Comment by rnrn
1 day ago
> The NMOS transistors used in the 6502 were quite large and worked on the basis of electrostatic charges ... as opposed to bipolar transistors that are inherently quantum in operation
Forming a conductive channel in silicon in any FET and semiconductivity in general is an inherently quantum effect too, right?
If you go deep enough in the details, everything is a "quantum effect".
However, in order to design and simulate a MOS transistor and most of the other semiconductor devices you do not need to use any quantum physics.
This should be made obvious by the fact that both the metal-semiconductor transistor (i.e. MESFET, patent filed on 1925-10-22) and the depletion-mode metal-insulator-semiconductor transistor (i.e. depletion-mode MOSFET, patent filed on 1928-03-28) have been invented at a time when quantum theory was just nascent, not yet applicable to semiconductors and certainly unknown to the inventor (Julius Edgar Lilienfeld; despite the fact that the FET operating principles were obvious, the know-how for making reproducible semiconductor devices has been acquired only during WWII, as a consequence of the development of diode detectors for radars, which generated the stream of inventions of semiconductor devices after the war ended).
For designing MOSFETs, you just need to use classical electrodynamics, together with several functions that provide the semiconductor material characteristics, like intrinsic free carrier concentration as a function of temperature, carrier mobilities as functions of temperature and impurity concentrations (and electric field at high fields), ionization probabilities for impurities, avalanche ionization coefficients, dielectric constants, and a few others.
It would be nice if instead of measuring experimentally all the characteristic functions for a semiconductor material one could compute them using quantum theory, but that is currently not possible.
So for semiconductor device design, quantum physics is mostly hidden inside empirically determined functions. Only few kinds of devices, e.g. semiconductor lasers, may need the use of some formulas taken from quantum physics, e.g. from quantum statistics, but even for them most of their mathematical model is based on classical physics.
> This should be made obvious by the fact that both the metal-semiconductor transistor (i.e. MESFET, patent filed on 1925-10-22) and the depletion-mode metal-insulator-semiconductor transistor (i.e. depletion-mode MOSFET, patent filed on 1928-03-28) have been invented at a time when quantum theory was just nascent,
I don't think that makes it obvious at all, given that the none of these invented devices actually worked, and the first working MOSFETs weren't until the late 50s after a research program of a few additional decades by a bunch of solid-state physicists at Bell Labs (who did know and develop quantum theories of solids - Shockley, Bardeen, Brattain - not successful in making a FET -Atalla, Kahng, many others)
"Electrons and Holes in Semiconductors" was published almost a decade before any functional MOSFET was constructed.
> For designing MOSFETs, you just need to use classical electrodynamics, together with several functions that provide the semiconductor material characteristics, like intrinsic free carrier concentration as a function of temperature, carrier mobilities as functions of temperature and impurity concentrations (and electric field at high fields), ionization probabilities for impurities, avalanche ionization coefficients, dielectric constants, and a few others.
It sounds like you are describing what's required to parameterize some of the traditional semi-classical models of MOSFETs and understand the operating principles at that level.
but FETs work by bending the energy levels of the conduction band so there needs to be a band to bend, and if there's no band gap at the fermi level you can't have a FET, which makes it seem pretty dependent on quantum effects to me even without going deeper than necessary to understand how it can work.
Maybe one could have been engineered with no idea why silicon has the special material properties that it does and why doping changes those properties but AFAIK it never was, and being able to explain and understand band structure seems pretty important to build a working device.
Traditionally I don't think it was considered to be specially a quantum effect. That, again was because bipolar transistors specifically work over a quantum band gap ... and bipolar transistors proceeded mosfets.
So only a quantum effect to the extent all effects are at some level quantum.