Transistor Construction

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Transistor Construction

• By Salvacion, Cupid Cynderlad A.
• Bachelor of Secondary Education-3
• CED115

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Transistor

• A three-layer semiconductor device consisting of
  either two n- and one p-type layers of material
  or two n-type layers of material.

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The former is called npn transistor
0.150 in
0.001 in
E
C
p
n
n
B
VEE
VCC
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The latter is called pnp transistor
0.150 in
0.001 in
E
C
p
p
n
B
VEE
VCC
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• The doping of the sandwiched layer is also
  considerably less than that of the outer layers
  (typically, 101 or less)
• This lower doping level decreases the
  conductivity (increase the resistance) of this
  material by limiting the number of free
  carriers.

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FOUR BASIC TECHNIQUES IN TRANSISTOR CONSTRUCTION

• GROWN
• ALLOY
• DIFFUSION
• EPITAXIAL

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GROWN TYPE

• It is made by drawing a single crystal from melt
  of silicon or Germanium whose impurity
  concentration is changed during the
  crystal-drawing operation by adding n- or p-type
  atoms as required.
  
  

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ALLOY TYPE

• This technique, also called the fused
  construction.
• The center section is a thin wafer, and the whole
  Structure is raised for a short time to a high
  temperature, above the melting point of indium
  but below that of Germanium.
• On, cooling, the Germanium contact w/ the base
  material, recrystallizes w/ enough Indium
  concentration to change it from n to p type.

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• Because of geometrical arrangement, almost all
  the emitter current flows a diffusion path toward
  the collector rather than the base.
• The collector is made larger than the emitter. So
  that the collector subtends a large angle as
  viewed from the emitter.

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DIFFUSION TYPE

• This technique consist of subjecting a
  semiconductor wafer to gaseous diffusion of both
  n- and p- type impurities to form both the
  emitter and the junctions.
• This process, the base-collector junction area
  is determined by a different mask.
• A thin layer of silicon dioxide is grown over the
  entire surface and photoetched, so that aluminum
  can be made by the emitter and the base leads.

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• Because of the passivating action of the oxide
  layer, most surface problems are avoided a very
  low leakage current result.
• There is also an improvement in the current gain
  at low currents and a noise figure.

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EPITAXIAL TYPE

• This technique is consist of growing a very thin,
  high purity, single-crystal layer of silicon on a
  heavily dope substrate of the same material.
• This augmented forms the collector on w/c the
  base and emitter may be diffused.
• All microelectronic bipolar transistors are
  fabricated in this manner.

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References Acknowledgements

• I would like to give thanks
• To the Almighty God the Father for the vigor that
  he had given to me.
• To all those who listen to my report.
• To the generous person who hasnt hesitate to
  help me finish this task, unfortunately he hasnt
  introduce his name.

• Microelectronic Digital and Analog
  Circuits and System By Jacob Millman,
  Ph. D pages63, 64 and 65.
• Electronics and Circuits Theory
  
• By Nashelsky and company

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• Thank you very much for listening to my report.
  
• Good afternoon to all.