Ultra-small Altum RF chips for the very highest frequencies

2 Jun 2020

In Eindhoven is the super specialized laboratory of Altum RF (located in hub Twinning of Twice Eindhoven on the TU/e Campus). As can be expected, the name stands for 'high radio frequencies'. Because that's what they do at Altum RF: they develop ultra tiny chips for antennas that can capture and amplify signals that are transmitted via high frequencies. 

Think, for example, of signals sent by satellites, or signals that will soon be used to send and receive data superfast via the new frequency band of 5G between 26.5 and 29.5 gigahertz that will be available from 2025. 

Super short wavelengths

The problem you have with such high frequencies is that the length of the waves is short, says Niels Kramer, director of Altum RF. A frequency of 30 gigahertz, for example, is only one centimetre. The higher the frequency, the shorter the wave. Now you would think: what difference does it make? One of the problems that that causes is that the electrical signals transmitted via those very high frequencies are easily attenuated, and that the distance between the antenna and the amplifier chip that is connected to it should not be too great.

Gallium

The usual material for chips, silicon, is therefore not suitable. It attenuates electrical signals that have to be transmitted via the high frequencies too much. That's why Altum uses gallium nitride, a semiconductor material made of gallium (a metal that can be extracted from coal) and nitrogen. Gallium can also be bonded to arsenic to make these types of chips. Then it is called gallium arsenide.

An advantageous property of this material is that electrons move more easily in it than in silicon, and that it conducts even better. This amplifies the electromagnetic wave so that the signal and its energy are not lost. Moreover, the electrical breakdown voltage is much higher than that of silicon. "The signal could not be amplified as much with silicon as with gallium," says Kramer. So there wasn't much choice.

Satellite communication

For some of these active antennas, up to a thousand of these chips can be used, Kramer says. "For satellite communications, for example. We also work for the ESA."

The disadvantage of gallium nitride is that it is very expensive. Therefore, it will not be used for the production of mobile phones. It will be the large telecom companies that will order the chips in large quantities for the production of base stations for the high frequency band of 5G. "We've already sent prototypes to multiple customers. They're now testing if they're functioning properly in their system."

The 5G ship was ready in two years, says Kramer. All in all, it was a job that was manageable. How quickly Altum RF can develop a 6G chip will become apparent when a customer comes along who wants it quickly, says Kramer. He won't start it any sooner.

6G chip in its early stages

The TU/e project that will deal with this in cooperation with electronics manufacturer NXP, MyWave, has nevertheless started in April. 
The challenge facing that team is enormous. Because 6G will probably use frequencies higher than 100 gigahertz from 2030 onwards, the length of which is therefore very short, the path it takes to the antenna will have to be even shorter than in the 5G chip. "We think that the antenna needs to be integrated into the chip. It can't be done otherwise. You'll come across whole new problems."

Kramer doesn't dare to predict whether this job will be done within two years. But as far as he is concerned, it is certain that they will succeed in making such an antenna-on-chip. "This is going to happen."

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