Permalloy in magnetic devices

Pomalloy is an essential ferromagnetic material in the manufacturing process of MEMS magnetic devices.

Pomalloy is an essential ferromagnetic material in the manufacturing process of MEMS magnetic devices. It can also be used for magnetic shielding to shield magnetic fields and is one of the “stuck neck” technologies.

What is permalloy?

Permalloy, is a special alloy with iron and nickel as its main components. In the chip manufacturing process, the composition requirements of the alloy are: Ni content 80% and iron content 20%.

What is ferromagnetism?

According to the type of magnetism, they are divided into ferromagnetic, paramagnetic and diamagnetic materials, while ferromagnetic materials refer to materials that can maintain magnetism in the absence of external magnetic field. Ferromagnetic materials usually include: iron, nickel, cobalt, gallium, etc.

What are the properties of permalloy?

High magnetic permeability & low loss: With high magnetic permeability (relative magnetic permeability is usually about 100,000) and low hysteresis loss, it can effectively guide and enhance the magnetic field, and has low loss during the cyclic magnetization process.

Low coercivity: Coercivity refers to the minimum magnetic field strength required to demagnetize a magnetic material after it reaches magnetization saturation. Materials with low coercivity are easily magnetized and demagnetized, and they respond very sensitively to external magnetic fields.

Near-zero magnetostriction: Magnetostriction is the phenomenon in which a material changes its size or shape during magnetization. Some materials expand or contract slightly when magnetized, an effect called magnetostriction. Near-zero magnetostriction means that the material undergoes little change in shape or size during magnetization.

Significant anisotropic magnetoresistance: Anisotropic magnetoresistance refers to the property that the resistivity of a material changes with the direction of the magnetic field. This property is useful in reading magnetically stored data and in magnetic sensors because they can detect changes in the direction and strength of magnetic fields.

Good mechanical strength.

Why 80% Ni, 20% Fe?

When the ratio of nickel to iron is 80:20, the alloy typically exhibits a face-centered cubic (FCC) crystal structure. This structure is characterized by high symmetry, which allows the material to have good plasticity and toughness while maintaining high magnetic permeability and low hysteresis losses.

When the iron content increases, the crystal structure gradually transforms from face-centered cubic (FCC) to body-centered cubic (BCC) structure, which usually results in a decrease in magnetic properties.

How does permalloy shield magnetic fields?

The principle of permalloy shielding the magnetic field is to change the path of the magnetic field lines passing through it. When a magnetic field encounters permalloy, the magnetic field lines are redirected to follow the permalloy material rather than penetrating the material. This allows the magnetic field lines to bypass the shielded area, thereby reducing or eliminating the magnetic field within that area.

How to make permalloy?

In magnetic devices, the thickness of permalloy is between 1-10um, and is generally produced by wafer electroplating. Moreover, the electroplating machine and electroplating solution of permalloy are very different from ordinary Ni single-substance electroplating, and the technical difficulty is relatively high. There is currently no mature supplier in China that can provide wafer-level permalloy.