Steps like oxidation, doping, epitaxy, photo-lithography, and metallization etc. are used in the designing process.


closed as unclear what you're asking by Marcus Müller, Leon Heller, RoyC, PeterJ, Voltage Spike Feb 16 '18 at 18:28

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  • 2
    \$\begingroup\$ Why do you assume that it is one particuar step that makes if costlier? Maybe there are a few (maybe even cheaper but more in number) steps. \$\endgroup\$ – Curd Feb 13 '18 at 9:25
  • \$\begingroup\$ Comparing what with what? Pretty sure a 100 A, U_DS = 400 V safe MOSFET is more expensive than a 0.1 uA, 2V BJT at the same speed. Then again, at the same f_max of a couple GHz, you'll find that BJTs are still affordable, but FET become technically challenging. You're not saying what kind of transistor you're comparing, and which part of the specs need to stay the same, and which are allowed to change. Hence, your question is I'll-posed. \$\endgroup\$ – Marcus Müller Feb 13 '18 at 9:47
  • \$\begingroup\$ @MarcusMüller He's probably talking about the transistors in logic ICs (there is a [vlsi] tag). But I agree it is unclear. \$\endgroup\$ – dim Feb 13 '18 at 11:59
  • \$\begingroup\$ This looks as a general question. BJT vs MOS. For example, standard voltage MOS from regular CMOS process (180 nm, 90 nm, etc.). \$\endgroup\$ – Tako Feb 19 '18 at 10:12

Compare BJT with MOS in this postion:

  • BJT: Fig. 1-10
  • MOS: Fig. 1-18

It should be clear now that MOS transistors require less production steps (hence lower cost) and allow higher density. Those are the reasons while MOS won with BJT. However, MOS transistors are surface devices. That's why they appeared later compare to BJT which active area is located deep in the bulk.


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