Papers by Keyword: Ceramic Substrate

Abstract: The marker method in studying the formation mechanism and defect structure of higher oxide during oxidation of lower oxide has been discussed. The approach to this problem needs specific treatment, both in experimental procedure and in the interpretation of results. It has been shown that the correct results of marker experiments in the case of highly defected substrates can be obtained, if these substrates before the marker deposition process are submitted to homogenization under highest oxidant activity, at which they remain stable at a given temperature. In addition, the nonstoichiometry must be considered in formulating appropriate chemical reactions, being the basis for foreseeing the location of markers in the interior of reaction product. The other very important problem consists in the possibility of the formation of reaction product not only on the surface of oxidized substrate but also inside of this substrate. In such a situation, the formulation of final conclusions concerning the crystalline lattice disorder from marker position should be combined with considerations of chemical reactions and transport processes occurring in a given substrate.

Abstract: DBC is a process where copper foils are bonded to ceramic substrates for manufacturing hybrid electronic circuits and packages with high power-handling capabilities. For aluminum nitride (AlN) ceramics, a heat-treatment is required to grow an oxide layer to promote the bonding with copper. The oxidation treatment, however, must be conducted in special conditions to avoid the occurrence of severe cracking. In this work, an alternative method is proposed to form an intermediate oxide layers for DBC to AlN substrates. By this method, eutectic powder mixtures (CuO-CaO and CuO-Al2O3 systems) were applied to dense AlN substrates and then heat-treated at 1200 °C for 1 h in air. Different types of AlN ceramics sintered between 1650 and 1700 °C for 4 h in nitrogen atmosphere with additives of the system Y2O3-CaO-SrO-Li2O were investigated. The prepared oxide layers (thickness of ~25 m) presented good microstructural joining with the AlN substrates (characterized by SEM and EDS analysis), and did not affect significantly the thermal conductivity in the working temperature range of electronic devices (~100 to 50 W/m.K determined by laser flash method between 100 and 200 °C) compared to the AlN substrates.

Abstract: An implantable antenna for the applications of biomedical telemetry has been widely studied in the modern medical science. The purpose of this study is to design and fabricate an implantable antenna which exhibits enhanced bandwidth (25%) and miniaturization for the use of implantation. In this letter, the microwave dielectric ceramic (MgTa1.5Nb0.5O6) substrate which possesses high dielectric constant (εr = 28) and high quality factor is used as the substrate of the implantable antenna, a CPW-fed monopole dual spiral structure is adopted as the antenna pattern and fabricated by the print-screening technique. The effects of shape, length, size, and thicknesses of the proposed antenna would be evaluated and investigated in this letter. In addition, the center frequency is required to conform to the band (402 ~ 405 MHz) provided by Medical Implant Communication Services (MICS). From the experimental results of the proposed antenna immersed in phantom fluid, the optimum antenna exhibits a miniaturized volume of 288 mm3, bandwidth of 134 MHz (33%), return loss 16.32 db at 404 MHz, the SAR of 142 W/Kg, and gain of 16 db, respectively.

Abstract: Electromagnetic meta-materials are artificial and periodical materials which both the permittivity and permeability are simultaneously negative. Electromagnetic meta-materials represent a new concept where composite materials are designed to display particular properties. The work which we had finished includes theoretical design and numerical simulation of the structure, fabrication of the samples and measurement of the properties. We designed electromagnetic meta-materials which composed by periodic split ring resonators (SRR) based on ceramics and then researched the influence by microwave guide. It is showed that the resonance frequency of meta-materials can be adjusted by dielectric constant and thickness of ceramic substrate.

Abstract: Polycrystalline silicon layers were grown on AlN ceramic substrates in a rapid thermal chemical vapor deposition system at high temperature (~1150°C). Larger columnar grains, > 5µm in size, were obtained by the zone melting recrystallization (ZMR) technique. The p-n junction is formed by a phosphorous diffusion process to make a solar cell. Solar cell devices based on this Si layer result possess an open-circuit voltage of about 0.17V and a short-circuit current of about 6.6mA/cm2.

Abstract: The thin-film of silicon deposited by RTCVD on pressureless sintered SiC substrate with the size of 30mm×20mm, which is cleaned by ultrasonic method and chemical treatment. The crystal size of silicon columnar grain can reach 190 µm and its preferred orientation is [111] after ZMR process.