What is a Thin Film Resistor : Working & Its Applications

Resistors are the most fundamental electrical and electronic components which are widely used in all electrical circuits. Generally, resistors restrict the current flow within a circuit to implement resistance. The products based on Film technology have developed adequately to change older carbon resistors. These are classified into two types thick film & thin film or metal film. These two film-type resistors are the most creative kinds of resistors used in various electronic devices. These types of resistors look small and smarter but are designed differently with different properties. So this article discusses one of the film type resistors namely thin film resistor.


What is a Thin Film Resistor?

Thin Film Resistor Definition: The resistor which uses a thin film resistive layer is known as the thin-film resistor. This layer is arranged on top of a ceramic base. As compared to the thick film resistor, the thickness of this resistor is very thin approximately 0.1 microns. Generally, these resistors are stable, more accurate, and have a better temperature coefficient so used in higher precision technologies. Both the thick film and thin film resistors look like same but their manufacturing processing is different.

Thin Film Resistors
Thin Film Resistors

Construction

The construction of the film resistor can be done through a sputtering process of the resistive material over the ceramic. After that, the surface can be etched through ultraviolet exposure & required etching techniques. This resistor uses different materials while making like bismuth Ruthanne, tantalum nitride, lead oxide, nickel-chromium & ruthenium oxide. After that, the etched film can be trimmed with lasers.

Construction of Thin Film Resistor
Construction of Thin Film Resistor

The width of the film decides the resistance however this can be adjusted through laser trimming if necessary. On the other hand, the film can be sputtered on a cylindrical face through axial leads; so the resulting components are normally known as metal film resistors instead of thin film, but the concept is similar although at the cost of parasitic inductance.

Properties

The properties of is thin-film resistor include the following.

  • The resistance Value ranges from 0.2 – 20 MΩ.
  • Tolerance ranges from ±0.1  to  ±2 %.
  • The temperature Coefficient is from ±5  to ±50 ppm/°C.
  • The maximum operating temperature is 155°C.
  • Maximum Operating Voltage is 50 to 500V.
  • Non-linearity is >110dB.
  • The current Noise is less than 0.1 µV/V.
  • Power Rating is 1/16  to 1 W.
  • Stability is ±0.15 to  ±0.5 ∆R/R %.
  • High-frequency behavior.

Thin Film Resistor Vs Thick Film Resistor

Thin film and thick film resistors are characterized based on the resistive layer used on the base or ceramic substrate. Although, these two resistors look like same their fabrication process and properties will be changed. The names of these resistors can be originated from the thickness of the layer used in the resistor. The difference between a thin-film resistor and a thick film resistor includes the following.

Thin Film Resistor

Thick Film Resistor

The resistive layer used by this resistor is a thin film. The resistive layer used by this resistor is a thick film
The thickness of the resistive layer used in this resistor is 0.1 micrometer The thickness of the resistive layer used in this resistor is a thousand times thicker.
These resistors include a metallic film that is placed on an insulating substrate. These resistors are produced through firing a particular paste, which is a blend of metal oxides & glass onto the substrate.
The thin-film resistor has a lower temperature coefficient. A thick film resistor has a high-temperature coefficient.

 

These resistors have a lower tolerance. These resistors have a higher tolerance.
Its capacitance is lower. Its capacitance is higher.
The production cost is expensive. The production cost is not expensive.
The manufacturing process of this resistor can be done by depositing a dense and uniform metallic alloy layer onto the ceramic base beneath a vacuum. So this layer works as the resistive layer. The manufacturing process of this resistor can be done by firing a paste into the substrate. Here the paste is a mixture of metal oxides and glass.

Characteristics

The main characteristics of a thin-film resistor are rated voltage, rated power, maximum element voltage, operating temperature range, and power derating curve.

Rated Voltage

The maximum AC/DC voltage that is used continuously within an ambient temperature can be given as;

E = √R*P

Where,

‘E’ is the rated voltage measured in volts.

‘R’ is resistance measured in ohms

‘P’ is rated power measured in watts

If ‘E’ is larger as compared to the maximum element voltage, then this is the rated voltage.

Rated Power

The rated power can be defined as the maximum power that can be used continuously within an ambient temperature. It changes based on size.  The products with long sides & widened terminals do extremely well in heat dissipation & can handle maximum power for equal size, allowing reduction & miniaturization of components.

Maximum Element Voltage

The max AC or DC voltage that can be applied continuously to the thin film resistor

Operating Temperature Range

The temperature range is where the resistor can be used constantly and that can be defined by the lowest and the highest operating temperature.

Power Derating Curve

The Derating curve will show the range of working temperature & highest power at every point of temperature. This curve mainly depends on the different product series. The power derating curve is also known as a current-carrying capacity curve or power rating curve.

Thin Film Resistor Color Code

Please refer to this link to know more about Resistor Color Code Calculation.

Stability and Reliability of Ti/Tin as a Thin Film Resistor

The results of thermal stability and reliability of Ti/TiN thin-film resistors will indicate that Ti/TiN thin film resistor has an outstanding 350°C of thermal stability. As compared TiN layer based on electrical measurements, the ‘Ti’ layer includes less electrical resistance. In addition, the major breakdown mechanism of the resistor can be activated thermally through Joule heating.

The activation of thermal energies can be determined as 1.3 eV for the Ti layer failure & 1.8 eV for the TiN layer failure. According to these results, Ti/TiN thin film resistors are estimated as electrically stable for a minimum of 10 years if the temperature of these resistors is kept under 311°C.

Both the films like Titanium & titanium nitride are widely used as glue layers within silicon microelectronic technology, anti-reflective layers & diffusion barriers. These two films are also helpful in the thin-film resistors fabrication for RFIC (radio frequency integrated circuits) & MMICs (monolithic microwave integrated circuits).

The most significant thin film resistor parameters are; TCR or temperature coefficient of resistance, thermal stability, reliability performance & specific resistivity.

Some engineers have studied both tantalum nitride & titanium nitride as potential thin-film resistors. But few investigations about the reliability of these resistors that are utilized within semiconductor circuits have been executed.

Furthermore, the first ‘Ti’ layer is deposited before the TiN layer deposition within the resistor fabrication because the ‘Ti’ layer works as a wetting layer. For the Ti/TiN loaded thin film resistors, the stability & reliability investigation characteristics are limited.

Advantages

The advantages of a thin-film resistor include the following.

  • These resistors achieve much less resistor temperature coefficients & tolerances.
  • They have less noise, lower capacitance & lower parasitic inductance.
  • The electrical performance of these resistors is high.
  • High-frequency response.
  • It provides a high power rating.
  • It has less noise.
  • These resistors can be trimmed for accuracy.

Disadvantages

The disadvantages of thin-film resistors include the following.

  • These components are delicate.
  • High cost.
  • Need to handle very carefully.

Applications

The applications of thin-film resistors include the following.

  • The function of a thin-film resistor is to use in applications where high accuracy, low noise, and high stability are required. These applications may include different equipment like measurement, test, medical, monitoring, instrumentation, precision, and audio applications.
  • These resistors are used in precision applications.
  • These resistors are used to control the op-amps gain and some other applications are stable voltage division, stable reference, ADC or DAC, and stable feedback loops
  • These resistors within a network form provide extra benefits in performance.
  • Thin-film resistors are used where higher precision is necessary like equipment monitoring & measuring in the aerospace & medical fields, audio computer chips, RF applications, telecommunications, power supply converters, HVAC systems, etc.

Thus, this is brief information about a thin film resistor. These resistors are used in different fields like medical, instrumentation, computer, audio, power supplies, telecom, HVAC, etc. Here is a question for you, what is a thick film resistor?

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