Dielectric materials for semiconductor
chips
Little funda about dielectric material:
Dielectric material characterize with very low electrical
conductivity (one millionth of a mho / cm), in which an
electric field can be sustained with a minimal leakage.
It can store electrical energy/charge.
The electrically sensitive molecules inside dielectric
material called polar molecules align by a pattern whenever
external electric voltage is applied. The polar molecules
align with the field so that the positive charges accumulate
on one face of the dielectric and the negative charges on
the other face.
Dry air is a good example of a dielectric material but
is a poor dielectric. Most of the dielectric materials are
solid such as porcelain (ceramic), glass, mica, plastics,
and the oxides of various metals. Some liquids and gases
can also good dielectric properties, vaccum and distilled
water are also dielectric materials.
Dielectric material is popularly used in capacitors to
reduce the size of the capacitor. The ceramic and plastic
film capacitors are good examples. Another major application
of Dielectric materials is in semiconductor chips to insulate
transistors from each other. Dielectric materials are also
used in various other electrical and electronic components.
Why the dielectric material is used in capacitor?
Dielectric material offers mechanical strength
By factor ? the capacitance is increased
The "dielectric breakdown", or maximum electric
field before conduction between the plates starts, can be
higher than for air, allowing high voltage ratings
Separation of the plate can be small, which also increases
capacitance
Dielectric strength may be defined as the maximum potential
gradient to which a material can be subjected without insulating
breakdown, that is
Where DS is the dielectric strength in kV/mm, VB the breakdown
voltage, and d the thickness.
Dielectric constant is the ratio of the amount of stored
electrical energy when a potential is applied, relative
to the permittivity of a vacuum.
SEMICONDUCTOR Applications
Due to improvement in dielectric material characteristics
used in semiconductor devices, the performance of semiconductor
device such as power consumption, speed, and size are improved.
Also semiconductor chips can integrate high capacitance
capacitors inside the chip to save the circuit from using
external decoupling capacitors between the power and the
ground planes.
These decoupling capacitors will reduce the transient voltage
on the voltage supply, which are caused by the current spikes
that occur when the transistors on the semiconductor circuit
switch on or off.
Since in the mid-1990s, the microelectronics industry has
innovated high- and low-k dielectrics (k is the dielectric
constant of a material) for continuing reduction of both
horizontal and vertical dimensions of integrated circuits
(ICs). Due to use of low K material the gate leakage current
and heat dissipation can be brought down. Low K materials
offer lower propagation delay, and lower cross talk enabling
devices to operate at higher frequencies i.e in the range
of giga hertz.
Low K dielectric materials:
In both the vertical and horizontal dimensions the reduction
in spacing of metal interconnects has created the need for
low-k materials that serve as interlevel dielectrics to
offset the increase in signal propagation time between transistors,
known as RC delay (R is metal wire resistance and C is interlevel
dielectric capacitance). To fulfill these requirements at
32nm and lesser IC fabrication nodes, innovation in dielectric
materials is must if the device density of ICs has to continue
at Moore's Law rate. Low K materials are used in multi level
interconnects, interlayer dielectrics, and for passivation
layers.
Some of the examples of low K dielectric material are,
Nanopourous Silica, Hydrogensilsesquioxanes (HSQ), Teflon-AF
(Polytetrafluoethylene or PTFE), Silicon Oxyflouride (FSG).
The present trend now is using dielectric with K of less
than 2.
High K dielectric materials:
The High K dielectric materials are needed for the storage
capacitors, and nonvolatile static memory devices. Wherever
high capacitance is required the high-K material is used.
High K dielectric material is used between gate and the
silicon in CMOS transistors to increase the capacitance
of the metal and silicon.
http://yuekuo.tamu.edu/Hkgd.htm
Conventional materials such as thermal and chemical vapour
deposition (CVD) SiO2 are being replaced with new materials
such as high k gate dielectrics, and carbon doped SiO2 for
low k interlevel dielectrics.
Some of the latest high k dielectric materials include:
--- SiNx with 4 < k < 10
--- Ta2O5, Al2O3, ZrO2, and HfO2 with 10 < k < 100
--- PZT with k<100
To find dielectric constant for thousands of chemical compounds
and elements visit the site http://www.clippercontrols.com/info/dielectric_constants.html
And
http://www.kayelaby.npl.co.uk/general_physics/2_6/2_6_5.html
