Multilayer

A multilayer is an assembly consisting of multiple layers arranged in a stack or laminate, each layer made of different material or having different properties. The overall behavior of a multilayer structure depends on interfacial properties, layer thickness, and the sequence of layers, which can be engineered to achieve specific mechanical, optical, electrical, or barrier performance.

In materials science and engineering, multilayer structures are used to tailor properties. Multilayer coatings consist of alternating layers with different refractive indices or hardness, enabling optical coatings such as dielectric mirrors or anti-reflective surfaces, as well as protective, wear-resistant films. Laminated composites combine layers of different materials to improve strength, toughness, or thermal stability.

In electronics and packaging, multilayer concepts appear in devices such as multilayer ceramic capacitors, where several ceramic sheets with embedded electrodes are stacked to increase capacitance, and in multilayer printed circuit boards, which stack conductive and insulating layers to create compact circuitry.

In computing and information processing, multilayer architectures underpin many artificial neural networks. A common form is the multilayer perceptron, which comprises input, hidden, and output layers of units that apply nonlinear activation functions to transform data. Deep learning uses networks with many layers to model complex patterns.