Foreword

5G, the fifth-generation broadband cellular network technology standard, is supposed to enable super-fast download speeds, end dropped and buffered calls, and greater connectivity to advance the development of self-driving cars, remote surgery and the Internet of Things.

In fact, 5G adoption is still in its early stages, Michael Hill, chief technology officer at Skyworks Solutions, an advanced semiconductor company based in California, said recently. In a paper published in Applied Physics Letters, published by the American Physical Union (AIP), Hill and his colleagues provide an overview of emerging 5G technologies and show how enhanced ceramic materials could play a key role in 5G development.

Ceramic materials have long been used in wireless communication network technology for mobile devices and base stations. As a result, enhanced ceramics have been a central focus for improving 5G capabilities. Hill's team, however, has developed a ceramic to augment a device critical to 5G applications: circulators.

The circulator, usually made of insulating ceramic material made of yttrium iron garnet, is a three-port device that acts as a traffic circle, keeping the signal flowing in one direction and allowing the receiver and transmitter to share an antenna. To significantly increase the energy density to accommodate higher frequencies, the researchers partially replaced yttrium with bismuth, a heavy element that increases the dielectric constant of the ceramics. Replacing bismuth also miniaturized the circulator.

(Image from the Internet)

For many years, many researchers have tried to solve some problems by doping yttrium iron garnet with other rare earth materials.

=== = Polycrystalline Bi replaces yttrium iron garnet ===

The dielectric frequency behavior of yttrium iron garnet has been replaced by polycrystalline Bi. The Y3-xBixFe5O12 sample was prepared by solid - state reaction method. The relative dielectric constant (εr) and loss Angle tangent (Tan δ) were measured by impedance analyzer in the frequency range from 1 kHz to 1GHz. The volume resistivity of the material was measured by a DC voltage source and a micro ammeter. The results show that Bi substitution greatly reduces the relative dielectric constant and loss tangent of yttrium iron garnet at a frequency below 100 kHz, and increases the volume resistivity of the material.

===La doping on yttrium iron garnet ===

Some researchers have prepared La-doped Y3Fe5O12 series ceramic samples by using the traditional solid-phase sintering method, and studied in detail the effects of La doping on the magnetic and magnetic dielectric properties. The results show that with the increase of La doping amount, the saturation magnetization and intrinsic magneto-dielectric effect first increase and then decrease, which is attributed to the non-monotonic change of Fe2+ content. It is suggested that the substitution of Y3+ by La3+ with a larger ion radius leads to lattice expansion and possible ion displacement of Y3Fe5O12, and the competitive effect of these two factors causes the Fe2+ content to increase at first and then decrease with the increase of La content. The non-monotonic variation of Fe2+ ion content leads to the corresponding variation trend of saturation magnetization and magnetic dielectric effect. Large saturation magnetization and magnetic dielectric effect are obtained at the same time when La content is 0.3, and the magnetic dielectric coefficient reaches -5% at room temperature at 106 Hz and 0.9T.This indicates that non-magnetic large ion radius doping can effectively regulate the magnetic and magnetic dielectric effects of YIG materials.

=== = Zirconium-doped yttrium iron garnet ===

(Y3-xCax)(Fe5-xZrx)O12 with the doping amount of x=0 ~ 0.5 was prepared by sol-gel method. Pure phase Yig-doped samples were obtained by low temperature sintering at 1100℃.With the increase of the doping amount of Zr, the XRD diffraction peak gradually shifted to a lower Angle, and the calculated lattice constant showed an increasing trend, indicating that the cell volume was increasing. Magnetic characterization showed that the MS value of the sample was the highest when the doping amount was x=0.3.With the increase of doping amount, the magnetic properties decrease due to the weakening of the super exchange effect. As the doping amount increases, the HC of the sample generally decreases. This is because, as a non-magnetic ion, the incorporation of Zr can reduce the magnetic anisotropy constant of Yig, thus reducing the coercivity of the doped sample.

High-power gallium nitride switches could replace circulators as the 5G battle continues to heat up, suggesting that 5G development is still in its early stages." Millimeter-wave technology is likely to remain in the Wild West for a while, as one technology is likely to be replaced only quickly by another," Hill said.

Reference source:

[1] "Enhanced ceramics" developed by US scientists may play a key role in the development of high-frequency 5G technology. CaiLian Press

[2] Effect of La doping on magnetic and dielectric properties of yttrium iron garnet ceramics, by Wu Huarui etc.

[3] Study on magnetic properties of low temperature sintered zirconium doped yttrium iron garnet (YIG), by Wang Lujie, etc.

[4] Dielectric frequency behavior of Bi substituted yttrium iron garnet, by Zhao Hongjie, etc.