Advantages of Mosfets over Bipolar Transistors in on-chip logic?

[samuwel]

Just wondering if someone could clear up a few questions I had and point me in the direction of some further reading around the subject.

Basically, I'm trying to understand why MOSFETs are used in on-chip logic as opposed to bipolar transistors. I'm under the impression that MOSFET's take up less chip area, is this the main driving factor behind the choice? Could someone elaborate a bit more on this if so?

As mentioned, all replies and suggestions of specific reading are welcome.

 

[yadavvlsi]

There are few point why MOSFET is preferred over BJT.
1. Ease of scaling: MOSFET drain current depends on the ratio its geometry (W/L). So MOSFET drain characteristic remain same as far as ratio of W/L is kept same. So theoretically MOSFET with W/L=4/2=2/1 will have same characteristic. In BJT current is not directly dependent on its geometry. It has exponential dependence on Vbe. So it is easy to scale down MOSFET compared to BJT. So you can have more transistor in smaller area i.e. you can implement more functionality lesser area.

2. Less power : CMOS logic consumes lesser power compared to BJT. Complementary logic in MOS give zero static power dissipation though it is not practically true. BJT have much higher power consumption.

3. Fabrication process: MOSFET have simpler fabrication process compared to BJT. BJT have much complex fabrication process which includes burried layer diffusion.

 

[mkrtich.nazaryan]

Advantages of Bipolar over Mosfets Transistors: Bipolar transistor is much more faster thank Mosfet. and in case when frequency is getting higher and higher the switching power of Mosfet could increase the switching power of Bipolar. Mosfet is good when you are using in digital design, because in logic stat 0 and 1 they have a very little leakage current. but even now when we have already Mosfet with 0.22nm channel length the leakage is already significant.

 

[goldsmith]

Dear Friends
Hi
We will have some reasons : the loss power of a mosfet at 50 percent duty cycle square wave will be about C*v^2*F(the loss power is low) . ploss at sturation region will be about 1/T integral rdson * ID^2 dt from 0 to ton . ( rdson is very low)
and we can drive it with negligible gate current. and we don't need to use chain mosfets to obtain high current gain ( like BJt)
and the speed of switching of mosfets is higher than bjt s .
and stability of them is higher than bjt s.
and their input impedance can be considered about infinite .
Best Wishes
Goldsmith