Thermal radiation in CMOS transistors

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Inside a CPU, when applying voltage to the gates of the CMOS transistor(high input), are the gate ore another components of a transistor will generate thermal radiation which will be absorbed by the neighboring transistor?
 
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  • #2
davenn
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Hi there
welcome to PF :smile:


When applying voltage to the gates of the CMOS transistor(high input), are the gate will generate thermal radiation which will be absorbed by the neighbouring transistor?
not a very clearly written question

what neighbouring transistors ?
Are you referring to multiple transistors on an IC die ?

EVERYTHING above 0K radiates thermal energy, by either radiation, conduction or convection
or some mix of all 3
 
  • #3
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Hi there
welcome to PF :smile:




not a very clearly written question

what neighbouring transistors ?
Are you referring to multiple transistors on an IC die ?

EVERYTHING above 0K radiates thermal energy, by either radiation, conduction or convection
or some mix of all 3
I mean transistors in the CPU, when voltage is applied to the CMOS gate of the transistor (high input) does the gate or another components of a transistor emit infrared radiation inside the CPU and do the neighboring transistors absorb this radiation? thanks
 
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  • #4
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As far as I know the gate is not expected to have any heat production worth mentioning. It is either the channel or the wires connecting the device to its environment where heat is generated.

It might be confusing that in (CMOS) logic devices the (internal) power dissipation is considered to be proportional to gate capacity (and frequency) since every 1-0 switching delivers one gate-worth charge towards the ground: but even in this kind of assumption the gate is just a capacitor without actual dissipation.
 
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As far as I know the gate is not expected to have any heat production worth mentioning. It is either the channel or the wires connecting the device to its environment where heat is generated.

It might be confusing that in (CMOS) logic devices the (internal) power dissipation is considered to be proportional to gate capacity (and frequency) since every 1-0 switching delivers one gate-worth charge towards the ground: but even in this kind of assumption the gate is just a capacitor without actual dissipation.
When voltage is applied to the gate, an electric field is created. Does this field affect the atoms of neighboring transistors? Or do the components of a CMOS transistor emit at least some kind of radiation when a gate voltage appears?
 
  • #6
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It is called 'crosstalk' and is a very complex issue in IC (or any other electronic) design.

Maybe you could try digging around 'crosstalk CMOS IC layout' and a bit more carefully specify your question.
 
  • #7
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It is called 'crosstalk' and is a very complex issue in IC (or any other electronic) design.

Maybe you could try digging around 'crosstalk CMOS IC layout' and a bit more carefully specify your question.
for example, a voltage (high input) is applied to the gate of the pMOS transistor inside the CPU, an electric field is created, electrons react to this field, and a p-channel is created. 1. Does infrared radiation occur when the channel opens?
2. Does the neighboring transistors absorb this radiation or is it completely block in the channel? thanks
 
  • #8
Baluncore
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With CMOS, when one gate switches a transistor on, there is another gate switching the complementary transistor off.

During the transition a very small amount of heat is generated that warms that part of the chip. Heat is generated only while the state is changing.

When the voltage on a gate input rises, the voltage on the output falls, so the electrostatic fields mostly cancel.
 
  • #9
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With CMOS, when one gate switches a transistor on, there is another gate switching the complementary transistor off.

During the transition a very small amount of heat is generated that warms that part of the chip. Heat is generated only while the state is changing.

When the voltage on a gate input rises, the voltage on the output falls, so the electrostatic fields mostly cancel.
for example, at the NOR gate, two pmos transistors are connected in series, when the voltage is applied to the gate of one of the transistors, will the transistor emit infrared photons that will propagate to the neighboring transistor?
Thanks
 
  • #10
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...infrared radiation...
I've never, ever, anywhere seen infrared radiation to be considered as anything important at the range of the components of a (general purpose) integrated circuit: guess the heat transfer capacity of Si limits the temperature difference (thus, the radiation effects) at that scale.

Could you please tell us why are you so fixed on IR radiation?
 
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  • #11
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No. IR radiation has

I've never, ever, anywhere seen infrared radiation to be considered as anything important at the range of the components of a (general purpose) integrated circuit: guess the heat transfer capacity of Si limits the temperature difference (thus, the radiation effects) at that scale.

Could you please tell us why are you so fixed on IR radiation?
Thanks for the answer, it’s just interesting when the p-channel (pmos) is created, will this channel emit thermal photons, and will these photons reach the neighboring transistors? Or will this channel is warm enough to transfer heat to an adjacent transistor?
 
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  • #12
davenn
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Thanks for the answer, it’s just interesting when the p-channel (pmos) is created, will this channel emit thermal photons, and will these photons reach the neighboring transistors? Or will this channel is warm enough to transfer heat to an adjacent transistor?
You are just repeating the same question over and over again without taking on board what all of us
have been telling you.

of course the whole chip gets hot, have you not noticed the big heatsinks and fans on modern CPU's
All that heat is an accumulation from all the sections within the chip
 
  • #13
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Thanks for the answer, it’s just interesting when the p-channel (pmos) is created, will this channel emit thermal photons, and will these photons reach the neighboring transistors? Or will this channel is warm enough to transfer heat to an adjacent transistor?
Yes. The thermal photons are emitted and this emission is used in the diagnostics of the both digital and power ICs. The radiative heat transport is not effective compared to thermal conduction in semiconductor ICs though - the emissivity of silicon or GaAs is low at thermal wavelengths, while thermal conductivity is close to that of metals. Therefore, nearly all thermal crosstalk effects in ICs are coming from thermal conduction (phonons transfer), not the radiation (photons transfer).
 
  • #14
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will this channel emit thermal photons, and will these photons reach the neighboring transistors?
The whole 'photon' thing is seriously misleading in this context. Every piece of material always emits (and absorbs) thermal radiation, what is an incoherent, continuous spectra mixed flow of photons.
Since this always happening, 'yes' is a kind of safe answer: however this answer (being a truism) has no real meaning or value.

So far this topic is kind of like being fascinated by the continuous change of traffic lights.
Yeah, traffic lights does that. That is what they are. Then what?

Could you please make an attempt to clarify your point to us?
 
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  • #15
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The whole 'photon' thing is seriously misleading in this context. Every piece of material always emits (and absorbs) thermal radiation, what is an incoherent, continuous spectra mixed flow of photons.
Since this always happening, 'yes' is a kind of safe answer: however this answer (being a truism) has no real meaning or value.

So far this topic is kind of like being fascinated by the continuous change of traffic lights.
Yeah, traffic lights does that. That is what they are. Then what?

Could you please make an attempt to clarify your point to us?
Thanks for the answer. I just did not know that radiation also occurs inside the material. And then when the voltage comes to the gate, the conductive channel will radiate more heat than when there is no voltage?
 
  • #16
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Yes. The thermal photons are emitted and this emission is used in the diagnostics of the both digital and power ICs. The radiative heat transport is not effective compared to thermal conduction in semiconductor ICs though - the emissivity of silicon or GaAs is low at thermal wavelengths, while thermal conductivity is close to that of metals. Therefore, nearly all thermal crosstalk effects in ICs are coming from thermal conduction (phonons transfer), not the radiation (photons transfer).
Thanks.
And the electric field created by the voltage at the gate will spread to the neighboring transistor?
 
  • #17
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Thanks.
And the electric field created by the voltage at the gate will spread to the neighboring transistor?
At normal circumstances, no. If "voltage spread" happens between adjacent nmos and pmos, the destructive "latchup" effect may happen.
 
  • #18
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At normal circumstances, no. If "voltage spread" happens between adjacent nmos and pmos, the destructive "latchup" effect may happen.
Thanks.
Does this mean that the electric field will not propagate beyond the channel at all?
 
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  • #19
berkeman
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Thanks.
Does this mean that the electric field will not propagate beyond the channel at all?
If it did, that would be a design/layout error.

Can you say why you are asking about this?
 
  • #20
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If it did, that would be a design/layout error.

Can you say why you are asking about this?
the electric field is infinite, just the intensity drops, is that right? Is there really such a good isolation between transistors in the CPU that the electric field will not at least slightly affect the neighboring transistors?
 
  • #21
berkeman
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the electric field is infinite, just the intensity drops, is that right? Is there really such a good isolation between transistors in the CPU that the electric field will not at least slightly affect the neighboring transistors?
You mean "infinite in extent", and sure. But it's a matter of the magnitude of the field -- if it is many orders of magnitude lower than it is inside the transistor, it will not have any measurable effects.

The gate field is very much localized under it, and it is shielded to some extent from nearby cells by the gate and drain...

https://wiki.analog.com/_media/university/courses/electronics/text/chptr8-f13.png?w=600&tok=fe77fe

1576072103538.png
 

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