Stretchable, flexible and tunable RF devices that are fabricated with Polydimethylsiloxane (PDMS) Electrically Conductive Composites (ECC) are presented. Using this composite material allows mechanical modulation of the device dimensions resulting in tuning of its frequency response. A planar loop antenna and a 5th order stepped impedance low pass filter operating around 1.5 GHz with tunability greater than 15% are shown. The ECC can reach an electrical resistivity as low as 10⁻⁴ Ω. cm, which is close to a metal resistivity. The materials are also ultra-low cost for massive fabrication. This technology opens the door for tunable RF devices on flexible and curvilinear packages.

We show how stretchable Poly(dimethylsiloxane) (PDMS) electrically conductive composites (ECC) can be fabricated to form flexible, stretchable multilayer interconnects. Multilayer integration through via-like structures enables increased component interconnection and reduced form factor. We show a unique process for forming stretchable multilayer interconnects in PDMS via a bench-top layer-by-layer assembly technique. The SCC is reliable under bending, tensile (ε=0.3) and compressive strains. Furthermore, we show how the processes and package designs developed can be applied to the fabrication of stretchable devices. The techniques presented to fabricate ultra-low cost, stretchable, 3D packages hold the potential serve as a package for future stretchable electronic and radio frequency devices.

A solvothermal method was used to synthesize functionalized graphene, which exhibits an ultrahigh capacitance. This solvothermal method allows a fine control of the density of functionalities on graphene surface. The structure of resulting functionalized graphene is characterized by X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), FTIR and Raman. Pseudocapacitance is provided by functionalities on graphene surface, such as carboxyl, carbonyl and hydroxyl. The significance of these functional also includes improving the wetting properties of electrode material, especially for supercapacitors using aqueous electrolyte. However, there is a penalty for functionalities since these oxygen-containing functional groups will disrupt the π-conjugated system and lower the electrical conductivity. Therefore for functionalized graphene as supercapacitor, a tradeoff exists between the high psudeocapacitance and low conductivity, both are arising from the surface functionalities. Our systematic study shows a successful control of the density of functionalities, which is essential to achieve high performance of graphene-based supercapacitors. The capacitance of graphene is measured in a three electrode system using cyclic voltammetry (CV) and galvanostatic charging/discharging techniques. At a proper reduction condition, a high capacity of 276 F/g was achieved at a discharging current of 0.1 A/g in H₂SO₄ solutions. The superior capacitive performance of functionalized graphene demonstrates the importance of surface property engineering, which will greatly promote the study and application of graphene-based supercapacitors.

Anisotropically conductive adhesives (ACA) are a promising alternative to solder interconnects for high performance electronic devices due to their increased I/O capabilities and reduced form factor. Previous studies have shown that modification of Au coated Ni/Cu bumps with conjugated self-assembly monolayers (SAMs) increases conductivity, current carrying capacity and reliability of ACA interconnects[1-3]. In this study, we kinetically control the assembly of p-Terphenyl-4,4”-dithiol (TPD) monolayers on Au bumps. Using a custom designed test vehicle we show how TPD SAMs can either increase or decrease the single bump resistance depending on the kinetics of the monolayer formation and its resulting structure. Future studies focusing on controlling monolayer assembly will determine the efficacy of conjugated SAMs at enhancing the conductivity and current carrying capacity of ACA interconnects.

The objective of this paper is to show how stretchable conductive composites can be utilized for the fabrication of ultra-low cost stretchable RF devices. We show a method to produce biocompatible highly conductive stretchable silicone composites via an in-situ nanoparticle formation and sintering process. Furthermore, we develop a simple, low cost, processing technique to fabricate stretchable RF transmission lines. These RF transmission lines are highly flexible, stretchable and robust. The S-parameter measurements show stable performance during mechanical deformation up to 6 GHz. Future development of this technology will enable ultra low cost consumer RF devices serving as a platform for future stretchable electronic devices.