MOS Capacitor Explained

/ edmundsj
If you want to see more of these videos, or would like to say thanks for this one, the best way you can do that is by becoming a patron - see the link above :). And a huge thank you to all my existing patrons - you make these videos possible.
The two-terminal MOS capacitor structure. How the metal/oxide/semiconductor layers form a capacitor, what charges are present where, and why we care.
This is part of my series on semiconductor physics (often called Electronics 1 at university). This is based on the book Semiconductor Physics and Devices by Donald Neamen, as well as the EECS 170A/174 courses taught at UC Irvine.
Hope you found this video helpful, please post in the comments below anything I can do to improve future videos, or suggestions you have for future videos.

[@aycakolay]

Thank you so much, finally a brief explanation that I couldn't find anywhere else

[@aryanisual]

first time i'm understanding something(concepts) which i couldn't relate before.... ! probably the best video over 2T mos capacitor, thanks a lot! continue your great work...

[@JordanEdmundsEECS]

Thanks!

[@n....8666]

This much of clearity is a new experience in itself. Oh god how lucky his students are. Teachers generally rush away these topics which are complex in the end with printed definition and no explanation. Thanks

[@krishdesai9647]

Man, I don't know if you'll see this but I love you, thank you for the videos on MOSFETS.

[@JordanEdmundsEECS]

Saw it :)

[@TheCzaach]

Wow! I've never seen such an explenation. These bands are really useful! Thank you sir!

[@burry218]

This is absolutely beautiful. Thank you so much. Its really pleasing to see how well you form links for clarity

[@JordanEdmundsEECS]

Thank you! I'm very glad you found that helpful.

[@phizaics]

So many hours of wasted effort trying to understand band bending but after watching your lectures finally it is all making sense. Great work!

[@nitesh8293]

Thankyou so much for making this concept so easy to understand

[@ib257]

THIS IS THE BEST EXPLICATION I SEE THANK U !!!! U MAKE IT VERY EASY !!!!

[@RohitAVS]

This is awesome, i understood so much, literally saved my semester! MR.JORDAN EDMUNDS YOU ARE A GODSEND

[@JordanEdmundsEECS]

And you sir are extremely kind :)

[@Jamesxyz234]

I shared it to my TA course's students for preparing for the MOS cap fabrication labs. Thanks Edmunds!

[@JordanEdmundsEECS]

Ah! That's so cool! Did they end up working as theory would predict? xD

[@amrohendawi6007]

well explained !!! I was suffering with german videos and lectures for a whole week to get this basic idea

[@JordanEdmundsEECS]

Thanks! I think I may have suffered through the same exact videos you did in my undergrad xD

[@EdgeMiz]

Thank you for this explaination, it helps me to begin understand how MOS works.

[@gameglimpses8861]

Your explanation and concepts are so cool

[@omerzohar3307]

This video is excellent and made things very clearer!

[@cameronsluiter323]

EE here. Really great to learn this material. I forget every couple of years and need to mull it over again and again.

[@diracchristoffel7045]

Thank you so much! I am a physics student working with the same book and the material is generally easy to understand but I was stuck at this chapter. You explained all the gaps I had so well!

[@JordanEdmundsEECS]

:D excellent choice doing physics. Very glad I could help.

[@kunalahuja2324]

Thank you for such a good explanation and keep the good work going.

[@martinsimbona6145]

I love these lecture series to the core. You're a wonderful teacher.

[@JordanEdmundsEECS]

Aw, thanks. This made me smile when I read it.

[@Amyhb69]

This is explained so clearly. Thank you

[@justclick1144]

Very nice explanation .. So calm explanation. Thank you

[@zinhaboussi]

thank you for existing you are saving my time

[@MohammadHussain-uj3ku]

Amazing a concept explained in 9 minutes fantastic job

[@JordanEdmundsEECS]

Thanks :D

[@syedihab5829]

Thank You so much for these videos made understanding much easier :)

[@bellaryna1597]

Thanks for this. I really appreciate this content.

[@guyinbar11]

Great explanation man! I'd like to learn more from you, so when you say the next video what do you mean? this isn't part of a playlist as far as I can see. Are there previous relevant videos?

[@user-uu8wb9xd6m]

beautiful explanation! Thank you

[@roshanantony64]

Great video sir! Thank you very much!

[@user-ou3ci5ej7k]

Thank you for this interesting explanation!

[@lecturesclub3156]

Nice explanation, it would help me in my next video where i am going to explain differences between JFET and MOSFET, Thank you so much

[@Hilltop1108]

You sir are a life saver.

[@JordanEdmundsEECS]

And you sir are too kind.

[@Fintas23]

Very well explanation thank you!!

[@LaVideOrange]

You are a life saver.

[@yonatanj4]

Good explanation ty!

[@user-cu2il3vz4v]

i love you.....your teaching was best.

[@Chongweisingapore]

Thanks this is the best understanding

[@netanellalazar3819]

your amazing. thank you~!

[@David-kj7el]

Love you man

[@user-zu5gf2pb4l]

thank you sir

[@tuffygrover6384]

THANK YOU

[@niccolof.2176]

Thank you!!!

[@RELAXANDLISTEN6440]

great sir

[@abheetl9743]

Nice video... but why do we find band bending when no voltage is applied to the gate? (Ofcourse, assuming the substrate is grounded).

[@benjoe429]

when applying gate voltage Ec, Ev and thus Ei bend downwards, but not Ef (according to your video on p-n junction diode applying bias voltage also bends Ef). Why is Ef not shifting due to the applied electric field?

[@cheesepie4ever]

You're a god thank you, saving my ass for my microelectronic materials unit

[@yuack2398]

Isn't depletion region stops widening when the voltage is beyond thrashold?

[@rishivarrey1176]

amazing

[@Mumbai101]

kzbin.info/www/bejne/iYjJeKKllrObhKM

[@JL_life]

Where does an attracted electron come from in inversion state? Could you please explain this little more in detail?

[@JordanEdmundsEECS]

That's a fantastic question, and it turns out to be *really* important. In the case of a pure MOS capacitor, the electrons can come from only one place - the p-type substrate. This can take awhile, because it relies on the spontaneous generation of electrons from the substrate (they aren't generated that fast, and we need a lot of them).

[@wiggiesmallsaka9011]

legend

[@eli_steiner]

when the voltage is applied in energy diagram, why are all the band levels bending, but not the Fermi-level? Kind of expected the fermi level to bend up (since it's usually changed with doping anyways) and all the rest to stay (Valence and cond. band energies seem to be more like material properties)

[@jordanedmunds4460]

The way that you find band bending is by assuming the Fermi level is constant throughout the entire structure. The fermi level has to do with *equilibrium*, you can think of it like you would a generalized force. If the fermi level isn't constant, stuff (electrons, holes) is moving. You're correct that its relative position to the conduction/valence band changes, but this is taken care of by the valence and conduction bands bending. The valence band and conduction band aren't really material properties per se. The distance from the conduction band to the vacuum level (called electron affinity) is, however, and this is constant for a given material (silicon, for example).

[@eli_steiner]

@@jordanedmunds4460 oooh oke the equilibrium makes sense... I gues if Ef were not constant, charges would just move until it is again, right? And thanks for pointig out the vacuum energy level, i didn't see that it would bend down with the rest, and therefore staying constant. Thanks for the quick explanation! (my oral exam is in 3h so just in time ;) )

[@sauravdev3088]

if u could do a video for accumulation mode it would be helpful

[@JordanEdmundsEECS]

Good point, can’t believe I haven’t done modes of operation.

[@JordanEdmundsEECS]

Just uploaded video on accumulation: kzbin.info/www/bejne/nHfPf3hnrpxjp5o depletion: kzbin.info/www/bejne/bYOwoKNri7SCjLM, and inversion mode: kzbin.info/www/bejne/pZvcgKqebt2qi9k. Hope you find them helpful.

[@user-nd6bf1yh2g]

some of them are near the gate, some of them are far away~ pretty catchy

[@joxa6119]

how the hole be repelled because of the electron? why it is not attracted?

[@kevinyang5904]

better than my professor

[@yepnah3514]

Hi, I have been trying to draw the energy band diagram for an SOS Cap. How would you draw this since we have two Si semiconductors? It is problem 11.26 www.autoelektrix.ru/eng-109/52/

[@Anas-qj6kk]

i meant mos def

[@burry218]

Hello, please can you let me know how I should view the Fermi Level? I don't understand why the Fermi level doesn't not move in the semiconductor but it does move in the metal...

[@burry218]

I'm trying to establish some common principles/ understanding so I can apply it to if V

[@JordanEdmundsEECS]

The fermi level has to do with the thermodynamic potential of the electron (how difficult it is to move that electron around in a solid). At equilibrium, the fermi level should be constant everywhere (that's literally the definition of equilibrium). To achieve this when in contact with a oxide/metal interface, the semiconductor will end up having some charges move around and its conduction / valence bands will bend. In a metal, there are so many free electrons and they move around so easily that we usually model it as an equipotential surface (everywhere inside the metal has the same voltage). You can also say there will be no electric fields inside the metal. If this is the case, there is nothing to "push around" the electrons and make it difficult for them to move, so there is no band bending we have to worry about. When you apply a voltage, you "drag" the fermi level of one side down (the metal if V_metal > 0) relative to the other side, and the fermi levels are now separated from each other. BUT, the vacuum level still has to be continuous, so the amount of band bending in the oxide and semiconductor changes so that this is still the case, and changes the number of charges on each side. If you were to apply a negative voltage to the metal, you would "drag" the fermi level of the metal in the opposite direction.

[@burry218]

@@JordanEdmundsEECS Thank you so much, this is very clear. So let me get this right, the reason why the Fermi level in the semiconductor stays constant is because there is no potential being applied to the semiconductor (say its connected to GND)? Am I in the right line of thinking?

[@burry218]

And if the potential of semiconductor relative to V_metal was raised, the Ev, Ec, Ei AND Fermi level of semiconductor would all be dragged down by that applied voltage, or would it just be the E-FermiSemi that would be translated?

[@JordanEdmundsEECS]

Not quite, but you’re on the right track. There is a *voltage* change within the semiconductor (that’s the same as saying the conduction/valence/vacuum bands bend), but this is exactly balanced out by the *chemical potential* caused by an electron gradient within the semiconductor, so the total potential *energy* (the Fermi level) within the semiconductor is constant.

[@nikitapandey6446]

Sir why do we apply for p-type semiconductor in most of the cases?

[@JordanEdmundsEECS]

There’s a historical reason and a pedagogical reason. The pedagogical reason is that it’s much easier conceptually to handle only one type, and then just generalize your knowledge at the end to both types. The historical reason is that Si-based n-channel transistors have always been better than p-channel resistors, and so initially most circuits were made with only n-channel devices (in a p-type body). So it used to be the more useful case to analyze.

[@nikitapandey6446]

Thank you for the response. I really appreciate it😊

[@mugiwara-no-luffy]

@@nikitapandey6446 good question to ask.

[@jean-rochdion4898]

i'm far to be a brain with electricity, just basic and i'm not sure. lol So my question: why Mos(silicon) and not full conductor (ex:gold) it's because of price/accessibility of the material. or about the option to be able of a selection of conductivity level? ex: gold will be a "too good conductor" for the capacitor? with only the option of full charge and discharge! maybe I say total BS and way out of context too...dont be shy to wake up me!! no problem with that at all... curious human in search of knowledge!

[@JordanEdmundsEECS]

Brilliant question. If your goal is to make a capacitor, it's usually a better idea to use an actual metal xD Aluminum is often the metal of choice (cheap, easy to work with). The reason we study MOS capacitors is because it's the first step to understanding a MOSFET. A MOS capacitor by itself is usually not very useful.

[@vysakhav]

Thanks very much sir