IPS display

IPS (In-plane switching) is a screen technology for liquid crystal displays (LCDs). It was designed to solve the main limitations of the twisted nematic field effect (TN) matrix LCDs in the late 1980s. These limitations included strong viewing angle dependence and low-quality color reproduction. In-plane switching involves arranging and switching the orientation of the molecules of the liquid crystal (LC) layer between the glass substrates. This is done, essentially, parallel to these glass plates.

The TN method was the only viable technology for active matrix TFT LCDs in the late 1980s and early 1990s. Early panels showed grayscale inversion from up to down, and had a high response time (for this kind of transition, 1ms is visually better than 5ms). In the mid-1990s new technologies were developed—typically IPS and Vertical Alignment (VA)—that could resolve these weaknesses and were applied to large computer monitor panels.

One approach patented in 1974 was to use inter-digital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates. However, the inventor was not yet able to implement such IPS-LCDs superior to TN displays.

After thorough analysis, details of advantageous molecular arrangements were filed in Germany by Guenter Baur et al. and patented in various countries including the US on 9 January 1990. The Fraunhofer Society in Freiburg, where the inventors worked, assigned these patents to Merck KGaA, Darmstadt, Germany.

Shortly thereafter, Hitachi of Japan filed patents to improve this technology. A leader in this field was Katsumi Kondo, who worked at the Hitachi Research Center. In 1992, engineers at Hitachi worked out various practical details of the IPS technology to interconnect the thin-film transistor array as a matrix and to avoid undesirable stray fields in between pixels. Hitachi also improved the viewing angle dependence further by optimizing the shape of the electrodes (Super IPS). NEC and Hitachi became early manufacturers of active-matrix addressed LCDs based on the IPS technology. This is a milestone for implementing large-screen LCDs having acceptable visual performance for flat-panel computer monitors and television screens. In 1996, Samsung developed the optical patterning technique that enables multi-domain LCD. Multi-domain and In Plane Switching subsequently remain the dominant LCD designs through 2006.

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