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Flexible and stretchable electronic components are currently at the heart of macroelectronics research. Materials useful for such applications are based on entropy elastic soft matter, combined with energy elastic functional elements. Examples include functional materials for sensing pressure and temperature changes, such as ferroelectrets, ferroelectric polymers, and nanocomposites of ferroelectric polymers and piezoelectric ceramics. Components for making flexible or stretchable electronic components additionally require electronic circuitry based on amorphous silicon or on organic semiconductors. Progress in such electronic elements is rapid, state of the art are elements which can easily operate at low voltage levels of 1 V. Combined with functional materials, sensing elements for temperature and pressure changes are easily achieved, as demonstrated with a few working examples of paper thin microphones, optothermal switching elements and skin-like electronics. Entropy-elastic elastomers form the basis for actuating elements, outlined by examples based on self organized actuating structures. Such materials can be also made functional by design, enabling fully reversible stretchable sensing elements for temperature, pressure and other physical parameters.
In this work, we present a novel printing technique that enables the usage of PDMS and ceramic powder mixed PDMS composites (we refer as “PDMS-ceramic composites” in this context), as a substrate for printing of copper conduction layers. This technique is based on microtransfer molding (μTM) and lift-off for pattern formation . Another key feature is the usage of microtextured PDMS and PDMS-ceramic composites before any copper film deposition. Our microtextured surface is composed of pyramid shaped wells (100 μm depth and 150 μm sides on PDMS surface). The poor adhesion between PDMS and copper is overcome by oxygen plasma application and titanium deposition before copper layer.
In order to demonstrate the convenience of this technique in RF applications, copper conduction lines (5 mm wide, different lengths) were printed on microtextured PDMS substrates. These transmission lines successfully maintained a low resistance during large strain. The printed lines have the DC resistance of 0.5 Ω and conductivity of 1.3e6 S/m, and the transmission analysis of these lines show good results especially in the MHz range when compared to copper tape measurements.
Apart from the conduction lines, the substrates can have ranging dielectric constants from 3 (no powder) to 23 (50% D270 powder, provided by TransTech) by volume mixing rule. Dielectric constant is important for RF applications, especially antenna designs. Therefore, provided with a range of dielectric constants, these composite substrates are a great promise in RF field for pliable antenna fabrication . For experiment purposes, some of the transmission lines are printed on these composite substrates as well as pure PDMS.
In this study, apart from the fabrication of transmission lines, this novel technique will be applied in a GPS antenna design for demonstration purposes. This antenna design is a single-fed circularly-polarized stacked antenna for tri-band GPS (L1, L2 and L5) applications . For the fabrication of the antenna, polymer-ceramic materials of ε1=16 and ε2=30 will be utilized as the substrates .
Silicon dioxide (SiO2) films were deposited on crystalline silicon substrate by inductively coupled plasma chemical vapor deposition (ICP-CVD). In this paper, various process parameter-gas flow rate, ICP RF power, Process pressure were discussed for the investigation of refractive index. And some properties of the SiO2 film are investigated. Since there was no external substrate heating during the deposition, the SiO2 film showed poor electrical characteristics, such as shifted flat-band voltage and high effective charge density. We have proposed He plasma pre-treatment in order to reduce the interface fixed charge and some post-treatment. Our experimental results shows that He plasma pre-treatment supply thermal energy for decomposition of reactant gas and to remove effective charges. Hydrogen post-treatment also enhances electrical characteristics. We measured the effect of the plasma treatment using FT-IR spectrum and C-V characteristics.
The prospect of large-area electronics on polymers, for flexible applications requires a study of thin film fracture mechanisms. To fabricate thin-film transistor (TFT) backplanes on polymer foils the substrate must first be passivated to protect the polymer substrate from chemicals used during processing and to protect the TFTs from substrate out gassing. Silicon nitride (SiNx) is commonly used for this purpose since it tends to adhere well to polymers and is easily deposited by PE-CVD. When rigid thin films such as SiNx are deposited onto compliant substrates, such as polymer foils, stresses caused by built-in strains and the mismatch in coefficients of thermal expansion can cause fracture. The deposited thin films may fracture, and also the polymer substrate below. Using focused-ion beam milling and scanning electron microscopy we analyzed two distinct thin film fracture morphologies for SiNx films on two different types of polymer substrate. One had a relatively low, the other a relatively high coefficient of thermal expansion. For both SiNx/substrate systems the SiNx was under residual compressive stress and the substrate under tension. In one case the compressive stress in the thin films cause them to debond, buckle, and crack. In the other case the tensile stress in the substrate causes it to tear, followed by the fracture of the SiNx film above.