Metal oxide film resistor - Definition, construction and ...

Metal Oxide Film Resistor Definition

The metal oxide film resistor is a type of fixed resistor that utilizes a metal oxide film as its resistive element to control the electric current flow to a specific level. According to recent data, these resistors are widely recognized for their stability, reliability, and ability to function well in high-temperature environments.

Understanding Metal Oxide

Metal oxide is a compound that forms through the chemical bonding of oxygen with other elements, creating a metallic compound consisting of various atoms like tin combined with oxygen. For metal oxide film resistors, the film is primarily composed of tin oxide.

What is Tin Oxide?

Tin oxide is a compound produced through the bonding of oxygen and tin.

Construction of Metal Oxide Film Resistors

The design of metal oxide film resistors closely resembles that of metal film resistors. The main distinction is the materials used for the film's construction. While metal film resistors utilize metals like nickel chromium, metal oxide film resistors employ metal oxides such as tin oxide.

In these resistors, a ceramic core is coated with a metal oxide, typically tin oxide. To enhance its resistivity, antimony oxide is added to the tin oxide. The film's resistivity largely hinges on the amount of antimony oxide mixed into the tin oxide.

The combination of tin oxide and antimony oxide effectively serves as the resistive element against the electric current. The ceramic core serves as an insulator, preventing heat transfer, which allows these resistors to endure high temperatures.

Metal end caps are affixed at both ends of the resistive element, with copper leads connected to these caps. Comparatively, metal oxide film resistors can handle higher temperatures than both metal film and carbon film resistors.

A helical cut through the metal oxide film achieves the desired resistance. This cutting process is halted once the target resistance value is reached, commonly employing lasers for precision.

Factors Affecting Resistance in Metal Oxide Film Resistors

The resistance of a metal oxide film resistor depends on several factors: the amount of antimony oxide incorporated, the thickness of the metal oxide film layer, and the width of the helical cut made in the metal oxide film.

Amount of Antimony Oxide Added

The addition of antimony oxide to tin oxide is crucial for increasing the resistance within metal oxide films. The higher the antimony oxide content, the greater the resistance to electric current.

An increased antimony oxide ratio significantly restricts electric current flow, while a lower ratio allows some electrical flow.

Width of Helical Metal Oxide Film Cut

The laser-induced helical cutting increases the resistive pathway, thus enhancing resistance against electric current. The width of this cut directly influences the resistance offered by the metal oxide film resistor.

Wider helical cuts provide minimal obstruction to electric current, facilitating a larger flow, whereas narrower cuts create greater resistance.

Metal Oxide Film Layer Thickness

The thickness of the metal oxide film layer inversely impacts the resistor's resistance. Heavier films grant a broader passage for electron movement, minimizing collisions with atoms. Consequently, thicker films enable a higher electric current flow.

Conversely, thinner films limit space, increasing the likelihood of electron collisions and reducing current capacity.

Advantages of Metal Oxide Film Resistors

• Economical compared to carbon composition resistors.
• Operates efficiently under high temperatures.
• Generates minimal noise.
• Compact design.
• High stability.
• Reliable performance.