2N140_PNP_Germanium_Alloy_Junction_Transistor_closeup

2N1307 transistor die with bond wires attached

The germanium alloy-junction transistor, or alloy transistor, was an early type of

bipolar junction transistor A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar ...

, developed at

General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...

and

RCA The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...

in 1951 as an improvement over the earlier

grown-junction transistor The grown-junction transistor was the first type of bipolar ''junction'' transistor made. It was invented by William Shockley at Bell Labs on June 23, 1948 (patent filed June 26, 1948), six months after the first bipolar point-contact transistor ...

. The usual construction of an alloy-junction transistor is a

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...

crystal forming the base, with emitter and collector alloy beads fused on opposite sides.

Indium Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts p ...

and

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 time ...

were commonly used to form the alloy junctions on a bar of N-type germanium. The collector junction pellet would be about 50 mils (thousandths of an inch) in diameter, and the emitter pellet about 20 mils. The base region would be on the order of 1 mil (0.001 inches, 25 μm) thick. There were several types of improved alloy-junction transistors developed over the years that they were manufactured. All types of alloy-junction transistors became obsolete in the early 1960s, with the introduction of the

planar transistor A diffused junction transistor is a transistor formed by diffusing dopants into a semiconductor substrate. The diffusion process was developed later than the alloy junction and grown junction processes for making bipolar junction transistors (B ...

which could be mass-produced easily while alloy-junction transistors had to be made individually. The first germanium planar transistors had much worse characteristics than alloy-junction germanium transistors of the period, but they cost much less, and the characteristics of planar transistors improved very rapidly, quickly exceeding those of all earlier germanium transistors.

Micro-alloy transistor

The micro-alloy transistor (MAT) was developed by

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 purchased ...

as an improved type of alloy-junction transistor, it offered much higher speed. It is constructed of a semiconductor crystal forming the base, into which a pair of wells are etched (similar to Philco's earlier

surface-barrier transistor The surface-barrier transistor is a type of transistor developed by Philco in 1953 as an improvement to the alloy-junction transistor and the earlier point-contact transistor. Like the modern Schottky transistor, it offered much higher speed than ...

) on opposite sides then fusing emitter and collector alloy beads into the wells.

Micro-alloy diffused transistor

The micro-alloy diffused transistor (MADT), or micro-alloy diffused-base transistor, was developed by

as an improved type of micro-alloy transistor; it offered even higher speed. It is a type of

diffused-base transistor A diffused junction transistor is a transistor formed by diffusing dopants into a semiconductor substrate. The diffusion process was developed later than the alloy junction and grown junction processes for making bipolar junction transistors (B ...

. Before using electrochemical techniques and etching depression wells into the base semiconductor crystal material, a heated diffused phosphorus gaseous layer is created over the entire intrinsic semiconductor base crystal, creating a N-type graded base semiconductor material. The emitter well is etched very shallow into this diffused base layer. For high-speed operation, the collector well is etched all the way through the diffused base layer and through most of the intrinsic base semiconductor region, forming an extremely thin base region.Wall Street Journal, Article: "Philco Says It Is Producing A New Kind Of Transistor", October 9, 1957, pg 19 A doping-engineered

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

was created in the diffused base layer to reduce the

charge carrier In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used ...

base transit time (similar to the

drift-field transistor The drift-field transistor, also called the drift transistor or graded base transistor, is a type of high-speed bipolar junction transistor having a doping-engineered electric field in the base to reduce the charge carrier base transit time. Inven ...

Post-alloy diffused transistor

The post-alloy diffused transistor (PADT), or post-alloy diffused-base transistor, was developed by

Philips Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters i ...

(but GE and RCA filed for patent and Jacques Pankove of RCA received patent for it) as an improvement to the germanium alloy-junction transistor, it offered even higher speed. It is a type of

. The Philco micro-alloy diffused transistor had a mechanical weakness that ultimately limited their speed; the thin diffused base layer would break if made too thin, but to get high speed it needed to be as thin as possible. Also it was very hard to control alloying on both sides of such a thin layer. The post-alloy diffused transistor solved this problem by making the bulk semiconductor crystal the collector (instead of the base), which could be as thick as necessary for mechanical strength. The diffused base layer was created on top of this. Then two alloy beads, one P-type and one N-type were fused on top of the diffused base layer. The bead having the same type as the base dopant then became part of the base and the bead having the opposite type from the base dopant became the emitter. A doping-engineered

was created in the diffused base layer to reduce the

base transit time (similar to the

Photo gallery

Image: TG51 Transistor 02.jpg, TG 51 PNP germanium alloy transistor Made by TEWA Poland Image: TG51 Transistor 03.jpg, TG 51 PNP germanium alloy transistor Made by TEWA Poland Image: 2N1307 transistor die.jpg, General Electric 2N1307 PNP germanium alloy transistor Image: 2N1307 transistor bond wires.jpg, General Electric 2N1307 PNP germanium alloy transistor Image: 2N404.jpg, RCA 2N404 Germanium PNP Transistor. Medium Speed Switch Image: ACY21.jpg, PNP germanium alloy transistor intended as AF amplifier / switch

References

External links