Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

[SOLVED] Are there any bipolar transistors whose voltages scale like MOSFETS?

Status
Not open for further replies.

quantized

Member level 2
Joined
Jul 6, 2012
Messages
51
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
1,887
Hi, I'm a mostly-digital guy who knows next to nothing about BJTs. However, lately I've started learning about current-mode logic, which has piqued my interest in BJTs.

In what appears to be an unpublished appendix from Rabaey/Chandrakasan/Nikolic's book, they write:

the BiCMOS gate inherits one of the most important deficiencies of the bipolar technology: built-in voltages such as VBE(on) do NOT scale.

As lithography technology progresses, the features sizes of both MOSFETs and various BJTs (Substrate-Well-Diffusion, SiGe HBT, etc) decrease. In the case of MOSFETs, this tends to decrease the acceptable operating voltage (although other problems like gate leakage arise). It seems like this does not happen for ordinary BJTs made out of diffusion-well-deepwell structures in CMOS processes, nor does it happen for bipolar transistors in BiCMOS processes.

However there are other BJT technologies like SiGe.

Is it universally true that the voltage parameters of a BJT do not scale with feature size, regardless of the type of BJT? This would seem to imply that the MOSFET-BJT power consumption gap is only going to get worse as time goes on.

Thanks.
 

Dominik Przyborowski

Advanced Member level 4
Joined
Jun 6, 2013
Messages
1,063
Helped
481
Reputation
964
Reaction score
455
Trophy points
1,363
Location
Norway
Activity points
7,962
In CMOS technology mosfets threshold voltage depends to a gate oxide thickness, doping profile and channel length so its changes from technology node to node.
In bipolar transistor, a base-emiter voltage depends only to semiconductor material which made a junction - for silicon its around 0.6V, for germanium 0.4V, for schotkeys junctions 0.3V.
 

quantized

Member level 2
Joined
Jul 6, 2012
Messages
51
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Activity points
1,887
In bipolar transistor, a base-emiter voltage depends only to semiconductor material which made a junction - for silicon its around 0.6V, for germanium 0.4V, for schotkeys junctions 0.3V.

Thanks Dominik! It makes sense now; BJTs don't have a gate oxide, which is the parameter whose scaling causes MOSFET threshold voltage to scale.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top