Low Temperature Co-fired Ceramic Substrate Research Articles

Characterization of LTCC-Thick Film Technology for 300°C Packaging

Economic geothermal well construction and reservoir characterization requires high temperature logging tools and sensors with the long-term operation capability of 300°C. Low temperature co-fired ceramic (LTCC) and thick film technology make them a potential candidate for building interconnects to SiC device and functional analog or digital circuits to operate at that temperature. In this work, single conductor layer LTCC substrates have been fabricated to characterize the thick film Au adhesion under 300°C aging. Via reliability has been evaluated on the multi-layer LTCC substrates under temperature cycling of 35–325°C. In addition, die attach, wire bonding and stud bumping assembly techniques has been investigated.

Compact concavo-convex cavity filters using multilayer substrate integrated waveguide

A compact bandpass filter based on concavo-convex cavity resonators is proposed. The reported resonator is developed from a conventional rectangular cavity resonator by introducing a concave surface. Compared to a conventional rectangular cavity, this new resonator has a low resonant frequency, compact size and a wider relative mono-mode bandwidth. Using the substrate integrated waveguide technique to integrate the concavo-convex cavity on a eight-layer low temperature co-fired ceramics substrate, a demonstration filter is designed, fabricated and tested to show the validity of the proposed structure.

Wideband waveguide to microstrip probe transition with LTCC technology

A novel broadband waveguide to microstrip probe transition based on low-temperature co-fired ceramic (LTCC) technology is presented and experimentally verified for the first time. To improve the bandwidth and impedance matching, a multilayer step-shape matching structure beneath the probe is buried in the LTCC substrate, which is implemented by installing conducting ground strips on different substrate layers connected by the staggered via side walls. A waveguide to microstrip probe transition is fabricated to verify the design with compact size. Measured results show good agreement with simulated results.

Stacked Patch Antenna Array on LTCC Substrate Operated at 28 GHz

This study develops a 28-GHz patch antenna array using LTCC (Low Temperature Co-fired Ceramic) technology, for use in applications of LMDS (Local Multipoint Distribution Service). The design comprises 2 × 2 stacked patch elements and parallel-fed networks, yielding a wide bandwidth and superior gain performance. Broadband performance is achieved by varying the dimensions of the parasitic patch. The arrays are excited through using a novel opposite-side feeding structure to prevent any electrical effect on the parasitic patch. Measurements correlate closely with the simulation results: a gain of 10.35 dBi and a bandwidth of 2.85 GHz (26.75–29.6 GHz) are achieved.

Sputter deposition of thin film MIM capacitors on LTCC substrates for RF bypass and filtering applications

Thin film capacitors for RF bypass and filtering applications were sputter deposited onto low temperature co-fired ceramic (LTCC) substrates. The capacitors were configured in a metal-insulator-metal (MIM) design featuring 200 nm thick Al electrodes and a 300 nm thick Al2O3 dielectric layer, with dimensions varied between ∼150×150 μm and ∼750×750 μm. DC current-voltage measurements (E ≤ 5 MV/cm) coupled with impedance analysis (≤15 MHz) was used to characterize the resulting devices. More than 90% of the devices functioned as capacitors with high DC resistance (>20 MΩ) and low loss (tan δ <0.1). A second set of capacitors were made under the same experimental conditions with device geometries optimized for high frequency (≥200 MHz) applications. These capacitors featured temperature coefficient of capacitance (TCC) values between 500 and 1000 ppm/°C as well as low loss and high self-resonant frequency performance (ESR <0.6 Ohms at self-resonance of 5.7 GHz for 82 pF). Capacitance and loss values were comparable between the capacitor structures of similar areas at the different frequency regimes.

High‐Frequency Characterization of Porous Low‐Temperature Cofired Ceramics Substrates

In this work, the permittivity of porous low‐temperature cofired ceramics (LTCC) DP 951 is measured and evaluated. Porosification is performed at originally dense LTCC substrates in the fired state by a wet chemical etching procedure using hot phosphoric acid. Choosing this approach, areas with tailored permittivity can be generated in one single LTCC layer. The etch time and the bath temperature precisely control the penetration, and hence, the porosification depth. Therefore, the decrease in dielectric constant of the LTCC substrate can be correlated to the thickness of the porous layer. The dielectric constant is measured using a ring resonator in the microstrip configuration. From the resonances occurring in the transmission S‐parameter |S21| spectrum between 1 and 10 GHz, the relative dielectric constant can be determined. Using 820‐μm‐thick substrates, a relatively low reduction from ɛr=7.8 to 6.45 is achieved when a porosification depth of about 35 μm is reached. Applying a fitting procedure, the dielectric constant of the pure porous layer is deduced to ɛr=2.3. Based on numerical simulations, the effective dielectric constant for a 100‐μm‐thick glass–ceramic layer, which is modified to a depth of 35 μm is calculated to 5.2, whereas the thickness represents a lower limit for commercially available tapes being typically implemented into the fabrication process of monolithic LTCC systems with integrated metallization planes. Compared with commercially available low‐K LTCC materials, this value is lower than all other commonly used tape systems.

Temperature Dependence of Resonances in Metamaterials

Metamaterials are increasingly being proposed for many different microwave applications. Metamaterials are highly resonant structures and metamaterial device design is based on the resonance frequency for both civilian and military applications. These applications are often in a high-temperature environment. In this paper, we have performed an experimental study of the shift in resonance frequency of selected metamaterials (split-ring resonators and thin wires) in the 25°C -400°C range using FR4 and low-temperature co-fired ceramic substrates. We have provided a theoretical explanation for the observed shift in resonance frequency by calculating the shift in frequency resulting from the temperature dependence of the substrate permittivity and electrical conductivity of the metal, as well as thermal expansion of the metallo-dielectric structures comprising the metamaterial. The measured downward shift of the resonance frequency with increasing temperature agrees very well with full-wave finite-element simulation. It is found that the change of permittivity of the substrate is the primary effect, while the thermal expansion of the metallic structure is a secondary effect. The reducing resonance strength is due to the decrease in electrical conductivity with rising temperature. This study can be applied to other metamaterial metallo-dielectric structures or other planar microwave resonators printed on dielectric substrates.

Wideband 4×8 Array Antennas with Aperture Coupled Patch Antenna Elements on LTCC

We proposed a <TEX>$4{\times}8$</TEX> array antenna with aperture-coupled patch antenna elements. The antenna was designed for 60 GHz operation and fabrication on the low-temperature cofired ceramic(LTCC) substrate(<TEX>$\varepsilon_r$</TEX>=5.8). The feedline with the stub was designed to enhance the radiating element bandwidth and the transition characteristics between the waveguide (WG) and microstrip line(MSL). Through the optimization of the antenna and feedline geometry, the antenna gain and the performance of the 10 dB bandwidth were 20.2 dBi and 13 % up, respectively. The measured results agreed with the simulated ones.

Electromigration resistance and long term stability of textured silver thin films on LTCC

Silver (Ag) is regarded as advanced material for metallization purposes in microelectronic devices because of its high conductivity and its enhanced electromigration resistance. Besides the typical use of silicon based substrate materials for device fabrication, thin film metallization on ceramic and glass–ceramic LTCC (low temperature co-fired ceramics) substrates gets more and more into focus as only thin film technology can provide the required lateral resolutions of structures in the μm-range needed for e.g. high frequency applications. Therefore, the reliability of Ag thin films is investigated under accelerated aging conditions, utilizing test structure which consists of 5 parallel lines stressed with current densities up to 1.5 × 10 7 A cm −2 at temperatures ranging from room-temperature up to 300 °C. To detect the degradation via the temporal characteristics of the current signal a constant voltage is applied taking the overall resistance of the test structure into account. The mean time to failure of the Ag metallization substantially depends on the degree of (1 1 1)-orientation which, in turn, is strongly affected by the plasma power P P during deposition. Therefore, Ag thin films deposited at P P = 1000 W feature a 7 times higher reliability than those deposited at P P = 100 W. Due to the enhanced stability of grains being (1 1 1)-oriented in textured thin films the material transport predominantly occurs along grain boundaries, whereas in Ag films without a (1 1 1)-orientation volume-related diffusion effects dominate due to the lower stability of these grains.

A Novel Multilayer UWB Antenna on LTCC

A new miniaturized multilayer ultrawideband (UWB) monopole antenna on the low-temperature co-fired ceramic (LTCC) is presented. This antenna is composed of two open asymmetrical rectangular loops and microstrip feed lines. The two open asymmetrical rectangular loops are seperated on different layers and partly overlaped with each other, which not only enhances the bandwidth but also minimizes the size of the overall antenna. The via holes are fully utilized to connect the radiation elements and microstrip feed lines on various layers of the LTCC substrate. The simulated and measured impedance and radiation performance are studied and compared, which shows that the proposed antenna provides a wide bandwidth from 3.6-10.6 Ghz.

Influence of the crystal orientation on the electrical properties of AlN thin films on LTCC substrates

In this study, the influence of the crystal orientation on the electrical properties of sputter deposited aluminium nitride (AlN) thin films on low temperature co-fired ceramics (LTCC) substrates is investigated. The degree of c-axis orientation can be tailored by the deposition conditions such as plasma power, gas pressure and gas composition in the deposition chamber. Due to the large surface roughness of LTCC substrates ( R a = ∼0.4 μm) the quality of thin films is lower compared to silicon. Between areas of columnar grains arranged perpendicular to the LTCC surface, defects like voids are generated due to the wavy surface characteristics. The impact of crystal orientation and temperature up to 400 °C on the electrical performance is evaluated, as these layers are targeted as potential candidates for dielectric heat spreaders on multilayered ceramic substrates for high frequency applications. These AlN thin films having a good c-axis orientation exhibit lower leakage current levels over the complete temperature range compared to those with a poor alignment with respect to this crystallographic plane. The leakage current behaviour, however, is dominated according to the Pool–Frenkel electron emission independent of the degree of c-axis orientation.

Effect of ENIG deposition on the failure mechanisms of thermomechanically loaded lead‐free 2nd level interconnections in LTCC/PWB assemblies

PurposeThe purpose of this paper is to investigate the effect of electroless NiAu (ENIG) deposition on the failure mechanisms and characteristic lifetimes of three different non‐collapsible lead‐free 2nd level interconnections in low‐temperature co‐fired ceramic (LTCC)/printed wiring board (PWB) assemblies.Design/methodology/approachFive LTCC module/PWB assemblies were fabricated and exposed to a temperature cycling test over a −40 to 125°C temperature range. The characteristic lifetimes of these assemblies were determined using direct current resistance measurements. The failure mechanisms of the test assemblies were verified using X‐ray and scanning acoustic microscopy, optical microscopy with polarized light, scanning electron microscope (SEM)/energy dispersive spectroscopy and field emission‐SEM investigation.FindingsA stable intermetallic compound (IMC) layer is formed between the Ni deposit and solder matrix during reflow soldering. The layer thickness does not grow excessively and the interface between the layer and solder is practically free from Kirkendall voids after the thermal cycling test (TCT) over a temperature range of −40 to 125°C. The adhesion between the IMC layer and solder matrix is sufficient to prevent separation of this interface, resulting in intergranular (creep) or mixed transgranular/intergranular (fatigue/creep) failure within the solder matrix. However, the thermal fatigue endurance of the lead‐free solder has a major effect on the characteristic lifetime, not the deposit material of the solder land. Depending on the thickness of the LTCC substrate and the composition of the lead‐free solder alloy, characteristic lifetimes of over 2,000 cycles are achieved in the TCT.Originality/valueThe paper investigates in detail the advantages and disadvantages of ENIG deposition in LTCC/PWB assemblies with a large global thermal mismatch (ΔCTE≥10 ppm/°C), considering the design and manufacturing stages of the solder joint configuration and its performance under harsh accelerated test conditions.

40 GHz Vertical Transition with a Dual-Mode Cavity for a Low-Temperature Co-fired Ceramic Transceiver Module

A new vertical transition between a substrate integrated waveguide in a low-temperature co-fired ceramic substrate and an air-filled standard waveguide is proposed in this paper. A rectangular cavity resonator with closely spaced metallic vias is designed to connect the substrate integrated waveguide to the standard air-filled waveguide. Physical characteristics of an air-filled WR-22 to WR-22 transition are compared with those of the proposed transition. Simulation and experiment demonstrate that the proposed transition shows a −1.3 dB insertion loss and 6.2 GHz bandwidth with a 10 dB return loss for the backto-back module. A 40 GHz low-temperature co-fired ceramic module with the proposed vertical transition is also implemented. The implemented module is very compact, measuring 57 mm × 28 mm × 3.3 mm.

End-to-End Differential Contactless Conductivity Sensor for Microchip Capillary Electrophoresis

In this contribution, a novel measurement approach for miniaturized capillary electrophoresis (CE) devices is presented: End-to-end differential capacitively coupled contactless conductivity measurement. This measurement technique is applied to a miniaturized CE device fabricated in low-temperature cofired ceramics (LTCC) multilayer technology. The working principle is based on the placement of two distinct detector areas near both ends of the fluid inlet and outlet of the separation channel. Both output signals are subtracted from each other, and the resulting differential signal is amplified and measured. This measurement approach has several advantages over established, single-end detectors: The high baseline level resulting from parasitic stray capacitance and buffer conductivity is reduced, leading to better signal-to-noise ratio and hence higher measurement sensitivity. Furthermore, temperature and, thus, baseline drift effects are diminished owing to the differentiating nature of the system. By comparing the peak widths measured with both detectors, valuable information about zone dispersion effects arising during the separation is obtained. Additionally, the novel measurement scheme allows the determination of dispersion effects that occur at the time of sample injection. Optical means of dispersion evaluation are ineffective because of the opaque LTCC substrate. Electrophoretic separation experiments of inorganic ions show sensitivity enhancements by about a factor of 30-60 compared to the single-end measurement scheme.

A compact and low‐loss LTCC diplexer with high‐band selectivity and high isolation for dual‐band applications

AbstractThis article presents a compact and low‐loss diplexer for dual‐band applications using a LTCC (low temperature co‐fired ceramic) multilayer technology. This diplexer is composed of the high‐pass filter (HPF) and low‐pass filter (LPF) in order to separate GSM (global system for mobile) and CDMA (code division multiple access) band. For enhancing band selectivity of the diplexer, a shunt capacitor and inductor are designed in the HPF and LPF, respectively. In addition, a transmission zero is designed at the stopband of the LPF using a shunt inductor for improving isolation characteristics. The diplexer is realized in a 6‐layer LTCC substrate with a relative dielectric constant of 7. The size of the fabricated diplexer including CPW pads is 3.45 × 4.0 × 0.7 mm3. A measured insertion loss (IL) and return loss (RL) of the GSM band are less than −0.54 dB and −10.50 dB, respectively. In the case of CDMA band, the IL of −1.13 dB and RL of below −6.16 dB are archived. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1134–1137, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25137

Multilayer Dual-Band Bandpass Filter in Low-Temperature Co-Fired Ceramic Substrate for Ultra-Wideband Applications

In this paper, we propose a new multilayer dual-band bandpass filter in a low-temperature co-fired ceramic (LTCC) substrate for ultra-wideband (UWB) applications. This bandpass filter consists of two wideband bandpass filters and matching circuits. It is for UWB applications, which use the band group 1 (3.168-4.752 GHz) and the band groups 3 and 4 (6.336-9.504 GHz) of multiband orthogonal frequency-division multiplexing systems. The basic characteristics of the bandpass filter are simulated with a circuit simulator and an electromagnetic simulator. We also verify the effectiveness of the presented filter through experiments using LTCC technologies. The measured results of the fabricated filters agree well with the simulated results, and we obtain the good wide-passband characteristics with the desired notch band. The insertion losses are less than 2.5 dB in the wide passbands, which satisfies the target characteristics. Moreover, out-of-band attenuation performances almost satisfy the target characteristics: for instance, the attenuation level is higher than 33 dB from 0.8 to 2.17 GHz, 17 dB from 2.4 to 2.48 GHz, and 26 dB from 5.15 to 5.35 GHz. The fabricated filter has a size of 7.5 × 3.8 × 0.386 mm3.

An FBAR‐ and LTCC‐based RF front‐end module for Wi‐Fi and WiMAX dual‐mode systems

AbstractA compact quad‐band RF front‐end module (FEM) is proposed for Wi‐Fi and WiMAX dual‐mode systems using film bulk acoustic resonator (FBAR) and low temperature co‐fired ceramic (LTCC) technologies. The quad‐band RF FEM consists of three LTCC bandpass filters, two diplexers, one FBAR filter, two single‐pole‐double‐throw switches, and one single‐pole‐four‐throw switch. The diplexers with the bandpass filters for each mode are fully embedded in the LTCC substrate, whereas the FBAR filter and three RF switches are placed on top of the substrate. The measured performance of the embedded diplexers with the bandpass filters is compared to the simulated one, resulting in good agreement between both performances. The implemented quad‐band RF FEM provides relatively low insertion loss with high attenuation at other passband for each mode. The overall size of the module is 6.0 mm × 5.0 mm with a substrate thickness of 0.6 mm. © 2010 American Association of Anatomists Microwave Opt Technol Lett 52: 753–757, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25023

Investigation of microstrip antenna array stacked structure realized on LTCC for 60 GHz band

AbstractThis article presents the 16‐element antenna array with parasitic microstrip antenna single element. Antenna designed to operate at 60 GHz and its structure based on low‐temperature cofired ceramic (LTCC) substrate. Gain more than 18 dBi and return loss bandwidth about 20% were obtained after antenna geometry parameters optimization. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 648–652, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25006

A Highly Integrated Triple-Band RF Front-End Module for WiMAX Applications

This paper presents a compact and highly integrated triple-band RF front-end module (FEM) for worldwide interoperability for microwave access (WiMAX) applications using multilayer low temperature co-fired ceramic (LTCC) technology. The proposed RF FEM is composed of a TX triplexer, an RX triplexer, and a TX/RX switch. Both TX and RX triplexers are fully embedded in an LTCC substrate and the TX/RX switch is placed on the substrate. The TX triplexer consists of 2- and 5-GHz lowpass filters, a 3-GHz highpass filter, and a matching circuit. On the other hand, the RX triplexer consists of miniaturized 2-, 3-, 5-GHz coupled-resonator bandpass filters and a matching circuit, which are stacked up for space saving. In TX path, the RF FEM provides an insertion loss of 1.8dB, 2.1dB and 2.5dB at 2-, 3-, and 5-GHz band, respectively, with a high second-harmonic suppression characteristic. In RX path, the RF FEM also provides a low insertion loss at three passbands with high attenuation at other passbands. The size of the proposed RF FEM is only 4.0mm × 5.0mm with a substrate thickness of 0.73mm. The measured results are in good agreement with the simulated results.

Optimization of fluidic microchannel manufacturing processes in low temperature co-fired ceramic substrates

The processing of starch powder and polymer based sacrificial layer for fabrication of microfluidic structures in low temperature co-fired ceramics (LTCC) is described in the paper. Sacrificial volume material (SVM) was placed into the channel of LTCC sheets to avoid sagging by supporting embedded, three-dimensional structures such as channels, cavities during firing. Sagging of laminated structures is a common problem in the processing of the LTCC. A series of experiments were carried out for different lamination schemes which affect the quality of LTCC sheets. Samples were tested by an acoustic microscope to reveal the internal inhomogeneities and delaminations. As a consequence of burnout, the increased fraction of evolving gases from SVM requires an adequate adaptation of the firing process to provide a residue-free burnout without damaging the structure. Using thermal analysis the intensity of the evaporating gases was determined during co-firing. Based on these results, the modification of the heating p rofile could be done. It is proposed that the fabrication of embedded structures in a multi-layer LTCC platform could be achieved by controlling SVM burnout with a modified heating profile. Using this approach, fabrication of embedded channels in LTCC substrate is demonstrated.