With the development of carbon nanotubes and graphene, scientists were given an entirely new collection of materials to work with: sheets and tubes that could be consistently made with thicknesses roughly those of individual atoms. These materials hold the promise of building electronic devices with dimensions smaller than is currently possible through any other process and with properties that can be tuned by using different starting materials.
So far, most of the attention has gone to re-creating new versions of familiar devices. But a new paper by a group of researchers in Shanghai looks into what can be done if you're not constrained by the sorts of devices we currently make in silicon. The result is a device that can perform basic logic in half the transistors silicon needs, can be switched between different logical operations using light, and can store the output of the operation in the device itself.
Small footprint transistor architecture for photoswitching logic and in situ memory (DOI: 10.1038/s41565-019-0462-6) (DX)
(Score: 0) by Anonymous Coward on Wednesday May 29 2019, @03:33AM (16 children)
I'm most confused by how a transistor works at all.
A transistor works with electricity. Electricity is either on.. or off. You have voltage, or you don't. How do you say, "IF there is voltage, THEN apply voltage." ? How do you get "if" out of literally presence or absence? There's no "if electricity then electricity else electricity" in "yes or no".
(Score: 4, Insightful) by RS3 on Wednesday May 29 2019, @04:41AM (2 children)
In the digital world we think of 1 or 0, on or off, and we design circuits and systems to behave this way. But the dirty little secret is that pretty much all of the digital circuits are analog under the hood. We decide what voltages constitute a digital 0 and 1. So for the most common digital logic circuitry, "TTL", we define a logic 0 as less than 0.8 V, and a logic 1 as above 2 V (and up to 5 V, because TTL runs on 5 V).
(Score: -1, Troll) by Anonymous Coward on Wednesday May 29 2019, @12:36PM (1 child)
Pretty much the most useless answer to the original question, but the highest rated.
(Score: 3, Insightful) by RS3 on Wednesday May 29 2019, @03:16PM
Great example of how you ACs are a cancer: your comment gives no useful information, nor contributes in any helpful or positive way.
AC = piss on parade.
Do you have a question, or are you just so full of crap you have to dump it anywhere you find an opportunity?
(Score: 5, Informative) by vux984 on Wednesday May 29 2019, @04:44AM (4 children)
You can kind of think of a transister much like an electromagnetic switch.
Suppose you had a single wire, with power applied to one end and an iron connector in the middle on a spring that keeps the circuit open; so electricity can't flow.
+ __________/ _________ -
Then you place an electromagnet just below the spring on a secondary circuit. When you turn the electromagnet on, it pulls the switch closed.
Apply power to the main circuit but not the electromagnet circuit, and the switch is open, and there's nothing getting through.
Apply power to just the electromagnet circuit, the switch closes, but there's nothing coming through.
But when you apply power to both circuits, the 2nd closes the switch on the main circuit, and the power from the first flows through.
A modern transister is the same idea, except using the properties of semiconductors to open and close the switch instead of a spring and a magnet. It's even the same construct with a main power 'emitter', connected to a 'drain', and then another lead is called 'gate'. You power the 'gate' lead and the electricity can flow from the source to the drain. The essential bit is that the application of current to the gate changes the conductivity of the material allowing the current to flow. hence the term "semi-conductors".
(Score: 0) by Anonymous Coward on Wednesday May 29 2019, @03:06PM
That's a PNP transistor. An NPN sets a ground path, then there's PN and 4 lead transistors.
(Score: 3, Informative) by RS3 on Wednesday May 29 2019, @03:49PM (2 children)
That's a great analogy. Silicon is called a "semiconductor" because just like the electromagnetic switch (relay) you described, we can control the flow of electrons through it by introducing an electric field somewhere in the middle of the flow. The physics is far too much to go into here.
There are many other semiconducting materials. Germanium was very popular in the 1950s and 60s, and is still used in a very few applications. Gallium-Arsenide is another popular one.
In your last paragraph you referred to some terms and they're a little mixed. It's not going to matter unless someone tries to design or build something.
Emitter, Collector, and Base are the parts of a BJT (Bipolar Junction Transistor) and they're generally NPN or PNP. The terms are somewhat descriptive, called: collector and emitter due to electron flow in an NPN, and base because it was the physical base plate of the original construction. Current between the base and emitter controls the current between the collector and emitter.
Source, Drain, and Gate are the parts of an FET (field-effect transistor), which was the first type invented. Main current flows through the source and drain, and the gate, well, gates that current, like the electromagnet in your analogy.
Simplified: the source and drain are connected to a (tiny) bar of either P or N doped silicon.
There are JFETs, where the gate is a PN junction (or NP), and IGFETs, or MOSFET as they're generally called, where the gate is an insulator and tiny metal plate. In either case, the volts applied to the gate (electron "charge") produces an electric field that causes more or less electron flow in the main semiconductor material, thus controlling the flow of electrons between the source and drain.
Electronic circuit-wise, FETs behave very much like vacuum tubes, or "electron valves" as the Brits descriptively call them. Electrons flow from the cathode to the plate, and are controlled by a voltage on the grid.
(Score: 2) by vux984 on Saturday June 01 2019, @03:21AM (1 child)
Argh. Thanks for the clarification. I'd meant to just stick with FET, source/drain/gate. Not sure why i said emitter. I was originally going to describe BJT as well but thought it would be simpler to stick to just one, and FET is, to my mind at least, the most accessible.
I'm a CS grad, I got some exposure to microarchitecture, bus design, clock signals, and pipeline design; and developed finite state machines with gates... but never got any formal education lower down than that. From what I've read even an "antique" FET transistor is too difficult to easily produce as a "science project". I'd have loved to have made one with the kids.
(Score: 2) by RS3 on Saturday June 01 2019, @06:43AM
You're quite welcome and please never feel badly about terminology. Emitter, source, electron spray nozzle, tomato, tomatto, potato, potatto, let's call the whole thing off! I mix up terminology all the time. People's names too.
Great ASCII sketch, btw!
It's awesome and impressive that you've learned so much about hardware in a CS program. Lots of great analogies- a valve, relay, floodgate. Somewhere in one of these discussions (maybe on another board?) I recently wrote about digital logic being largely CMOS- FETs, but BJTs are used a lot too. As an EE I should know why you'd choose one over the other but I'm not 100% sure. Over the years we've seen both types used for digital, analog, high-speed/frequency, high power, high voltage, etc. Now we have FETs that have extremely low ON resistance so they're being used for power circuits, but so are IGBTs.
Yeah, it would be super-cool to build an FET. You need very pure silicon, and I'm not sure how it's done but it's easy enough to look up. There was (and still is) a silicon lab at my college. I don't think I ever went in there- wasn't interested in device physics, but it turns out to be very lucrative. Hmmmm. Anyway, in my days they weren't able to produce usable silicon- too much impurity, but now that lab makes chips, it's all lit with amber lighting (not sure why), some low class number clean room, air locks / air showers, clean suits, etc. My hunch is the silicon is purified with a lot of heat in a vacuum chamber, and it's grown as a big crystal- need the lattice structure for electron flow, and then infusing ("doping") boron or arsenic or whatever. I love the physics but the actual manufacturing bored me, and otherwise I'm into manufacturing. All the hard work we EEs do- we even breath arsenic vapors to give you guys something to play with. :-}
Your homework assignment: read about 4-layer silicon devices (SCRs, TRIACs) (an SCR stays "on" as long as there's current flowing through it, so it's a 1-transistor memory cell, rather than a 2-transistor "flip-flop"). I'm full of useless information...
(Score: 1, Interesting) by Anonymous Coward on Wednesday May 29 2019, @05:35AM
My only thought to add regarding explaining transistors would be that in very general terms a transistor could be thought of similar to a rudder, if there is some powerful input available it can be guided (which direction the power goes) using a relatively weaker input. The transistor can be used like that where when properly set up a small input at one terminal can control the rate that power can flow at the other terminals. The usefulness is using a weaker electric signal to regulate, to increase or decrease another signal or power source. In very general terms the transistor is often compared to a relay - an electrically controlled switch. The mechanism though, in a transistor is one where there is something like a draw bridge where application of a signal let's the bridge down. I hope that helps.
(Score: 0) by Anonymous Coward on Wednesday May 29 2019, @06:21AM (1 child)
three layers of silicon, alternating in electrical charge, the charge property is determined by the chemical composition of the silicon when 'doped' by different elements.
One terminal connects to each layer.
apply the appropriate charge to the middle layer and you negate the charge difference between the two outer layers, allowing current to flow across the device.
this gets you hard switching, on and off.
for amplification, you pre-bias the transistor with resistors, so it's almost conducting, then when you feed a signal in it should amplify it.
(Score: 2) by RS3 on Wednesday May 29 2019, @08:18AM
Yes, you've described a BJT- Bipolar Junction Transistor, and they're used in all kinds of circuits, including TTL logic. But most of RAM, CPU, GPU, etc., are MOSFET (metal oxide semiconductor field-effect transistor).
(Score: 0) by Anonymous Coward on Wednesday May 29 2019, @06:26AM
Nobody's perfect, don't blame yourself.
The transistor works if and only if it has electricity, that's a given (your considerations above are void of any meaning, forget about them).
Then:
1. a transitor-as-we-know-it has one input and one output
2. when operating in logic/binary mode, a single transitor-as-we-know-it you can implement only a "unary gate": either a repeater (if value in input then value in output) or a NOT gate (if value in input then NOT value in output). If you want a binary logic operation, you'll need to use at least two transitors.
Now, here come these guys who say: "we implemented a transistor with two inputs and one output".
"Hey, ho!" you say. "What's the truth table [wikipedia.org] of the output in depending the values in inputs"
So they say: "Here's the nice thing. If we keep the thing in the dark, an ON output can be iff both inputs are ON - so here we have an AND gate. However, if we shine a flashlight with a particular wavelength on that transistor, it's enough that only (and any) one of the inputs is ON for the output to be ON too - so there you have the OR gate".
(Score: 1, Informative) by Anonymous Coward on Wednesday May 29 2019, @03:28PM
think of transistors simplistically as voltage controlled variable resistors. in a MOSFET, applying voltage to the gate (different FET styles have different forward bias requirements) changes the conductivity of the main channel (source to drain). In digital logic, the main channel is driven to either saturation (full on - minimum resistance) or cutoff (full off - maximum resistance).
(Score: 0) by Anonymous Coward on Wednesday May 29 2019, @05:20PM
A transistor is like a valve controlling the flow of electricity. You turn the valve on or off by applying a voltage or not to the control input ("base" or "gate" depending on type of transistor), and in turn electrical current flows through the transistor (or not) between the inflow and outflow ports ("collector" and "emitter", or "drain" and "source" depending...)
(Score: 2, Insightful) by janrinok on Wednesday May 29 2019, @05:26PM
There are literally hundreds of sites on the Web that will explain this to you in any desired degree of complexity. Google for one or two of them...
I strongly suspect that you a just trolling, but I'll wait and see what other 'contributions' you make to this and other discussions before deciding.
[nostyle RIP 06 May 2025]
(Score: 0) by Anonymous Coward on Thursday May 30 2019, @05:55AM
"A transistor works with electricity. Electricity is either on.. or off. You have voltage, or you don't."
No on both assertions.
1) Transistors are CURRENT operated. The voltage drop across the Base-Emitter junction is pretty stable.
2) Electricity is not either on or off, it's got a (nearly) infinite number of conduction states (all depending on the current across the PN (or NP) junction).
3) There are things called photo-transistors that operate by 'shining' light on the PN (or NP) junction.
(Score: 1, Funny) by Anonymous Coward on Wednesday May 29 2019, @06:28AM
That is all.