Yes, the control of implants and diffusions are still better than lateral dimensions, which is dependent on your photolithography capability. For example, a transistor with a ft of about 50 GHz has a base width about 45 nm, which is beyond current production photolithography capability.1. Vertical Bipolars have a smaller Base region than lateral.
Q. Just a little confused, shouldn't we be able to accurately control lateral dimensions in a fabrication process than vertical ones? So does that mean the smallest base width we can accurately control in a fabrication process is still more than the base width we can have in a vertical BJT?
Yes, the substrate current from the parasitic verticle component increases the base current of your lateral BJT.2. Lateral BJTs are inferior since they have a parasitic vertical BJT
Q. What degrading effects does that vertical BJT have on our main lateral BJT perfomance? One thing I am guessing is substrate currents.
Wider base translates to higher base transit time.3. Because of wider base in lateral BJT they are slower because more stored charge in the base region and hence lower ft.
You will get a better Early voltage * beta product with a verticle BJT.MORE Questions:
1. How does the early voltage of the 2 devices compare?
The current carrying capability of the lateral device is worst therefore, the transistor size is usually much larger than the verticle device to carry the same amount of current.2. How does the size in layout of the 2 devices compare?
This is due to the high base resistance of the lateral device. The base connection of a lateral device is usually made through the epi/well, which is high resistance.3. I heard that the β in one of them falls more rapidly for increasing Ic..., can somebody elaborate