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Fujitsu Develops GaN HEMT For High-output Mm-wave Transceivers

The gallium nitride device integrates multiple chips within a single unit to enable more compact radars and wireless communications equipment
Fujitsu Laboratories Limited has developed a GaN HEMT-based transceiver module technology that features an output of 10 W.


A HEMT is a field-effect transistor that takes advantage of operation of the electron layer at the boundary between different semiconductor materials that is relatively rapid compared to that within conventional semiconductors. HEMT technology now underpins much of today's fundamental IT infrastructure, including satellite transceivers, wireless equipment, GPS-based navigation systems, and broadband wireless networking systems.


The device operates at frequencies up to the millimetre-wave band which is the radio band between 30 and 300 GHz. It is used for high-capacity wireless communications, automobile radar, and other applications.


Until now, developing high-output modules that operate in the millmetre-wave band has required modules consisting of separately packaged components to allow for sufficient heat dissipation. As a result, it has been difficult to produce compact modules.


What's more, because the occurrence of signal loss tends to increase in internal module terminal connector components at higher frequencies, reaching millmetre-wave operations has proved to be challenging.


The new high-output millmetre-wave transceiver module developed by Fujitsu Labs uses a heat sink embedded with multilayer ceramic technology capable of efficiently dissipating heat. Compared to previous designs, heat dissipation improved by a factor of five times, enabling 10 W-class output levels.


Fujitsu Laboratories devised a wideband connector structure that reduces loss at higher frequencies in the heat sink. With the new connector structure, high frequency signals passing through the module can be transmitted at up to 40 GHz, two times the frequency levels of previous designs.


With dimensions of 12 mm × 36 mm × 3.3 mm, the new module measures less than 1/20 the size of conventional combined unit.


Using the new technology, it is possible to combine multiple chips within a single unit, thereby enabling the development of more compact radar devices and wireless communications equipment.


Details of the new technology will be presented at the IEEE MTT 2013 International Microwave Symposium (IMS2013), to be held beginning June 2nd in Seattle, Washington.


GaN HEMT


GaN is used as a material in blue LEDs. Compared to the conventional semiconductor materials of silicon and GaAs, GaN features a high electron transfer rate and relative resistance to the breakdown caused by voltage. Given these characteristics, GaN HEMTs - or transistors that use GaN - show promise for high-output, exceptionally efficient operations.


Background


In line with the advancement of a network-based society, radio wave demand in a variety of wireless systems is expected to increase even further. For example, in the field of smartphones and other wireless communications, there is a shortage of available frequencies. Using millmetre waves to accommodatethis increase in demand is being given consideration. Likewise, aircraft currently employ the 10 GHz frequency band, but a move toward usage of higher frequencies is expected to take place in the future.


Current generations of high-output millmetre-wave transceiver modules consist of separately packaged transmitter and receiver components. Being able to integrate both functions in a single unit, however, will enable equipment to become more compact.





Figure 1: Usage scenarios for the millmetre-wave band


Technical Issues


Transceiver modules, needed for millmetre-wave communications and radar, must possess wideband capabilities for operating in the millmetre-wave band, as well as high-output performance sufficient enough to cover wide geographic areas.


When developing a transceiver module with 10 W-class high-output power, it is critical to improve the transceiver module's heat dissipation characteristics, as heat generation intensifies in tandem with higher output levels.


What's more, it is also necessary to reduce signal loss in connector components. This is because, at higher frequencies, loss increases in the components connecting the chip and the wiring that transmits a signal.


Newly Developed Technology


Fujitsu Laboratories has developed a compact, high-output transceiver module that uses GaN-HEMT and operates in the millmetre-wave band.





Figure 2: Diagram of the millmetre-wave GaN transceiver module





Figure 3: Photo and structure of the millmetre-wave GaN transceiver module


Results


This new technology will make it possible to achieve high-output transceiver functionality with a single unit, thereby leading to improved performance and more compact and lighter equipment for wideband communications and radar systems.


Future Developments


Fujitsu Laboratories plans to put this technology to use in a wide range of applications that require compact modules with high output across wide bandwidths, including wireless devices and radar systems.




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