Nissan Research Institute develops 10V AC driven surface-emitting red LED components

The Japan Industrial Technology Research Institute has developed a surface-emitting red LED element that is driven by an AC voltage of only about 10V. According to the research institute, the luminous voltage is less than 1/10 of the previous LED components. The realization of the low-voltage driving surface emitting red EL element not only reduces the volume of the power supply, but also has a wide viewing angle due to surface illumination. In the future, with the progress of high brightness and multi-color, it is expected to be used for lighting fixtures, light sources, displays, and the like.

The material of each layer of the LED element developed this time is a perovskite type oxide. The material is chemically stable and has characteristics of almost constant oxidation and heating. Therefore, processes such as packaging can be shortened and the manufacturing process can be simplified. Previously, it was found that most of the perovskite-type oxides emitted significant fluorescence due to ultraviolet radiation, and thus they were made into a light-emitting layer film. This time, these perovskite-type oxides and an insulator film were laminated, and an attempt was made to develop an LED element having good stability.

The newly developed LED element is formed by a pulsed laser deposition method (PLD method) on an electrode substrate to form an insulating layer, a light-emitting layer, and an insulating layer. The source used an ArF excimer laser (wavelength 193 NM). The production conditions were a substrate temperature of 700 ° C and a production environment of 10 PA oxygen. After heat treatment in the atmosphere, a transparent electrode is formed by a PLD method to form an LED element.

The materials of the electrode substrate, the light-emitting layer, and the insulating layer are as follows. Materials with less resource constraints are used. First, the electrode substrate was made of 1% niobium (Nb) barium titanate (1% Nb-SrTiO3). The luminescent layer was added with a trace amount of praseodymium (Pr) as a luminescent center in the A portion of the perovskite-type oxide (ABO3) calcium strontium titanate ((Ca0.6Sr0.4)TiO3). The insulating layer is made of perovskite-type oxide barium titanate (SrTiO3). The film was continuously grown by the PLD method, and a structure in which two insulating layers were sandwiched between the light-emitting layers was formed, and a "double-insulated structural thin film EL element" was experimentally produced. The upper transparent electrode is an ITO (indium tin oxide) or SnO 2 film.

First, an EL element having a single layer of a light-emitting layer was formed, and when an AC voltage of 14 V and 1 KHz was applied thereto, the entire surface of the transparent electrode was illuminated. The luminescence spectrum shows a sharp peak at a center wavelength of 612 nm. This is considered to be the cause of the migration from 1D2 to 3H4 energy source of Pr3+, and the voltage at which light emission starts is about 10V. Moreover, in the case of fabricating a double-layer light-emitting layer element, a strong red-surface light emission can be obtained with a voltage of about 24 times that of the single-layer light-emitting layer LED element.

In addition, the results of this research will be published in the German science magazine Advanced Materials.

Figure 1 Luminescence of the LED component using the perovskite oxide

Figure 2 Schematic diagram of the LED components developed this time

Fig. 3 Photograph of the light-emitting spectrum of the LED element produced by trial production and the element of the light-emitting element: double-insulating structure film EL element of single-layer light-emitting layer (left), double-insulation structure film EL element of double-layer light-emitting layer (right)

Figure 4 Comparison of characteristics of various EL components