ELEKTRONIKOS ĮTAISAI
1
2009
Integrated diodes
pn junctions of transistor structures can be used as integrated diodes. The
choice of the junction is limited by the considerations of switching speed and
breakdown voltage.
The forward
voltage drop only
slightly depends
on the forward
current.
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ELEKTRONIKOS ĮTAISAI
2
2009
Integrated diode
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ELEKTRONIKOS ĮTAISAI
3
2009
Integrated capacitors
Capacitors in ICs are fabricated by using either the depletion region
capacitance of a reverse-biased pn junction, the MOS structure, or thin-film
deposition.
A typical diffused junction capacitor uses
the capacitance of the base-collector
junction. The capacitance of such a
component is typically 100 pF/mm2 with
reverse voltage of around 1 V.
Capacitance depends on the applied
reverse bias. The capacitor has an
access resistance, associated with the
built-in resistance of the epilayer
between the active region of the
capacitance and a contact.
It is also possible to use the emitter-base
junction to form an integrated capacitor.
Its capacitance per unit area is around
1000 pF/mm2.
This increase is at the expense of a
reduction in breakdown voltage, which
limits operating voltages to less than 5 V.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
4
2009
Integrated capacitors
An MOS capacitor is a parallelplate capacitor with SiO2 (whose
thickness is about 50 nm) as the
dielectric. A surface thin film of
metal (aluminium) is the top plate.
The bottom plate consists of the
heavily doped n+ region.
Because of the heavily doped
bottom layer, MOS capacitors are
nonpolarized capacitors.
The upper plate can be the
polysilicon layer used to obtain the
gate regions of the MOS
transistors.
The capacitance of junction or MOS
capacitors is quite small, typically
less than 100 pF.
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stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
5
2009
Integrated capacitors
Planar capacitor
"Trench" capacitor
http://images.google.lt/imgres?imgurl=http://www.tf.unikiel.de/matwis/amat/elmat_en/kap_5/illustr/capacitor1.gif&imgrefurl=http://www.tf.unikiel.de/matwis/amat/elmat_en/kap_5/backbone/r5_1_4.html&h=160&w=480&sz=5&hl=lt&start=88&tbnid=yVk81RngIePOjM:&tbnh=
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6sa%3DN
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
6
2009
Integrated capacitors
The deviation of capacitance of integrated capacitors is usually great (to
20 %).
If permissible deviation is less, thin film capacitors are used. Silicon dioxide
SiO2 or aluminium oxide Al2O3 can be used as a dielectric layer.
The use of tantalum films can increase the capacitance per unit area by a
factor of 10. A controlled growth of tantalum pentoxide (Ta2O5) is used for the
dielectric, and metallic tantalum is deposited for the top plate (since
aluminium is soluble in Ta2O5).
The increased capacitance is obtained at the expense of additional
processing steps.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
7
2009
Integrated capacitor
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ELEKTRONIKOS ĮTAISAI
8
2009
Integrated resistors
Resistors in monolithic integrated
circuits use the bulk resistivity of
one of the transistor regions. The
most common technique is to use
the diffused or implanted p-type
base region of the bipolar
transistor.
The n-type epitaxial layer (the
collector region) serves to isolate
the p-type resistor from other chip
components.
Actual sheet resistance for the
base diffused layer is typically 100
- 250 Ω/. So, resistors in the
range 50 Ω - 10 kΩ can be
provided.
The high-value resistors are often
folded to conserve chip area.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
9
2009
Integrated transistor and resistor
http://www.necel.com/en/faq/faq_opcomp12.gif
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stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
10
2009
Integrated resistor
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ELEKTRONIKOS ĮTAISAI
11
2009
Integrated resistor
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ELEKTRONIKOS ĮTAISAI
12
2009
Integrated resistors
A pinch-resistor, in which additional
floating emitter diffusion is
incorporated, can provide high
resistance values.
For low-value resistors the emitter
n+ layer, which has a sheet
resistance typically in the range 1 10 Ω/, can be used.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
13
2009
Integrated resistors
The deviation of resistance of IC resistors is usually great (to 20 % when the
base region is used, and to 50 % for pinch-resistors).
Diffused resistors are all relatively extravagant in their use of chip area. For
example, one 1 kΩ resistor might occupy the same area as 10 bipolar
transistors. That is why integrated resistors tend to be omitted altogether if
possible in modern ICs or replaced by the active resistance of a BJT.
In MOS technology, polysilicon layer resistors and ion-implanted resistors are
used. The third type of resistor is the MOS transistor itself. When biased in the
ohmic region, the MOSFET behaves as a resistance. In addition, both
enhancement and depletion MOSFETs are used as non-linear resistors in the
saturation region.
The technique of vapour thin-film deposition can also be used to fabricate
resistors for integrated circuits. The ohmic value of a thin-film resistor may be
trimmed by cutting away part of the resistor with a laser beam.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
14
2009
Some layers of conductors, isolated by crossover oxide are used in complex ICs.
Multiple interconnect layers
IBM photomicrograph (Si has been removed!)
Metal 2
M1/M2 via
Metal 1
Polysilicon
Diffusion
Mosfet (under polysilicon gate)
6.004 – Fall 2001
VGTU EF ESK
9/13/01
stanislovas.staras@el.vgtu.lt
L03 - CMOS Technology
14
ELEKTRONIKOS ĮTAISAI
15
2009
Conductors
Aluminium conductors are used to interconnect elements of ICs. But it is
impossible to avoid crossovers of conductors. So, some layers of conductors,
isolated by crossover oxide are used in complex ICs.
The wiring required to interconnect transistors must scale at the same rate as
the transistors in order to take advantage of improvements in size and speed.
The industry is currently moving from aluminum to lower-resistance
copper metallurgy, which can decrease both wiring resistance and
capacitance. Research is also underway to move from silicon dioxide
insulators between wiring levels to various low-dielectric-constant
insulators, which can further decrease wiring capacitance.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
16
2009
The bridge-like cross
Some crossovers can be avoided using bridge-like crosses. Such a bridge-like
cross is a diffused resistor. Its resistance is 3 - 5 ohms. It is also important that
an isolated island is needed for the bridge-like cross. This reduces the
complexity factor of the IC.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
17
2009
The bridge-like cross
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ELEKTRONIKOS ĮTAISAI
18
2009
The bridge-like cross
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
19
2009
Contact pads
Individual processing of chips
includes the connection of package
leads to the contact pads of chips.
Most contact pads are deposited on
SiO2 layer and isolated from the
semiconductor substrate. But the thin
dielectric layer can be easily damaged
during the chip mounting (chip
bonding). That causes the failure of
the chip. Therefore isolated islands
are used below the contact pads to
avoid failure .
Such an isolated island is not
necessary below the contact pad to
which the greatest negative voltage is
applied. This contact pad is specially
connected to the substrate through
the window opened in the SiO2 layer.
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
20
2009
http://www.answers.com/topic/integrated-circuit
VGTU EF ESK
stanislovas.staras@el.vgtu.lt
ELEKTRONIKOS ĮTAISAI
21
2009
Elements
Isolation of
of elements
MOS ICs
http://www.answers.com/topic/integrated-circuit
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