Vacuum tubes on silicon

Read an interesting article the other day about researchers at NASA having invented a vacuum tube on a chip (see ExtremeTech, Vacuum tube strikes back). Their report was based on an IEEE Spectrum article called Introducing the Vacuum Transistor.

Computers started out early in the last century being mechanical devices (card sorters), moved up to electronic sorters/calculators/computers with vacuum tubes and eventually transitioned to solid state devices with the silicon transistor. Since then the MOS and CMOS transister have pretty much ruled the world of electronic devices.

Vacuum tube?

Vacuum tubes had a number of problems not the least of which was power consumption, size and reliability. It was nothing for a vacuum tube to burn out every couple of times it was powered on and the ENIAC (panel pictured here) had over 17,000 of them, took over 200 sq meters of space, used a lot (150KW) of power and weighed (27 metric) tons.

Of course each vacuum tube was the equivalent of just one transistor and the latest generation Intel Quad Core processors have over 2B transistors in them. So to implement an Intel Quad Core processor with vacuum tubes this might take over 3,000 football fields of space and over 17GW for power/cooling.

There were plenty of niceties with vacuum tubes not the least of which was their nice ruler flat frequency response, ability to support much higher frequencies, significantly less prone to noise and had less problems with radiation than transistors.  This last item meant that vacuum tubes were less susceptible to electromagnetic pulses. Many modern musical/instrument amplifiers are still made today using vacuum tube technology due to their perceived better sound.

But the main problems was their size and power consumption. If you could only shrink a vacuum tube to the size of a MOS field effect transistor (FET) and correspondingly reduce its power consumption, then you would have something.

NASA shrinks the vacuum tube

NASA researchers have shrunk the vacuum tube to nanometer dimensions in a vacuum- channel transistor. They believe it can be fabricated on standard CMOS technology lines and that it can operate at 460GHz. 

This new vacuum-channel transistor marries the benefits of vacuum tubes to the fabrication advantages of MOSFET technology. Making them as small as MOSFET transistors eliminates all of the problems with vacuum tube technology and handily solves a serious problem or two with MOSFETs.

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One problem with MOSFET technology today is that we can no longer speed it up any faster than a 4-5GHz.  This limit was reached in 2004 when Intel and others determined that clock speed couldn’t be sped up much more without serious problems resulting and as a result, they started using additional transistors to offer multi-core processor chips.  A lot of time and money is continuing to be spent on seeing how best to offer even more cores but in the end there’s only so much parallelism that can be achieved in most applications and this limits the speed ups that can be attained with multi-core architectures.

But a shrunken vacuum tube doesn’t seem to have the same issues with higher clock speeds.  Also, there is a serious reduction in power consumption that accrues along with reduction in size.

The vacuum in a vacuum tube was there to inhibit electrons from being interfered with by gases. With the vacuum-channel transistor they don’t think they need a vacuum anymore due to the reduction of size and power being used but there’s a little problem on how to creating a helium filled enclosure which they feel will work instead of a vacuum. NASA feels that with todays chip packaging this shouldn’t be a problem.

Also, their current prototypes use 10V but other researchers have reduced other vacuum-channel transistors to use only 1-2v. As of yet the NASA researchers haven’t fabricated their vacuum-channel transistors on a real CMOS line but that’s the next major hurdle.

Imagine a much faster IT

A 400GHz processor in your desktop and maybe a 200GHz processor in your phone/tablet could all be possible with vacuum-channel transistors. They would be so much faster than today’s multi-core systems, that it would be almost impossible to compare the two. Yes there are some apps where multi-core could speed things up considerably but something that’s 10X faster than todays processors would operate much faster than a 10 core CPU. And it still doesn’t mean you couldn’t have multi-core vacuum-channel systems as well.

SSD or NAND flash storage is essentially based on CMOS transistors and the speed of flash is a somewhat of a function of the speed of its transistors.  A 400GHz vacuum-channel transistor could speed up flash storage by an order of magnitude or more. Flash access times are already at the 7µsec level (see my posts on MCS and UltraDIMM storage here and here).  How much of that 7µsec access time is due to the memory channel aand how much is a function of the SanDisk SSD storage is an open question. But whatever portion is on the SSD side could be potentially reduced by a factor of 10 or more with the use of vacuum-channel transistors.

From a disk perspective there are myriad issues that effect how much data can be stored linearly on a disk platter. But one of them is the speed of switching of electromagnetic  (GMR) head and the electronics. Vacuum-channel transistors should be able to eliminate that issue at least in the electronics and maybe with some work in the head as well so disk densities would no longer have to worry about switching speeds. Similar issues apply to magnetic tape densities as well.

Unclear to me how faster switching time would impact network transmission speeds. But it seems apparent that optical transmission times have already reached some sort of limit based on light frequencies used for transmission. However, electronic networking transfer speeds may be able to be enhanced significantly with faster speed switching.

Naturally, WIFI and other forms of radio transmission are seriously impeded by the current frequency and power of electronic switching. That’s one of the reasons why radio stations still depend somewhat on vacuum tubes. However, with vacuum-channel transistors problems with switching speed go away.  Indeed, NASA researchers believe that their vacuum-channel transistors should be able to reach terahertz (1000GHz) transmission switching. Which might make WIFI almost faster than any direct connect networking today.

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Photo Credit(s): ENIAC panel (rear) by Erik Pittit, The Vacuum Tube Transistor from IEEE Spectrum

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