Ferrite Low Temperature Co-fired Ceramic Research Articles

Influence of sintering temperature on the magnetic properties of LTCC ferrite tape for multilayer component applications

Influence of sintering temperature on the complex permeability, the core loss density and B-H hysteresis loop of ferrite low-temperature co-fired ceramic (LTCC) multilayer toroidal cores is presented. Ferrite LTCC toroidal cores are fabricated from 22 layers of ESL 40011 tapes sintered at 885, 1000, 1100 and 1200 °C. Applying the sinusoidal excitation, the measurements are performed in the frequency range from 10 kHz to 5 MHz and for magnetic flux density from 2 to 100 mT. The measurements of sintered multilayer cores were done in order to investigate the difference in magnetic properties among those samples. This investigation enables to find optimal sintering temperature of multilayer ferrite cores which used in different multilayer magnetic component applications.

A Ferrite LTCC-Based Monolithic SIW Phased Antenna Array

In this paper, we present a novel configuration for realizing monolithic substrate integrated waveguide (SIW)-based phased antenna arrays using Ferrite low-temperature cofired ceramic (LTCC) technology. Unlike the current common schemes for realizing SIW phased arrays that rely on surface-mount component (p-i-n diodes, etc.) for controlling the phase of the individual antenna elements, here the phase is tuned by biasing of the ferrite filling of the SIW. This approach eliminates the need for mounting of any additional RF components and enables seamless monolithic integration of phase shifters and antennas in SIW technology. As a proof of concept, a two-element slotted SIW-based phased array is designed, fabricated, and measured. The prototype exhibits a gain of 4.9 dBi at 13.2 GHz and a maximum $E$ -plane beam-scanning of ±28° using external windings for biasing the phase shifters. Moreover, the array can achieve a maximum beam-scanning of ±19° when biased with small windings that are embedded in the package. This demonstration marks the first time a fully monolithic SIW-based phased array is realized in Ferrite LTCC technology and paves the way for future larger size implementations.

Study of a Ferrite LTCC Multifunctional Circulator With Integrated Winding

This paper shows a study of a new ferrite low-temperature cofired ceramic (LTCC) circulator with integrated winding. The external magnets used in traditional circulators must be strong to overcome the ferrite’s demagnetization factor. The novel circulator presented herein uses an embedded winding within the ferrite to magnetize the material from the inside, thereby significantly reducing the demagnetization effects. Because of the controllability of the bias field, the resulting device is also multifunctional: when the windings are energized by a current, the device operates as a dynamic circulator in which the circulation direction can be changed by switching the direction of the current. If an external magnet is placed on the circulator, its operating frequency can be changed by adjusting the bias current. Unlike other LTCC circulators with external magnets, the proposed device can even operate as a power splitter by removing the bias current. A circulator prototype has been characterized in three states: unbiased, biased by windings, and biased by windings and external magnets. When no current is applied, the transmission of each port is about −5 dB with a return loss better than 20 dB at 14.8 GHz. When a current of 300 mA is injected into the windings, the measured insertion loss and isolation of the circulator are approximately 3 and 8 dB, respectively, whereas the return loss is better than 20 dB at 14.2 GHz. When external magnets are added in addition to a current of 200 mA, the insertion loss and isolation improve to 1.6 and 23 dB, respectively, at 14.2 GHz. The variation of the circulator’s working frequency is 0.6 GHz. This is achieved first by the change of internal magnetization $\boldsymbol {M}$ when current is less than 120 mA, then the heat due to the winding increases the ferrite’s $\mu _{\textrm {eff}}$ , leading to more frequency shifting. The total size ( $L \times W \times H$ ) is $8~\textrm {mm} \times 8~\textrm {mm} \times 1.1$ mm.

The Effect of Self-Heating on the Performance of a Tunable Filter With Embedded Windings in a Ferrite LTCC Package

Traditionally, ferrite-based tunable filters are biased by large and bulky electromagnets, which require high currents to overcome the dissipated fields at the air interface between the electromagnet and the ferrite substrate. This problem has been solved by implementing the windings inside the package using ferrite low-temperature co-fired ceramic (LTCC). However, these embedded windings, which are densely packed, generate heat that affects the characteristics of the ferrite material. In this paper, we investigated the heat effects due to embedded windings in ferrite LTCC filters. We also incorporated the heating effects into an electromagnetic simulation model and achieved a good agreement between the simulations and the measurements. We found that increasing the temperature of the filter module from 0 °C to 190 °C by external heating causes the center frequency of the filter to shift by about 1 GHz. Alternatively, when a dc current is passed through the bias windings, heat is generated in the windings to a temperature of 250 °C measured at 260 mA of current. This heat causes the tunability of the filter to increase by more than 2%.

Reliability of Au-Ti for High Temperature Termination on Ferrite LTCC Inductors

While ferrite Low Temperature Co-fired Ceramic (LTCC) inductor and transformer developments have undergone thermal shock and high temperature aging that focused on the stability of their electrical characteristics (resistance, inductance), little attention has been paid to their termination reliability at high temperatures. Testing has been done on AgPt and AgPd terminations with Ag5Cd95 and Pb88Sn10Ag2 solders for 2000 and 25 hrs, respectively. However, Ag5Cd95 is unusable in commercial applications due to ROHS restrictions while Pb88Sn10Ag2 is undesirable because of the high lead content. Sn96 solder and wire bonding are common attachment methods that have not been vetted. Initial investigations show that high Sn solders may interfere with bonding between the AgPt and AgPd termination materials and the ferrite bulk of the part. An alternative terminal structure for using Sn96 solder is created by electroplating Au and Ni; however, electroplating to ferrite is challenging due to the masking involved. Also, the preferred materials for wire bonding are thick film, thin film or electroplated Au. To this end an alternative termination structure using Au sputter deposited onto sputter deposited Ti is being investigated. This structure was chosen for its potential to be a lower cost alternative to thick film Au and for its potential for simpler manufacturing than electroplating. Tests involved measuring bond strength and resistance after thermal ageing and thermal shock. Baseline solder joint pull tests show strength comparable to other termination methods. Some issues with solder wetting of the terminals have been noted.

Embedded Ferrite LTCC Inductors

This paper presents for the first time one realization of simple planar inductor realized inside the stack of ferrite LTCC (Low Temperature Co-fired Ceramic) tapes. Presented inductor is one layer square spiral fabricated in the LTCC technology. In order to point out benefits of implementation of ferrite material on inductor inductance, the same inductor geometry was fabricated between two dielectric LTCC tapes. Commercially available LTCC material (both ferrite and dielectric) were implemented for the realization of proposed inductors. Designed structures were characterized and obtained experimental results show that even implementation of a very thin layer of ferrite material around inductor lines drastically increases its inductance. For the same inductor design that occupies the same chip area the inductance enhancement over 11 times is achieved. In addition this enhancement is followed with maintenance of good performance of the inductor.

Ferrite LTCC-Based Antennas for Tunable SoP Applications

For the first time, ferrite low temperature co-fired ceramic (LTCC) tunable antennas are presented. These antennas are frequency tuned by a variable magnetostatic field produced in a winding that is completely embedded inside the ferrite LTCC substrate. Embedded windings have reduced the typically required magnetic bias field for antenna tuning by over 95%. The fact that large electromagnets are not required for tuning makes ferrite LTCC with embedded bias windings an ideal platform for advanced tunable system-on-package applications. Measurements of rectangular microstrip patch antennas on a ferrite LTCC substrate display a maximum tuning range of 610 MHz near 12 GHz. Two different bias windings and their effect on the antenna performance are discussed, as is the effect of antenna orientation with respect to the bias winding. The antenna radiation patterns are measured under biased and unbiased conditions, showing a stable co-polarized linear gain.