Bipolar process(MicroElectronics)

[Abisheak]

Hello everyone,
why does bipolar process operate at high frequencies?

thank you

 

[grvkpr18]

I think this is because BJT's operate at higher voltage than CMOS. The current levels are high. So, they can drive higher loads as compared to CMOS.

 

[Abisheak]

thanks buddy.actually am a CSE student but interested in learning VLSI.i got no idea as whether to learn chip designing or chip programming. could u please suggest me ?

 

[dick_freebird]

Depends what you mean by "high".

High voltage BJTs tend to be slow (dominated by the high
voltage driven light doping in collector and wide base
widths, prone to long lifetimes and high charge storage).

Modern RF silicon (SiGe) HBTs are the fastest silicon
amplifier device and can be used for logic at a high cost
in power. You'll see them in RF and fiber optic front ends.
But as soon as the bit rate gets comfortably within CMOS
range, that's what will be used for density and quiescent
power.

SiGe devices have a narrow, very high mobility base and
are highly engineered. As frequency goes up, BVceo has
come down substantially, limiting the power level at the
high frequencies. Not a problem for logic, but limiting the
power levels of RF amplifiers and such.

SiGe CML logic can run reduced signal swings which is
a speed advantage. You could make such structures
using MOS, too, but would then lose the quiescent
current advantage and be using a speed-inferior
device.

SiGe devices roughly double the masking layers below
1st metal, a significant cost adder.