A diffused junction transistor is a transistor formed by diffusing

dopant A dopant, also called a doping agent, is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. Wh ...

s into a

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

. 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, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...

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's

micro-alloy diffused transistor The germanium alloy-junction transistor, or alloy transistor, was an early type of bipolar junction transistor, developed at General Electric and RCA in 1951 as an improvement over the earlier grown-junction transistor. The usual construction of ...

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: :"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 give ...

diffuse more rapidly than

donor A donor in general is a person, organization or government which donates something voluntarily. The term is usually used to represent a form of pure altruism, but is sometimes used when the payment for a service is recognized by all parties as rep ...

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 Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...

). The base formed beyond it because of the more rapid diffusion of the acceptor (for example,

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It h ...

). 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 with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

. 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 technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globa ...

made the first grown-junction silicon transistors in 1954. The diffused silicon mesa transistor was developed at

in 1955 and made commercially available by

Fairchild Semiconductor Fairchild Semiconductor International, Inc. was an American semiconductor company based in San Jose, California. Founded in 1957 as a division of Fairchild Camera and Instrument, it became a pioneer in the manufacturing of transistors and of int ...

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 HoerniFairchild 2N1613
Transistor Museum, Historic Transistor Photo Gallery. at

in 1959. The

planar process The planar process is a manufacturing process used in the semiconductor industry to build individual components of a transistor, and in turn, connect those transistors together. It is the primary process by which silicon integrated circuit chips ...

used to make these transistors made mass-produced monolithic integrated circuits 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,

, . {{Electronic components Transistor types