## 2 High-\(k\) Dielectric Polymers
It is evident that dielectric properties of polymer nanocomposites can be enhanced by the reinforcement of high-\(k\) dielectric nanoparticles, carbon allotropes, conducting polymers and organic crystalline materials [82; 83]. However, polypropylene (PP)/carbon nanotube (CNT) nanocomposites reported by [PERSON], et al. showed negative permittivity even at the low CNT loading, because of the low-resistance behavior of CNTs [84; 85]. Since poly(vinylidene fluoride) (PVDF) is a well known high-\(k\) polymer matrix showing the dielectric constant of about 12 at 1 kHz, a lot of research works were found. The flexibility, high dielectric permittivity, the piezoelectric, pyroelectric response, and the low acoustic impedance properties of PVDF demonstrate its potential applications in various electronic fields. A novel all-organic polyaniline-dodecylbenzenesulfonic acid (PANI-DBSA) and PVDF dielectric composites showed high-dielectric permittivity. For 20 wt% of PANI-DBSA doping to PVDF, resulted a dielectric permittivity of 150.0 at 25 \({}^{\circ}\)C [86], whereas PVDF and poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) filled with magnesium oxide nanofillers showed dielectric permittivity within the range  
Figure 3: Pictograph representing (**a**) the bottom-gate top-contact organic thin film transistor (OTFT) on the polypropylene carbonate (PPC) substrate, and (**b**) a typical design of OTFTs. Adapted with permission from [80], Springer Nature, 2018.  
of 10-22 at 25 \({}^{\circ}\)C [87]. [PERSON], et al. reported composite thick films (thickness \(\approx\) 85 \(\upmu\)m) composed of PVDF/CaCu\({}_{3}\)Ti\({}_{4}\)O\({}_{12}\) nanocrystals with a relatively high dielectric permittivity of 90.0 at 100 Hz [88]. Today, polyester films or polyethylene terephthalate (PET) substrates have received considerable interest due to their inherent surface properties and designed engineering probabilities [89, 90]. The PET substrates can be laying down to design thin film transistor arrays and in the construction of multimodal vibrational haptic interfaces [91]. [PERSON], et al. compared the properties of epoxy-coated (wood pulp) cellulose nanofibril (CNF) thin films with PVDF and investigated the microwave dielectric properties for potential broad applications in flexible high-speed electronics. They reported the dielectric constant of 2.6 for epoxy-coated-CNF and dielectric loss values in the range 0.03-0.042. However, the epoxy coated-CNF has proven to be more suitable for flexible microwave applications than for PET films [92]. [PERSON], et al. reported that the coating of photoresist SU-8 on a silicon-(100) wafer substantially improves the flexibility and can be used for high-performance flexible electronics [93], whereas developed glass/SU-gold electrodes by [PERSON], et al. were extremely transparent, and stable in the biological culture medium, which exhibited biocompatibility similar to glass [94]. Flexible and bendable (to 90\({}^{\circ}\)) tactile sensor arrays were also developed by [PERSON], et al., consisting of aluminum nitride, based on micro-electro-mechanical system (MEMS) technology, where polydimethylsiloxane (PDMS) and a SU-8 photoresist layer were used as the supporting layers [95]. By the addition of various plasticizers, the mechanical stiffness and electrical permanence of PVC can be altered [96]. Even with the doping of modified inorganic nanoparticles, the fine-tuning of dielectric properties can be done and used to design high-performance actuators [70, 97, 98]. Some reports also demonstrate that the graphene oxide and plasticizer doping to PVC behaves as a soft actuator for artificial muscle applications [99, 100, 101]. The controlled robustness of plasticized thermoplastic PVC gels finds suitable applications in modular constructions of 3D-printable artificial muscles and sometimes the mechanical actuations are so effective they behave like human muscle [102, 103, 104]. More recently, ultra-high permittivity dielectric gels were fabricated and reported by [PERSON], et al. [105].