Thick-film Process Research Articles

Design of a 60-GHz Substrate Integrated Waveguide Butler Matrix—A Systematic Approach

A 60-GHz substrate integrated waveguide Butler matrix designed based on a systematic approach is fabricated by a standard single-layer print circuit board process, which is more economical for mass production than are the advanced processes such as low-temperature co-fired ceramic, thick-film process, etc. The systematic approach involves design equations, simulations, and measurements. Starting with a set of explicit design equations for the short-slot couplers, one calculates the structure dimensions. The calculated dimensions are then optimized with full-wave simulation to finalize the design of the key components, including the couplers and phase shifters. With the use of a noncoaxial multiport measurement technique, the characteristics of the components are acquired through a probe station and a two-port vector network analyzer. Measurement technique plays a critical role in the systematic design approach. By measuring at the intrinsic ports or the wave ports defined in the full-wave simulations, the components are unambiguously verified and then integrated to complete the design of the Butler matrix. The resulting Butler matrix is also verified by the measured eight-port <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -matrix, which is shown in good agreement with the simulated one. As the measured results of the Butler matrix show, for the operating bandwidth from 58 to 62 GHz, the reflections and isolations are lower than -13.5 dB and the insertion losses are below 2.5 dB. Much like the measured results of the components, the measured eight-port <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -matrix not only verifies the design of the Butler matrix, but also will facilitate the follow-on design of a switched-beam antenna array.

Evaluation of Glass Frits for Development of Lead-Free Thick Film Resistor

Glass frit is a major component of thick film resistor (TFR) for the production of hybrid circuits. More than thirty commercial lead-free glass frits with different compositions have been evaluated for developing a lead-free thick film resistor that is compatible with typical industry thick film processing and has comparable electrical properties as the lead bearing counterpart. Two glass compositions were selected out of 33 candidates for preparation of RuO2 based TFR inks, which were screen printed on alumina substrates and fired at 850°C. The preliminary results of these resistors showed that the sheet resistance spanned from 400 ohms per square (Ω/□) to 0.4 mega-ohms per square (MΩ/□) with 5–15% RuO2 and the hot temperature coefficient of resistance (HTCR) fell in a range of ±350ppm/°C.

Microwave dielectric properties and microstructures of Nb 2O 5-Zn 0.95Mg 0.05TiO 3 + 0.25TiO 2 ceramics with Bi 2O 3 addition

The effects of Bi 2O 3 addition on the microwave dielectric properties and the microstructures of Nb 2O 5-Zn 0.95Mg 0.05TiO 3 + 0.25TiO 2 (Nb-ZMT′) ceramics prepared by conventional solid-state routes have been investigated. The results of X-ray diffraction (XRD) indicate the presence of four crystalline phases, ZnTiO 3, TiO 2, Bi 2Ti 2O 7, and (Bi 1.5Zn 0.5)(Ti 1.5Nb 0.5)O 7 in the sintered ceramics, depending upon the amount of Bi 2O 3 addition. In addition, in order to confirm the existence of (Bi 1.5Zn 0.5)(Ti 1.5Nb 0.5)O 7 phase in the samples, the microstructure of Nb-ZMT′ ceramic with 5 wt.% B 2O 3 addition was analyzed by using a transmission electron micrograph. The dielectric constant of Nb-ZMT′ samples was higher than ZMT′ ceramics. The Nb-ZMT′ ceramic with 5 wt.% Bi 2O 3 addition exhibits the optimum dielectric properties: Q × f = 12,000 GHz, ɛ r = 30, and τ f = −12 ppm/°C. Unlike the ZMT′ ceramic sintered at 900 °C, the Nb-ZMT′ ceramics show higher Q value and dielectric constant. Moreover, there is no Zn 2TiO 4 existence at 960 °C sintering. To understand the co-sinterability between silver electrodes and the Nb-ZMT′ dielectrics, the multilayer samples are prepared by multilayer thick film processing. The co-sinterability (900 °C) between silver electrode and Nb-ZMT′ dielectric are well compatible, because there are no cracks, delaminations, and deformations in multilayer specimens.

A low-cost, high-yield fabrication method for producing optimized biomimetic dry adhesives

We present a low-cost, large-scale method of fabricating biomimetic dry adhesives. This process is useful because it uses all photosensitive polymers with minimum fabrication costs or complexity to produce molds for silicone-based dry adhesives. A thick-film lift-off process is used to define molds using AZ 9260 photoresist, with a slow acting, deep UV sensitive material, PMGI, used as both an adhesion promoter for the AZ 9260 photoresist and as an undercutting material to produce mushroom-shaped fibers. The benefits to this process are ease of fabrication, wide range of potential layer thicknesses, no special surface treatment requirements to demold silicone adhesives and easy stripping of the full mold if process failure does occur. Sylgard® 184 silicone is used to cast full sheets of biomimetic dry adhesives off 4” diameter wafers, and different fiber geometries are tested for normal adhesion properties. Additionally, failure modes of the adhesive during fabrication are noted and strategies for avoiding these failures are discussed. We use this fabrication method to produce different fiber geometries with varying cap diameters and test them for normal adhesion strengths. The results indicate that the cap diameters relative to post diameters for mushroom-shaped fibers dominate the adhesion properties.

Feasibility study on rapid thermal processing

The rapid thermal processing is widely used for heating of substrates in microelectronics. The use of radiation (UV/Visible/IR) as source of energy provides several advantages. Apart from thermal effects, photonic effects play a significant role in the RTP. Using array of tungsten halogen lamps as a continuous source of radiation, RTP covers a wide range of processing steps such as annealing, dielectric fabrication, metal alloying, diffusion and chemical vapor deposition. This paper reports an attempt made to use RTP in the field of thick film processing. Firing of thick films is an important high temperature step. The desirable physical and chemical properties of the films can be obtained through firing. A paste consisting of active chemicals, solvent, binder, glass powder is transferred on the substrate by means of screen-printing techniques. Further heating the substrates to about 600 °C fires this patterned thick film. This paper reports a novel technique for firing the paste in RTP system. The parameters viz. temperature and time were optimized for resistive paste of Cd–Cu–Cl. The thick films thus obtained were studied for their photosensitivity, I– V characteristics and microscopic structures.

Millimeter Wave Substrate Integrated Waveguide Antennas: Design and Fabrication Analysis

The paper presents a new concept in antenna design, whereby a photo-imageable thick-film process is used to integrate a waveguide antenna within a multilayer structure. This has yielded a very compact, high performance antenna working at high millimeter-wave (mm-wave) frequencies, with a high degree of repeatability and reliability in antenna construction. Theoretical and experimental results for 70 GHz mm-wave integrated antennas, fabricated using the new technique, are presented. The antennas were formed from miniature slotted waveguide arrays using up to 18 layers of photo-imageable material. To enhance the electrical performance a novel folded waveguide array was also investigated. The fabrication process is analyzed in detail and the critical issues involved in the fabrication cycle are discussed. The losses in the substrate integrated waveguide have been calculated. The performance of the new integrated antenna is compared to conventional metallic, air-filled waveguide antennas, and also to conventional microstrip antenna arrays operating at the same frequencies.

Zeolite-based Impedimetric Gas Sensor Device in Low-cost Technology for Hydrocarbon Gas Detection.

Due to increasing environmental concerns the need for inexpensive selective gas sensors is increasing. This work deals with transferring a novel zeolite-based impedimetric hydrocarbon gas sensor principle, which has been originally manufactured in a costly combination of photolithography, thin-film processes, and thick-film processes to a low-cost technology comprising only thick-film processes and one electroplating step. The sensing effect is based on a thin chromium oxide layer between the interdigital electrodes and a Pt-loaded ZSM-5 zeolite film. When hydrocarbons are present in the sensor ambient, the electrical sensor impedance increases strongly and selectively. In the present work, the chromium oxide film is electroplated on Au screen-printed interdigital electrodes and then oxidized to Cr2O3. The electrode area is covered with the screen-printed zeolite. The sensor device is self-heated utilizing a planar platinum heater on the backside. The best sensor performance is obtained at a frequency of 3 Hz at around 350 °C. The good selectivity of the original sensor setup could be confirmed, but a strong cross-sensitivity to ammonia occurs, which might prohibit its original intention for use in automotive exhausts.

Enhancement of Dimension Uniformity of Wet-Etched Thick Insulator Holes in Triode Carbon Nanotube Field-Emission Display Devices

A triode structure carbon nanotube field-emission display was fabricated using the thick-film process. The critical dimensional uniformity of wet-etched thick insulator holes was enhanced by changing the wet etching mechanism from vertical dip-etching to horizontal spray-etching. The profile of the insulator holes fabricated using the new etcher was similar to anisotropic. After optimizing the operation conditions of the new etcher, the dimensional uniformity of the insulator holes increased to 97.7%. The optimal concentration of etchant was 2.2 wt % for achieving the least side etching of the insulator holes. The carbon nanotube paste was pattern-printed into the insulator holes. The uniform size of the insulator holes implied that the carbon nanotube distribution was similarly among the insulator holes. This result showed an improved uniform field emission image over the panel from 59 to 83.85%.

Dependence of CVD diamond growth rate on substrate orientation as a function of process parameters in the high microwave power density regime

AbstractThe use of diamond as a material for high power electronics requires high‐purity monocrystalline thick diamond films. Hence it is extremely important to have perfect control of the morphology during the entire growth process, so that the useable surface be maximized and residual stresses (which may cause cracking of the sample during the growth process) be limited. To assist in this work, a 3D geometric growth model has been recently developed, taking into account the growth rate of the different crystallographic planes: {100}, {110}, {111}, and {113}. The knowledge of the growth rate along the different directions as a function of growth parameters (substrate temperature, methane concentration, and nitrogen content in the gas phase) was the missing link between simulations and effective thick film processing. This knowledge is here embodied in the measurements displayed in this paper. In particular, we report on a way of limiting the occurrence of specific facets with deleterious effects on stress and crystal cracking probability. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

상용 LTCC 소재의 슬러리 제조 공정에서 분산성 평가 및 최적화

Laminated LTCC components of high integrity, fabricated by thick film process, are applied to industrial field of IT technology along with miniaturization trend of electronic devices. Dispersion states were examined by several evaluation methods with MLS-22, which is one of commercial LTCC powders, to achieve optimal dispersion as basis for stable LTCC fabrication process. Slurry viscosity, surface roughness of dip-coated slide glass, sedimentaion of slurry, and SEM observation of dried surface were utilized with respective amount change of various commercial dispersants. Among these commercial dispersants, optimal dispersion state was obtained with 0.4 wt% of BYK-111, from the results of various evaluation methods.

Fabrication of embedded fine line inductors by constrained sintering and formulation of photoimageable conductive paste

For miniaturisation and precision of electronic device, the new technologies such as photoimageable thick film process were combined with conventional thick film process, and constrained sintering with near zero shrinkage in the x and y direction has been proposed. In this research, photoimageable conductive paste for forming embedded components via constrained sintering by low temperature cofired ceramic (LTCC) technology was formulated. Afterwards, by optimising paste formulation, formation process of fine line and sintering method, miniaturised LTCC components especially embedded fine line inductors were fabricated and their properties such as line resolution, surface morphology and yield were investigated. As a result, embedded fine line inductors formed by constrained sintering with fine line resolution of 20 μm and yield over 90% were acquired.

Application of inclined-exposure and thick film process for high aspect-ratio micro-structures on polymer optic devices

In this paper we apply an inclined-exposure technology, while also using a polymeric material to make 3D optical micro-structure like dove prism and hardened reflecting mirrors in blue-DVD pickup head module. In contrast to the more common type of inclined mirrors, single-lensed reflecting mirrors, the micro-reflecting mirror being developed within the scope of this paper possesses the qualities that it requires no metal for its reflecting surface, and it is structurally stable. When used in micro-optical systems, it is less prone to experiencing structural changes and impact to the system’s optical paths as a result of heat generated from the light source. The fabrication technology for dove prism being developed can be used to easily fabricate highly integrated micro-optical systems. The structure being fabricated can reach a height of 1.8 mm, while the degree of surface roughness meets the necessary Marechal optic quality criterion. In this paper we will also issue of the structure of the SU-8 material being wider at the top and narrower at the bottom due to short-wavelength light source having shallower penetration. The polymeric material used has a high penetration rate of 95% (red light), and is low in cost. As such, we may apply and consolidate micro-structures in TIR, CD/DVD, SPR, and micro-PIV systems, or optical systems in general. These novel methods can be employed for the fabrication of nontraditional 3D structures on photo polymer for Optical MEMES applications.

Utility of nonwovens in the production of integrated electrical circuits via printing conductive inks

This study reports on the printing of conductive inks directly onto nonwovens to produce circuits and embedded systems. The approach adopted applies polymer thick film (PTF) processing technologies directly onto compliant, flexible, nonwoven substrates. The paper reports on the characterization of various PTF conductive inks and printed transmission lines. The performance metrics related to the circuits are impacted by the ink viscosity and by the contact angle of the ink on the surface of the nonwoven structure. These parameters dictate the manner in which the ink is distributed onto and into the substrate. The manner in which ink droplets interact with the surface of the substrate determines the mechanisms responsible for both in-plane flow and through-the-plane flow of the ink.

Monolithic Integration Fabrication Process of Thermoelectric and Vibrational Devices for Microelectromechanical System Power Generator

This paper describes a fabrication process to integrate different types of energy-converting microelectromechanical system (MEMS) devices for a power generator. MEMS structures and a fabrication process for the monolithic integration are proposed for the purpose of accumulating small amounts of energy from various surrounding environments. For the MEMS power generator, thermocouples and movable plates are simultaneously fabricated in thick-film formation processes with deep reactive ion etching of silicon and gold electroplating. The fabricated thermoelectric devices of gold and silicon produced voltages in accordance with the temperature difference at the thermocouples. The vibrational devices with gold movable plates resonated with external vibrations. These results confirm that the monolithic integration process of MEMS devices can be established for harvesting thermal and vibrational energies from their surroundings.

43.4: Characteristics of MgO Nano‐Sized Powder Layer via Electrophoresis Deposition as Electron Emission Layer for ac‐PDPs

AbstractMgO electron emission layer for ac‐PDPs was formed via electrophoretic deposition process and its characteristics were evaluated. Luminance efficiency of test panels using such electron emission layer was evaluated. The layer formed by the electrophoretic deposition process revealed enhanced adhesion to dielectric layer and better packed density compared with formed via conventional thick film process such as printing and spin coating process.

LTCC 내장형 미세 라인 인덕터 구현을 위한 감광성 Ag Paste 조성에 관한 연구

Line width under 100 ㎛ with good resolution is difficult to achieve using conventional thick-film process utilizing screen printing method. However, combined with lithography technology finer line and space for miniaturization and highly integrated package is achievable. In this study, photosensitive Ag paste of optimum formulation used for thick film lithography technology was fabricated by various Ag powder, glass powder and additives. As the result, line width of 30 ㎛ with good definition and reduced mismatch during co-firing with LTCC substrate was acquired. Formulated Ag paste was used to pattern embedded fine line inductor with over 90% yield.

Piezoelectric thick films and their application in MEMS

Piezoelectric thick films (up to 10 μm thick) and piezoelectric micromachined ultrasonic transducer (pMUT) have been successfully demonstrated at low temperatures of 650 °C using a composite thick film processing route. Submicron-sized PZT powder was dispersed into sol–gel solution to form homogeneous slurry for spin-coating on silicon substrate. Issues associated with recipe of the slurry, deposition process and sintering of films have been summarized with a view to optimizing the properties of the films and pMUTs. Typical microstructure, ferroelectric and piezoelectric properties of the composite films are given. Thermal stability of bottom electrode, a key issue about device fabrication, has also been investigated. The ultrasound-radiating performance of the pMUT element in response to a continuous alternating current driving voltage has been reported. The generated sound pressure level is 116.8 dB at 76.3 kHz at a measuring distance of 12 mm. The pMUT is suitable for application of airborne object recognition.

Development of WO3-Based Thick-Film Hydrogen Sensors

ABSTRACT Hydrogen gas sensors based on semiconducting tungsten trioxide (WO3) were produced using a commercially attractive thick-film screen printing process. WO3 powders were doped with 1 mole % Pt or Pd and attrition-milled to produce precursor powders for sensor fabrication. The sensors were fired in air using various temperature/time profiles. SEM and XRD techniques were used to investigate the phase composition and microstructural properties. The influence of processing conditions, additives, sensor operating temperature and partial pressure of H2 gas on the response characteristics of the sensors was investigated. Sensors were also produced from un-doped material and tested under identical conditions to establish the baseline data. The data indicates that high-sensitivity H2 gas sensors can be produced through the manipulation of powder composition and processing conditions. The response characteristics of WO3- based sensors were found to be significantly influenced by the sensor operating temperature, the type of dopant used as well as the H2 gas concentration.

Fabrication of a millinewton force sensor using low temperature co-fired ceramic (LTCC) technology

This study is aimed at outlining the fabrication of a novel piezoresistive force sensor using LTCC technology, which operates at millinewton range, yet is compatible with low cost thick-film fabrication process. Mechanical and electrical characterization of the device is explained in terms of processing conditions, including the principle of force sensing and materials employed. The improvement of device functionality by modifying commercially-available thick-film conductors is described. The sensors are found to be efficient in responding to forces below 100 mN.

Microwave and magnetic properties of self-biased barium hexaferrite screen printed thick films

The interest in barium hexaferrite thick films, particularly with high remanent magnetization, is driven by the development of small planar ferrite microwave devices. We report here processing and microwave characterization of BaFe12O19 ferrite thick films (100–400μm). The films were deposited on silicon and alumina substrates by screen printing, oriented under a magnetic field of 8kOe, then annealed at 250°C and sintered at temperatures ranging from 850to1300°C. Scanning electron microscopy and x-ray diffraction exhibited strong crystallographic alignment of c-axis crystals perpendicular to the film plane. The magnetization measurement indicated that a typical dense film with 270μm thickness yielded a high squareness (Mr∕Ms) of 0.93. Ferrimagnetic resonance (FMR) measurements were performed in the frequency range of 40–55GHz. From the linear dependence of FMR frequency on the external field, a g factor of 2.03±0.08 was deduced, while the smallest linewidth was obtained to be 1.2kOe at 40GHz. The broadening of the FMR linewidth arises predominantly from magnetic inhomogeneities in the polycrystalline films. The thick films have great potential for use in future microwave and millimeter wave monolithic integrated circuits.