications, and insulation, and can often be made in soff formats with flexibility, foldability, and stretch-ability. On the contrary, electronics represent a totally different field, where devices are usually rigid, and retain static shapes once fabricated. The overlapping between these two soft and stiff worlds has not yet been seen until a few years ago. 

The simple motivation to soften conventional electronic devices is that we as human beings are in soft, biological formats, and wish to turn electronics into similar manner as our bodies. Not only for enhanced user experience, but also for enabling a broad spectrum of new applications. Reversible deformability, transparency, and lightweight are desired features for future electronics. Devices based on this new technology will be fold-able, twistable, and stretchable into almost arbitrary curvilinear shapes. Application examples may range from ultrathin, conformable health monitoring tapes that seamlessly attach to the skin, electronic/second skin, to elastomeric medical implants that are truly biocompatible to the tissues. 

---

Figure 18.1 Silicone-based soft electronic devices a) A reversibly stretchable, body-worn wireless strain sensor, b) A microfluidic, soft RF radiation sensor.

Taking one step further, the emerging field of silicone-based soft electronics has been advanced to build multilayer configurations, with the demonstration of a microfluidic, reversibly stretchable, large-area wireless strain sensor [31],... 

Figure 18.19 Manufacturing process for multilayer silicone-based soft electronics.

Figure 18.20 Schematic of the hybrid integration process for a multilayer silicone-based soft electronic device.

Figure 18.2 Fabrication process of single-layer, silicone-rubber-based passive soft electronics.

Silicone-Based Integrated Active Soft Electronics... 

Trimethylsilyl compounds with electron-withdrawing substituents (CN, I, Cl, Br, N, NCO, CNO, etc.) have been used in syntheses based on the hard-soft reactivity principle, with the silicon atom having electropositive and the substituent electronegative character. The bond between the pseudo-halide trifluoromclhyl and the trimethylsilyl center should also polarize with the trifluoromclhyl group bearing substantial negative charge.23-24... 

---