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Experimental Transistor Breaks 600 Gigahertz
neutron_p writes "The goal of a terahertz transistor for high-speed computing and communications applications could now be within reach. A new type of transistor structure, invented by scientists at the University of Illinois, has broken the 600 gigahertz speed barrier.
A new type of transistor - built from indium phosphide and indium gallium arsenide - is designed with a compositionally graded collector, base and emitter to reduce transit time and improve current density. With their pseudomorphic heterojunction bipolar transistor, the researchers have demonstrated a speed of 604 gigahertz - the fastest transistor operation to date."
Assuming you mean the speed that will be marketed to the public, thats impossible to tell without knowing Intel, AMD, or IBM trade secrets.
That speed is dependent on the "critical path"s of the chip's logic systems & subsystems, the switching speed of a single transistor is merely a factor in that equation.
More and more we here about these new HBT circuits that are faster than all get out.
The truth is that nothing will replace CMOS anytime soon. The infrastructure is already there, and it is being optimized over and over again and has a huge work force to man it.
I once heard someone ask Intel is they ever plan to switch to HBT for speed. Their response is, and will probably be for a while, that why would they switch technologies after investing $50 billion a year in their CMOS foundries etc.
These advancements may never make it to the point that the average consumer will take notice of them.
And it may be that these academic inventions will never find any market relevance.
It all depends on the wiring delay and how many transistors deep a pipeline stage is.
fMax of a pipeline stage is 1/(switching times+wiring delays) under worst case thermal conditions. The wiring delays will stay about the same unless they're also improved by the new process, which is unlikely.
A 600GHz transistor, with really deep pipelines like the P4, and very good interconnect technology might allow 20-50GHz operation; but there are many other things to contend with (like thermals/dissipation) that can limit speed. Thermals, in turn, depend on the amount of capacitance being switched, which isn't specified here.
Even being an EE I could not answere that as Intel probably keeps that a closely guarded secret. That said, the main delay time in an Intel and AMD chip today is not the transistors, but the propogation time due to RC (resistance capacitance) in the signal path over long distances (relative to the chip size). Given that, they _may_ be able to double the Ghz, but that is all until they solve those problems. If they had a room temerature super conductor they could put in there, it would be easier to say.
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It has to do with how many gate stages the processor had in each pipeline stage - if the worst case stage has 14 gate delays, then the processor would theoretically be able to run at about 600/14GHz.
HOWEVER, there is no way the chip would actually get that close - this 604GHz oscillator is probably a single ring on a chip containing many oscillators. The average speed could easily be more in the 400-500GHz range.
Also, these transistors are BJTs, which are useless in very large xtor count chips due to their much higher current density, so it's unlikely you'll see a computer made out of them ever (processors have been almost exclusively CMOS for over 20 years)
Another article covering it here [www.newscientist.org].
The transistors in a 3.4 GHz chip are capable of switching faster than 3.4 GHz. The chip as a whole runs at that particular speed because heat dissipation becomes problematic at higher speeds. The individual components are there, but we haven't figured out how to put them all together yet to achieve higher speeds. A processor is MUCH more complicated than a single transistor... Don't expect to see 600 GHz chips made out of 600 GHz transistors. Once we get to 10 THz transistors, you might start thinking about 600 Ghz chips...
This is one just one of many reasons why silicon chip manufacturing is such an environmental nightmare....
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I agree with you on the usefulness outside of processors, digital logic, etc... But even companies like Freescale (ex- Motorola) and ADTRAN, all doing communications, use a derivitive of CMOS. Why? Because of infrastrucutre and economics. What you can do in HBT, CCD, etc you can get similar functionality and even speed (heard of strained silicon?) from CMOS.
But yes, there will be more indium phosphide op-amps, as there are currently on the market, aimed towards the high speed communications market.
I think these transistors, if found to be manufacturable, will probably be used in communications not digital logic.
Indeed. The transistors used for digital circuits (i.e., computers) are mostly MOSFETs. The chief benefit of MOS transistors is that no current goes into the gate, so power is only used when switching from one state to the other (i.e. from a 1 to a 0).
Bipolar transistors have a base current (albeit small), so they draw power even when responding to a constant signal. However, they're faster and can output a lot more current than MOSFETs, so they do have plenty of other applications.
I thought that was velocity. AFAIK, "speed" can also be used to mean "rapidity", that is how fast something happens. OTOH, "velocity" can only be used to mean how fast something moves, which is the definition you mention.
No microprocessor any time soon is likely to be constructed using bipolar junction transistors (BJTs) such as this one, pseudomorphic or otherwise. Microprocessors are generally constructed using metal-oxide-semiconductor field-effect transistors (MOSFETs), in a power-conserving organizational standard known as complementary metal-oxide-semiconductor (CMOS).
I know special methods exist to predict the f_s from low-frequency measurements. Maybe they measure the amplification at a some 'low' frequencies (GHz range) and extrapolate the gain-bandwidth pruduct from this?
I work at the local computer repair shop while going to school, and right now we check every incoming system for bristling capacitors. About 25% of the time they have bad capacitors. Why? Heat from the CPU is causing them to overheat, expand, and become useless.
If you haven't looked at your own motherboard recently, make a point to. Capacitors should have entirely flat tops. Anything else means they are on the way to destruction.
Jiga = giga... Back in the old days before processors and memory had the "giga" term that we've come to know and love, some people pronounced the "g" softly, like "j" as in "george", and these words were featured in movies like Back to the Future.
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That name is quite descriptive, for the right public. People at academia use to describe on the names everything that is different from the usual.
That make some very bad titles, but is very usefull to gather articles fast and to generate unique names.
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Spectrum analyzers could "see" up to 325 GHz directly in the early Eighties. So I'd guess that newer and better waveguide mixers are available now. A Tek 2782 or 2784 analyzer could theoretically display a harmonically-downmixed signal 1.2 THz, although I have no idea how you were supposed to acquire the signal in the first place.
You may not be able to see a single one-picosecond pulse in the time domain, but if you fire off a bunch of them in succession, you can build a picture of the waveform with repetitive sampling techniques. Technology was available in the 1960s to perform repetitive sampling in the 20-picosecond regime, so someone like Tek or Agilent or Picosecond Pulse Labs may have a sampling gate that can do the job.
I would recommend surfing around at PPL's site if you're seriously interested in this stuff. There may also be some photonic tech involved in the measurement; I haven't RTFA yet.
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You're right, I just looked at the Appl. Phys. Lett. paper. They measured it to 50 GHz and curve-fitted it to get 604 GHz, assuming a 20 dB/decade drop-off. 50 GHz can be measured with a HP network analyser.
By heterodyning with (multiplying by) a lower frequency. Look up formula for sin(at) x sin(bt).
Note also that harmonics of a given frequency can be created by passing it through a nonlinearity.
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Actually, if you look at the paper, they only measured up to 50 GHz and extrapolated a linear (in dB) decay of the gain, and found a zero crossing at 604 GHz. So they didn't measure anything at all at 600 GHz; they only found device behavior that indicated that there would be a response up to that frequency.
Filters of known frequency response can be made by knowing only their geometry. Pass the signal through several filters of different frequency responses (one at a time) and feed the output of the filter into a resistive material. Measure the temperature of the resistive material. The peak frequency of the filter which warms the resistive material the most is the (approximate) frequency being generated.
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This is done all the time in sub-mm astronomy.
The way to do it is heterodyne detection. In order to do this you need a mixer and a local oscillator. You can purchases special Schottky diode mixers that are engineered for this application.
Your local oscillator can be an off the shelf line-tunable Far-IR laser. These lasers are based on rotational transitions in small molecules in the gas phase. These lasers are pumped with a CO2 laser. If the conditions are right, the dynamics of vibrational to rotational energy transfer give you a population inversion. These lasers make nice local oscillators because they have been used for years for sub-mm wave astronomy and the frequencies of their lines are known to a large number of significant figures.
Once you have a local oscillator and a mixer, you can measure the beat frequency with an off-the-shelf spectrum analyzer.
Reply to you and the poster immediately above:
;) By compositionally graded, they mean that the junctions between the n and p regions have a specific type of gradation. In other words, they aren't uniform. I can't explain this without pictures.
This actually makes perfect sense to me. One of the specializations I took at school was electronic devices, which details the flow of electrons in semiconductors. I'll try to explain it. It's a tough job without pictures.
Indium Phosphide and Indium Gallium Arsenide are the materials used to construct the device. Generic transistors use Silicon, and you've no doubt heard of Gallium Arsenide. These are just made from a different material.
The collector, base, and emitter are the three parts of a bipolar junction transistor. Colloquially, that's a "transistor". If you're talking about a MOSFET, you'd say "MOSFET". I'm not sure if you'd capitalize it when speaking.
Transit time is how long it takes for one electron to take the trip across the transistor. Current density is current over area. It is defined in many way, but it all stems from the true form of Ohm's law. (Not the V=IR that everyone is familiar with, but J = oE )
The pseudomorphic heterojunction BJT is just a specific description of the junction type. Like the other junction, there's now way I can describe this to you without a picture.
If you know what this guy is talking about, he is making perfect sense. Look up some books online and get ready to brush up your multivariate calculus.
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When I finally learned the details of measurements for transistors like these I was disappointed.
Basically, they feed a signal into the base of the transistor, and an amplified version of the signal appears on the collector. As you increase the frequency of oscillation of the input signal, the signal amplification decreases. The frequency at which the gain has decreased to one (that is where the output signal is the same size as the input) is the frequency they are reporting here (its called Ft).
The dissapointing part relates to your question. The gain decreases with constant slope in relation to frequency. So you measure the gain up to the maximum frequency of your equipment, and then keep extrapolating the data until it reaches the gain=1 point.
The last time I was in these guys lab, the test equipment max frequency was 100 GHz, so they probably extrapolated the last 500 GHz.
I found the extrapolating part a disappointment. Who knows what kind of previously unobserved effects would turn up if the test equipment went to higher frequencies? Its cheating to say it reaches 600 GHz. The data implies that it might, if they can ever test it.
It's not the distance light can travel in that time period that matters. Typically its also not a "signal" every 1.6 picoseconds, its a change in polarity or electromotive force (i.e. Volts). You would utilize such a device more efficiently in class C operation, where the transistor is biased above ground, and only conducts for 180 degrees.
Think of it like a hose that you squeeze and let go of 600 billion times a second. The electrons don't have to necessarily change direction, just magnitude (and following ohms law, current) 600 billion times a second.
Lousy facepalm.
I think these transistors, if found to be manufacturable, will probably be used in communications not digital logic. No probably about it. Communications applications are by far and away the heaviest driving factor in (read: give the most money to) THz and ultra-high speed data processing. Demand for high-speed internet is rising as more people are subscribing and applications such as HDTV and VOIP are using more bandwidth. Of course, in order to keep up with these demands, routers need to be able to handle more and more information. Of course, even if it is infeasible and improbable for us to see this technology in our processors (as mentioned in many other posts), communication isn't the only use for THz architecture. THz emitters and detectors could be used for a lot of detection and exploration purposes, e.g. molecular compositions, plasma observation, and molecular astronomy.