Fundamental concepts of integrated-circuit technology M. Rudan University of Bologna.

Fundamental concepts ofFundamental concepts ofintegrated-circuit technologyintegrated-circuit technology

M. Rudan

University of Bologna


Fundamental concepts of integrated-circuit technology M. Rudan

SILICON PLANAR TECHNOLOGY

10 in = 25.40 cm12 in = 30.48 cm

300 μm = 0.3 mm

Wafer

Chip



SILICON PLANAR TECHNOLOGY

300 μm = 0.3 mm

10 ÷ 20 μm

Bulk

Devices



N-TYPE DOPING (I)

10 ÷ 20 μm

Bulk

Adding suitably-chosen atoms increases the local concentration of free charge

n+



N-TYPE DOPING (II)

10 ÷ 20 μm

Bulk

Typically, the wafer is also lightly doped (from factory)

n+

n silicon (n- silicon)



N-TYPE DOPING (III)

The conductivity of pure (intrinsic) silicon (Si) is low: the material is a semiconductor. It is a IV-type material.

The addition of a small amount of V-type material, like phosphorus (P), arsenic (As), or antimony (Sb) increases the local concentration of free electrons.

The added materials are called dopants or impurities, of donor type.

The doped silicon is called extrinsic of n-type. It is not a chemical compound, e.g., of Si and P.



N-TYPE DOPING (IV)

The larger concentration of free electrons makes the local electrical conductivity to increase.

In an intrinsic semiconductor the electrical conductivity increases as temperature increases (opposite to conductors).

In a doped semiconductor the conductivity becomes independent of temperature at least in a range of temperatures.

The inclusion of dopants makes it possible to externally control the electrical conductivity.



P-TYPE DOPING (I)

The semiconductors allow for another type of doping, “dual” with respect to the n-type.

The addition of a small amount of III-type dopants, like boron (B), aluminum (Al), gallium (Ga), or Indium (In) increases the local concentration of free positive charges, called holes.

The doped silicon is called extrinsic of p-type. The dopants are of the acceptor type.

Holes are fictitious particles. The particles that actually carry the current are always electrons.



P-TYPE DOPING (II)

10 ÷ 20 μm

Bulk

Adding suitably-chosen atoms increases the local concentration of free charge

p+



P-TYPE DOPING (III)

The larger concentration of free holes makes the local electrical conductivity to increase.

Also in a p-type doped semiconductor the conductivity becomes independent of temperature at least in a range of temperatures.

The inclusion of n-type or p-type dopants makes it possible to externally control the electrical conductivity and also to obtain regions with a different type of dominant free charge.



N- AND P-TYPE DOPING

The electrons and holes are also collectively called carriers.

In an n-type region, the electrons are called majority carriers. A few holes are also present, that are called minority carriers.

In a p-type region, the holes are called majority carriers. A few electrons are also present, that are called minority carriers.

Under the influence of a given electric field, electrons and holes are accelerated in opposite directions.



P-TYPE DOPING (IV)

10 ÷ 20 μm

Bulk

p+

Typically, the wafer is also lightly doped (from factory)

p silicon (p- silicon)



P-N JUNCTION (I)

10 ÷ 20 μm

Bulk

p+

Two adjacent regions with opposite doping form a p-n junction.

n silicon (n- silicon)



P-N JUNCTION (II)

10 ÷ 20 μm

Bulk

n+

p silicon (p- silicon)

Two adjacent regions with opposite doping form a p-n junction.



P-SUBSTRATE MOS CAPACITOR

p silicon (bulk)

VG = 0

SiO2 (insulator)

Gate and bulk contactsVG > 0

Layer of electrons

Layer of missing electrons

The drawing is not in scale.



N-SUBSTRATE MOS CAPACITOR

n silicon (bulk)

VG = 0

SiO2 (insulator)

Gate and bulk contactsVG < 0

Layer of holes

Layer of electrons




N-CHANNEL MOS TRANSISTOR (MOSFET)

p silicon (bulk)

VGB = 0

Gate and bulk contactsVGB > 0

Layer of electrons

Layer of missing electrons


SiO2 (insulator)Source DrainConductive channel



P-CHANNEL MOS TRANSISTOR (MOSFET)

n silicon (bulk)

VGB = 0

Gate and bulk contactsVGB < 0

Layer of holes

Layer of electrons


SiO2 (insulator)Source DrainConductive channel

Fundamental concepts of integrated-circuit technology M. Rudan University of Bologna.

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