Diffused junction transistor: Difference between revisions

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{{Short description|Type of transistor}}

{{refimprove|date=February 2011}}

A '''diffusiondiffused junction transistor''' is a [[bipolar junction transistor]] (BJT) formed by diffusing [[dopant]]s into a [[semiconductor]] [[Wafer (electronics)|substrate]]. The diffusion process was developed later than the [[Alloy-junction transistor|alloy -junction]] and [[Grown-junction transistor|grown junction]] processes for making bipolar junction transistors (BJTs).

[[Bell Labs]] developed the first prototype diffusiondiffused junction bipolar transistors in 1954.<ref>[http://semiconductormuseum.com/PhotoGallery/PhotoGallery_Prototype_DiffusedBase.htm Transistor Museum, Historic Transistor Photo Gallery, '''Bell Labs Prototype Diffused Base Triode'''], Transistor Museum, Historic Transistor Photo Gallery.</ref>

==Diffused-base transistor==

The earliest diffusiondiffused junction transistors were '''diffused-base transistors'''. These transistors still had alloy emitters and sometimes alloy collectors like the earlier alloy-junction transistors. Only the base was diffused into the substrate. Sometimes the substrate formed the collector, but in transistors like [[Philco]]'s [[micro-alloy diffused transistor]]s the substrate was the bulk of the base.

==Double diffusion==

At Bell Labs [[Calvin Souther Fuller]] produced basic physical understanding of a means of directly forming the emitter, base, and collector by double diffusion. The method was summarized in a history of science at Bell:<ref>S. Millman editor (1983) ''A History of Engineering and Science in the Bell System'', volume 4: Physical Sciences, [[Bell Labs]] {{ISBN|0-932764-03-7}} p. 426</ref>

:"Fuller had shown that [[acceptor (semiconductors)|acceptor]]s of low [[atomic weight]] diffuse more rapidly than [[donor (semiconductors)|donor]]s, which made possible n–p–n structures by simultaneous diffusion of donors and acceptors of appropriately different surface concentrations. The first n layer (the emitter) was formed because of the greater surface concentration of the donor (for example, [[antimony]]). The base formed beyond it because of the more rapid diffusion of the acceptor (for example, [[aluminum]]). The inner (collector) boundary of the base appeared where the diffused aluminum no longer over-compensated the n-type background doping of the original [[silicon]]. The base layers of the resulting transistors were 4 μm thick. ... Resulting transistors had a [[cut-off frequency]] of 120 MHz."

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|isbn=9780262014243

|url=https://books.google.com/books?id=LaZpUpkG70QC

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}}, p.&nbsp;11.</ref>

The diffused silicon '''mesa transistor''' was developed at [[Bell Labs]] in 1955 and made commercially available by [[Fairchild Semiconductor]] in 1958.<ref>{{Harvnb|Lécuyer|Brock|2010|pp=10–22}}</ref>

These transistors were the first to have both diffused bases and diffused emitters. Unfortunately, like all earlier transistors, the edge of the collector–base junction was exposed, making it sensitive to leakage through surface contamination, thus requiring [[hermetic seal]]s or [[Passivation (chemistry)|passivation]] to prevent degradation of the transistor's characteristics over time.<ref>{{cite web |url=https://spectrum.ieee.org/semiconductors/design/the-silicon-dioxide-solution |archive-url=https://web.archive.org/web/20110215031520/http://spectrum.ieee.org/semiconductors/design/the-silicon-dioxide-solution |url-status=dead |archive-date=February 15, 2011 |title=The Silicon Dioxide Solution: How physicist Jean Hoerni built the bridge from the transistor to the integrated circuit|author1-link=Michael Riordan (physicist) |first=Michael |last=Riordan |work=IEEE Spectrum |date=December 2007 |accessdateaccess-date=November 28, 2012 |publisher=IEEE}}</ref>

==Planar transistor==

[[File:NPN BJT (Planar) Cross-section.svg|thumb|Simplified cross section of a planar ''npn'' bipolar junction transistor]]

The '''planar transistor''' was developed by Dr. [[Jean Hoerni]]<ref>[http://semiconductormuseum.com/PhotoGallery/PhotoGallery_2N1613.htm Fairchild 2N1613], Transistor Museum, Historic Transistor Photo Gallery, '''Fairchild 2N1613'''].</ref> at [[Fairchild Semiconductor]] in 1959. The [[planar process]] used to make these transistors made mass-produced monolithic [[integrated circuit]]s possible.

Planar transistors have a silica [[passivation (chemistry)|passivation]] layer to protect the junction edges from contamination, making inexpensive plastic packaging possible without risking degradation of the transistor's characteristics over time.

The first planar transistors had mucha worseswitching characteristics{{clarify|date=Januaryspeed much 2016}}lower than [[alloy junction transistor]]s of the period, but as they could be mass-produced, and alloy junction transistors could not, they cost much less, and the characteristics of planar transistors improved very rapidly, quickly exceeding those of all earlier transistors and making earlier transistors obsolete.{{cn|date=January 2016}}

==References==

{{reflist}}

* S. Millman editor (1983) ''A History of Engineering and Science in the Bell System'', volume 4: Physical Sciences, [[Bell Labs]] {{ISBN|0-932764-03-7}} .

* F.M. Smits editor (1985) ''A History of Engineering and Science in the Bell System'', volume 6: Electronics Technology, pp 43&ndash;57, [[Bell Labs]], {{ISBN|0-932764-07-X}} .

{{Electronic components}}

[[Category:Transistor types]]