## 2 High-\(k\) Dielectric Polymers  
Compared to conventional rigid silicon technology, the inherent desirable properties of high-\(k\) polymer nanocomposite materials offer a new dimension to the field of flexible and stretchable electronics [42; 43]. The main benefits of polymer-based capacitor devices are unique in design with flexibility and the ease of processing. Therefore, no critical dimensions are required to utilize the materials to produce moderate high-voltage operating electronic devices as non-planar and flexible substrates [44; 45]. Moreover, the incorporation of high-\(k\) nanostructured hybrid materials to the dielectric polymer matrix can regulate the mechanical stiffness and tunes the electronic properties. Thus, we can notice flourishing research in developing inorganic/organic hybrid nanomaterials and this contributed to the significant growth in accomplishing high-\(k\) polymer nanocomposites for technological applications [46; 47]. Typically, enhanced dielectric breakdown strength can be achieved by loading nanoparticles into dielectric polymers. Firstly, a compatible solvent is used to disperse the nanoparticles and later embedding into the dielectric polymer matrix. This solution-mixing technique is the best known method to synthesize high-\(k\) polymer nanocomposite materials with superior dielectric breakdown strength [48; 49; 50]. Considering the breakdown strength, some of the important polymers are listed in Table 1. Based on breakdown strength [51; 52; 53], polytetrafluoroethylene (PTFE) and polypropylene (PP) will be the best choice [54; 55]. However, the compatibility with solvents and the ease of thin film processing are also key parameters, which will decide the final application of the polymer composites. Because of the ease in thin film fabrication, polyvinylidene fluoride (PVDF) composites are an ideal choice. We notice plentiful research reports on PVDF composites on mechanical and acoustic sensors, actuators, energy harvesting and nonvolatile memory applications, because of its piezo-, pyro- and ferro-electric properties [56; 57; 58; 59; 60; 61]. Since SU-8 structure blocks can be photo-definable, photo-patternable high-\(k\) dielectrics on it can result in embedded capacitor applications [62; 63; 64]. Furthermore, polyvinyl chloride (PVC) is a widely used thermoplastic polymer, due to its versatile nature with plasticizers and high-\(k\) dielectrics nanoparticles, it can be successfully used in consumer electronics [65; 66; 67; 68; 69; 70]. Due to the increasing demand for flexible and soft smart devices, our research group fabricated soft vibrotactile actuators based on silicon dioxide nanoparticles embedded in plasticized PVC gels. The soft gels were used as a dielectric layer in the designed vibrotactile actuators. To maximize the elastic restoring force, a wave-shaped ePVC gel was designed. The design of the soft vibrotactile actuator is presented in Figure 1[70]. The proposed soft vibrotactile actuator based on plasticized PVC/silicon dioxide nanoparticle composites showed broad amplitude variation in a wide frequency range and created a variety of haptic sensations to the users. To improve the robustness, processability and breakdown strength of the polymer nanocomposites, it is also important to consider the polymerization techniques, where the grafting of polymer brushes on inorganic nanoparticles can certainly enhance the compatibility of polymer-inorganic hybrid nanoparticles with dielectric polymer matrix [71; 72; 73]. [PERSON] et al. defined that even by the intrinsic tuning of poly(styrene-butadiene-styrene), with polar organic groups such as methyl thioglycolate, results in self-healing dielectric elastomers as new actuators materials. The step to achieve these materials was via a one-step thiol-ene \"click\" reaction followed by low-temperature UV curing. The reported materials exhibited improved relative dielectric permittivity to 11.4 at 10\({}^{3}\) Hz, with a low dielectric loss [74]. A synthetic strategy developed by [PERSON] et al.