For those of you who got stuck at the part where he says that the increased negative charge near the channel requires a more positive potential to balance the excess negative charge, I have an alternate explanation. For this consider the body terminal to be at the base of the MOS. Now when you apply a negative potential, the electrons present in the channel are repelled more towards the insulating layer and so the channel depth reduces. In order to obtain the same channel depth as that of a MOS with no body voltage, you will have to increase the positive voltage at the gate(Vt).
I'm pretty impressed by how well you explain things. this was one of the most clearly explained videos I've ever seen on youtube, Thanks for uploading!
For those of you who are confused on why a increase depletion region leads to an increase in V th, I think you guys may be confusing depletion region and inversion layer. a depletion region is a situation where holes in the p type are filled and electrons won't recombine however now a depletion region is not conductive, why? because adding an electron to say a boron doped p type will make the overall atom negative. This will now repel any electron trying to cross the channel. What the gate does is increase the voltage so that it attracts the electrons from the n type junction more than the depletion region repels it. Now in case of the body effect we have even more holes missing making the whole depletion layer much thicker and therefore much more negative and replusive, so now to overcome the em effect the voltage must be higher. Yes the channel width seems wider so I imagine max current might be better? idk but we are always talking about the balancing of charge so the depletion field doesn't repel the electrons trying to cross
The sentence at the end made it very simple. Increase in threshold voltage (VT) due to decrease in body or bulk voltage (VB) is called body effect. As you can consider the body itself as a fourth 4th terminal.
yes but since its a MOS capacitor the positive plate/ Gate side must also have same amount of positive charge. To gain more positive charge we need to apply more voltage at gate terminal
@@dheerajha6638 can you explain why the generation of additional negative ions on the body side induce an equal magnitude of positive charge on their own?
@@tengisdashmunkh1787 the number of positive ions must be equal to negative ions. If its nt there then the electric flux won't end at all. This cannot happen
Thanks very much for such a great explanation. I believe that these concepts are not really easy to thoroughly comprehend when you are just beginning to study semiconductors, but the way you presented was phenomenal.
I still cant fully understand the part at 4:14, more negative irons should have more electrons, so it should be more easy to form the inverse layer, why are we need more gate voltage there? Thanks so much for explaining!
Very clear and concise. One picky suggestion though, maybe you could have used the word 'equilibrium' at 5:10 to explain the balance of +ve and -ve charges between the gate terminal and the inversion/depletion layer? Otherwise a good explanation.
Well, I've been reading about techniques to reduce leakage power of a circuit. And body biasing is a suggested technique. With biasing the body to a lower V, an increase in the Vth is observed, which keeps the leakage current even lower when the circuit is in standby mode. Thanks, as you made it clearer to me.
very nicely explained sir understood body effect properly the change in threshold voltage due to body voltage is called as back gate effect or body effect 😀
This video is misleading. Vt increases for negative body bias, but it is NOT because the amount of negative charges increases in the channel region. It is because, negative bias at substrate results in a wider depletion region, that is why a larger bias is required at the gate to form the channel region (larger Vt).
hi nice video. A small comment when you describe the increase in negative charge in the substrate (~4:12) you are correct. But it my help to think of its effects in a slightly different way. The surface potential in the channel will remain constant because you have a grounded source, thus the electric field will remain constant across the oxide region, and thus the gate charge remains constant. But to maintain charge neutrality the charge on the gate must equal the charge in the channel plus the charge in the substrate, therefore the channel charge must reduce. The reduction in channel charge causes a likewise reduction in drain current, this is equivalent to a change in threshold voltage. So a higher Vg is necessary to maintain the drain current. The change in threshold due to substrate current is commonly modelled as a function of gate oxide thickness and channel doping for this reason. Its basically what you describe, but phrased differently.
Every thing was explained precisely but you made a mistake i one part. When Vb > 0 than it will attract electrons (which are minority charge carriers) towards body thus decreasing No. of electrons in channel. In that case the gate voltage has to increase to maintain enough amount of electrons in channel for conduction and that is why Threshold voltage increases.
Am I right in thinking this isn't always an undesirable effect. Reverse body biasing a MOSFET increases the Vt, therefore reducing the static leakage current when the device is not switching as it is "more strongly off"?
We already have enough electrons at gate region to form a conduction channel from drain to source. why should the negative and positive charges near gate necessarily be equal for conduction channel ?? anybody ??
A good exemple is Flash applications, where a charge pump can be used to force the bulk below 0, helping to push the electrons at the silicon/oxide interface, enhancing the carrier injection.
You may also keep Vb=0, and you increase Vs. It happens in, e.g., MOSFETs in series like in cascode, when you simplify your chip layout and you keep one common bulk with Vb=0, but the source of the "upper" MOSFET has Vs>0. So, you end up with the same situation when Vb is lower than Vs.
ctnrb if u connect directly p substrate to groud using metal it forms Schottky diode and its form unidirectional current to flow hence we need current either directions to over come this heavily doped p diffusion to connect it to ground and also provide gud ohmic contact with low resistance
ghanshyam patil it doesnot fall below 0v but when the source voltage goes higher than 0v the body is at lower voltage than the source. its all relative.
Can somebody help me in this as he said when Vb less than Vs ,Vb becoming negative means is there anything like we have to consider it like n type becoz he said holes are getting attracted!!
because the negative charges at drain to source should be equal to positive charges at the gate to start the conduction but here the negative charges are here majority so thats why gate voltage is increased to have more positive charges at gate.
the gate voltage must increase because, the voltage at the drain and source are equal so there is no flow of current , to make the electrons flow from one side to another side we increase the gate voltage more, after increasing the gate voltage at perticular point the electrons will flow , so we can say that, amount of voltage required to flow the electrons is called threshold voltage and it is denoted by vth.
A forward biased bulk to source pn junction would result I expect, the Bulk terminal would attract -ve charge, reducing that in the depletion layer between Vs and Vd. To maintain equilibrium Vg would need to be lowered to reduce +ve charge at the Gate terminal which effectively lowers the Vth(turn-on) voltage.
Before recording a so-called lecture, how about read some material, understand what it is that you are going to talk about and then start ... you seem not to understand device physics very well.
![ILLSLICK - WINTER IS COMING [Official Video]](http://i.ytimg.com/vi/dwTMeM1zIhQ/mqdefault.jpg)
a fan from india . this guy is so precise when he speaks . he explains and the concept just sticks to your mind .
For those of you who got stuck at the part where he says that the increased negative charge near the channel requires a more positive potential to balance the excess negative charge, I have an alternate explanation. For this consider the body terminal to be at the base of the MOS. Now when you apply a negative potential, the electrons present in the channel are repelled more towards the insulating layer and so the channel depth reduces. In order to obtain the same channel depth as that of a MOS with no body voltage, you will have to increase the positive voltage at the gate(Vt).
Channel depth increase right because electrons having 3 rows now.can I get more clarity on this?
I'm pretty impressed by how well you explain things. this was one of the most clearly explained videos I've ever seen on youtube, Thanks for uploading!
For those of you who are confused on why a increase depletion region leads to an increase in V th, I think you guys may be confusing depletion region and inversion layer. a depletion region is a situation where holes in the p type are filled and electrons won't recombine however now a depletion region is not conductive, why? because adding an electron to say a boron doped p type will make the overall atom negative. This will now repel any electron trying to cross the channel. What the gate does is increase the voltage so that it attracts the electrons from the n type junction more than the depletion region repels it. Now in case of the body effect we have even more holes missing making the whole depletion layer much thicker and therefore much more negative and replusive, so now to overcome the em effect the voltage must be higher. Yes the channel width seems wider so I imagine max current might be better? idk but we are always talking about the balancing of charge so the depletion field doesn't repel the electrons trying to cross
Your explanation makes a lot of sense. Cant thank you enough. Was looking for the answer. Much love brother.
The sentence at the end made it very simple.
Increase in threshold voltage (VT) due to decrease in body or bulk voltage (VB) is called body effect.
As you can consider the body itself as a fourth 4th terminal.
Very clear explanation of the concept, Thank you.
You're 7 min lecture explained this effect better than what my prof did in an hour! Thx!
When vbs>0, vt will decrease. This draws electron to the channel, so more electron makes the gate easier to conduct
I think in this case , if vb the additional layer of fixed negative ions SHOULD DECREASE THE THRESHOLD VOLTAGE
yes but since its a MOS capacitor the positive plate/ Gate side must also have same amount of positive charge. To gain more positive charge we need to apply more voltage at gate terminal
@@dheerajha6638 can you explain why the generation of additional negative ions on the body side induce an equal magnitude of positive charge on their own?
@@tengisdashmunkh1787 the number of positive ions must be equal to negative ions. If its nt there then the electric flux won't end at all. This cannot happen
Thanks very much for such a great explanation. I believe that these concepts are not really easy to thoroughly comprehend when you are just beginning to study semiconductors, but the way you presented was phenomenal.
Thanks so much. VERY good explanation. I was tired of hearing my professor talk about this "body effect" without giving an explanation!
Thanks man. watchng this in 2024 before my exam.
Read through two books on this topic... but couln't understand the core concept. You made it look extremely simple. Thankyou very much!
I still cant fully understand the part at 4:14, more negative irons should have more electrons, so it should be more easy to form the inverse layer, why are we need more gate voltage there? Thanks so much for explaining!
He is not right. It reduce the threshold voltage.
Very clear and concise. One picky suggestion though, maybe you could have used the word 'equilibrium' at 5:10 to explain the balance of +ve and -ve charges between the gate terminal and the inversion/depletion layer? Otherwise a good explanation.
Beautiful illustration
Well, I've been reading about techniques to reduce leakage power of a circuit. And body biasing is a suggested technique. With biasing the body to a lower V, an increase in the Vth is observed, which keeps the leakage current even lower when the circuit is in standby mode. Thanks, as you made it clearer to me.
very nicely explained sir understood body effect properly the change in threshold voltage due to body voltage is called as back gate effect or body effect 😀
It was really very helpful. Thank you!!
This video is misleading. Vt increases for negative body bias, but it is NOT because the amount of negative charges increases in the channel region. It is because, negative bias at substrate results in a wider depletion region, that is why a larger bias is required at the gate to form the channel region (larger Vt).
my friend told me about this video and said " why it doesnt have audio"?
he is deaf from one ear though.
hi nice video.
A small comment when you describe the increase in negative charge in the substrate (~4:12) you are correct. But it my help to think of its effects in a slightly different way.
The surface potential in the channel will remain constant because you have a grounded source, thus the electric field will remain constant across the oxide region, and thus the gate charge remains constant. But to maintain charge neutrality the charge on the gate must equal the charge in the channel plus the charge in the substrate, therefore the channel charge must reduce.
The reduction in channel charge causes a likewise reduction in drain current, this is equivalent to a change in threshold voltage. So a higher Vg is necessary to maintain the drain current. The change in threshold due to substrate current is commonly modelled as a function of gate oxide thickness and channel doping for this reason.
Its basically what you describe, but phrased differently.
Thank you for the explanation, it helped me.
Every thing was explained precisely but you made a mistake i one part. When Vb > 0 than it will attract electrons (which are minority charge carriers) towards body thus decreasing No. of electrons in channel. In that case the gate voltage has to increase to maintain enough amount of electrons in channel for conduction and that is why Threshold voltage increases.
In this case , if vb
Bro u are keeping the vgs constant initially
you explain it so so great !
it had been confusing me for a long time
i finally understand it now !
thank you very much !!!
Good explanation.
Omg !! Awesome explanation ,can you please explain the other second order effects too.
Very easy to understand thanks
my left ear enjoyed this :D
What is the relationship of the p substrate doping with the back gate voltage?
Nice explained.
Am I right in thinking this isn't always an undesirable effect. Reverse body biasing a MOSFET increases the Vt, therefore reducing the static leakage current when the device is not switching as it is "more strongly off"?
Excellent one 👌
well clarified!! But essentially in which kinds of reasons will the body voltage change?
Nice explanation. Thank you.
Excellent explanation brother... would be greatful if you make a small videoclip on cmos latchup
TH-cam is a better place with these videos.Thanks! :)
nice explanation
thanks for your video. can you give me more details about the short channel effect and solutions?
Nicely explained!
When I make an inverter, I get the opposite effect. When Vb > 0, the threshold increases, and when Vb
I am pretty sure you are right and the video is wrong. Silly mistake but still a valid explanation.
Very clear understanding sir!
We already have enough electrons at gate region to form a conduction channel from drain to source.
why should the negative and positive charges near gate necessarily be equal for conduction channel ?? anybody ??
sorry your question is not so clear, can you make it clear.
sometime we need higher Vth and sometime lesser Vth ,both have its own advantage and disadvantages
very nice video
Spellbinding explanation!
thanks buddy, you are so precise and clear
superb bro
Hey i just want to know are you still alive bro😁. Why? Because i am watching video after ten years lol 🤣
Hi can u tell total second order effects ,and types
What exactly do you mean by source and channel are reverse biased at around 1:54 of the video
How can this effect be used in our advantage when designing analog switches? Taking the Transmission Gate as an example.
What happened when vb is greater than vs?
Why is the audio in only my left ear 😭
Nice explanation tho 👍
Wouldn't more electrons at the channel make it easier to conduct thus decrease the threshold voltage?
ww785612 Not more electrons actually. Should be wider depletion region, which makes it harder to create the channel.
@eneradi...even i have same question as above by BrtotherCavil...........can u explain the vertical conduction phenomena deeply...
1:40 when the video really starts
where can i find the supportive explanation.....?
what is the reason of decrease in bulk voltage in comparison to source voltage even if both are connected to the same voltage(ground)
thanks :)
Wonderful video, you've really helped me, thank you so much
Why would the p+ bulk region voltage go below 0v?
A good exemple is Flash applications, where a charge pump can be used to force the bulk below 0, helping to push the electrons at the silicon/oxide interface, enhancing the carrier injection.
You may also keep Vb=0, and you increase Vs. It happens in, e.g., MOSFETs in series like in cascode, when you simplify your chip layout and you keep one common bulk with Vb=0, but the source of the "upper" MOSFET has Vs>0. So, you end up with the same situation when Vb is lower than Vs.
what is the effect of body bias then?
this just saved me 2 hrs while im preparing for exam!
Thank you, good explanation
great video ....
Why do we put p+diffusion in p substrate and connect that to ground? Why can't we directly connect the p substrate to ground?
ctnrb if u connect directly p substrate to groud using metal it forms Schottky diode and its form unidirectional current to flow hence we need current either directions to over come this heavily doped p diffusion to connect it to ground and also provide gud ohmic contact with low resistance
Why are they called second order effect?
Under what reasons do bulk voltage fall below 0v ?
ghanshyam patil it doesnot fall below 0v but when the source voltage goes higher than 0v the body is at lower voltage than the source. its all relative.
Why do we put p+diffusion in p substrate and connect that to ground? Why can't we directly connect the p substrate to ground?
Can somebody help me in this as he said when Vb less than Vs ,Vb becoming negative means is there anything like we have to consider it like n type becoz he said holes are getting attracted!!
Great video, thanks!
Really appreciateable , great video
u explained based on quantitative analysis....but how qualitatively is it correct...means how threshold voltage is increasing when Vbs
a new capacitance are formed like as tox between channel and body so it behave as a back gate
Thank u so much. It was really very helpful.
thanks !! 🎇✨🎆🎉 simple to understand
And for a P type MOSFET, what happens?
i love you
thank you!!! it was very helpful..
thank you, bro! great video!
Thank you :)
the video is awesome!!!!!thnx for the video!
thank u
i didnot get why the gate voltage must increase ??
because the negative charges at drain to source should be equal to positive charges at the gate to start the conduction but here the negative charges are here majority so thats why gate voltage is increased to have more positive charges at gate.
Why should the negative charges at drain to source should be equal to positive charges at the gate to start the conduction
Syed muhammad Musab
FOR CONDUCTING I THINK...
the gate voltage must increase because, the voltage at the drain and source are equal so there is no flow of current , to make the electrons flow from one side to another side we increase the gate voltage more, after increasing the gate voltage at perticular point the electrons will flow , so we can say that, amount of voltage required to flow the electrons is called threshold voltage and it is denoted by vth.
Thanks a lot❤️
what if i increase the voltage of VBS?
A forward biased bulk to source pn junction would result I expect, the Bulk terminal would attract -ve charge, reducing that in the depletion layer between Vs and Vd. To maintain equilibrium Vg would need to be lowered to reduce +ve charge at the Gate terminal which effectively lowers the Vth(turn-on) voltage.
Why do we put p+diffusion in p substrate and connect that to ground? Why can't we directly connect the p substrate to ground?
It seems as a mis-explanation to me. The wider depletion region should be right answer.
+francisliubin right, then Qi doesn't change, but Qd changes the whole charge changes which is reflected by Qtotal/Cox and Vt=Vfb+2psib-Qtotal/Cox
great job (Y)
Su0er explanation
omg i fnally understand this!!!
Thanks man!
What if VB > VS?
I suppose that source-bulk becomes a foward biased diode... and that's a thing you don't want in a mosfet! But I'm just guessing!
nothing
I can't hear nothing mate
wow man!
I feel the causality of your explanation is off. None the less, great effort in making the video.
nw i understood
Before recording a so-called lecture, how about read some material, understand what it is that you are going to talk about and then start ... you seem not to understand device physics very well.
As i understand it, there will be body effect if you both increase or decrease Vthresh? And this is on an NMOS, is it similar for PMOS just backwards?