Thin Film and Thick film Resistors

1. Bahir Dar University
Material Science and Engineering
Thin Film and Thick Film Resistors
Prepared By: Biruk Gedif
BDU- Material Science and Engineering 1

2. Outline
1.Introduction
2. Methods of Film Deposition
3.Thin film Resistor
4.Thick film Resistor
5.References
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3. Film
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Thickness ≤ 0.1µm
It is a layer of material ranging from fractions of a nanometer
(monolayer) to several micrometers in thickness.
Around thousands
time thicker.
What is thin film, thick film and resistor?
The resistor is a passive
electrical component to
create resistance in the
flow of electric current.
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4. BDU- Material Science and Engineering 4
 PVD and CVD are the most common methods for
transferring material atom by atom from one or more
sources to the growth surface of a film being deposited
onto a substrate.
 PVD  without any chemical reaction
 CVD  with chemical reaction
How Film?

5. BDU- Material Science and Engineering
Physical Vapour Deposition(PVD)
Steps in thin film growth
 Gasify the source (or target) using physical
method (heating, electron-beam evaporator,
intense photon beam, energetic ions)
 Transport
 Condensation on substrate
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Evaporation T >> Ts (temperature of substrate)
 Performed under vacuum

6. BDU- Material Science and Engineering
 In a sputtering deposition source, ions from a glow discharge bombard a
target made of the source material, which is the cathode of the discharge.
 Atoms ejected from the target condense on a substrate, which is often the
anode of the discharge
DC sputtering RF sputtering
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7. BDU- Material Science and Engineering
 A chemical reaction between a volatile compound of the material from
which the film is to be made with other suitable gases so as to facilitate
the atomic deposition of a nonvolatile solid film on a substrate.
Chemical Vapour Deposition(CVD)
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8. BDU- Material Science and Engineering
 Pyrolysis (thermally activated decomposition)
 SiH4 (g)  Si (s) + 2 H2 (g)
 Oxidation :
 SiCl4 (g) + 2 H2 (g) + O2 (g)  SiO2 (s) + 4 HCl (g)
 3 SiH2Cl2 (g) + 4 NH3 (g)  Si3N4 (s) + 6 H2 (g) + 6 HCl (g)
Some examples of CVD processes
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9. BDU- Material Science and Engineering
Thin film resistors have a metallic film that is
vacuum deposited on an insulating substrate.
Thin film is more accurate, has a better
temperature coefficient and is more stable.
 relatively high tolerances
 low noise
more accurate, has a better temperature
coefficient and is more stable.
Thin Film Resistors
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10. BDU- Material Science and Engineering
Thin Film Technology
 The resistive layer is sputtered (vacuum deposition)
onto a ceramic base. This creates a uniform metallic
film of around 0.1 micrometer thick. Often an alloy of
Nickel and Chromium is used (Nichrome).
 The layer is dense and uniform, which makes is suitable
to trim(fit) the resistance value by a subtractive process.
 By laser trimming patterns are created to increase the
resistive path and to calibrate the resistance value.
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11. BDU- Material Science and Engineering
 Thick film resistors are produced by firing
a special paste onto the substrate.
 The paste is a mixture of glass and metal
oxides.
 Thick film is preferred for applications
where these high requirements are not
critical since prices are much lower.
Thick Film Resistors
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12. BDU- Material Science and Engineering
 By far the most used resistors in electrical and electronic
devices. They come usually as chip resistor (SMD), and
have the lowest cost compared to any other technology.
 The resistive material is a special paste with a mixture of
a binder, a carrier, and the metal oxides to be deposited.
The binder is a glassy frit and the carrier exists of organic
solvent systems and plasticizers. Modern resistor pastes
are based on oxides of ruthenium, iridium and rhenium.
Thick Film Technology
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13. BDU- Material Science and Engineering
 This is also referred to as a cermet
(Ceramic – Metallic). The resistive
layer is printed onto a substrate at
850°C. The substrate is often 95%
alumina ceramic.
 After the firing of the paste on the
carrier, the film becomes glasslike,
which makes it well protected
against moisture.
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Fig: The complete firing process
Advantage of thick film over thin film
technology
 Low cost
 No high tolerances
 Low TCR or high stability
 ability to handle more power
 Provides a wider range of resistance value

14. BDU- Material Science and Engineering
Thickness dependent resistivity
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They are produced with different layer thicknesses to
accommodate a range of resistance values.
Thin and thick
film resistors are
characterized by a
resistive layer on a
ceramic base.

15. BDU- Material Science and Engineering
References
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1. http://www.resistorguide.com/thin-and-thick-film/
2. Resistors for Down Hole Applications
www.vishay.com/doc?49025
3. Vishay Dale Thin Film Resistors Selector Guide
www.vishay.com/doc?49188
4. SMD Resistors Selector Guide
www.vishay.com/doc?49252

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Thank You !