Similar to glasses for augmented reality, transparent displays can enable a view of the workpiece or the exhibits in a shop window on a machine and convey additional information.They are available in different technologies.A color display consists of individual pixels.Normally each pixel is made up of three sub-pixels in the primary colors red, green and blue.Color gradations are represented by driving with less than 100 percent current or voltage.The picture elements are interconnected as a matrix and controlled line by line.In addition to the control information for the image content, the wiring level also contains the power supply lines, depending on the display type.The more power a picture element needs to operate, the lower the resistance and therefore the more massive they have to be.With a passive matrix LCD, applying a voltage is enough to make the liquid crystal molecules switch;With technologies such as LEDs, a current must flow to make the LED light up.First of all, a distinction must be made between emissive and modulating display technologies.This means whether the display itself emits light or modulates the light of a light source that shines from behind.Figure 1 (not to scale) shows the structure of an emissive transparent display.The active pixel occupies only a small area because it is not transparent itself.The remainder of the sub-pixel is available for the pixel's drive and supply lines.The conductivity increases with the thickness of the material, but the transparency decreases.Figure 2 shows the pixel structure of a modulating display.In order to use the light source efficiently, most of the sub-pixel consists of the modulating part.The color filter is located here on liquid crystal displays.Each sub-pixel is controlled by a transistor that charges a capacitor with the desired voltage level depending on the gray level.The control lines are located between the subpixels.For example, the dimensions for a 55-inch display with FHD resolution (1920 x 1080) are 630 µm for a pixel and 210 µm for a sub-pixel, minus the gaps.Depending on the application and the viewing distance, different display technologies are used.While Apple tries to achieve the highest possible pixel density (dot pitch) with the minimum distance between the pixels (gap) with the »Retina« displays, it is exactly the opposite with transparent displays: the luminous pixels are not transparent, but the space between them is they can be made transparent.The term "aperture" in displays means the area from which the light emerges in relation to the total size of an area used for a pixel.The emissive display in Figure 1 has a small active area from which the luminous flux emerges.This design is favorable for a transparent display where the active area is opaque because the larger proportion of the area allows light to pass through from behind.The opposite is true for the modulating display in Figure 2, since the large areas block or allow the light passing through.Here, in each pixel, the area used for the transistor and capacitor is opaque.The areas required for the wiring either shine through permanently (in the case of a transparent display) or are made opaque in the case of a normal TFT with a black print (black mask).The basic requirement for transparency is that the display technology allows light to pass through the panel.A side note: This is not the case with reflective TNs such as those in pocket calculators or e-papers.The transparent display can then hide individual segments (e.g. TFT) or add content (transparent OLED or transparent LED module).TFT thin-film transistor displays are based on semiconductor technology.Electric fields affect the position of liquid crystals sandwiched between two sheets of glass.Polarizing filters are laminated to this cell, which only let light through in one direction of polarization.The polarization direction of transmitted light is changed pixel by pixel by the field and it can reach the viewer's eye.The light source is behind the display, the display itself only acts as a light valve.Due to the many layers and filter foils, the transmission of a TFT is significantly less than ten percent.Therefore, the background has to be very well lit in order to achieve an acceptably bright image.Typical applications are therefore backlit showcases and vending machines, i.e. devices where the manufacturer can set the brightness of the lighting himself.Sharp is taking a different approach: the newly developed transparent TFT only changes between the display of a color and the transparent state.However, the special display technology allows a high transparency of 60 percent.This is ideal for applications where the main purpose of the display is to switch between transparent and opaque.There are two variants: one that is transparent with no energy, and one that is opaque.It is not bistable.T-OLED When a current flows through the materials of an OLED, electrons and holes recombine.The energy released in the process escapes as visible light.Different material pairings result in different wavelengths, which are perceived as different colors.OLEDs are not transparent;in the normal design, the pixels emit the light through the substrate, which reduces the brightness.With a transparent OLED, the challenge is to design the lines on the display in such a way that they are transparent and electrically conductive at the same time.Compared to TFT, they also need to be able to carry a current flow in order for the OLED elements to light up.Unlike TFTs, which filter the light that passes through, OLEDs emit light themselves.The new technology from LG Display does not have much in common with that known from OLED TVs: the so-called stack has been completely redeveloped, and the materials for the lines are made of IGZO, which offers a number of advantages over the ITO otherwise used.This made it possible to achieve a transparency of 40 percent with brilliant colors at the same time.TLM transparent LED modules consist of foils that are covered with conductor tracks made of transparent material, e.g.B. ITO coated.RGB LEDs with an integrated driver are mounted there at intervals of 10 to 20 mm.The film is flexible and has an adhesive layer on the back.This makes it easy to laminate onto a carrier glass, such as a shop window pane.The dimensions of individual modules are so compact that displays of almost any size can be created by aligning them.The foil can be cut so that non-rectangular displays in the grid of the LED pitch are also possible.Take part in this survey about the semiconductor market and enter a prize draw for an amazon voucher of 100 €.© 2022 WEKA FACHMEDIEN GmbH.All rights reserved.