Locator: 48831CHIPS.
I continue to enjoy John Orton's book on semiconductors.
I am finding is so fascinating that I am transcribing significant amounts to be placed on the blog.
The first example was section 3.1 transcribed here.
Do
a word search, "serendipity" at this post. No less than three events in
the early invention of the transistor were due to serendipity, were
serendipitous, or were fortuitous.
Now, transcribing section 4.2
we have yet another serendipitous / fortuitous / accidental discovery
which was critical for development of the microchip / transistor /
semiconductor. Link here. To wit:
4.2 The metal oxide silicon transistor. It begins:
The
Metal Oxide Silicon (MOS) transistor was yet another product of the
fertile ground cultivated by Bell Telephone Laboratories and, once
again, it involved just a small element of good fortune. The critical
step in its evnention was the (accidental!) discovery that the Si
surface can be oxidized to form a highly stable insulating film which
possesses excellent interface qualities (i.e. the interface between
the oxide layer and the underlying silicon). We have already commented
on the importance of this interface in passivating Si planar transistors
which, in turn, led to the practical realization of integrated circuits. The further application in the metal oxide silicon field effect transistor (MOSFET) turned out to be a singularly important bonus.
[Comment:
so, now in the very beginning of the transistor story four discoveries
that were serendipitous (serendipity), fortuitous, or accidental.
Absolutely amazing.]
Continuing:
We saw in the previous chapter that the quest for a FET (which would function in a manner closely parallel to that of the thermionic valve) had already acquired something of a history.
It was a patent awarded in 1930 to a Polish physicist, Julius Lilienfield (who emigrated to America in 1926), that thwarted William Shockley in his original attempt to patent such a device but, even more frustratingly, the existence of high densities of surface states on Ge and Si which prevented the Bell scientists from actually making one.
Even though the application of a voltage to a "gate" electrode may have been successful in inducing a high density of electrons in the semiconductor region beneath it, these electrons were not free to influence the semiconductor's conductivity because they were trapped in surface (or interface) states.
What was needed was a surface (or, more probably, an interface) characterized by a low density of these trapping states (of order 10^15 m^-2 or less) but, at the time, no one knew how to produce it.
Brattain and Bardeen had continued to study the problem of surface states until 1955, eight (8) years after their invention of the point contact transistor, but it was not until 1958 that another Bell Group under "John" Atalla discovered the low density of states associated with a suitably oxidized SI surface. It was necessary ...
... and... and then a long paragraph explaining the next process ... ending ...
... However, the key result was that their densities were below the above limit of 10^15 m^-2, thus making possible the development of a practice FET. This was finally achieved at Murray Hill in 1960. Within a few years RCA pioneered the introduction of MOS devices into integrated circuits and this technology rapidly came to dominate that of bipolar (e.g. n-p-n) devices in many applications.
Then a long paragraph of technical details, describing a process which is known as "inversion," the channel itself often being refrerred to as a "inversion layer."
Another short technical paragraph.
Then, another long technical paragraph, bottom of page 102, which begins:
A virtue of these curves ...As already explained in Box 4.1, digital signal processing (which is fundamental to present-day-computing and information transfer) depends on the use of short voltage (or current) pulses which are generated and moved around an array of electronic circuits in incredibly complicated fashion but the basis is, nevertheless, simple. At any point in the circuit, "information" is represented by the presence (digital "1") or absence (digital "0") of a pulse voltage. Typically its amplitude is about 5 V but the exact value is less important than the ability of monitoring circuitry to determine, with a high degree of certainty, that the pulse is either present or absent......
Now, skip ahead to the end of section 4.2:
In summary, then, we see that, by the early 1960s, the two principal active devices, bipolar and MOS transistors had become available to the electronic engineer and the story from this point is one of continuing miniaturization to improve speed and packing density in IC design and on the other hand, the development of large-scale devices with large voltage-handling capacity for use i high power applications.
Which device to use in which application depended, of course, on the specification required.
In general, MOSFETs have an advantage in IC design on account of their lower power dissipation and modest demand on silicon area, though bipolar devices are capable of faster switching speeds at the expense of more power dissipation and greater demand on space.
The dissipation advantage inherent in the use of MOS devices was further enhanced in the late 1960s by the development of Complementary MOS (CMOS) circuity in which each switching element takes the form of a pair of transistors, one NMOS and one PMOS, the important feature being that power is dissipated only when the switch operates -- in the quiescent state (whether storing a digital 0 or 1). no current flows.
Section 43. Semicoductor technology. Oh, no. This section starts at the bottom of page 107 and doesn't end until page 120, and it begins:
In one sense (the commercial sense), this section is the most important in the book!
The reader should already be persuaded of the important part played by well controlled semiconductor materials in the development of transistors and integrated circuits. Without high-quality germanium the transistor could never have been discovered and without high-quality silicon the integrated circuit would still be a mere concept.
However, even greater importance attaches to the role played by technology.
Without the amazing skills built up by semiconductor technologists we might still be trying to wire together crude individual transistors on printed circuit boards, rather than linking powerful integrated circuit chips to build fast computers with almost unimaginable amount of memory.
A long, long paragraph. Then:
...but this still leaves unanswered the question of how to define their precise positions [the precise position of transistors on a chip]. This step, known as "photolithography," probably representing the most important single contribution to the technology, originated in the printing industry and was adapted for microelectronic applications by a number of American companies such as Bell, TI,and Fairchild at the beginning of the 1960s. As an aid to understading it, we refer to the earlier process of making mesa transistors, depeding on selective etching to form the local bumps on the semiconductor surface which defined the active device area.
Interestingly, this process is wll described in Simon Winchester's book.
