The first alternative to a carbon composition resistor is a metal oxide film resistor. These resistors are very easy to manufacture as compared to metal film resistors. Firstly we have to know that metal oxide is one kind of metallic compound that is formed due to the chemical bonding among the oxygen atom as well as other elements. So it includes a minimum of two or above different kinds of atoms like a tin with oxygen. Thus, tin oxide is utilized for designing these resistors. These resistors are the most frequently used resistors because they have superior performance as compared to carbon film & carbon composition resistors. So this article discusses an overview of a metal oxide film resistor, it’s working, and its applications.
What is Metal Oxide Film Resistor?
Metal oxide resistor definition is; the fixed value and axial resistors which are made with the ceramic rod that is covered with a metal oxide thin film like tin oxide are known as metal oxide film resistor. These resistors should not be confused with metal oxide varistors because they are made with silicon carbide or zinc oxide. These resistors are used mostly wherever power dissipation is necessary. The metal oxide resistor diagram is shown below.
Specifications
The performance guide of the metal oxide film resistor is given below.
- The available tolerance typically is ±1%, ±2%, ±5%, ±10%,
- Its resistance value ranges from 1Ω to 10MΩ.
- Maximum noise is 0.2 µV/V.
- The temperature coefficient is ±300 ppm/°C.
- The voltage coefficient is 0.0005 %/V.
- The resistor temperature maximum is 300°C.
- It has outstanding long-time stability.
- It has overload or high surge capability.
- The standard resistance tolerance is ±5%.
Construction of Metal Oxide Film Resistor
The metal oxide film resistor construction is the same as the metal film resistor except for the material used to construct the film. This resistor uses tin oxide to construct the film which is made with tin oxide as well as antimony oxide which works as the resistive element for the electric current. Thus, this material restricts the current flow to a certain level.
The manufacturing procedure of a metal oxide film can be done with chemical deposition techniques & almost ceramic carriers are used as substrates always. The deposition procedure is obtained by the pure metals reaction with gas at low pressure & high temperature. The metal oxide film is most frequently produced with a chemical deposition process. Here tin oxide is the common metal oxide film that is created by heating the body of this resistor within a tin chloride steam.
Usually, other metal oxide film uses a different deposition procedure. Initially, a thin metal film is applied, after that it is reacted by oxygen. So the desired composition is attained by simply measuring the resistance.
The working of this resistor is; once the film is applied to the body of the resistor then the final value of resistance can be achieved by applying a helical cut. Usually, this can be done by laser cutting but earlier it was done by sandblasting or grinding. Here, the spiral cut on the resistor will make the resistance path longer & also increases the value of resistance up to a hundred times higher. The value of resistance can be controlled precisely by cutting. The resistance of his resistor mainly depends on the antimony oxide amount of added to the tin oxide; the helical metal oxide film cut width & the metal oxide film layer thickness.
Characteristics
The characteristics of a metal oxide film resistor are given below.
- These resistors give better performance as compared to other resistors like carbon film & metal film resistors like voltage rating, power rating, surge capacity, high-temperature operation & overload capabilities.
- So these resistors are preferred mainly for high-endurance applications.
- These resistors’ stability properties are lower than metal film resistors.
- These have very poor properties for tolerance & low values.
- The temperature coefficient of metal oxide film resistors is higher as compared to metal film resistors like 300 ppm/0C.
- These resistors use tin oxide as a resistive material that is contaminated by antimony oxide to enhance resistivity.
- The antimony oxide amount added will determine the resistance level, the metal oxide film layer thickness & the helical metal oxide film cut width.
- These resistors can withstand high temperatures as compared to metal film or carbon resistors. The noise property of these resistors is the same of carbon resistors.
Metal Oxide Film Resistor Color Code
Generally, cylindrical resistors are color coded with bands/markings to identify the values of resistance & tolerance very quickly like metal film, carbon film, fuse, winding, metal film, and metal oxide film resistors. So the resistance value can be found based on the color code of the resistor. Resistors are available in four to six color bands on the resistors which specify the value of resistance.
Please refer to this link for: Resistor Color Code.
Please refer to this article for the Difference between Metal Oxide Resistor & Metal Film Resistor.
Advantages & Disadvantages
The advantages of a metal oxide film resistor are discussed below.
- The performance of this resistor is high compared to metal film & carbon film resistors.
- These resistors are used by many designers in high-endurance applications.
- These are not expensive as compared to carbon composition type resistors.
- They have superior high surge current capacity.
- These operate at higher temperatures.
- They have high stability & reliability.
- These are available in small sizes.
- They produce less noise.
The disadvantages of a metal oxide film resistor are discussed below.
- These are not appropriate for high-frequency-based applications.
- Nowadays these are not commonly used.
- Its installation is difficult.
Applications
The applications of a metal oxide film resistor are discussed below.
- These are the main types of resistors within basic circuits.
- These resistors are used where power dissipation is required above 1 W.
- These are used where high stability is necessary.
- These are used in medical equipment & telecommunication.
- These are used in power applications around several watts
Thus, this is an overview of a metal oxide film resistor – working, characteristics, advantages, disadvantages, and its applications. This is a fixed-type resistor that uses a resistive element like metal oxide film to restrict the electric current flow to a certain level.
