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Fujitsu GaN Amp achieves record power density for 75-110GHz comms


New HEMT PA allows for longer distance, lower power, higher capacity communications

Fujitsu and Fujitsu Laboratories have developed a GaN HEMT power amplifier for W-band (75-110 GHz) transmissions that has a record-breaking output power density of 4.5 watts per millimeter of gate width.

The previous world record for power amplifier output density in the W-band for transmitters was 3.6 watts per millimeter of gate width with technology also developed by Fujitsu Laboratories.

Fujitsu anticipates that over 10km, this power amplifier will achieve high-bandwidth communications at 10Gbs.

Details of this technology will be announced at the 12th International Conference on Nitride Semiconductors (ICNS-12), to be held in Strasbourg, France, from July 24 until July 28th.

Development Background

Wireless data traffic from mobile communications has increased dramatically over the last few years, and with the spread of 5G and IoT devices it is predicted to increase at an annual growth rate of 1.5 times until the year 2020.

In order to build this sort of high capacity next-generation wireless communications network, attention has been focused on wireless communication technology using the high frequency W-band. The range of frequencies that can be used in the W-band is very broad, and because communication speed can be rapidly increased in this band, it is well-suited for this kind of high bandwidth wireless communication.

To increase distance and capacity, it will be necessary to expand the frequency bandwidth that can be amplified while simultaneously supporting modulation methods that can transmit more information within the same frequency bandwidth, and a strong requirement is to have less distortion when the signal is amplified.

In order to both increase the distance and capacity and decrease energy consumption with InAlGaN HEMTs, Fujitsu has developed two technologies that effectively reduce internal resistance and current leakage.

Technology to reduce internal resistance

Fujitsu has developed device technology that can reliably reduce resistance to one tenth that of previous technology when current flows between the source or drain electrodes and the GaN-HEMT device. The technology uses a manufacturing process that embeds GaN plugs directly below the source and drain electrodes, which generate electrons at high densities (fig. 1 below).

It is necessary to transport the electrons that come from the source electrode to the two dimensional electron gas field as smoothly as possible. The structure of the previous technology causes the electron supply layer to become a barrier, however, and internal resistance increases between the source electrode and the two dimensional electron gas. By applying this new technology, Fujitsu succeeded in running high currents through the transistor with significantly less resistance (fig. 2 below).

Technology to control current leakage

A current leakage occurs when the two dimensional electron gas, which moves at high speed on the boundary at the top of the channel layer, takes a detour below the gate when the transistor is in its off-state. This leakage causes deterioration in the operational performance of the power amplifier. Normally, it is possible to reduce current leakage by placing a barrier layer beneath the channel layer, but in that case the amount of two dimensional electron gas also decreases, and leads to a reduction of the drain current.

This new technology maintains high drain currents by effectively distributing InGaN to create a barrier layer below the channel layer. This reduces electron detours during operation, successfully providing significant reductions in current leakage (figures 1 and 2).

Future Plans

Fujitsu aims to apply this technology broadly to the development of power amplifiers for purposes that call for wireless communications that offer long range and higher capacity, while offering easier installation than fiber optics. The goal is to commercialize this technology in high speed wireless communication systems by 2020, with an aim to employ it in such situations as a method of restoring communications when fiber optic cables have been severed by natural disasters or as a way of setting up temporary communications infrastructure when holding events.

Part of this research was carried out with support from Innovative Science and Technology Initiative for Security, established by the Acquisition, Technology & Logistics Agency (ATLA), Japan Ministry of Defence.

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