Alignment layer

Alignment layers, or alignment films, are thin films which are a crucial component of <a href="/facts/Liquid-crystal_display/8B6xGBEz">liquid crystal displays</a> (LCDs). They are applied to the surfaces of the <a href="/facts/LCD_manufacturing/3QAk6IEB">glass substrates</a> that contain the <a href="/facts/Liquid_crystal/ehCCST89">liquid crystals</a>. The primary function of these layers is to control the orientation of the liquid crystal molecules, which is essential for the proper operation of the display. The alignment layer controls the alignment of the liquid crystal immediately adjacent to itself, and long-range interactions force that alignment to extend significantly into the crystal itself.
Alignment layers ensure that liquid crystal molecules are aligned in a specific direction when no <a href="/facts/Electric_field/tt4MooBs">electric field</a> is applied. This is critical for the display's function; for example, in <a href="/facts/Twisted_nematic/vIgktRAy">twisted nematic</a> (TN) displays, the alignment layers on the two glass <a href="/facts/Substrate_(materials_science)/LwwkV6rX">substrates</a> are oriented at right angles to each other, creating a 90-degree twist in the liquid crystal molecules, allowing display to modulate light effectively when an electric field is applied. By applying a <a href="/facts/Voltage/EN2po6N2">voltage</a> across the liquid crystal layer, however, the orientation of the molecules can be altered, affecting the passage of light through the display, and enabling the control of brightness and <a href="/facts/Contrast_(vision)/zD9F91Je">contrast</a>.
As of 2025, the two main techniques used to produce alignment layers are rubbing and photo-alignment. The rubbing method is a process that is nearly 100 years old—by rubbing <a href="/facts/Spin_coating/IsgQN2nK">spin-coated</a> <a href="/facts/Polymer/eF32E50K">polymers</a> with <a href="/facts/Velvet/6lTpUVTf">velvet</a> cloth. As this process presents difficulties when used to make larger displays, other options have been investigated. The rubbing method can result in static electricity issues, dust deposition, and scratches.

Alignment layer open-in-new

Alignment layer