A diffused junction transistor is a
transistor
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
formed by diffusing
dopant
A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as electrical or optics, optical properties. The amount of dopant is typically very low compared to the material b ...
s into a
semiconductor
A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...
substrate. The diffusion process was developed later than the
alloy-junction and
grown junction processes for making bipolar junction transistors (BJTs).
Bell Labs
Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...
developed the first prototype diffused junction bipolar transistors in 1954.
Diffused-base transistor
The earliest diffused 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
Philco (an acronym for Philadelphia Battery Company) is an American electronics industry, electronics manufacturer headquartered in Philadelphia. Philco was a pioneer in battery, radio, and television production. In 1961, the company was purchase ...
's
micro-alloy diffused transistors 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:
:"Fuller had shown that
acceptors of low
atomic weight
Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...
diffuse more rapidly than
donors, 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
Antimony is a chemical element; it has chemical symbol, symbol Sb () and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (). Antimony compounds have been known since ancient t ...
). The base formed beyond it because of the more rapid diffusion of the acceptor (for example,
aluminum
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
). 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
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
. The base layers of the resulting transistors were 4 μm thick. ... Resulting transistors had a
cut-off frequency of 120 MHz."
Mesa transistor
Texas Instruments
Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...
made the first grown-junction silicon transistors in 1954.
The diffused silicon mesa transistor was developed at
Bell Labs
Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...
in 1955 and made commercially available by
Fairchild Semiconductor
Fairchild Semiconductor International, Inc. was an American semiconductor company based in San Jose, California. It was founded in 1957 as a division of Fairchild Camera and Instrument by the " traitorous eight" who defected from Shockley Semi ...
in 1958.
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 seals or
passivation to prevent degradation of the transistor's characteristics over time.
Planar transistor
The planar transistor was developed by Dr.
Jean Hoerni
Jean Amédée Hoerni (September 26, 1924 – January 12, 1997) was a Swiss-born American engineer. He was a silicon transistor pioneer, and a member of the "traitorous eight". He developed the planar process, an important technology for reliably ...
Fairchild 2N1613
Transistor Museum, Historic Transistor Photo Gallery. at Fairchild Semiconductor
Fairchild Semiconductor International, Inc. was an American semiconductor company based in San Jose, California. It was founded in 1957 as a division of Fairchild Camera and Instrument by the " traitorous eight" who defected from Shockley Semi ...
in 1959. The planar process used to make these transistors made mass-produced monolithic integrated circuit
An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...
s possible.
Planar transistors have a silica 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 a switching speed much lower than alloy junction transistors 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.
References
* F.M. Smits editor (1985) ''A History of Engineering and Science in the Bell System'', volume 6: Electronics Technology, pp 43–57, Bell Labs
Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...
, .
{{Electronic components
Transistor types