High Frequency Loss Mechanism in Polymers Filled with Dielectric Modifiers
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High Frequency Loss Mechanism in Polymers Filled with Dielectric Modifiers. J. Obrzut A. Anopchenko, K. Kano and H. Wang1 Polymers Division, National Institute of Standards and Technology Gaithersburg, MD 20899. 1 Michigan Technological University, Houghton, MI 49931.
ABSTRACT We analyzed the high frequency dielectric relaxation mechanism in high-k composite materials using film substrates made of low loss organic resin filled with ferroelectric ceramics and with single wall carbon nanotubes (SWNT). We performed broadband permittivity measurements of high-k film substrates at frequencies of 100 Hz to about 10 GHz. In order to analyze the effect of the dielectric thickness, dielectric constant, loss and conductive loss on the impedance characteristics, we used a High Frequency Structure Simulator to perform a full wave numerical analysis of several power planes. Small angle neutron scattering (SANS) was used to probe the dispersion of SWNTs in polymer matrices. It was found that organic-ceramic composites exhibit an intrinsic high frequency relaxation behavior that gives rise to frequency dependent dielectric loss. The highest frequency relaxation process dominates the overall loss characteristic. In the case of polymers modified with SWNTs, we observed that 2 % mass fraction of p-doped semi-conducting SWNTs increases the dielectric constant by 3 orders of magnitude, in apparent violation of the mixing-rule. The hybrid material appears to have preferential coupling within the dispersed phase. The experimental data and numerical simulation indicate that these materials can play a significant role as embedded passive devices with functional characteristics superior to that of discrete components.
INTRODUCTION There is a demand for electronic devices that operate at higher frequencies, lower voltages, and larger currents. At the same time, end users require increased functionality, smaller form factors, and lower cost. Hybrid materials made of organic polymer resins offer a promise of plastic composites with enhanced electronic properties [1] and low temperature processing. Recently, high dielectric constant polymer- ceramic composites have been shown to have the desirable electromagnetic characteristics for embedded distributed capacitance (EDC) over a broad frequency range, including the microwave[2]. Advantages include improved electrical performance, reduced board size, and potential improvements in reliability through the elimination of solder joints. Carbon nanotubes are structurally unique in that the tube diameter can be small, approaching in dimension the gyration radius of the polymer. However, the aspect ratio between length and diameter can be several orders of magnitude larger. Consequently, structural, electrical, thermal and optical properties of polymers can be greatly enhanced with a relatively small amount of carbon nanotube modifier [3]. Thus, there is a lot of interest in elucidating the
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fundamental principles governing the functionalization and dispersion of dielectric modifiers
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