优化LED芯片尺寸并提高Micro LED显示器的功率效率

Abstract: Micro-LED (light-emitting diode) is a potentially disruptive display technology, while power consumption is a critical issue for all display devices. In this paper, we develop a physical model to evaluate the power consumption of micro-LED displays under difffferent ambient lighting conditions. Both power effiffifficiency and ambient reflflectance are investigated in two types of full color display structures: red/green/blue (RGB) micro-LEDs, and blue-LED pumped quantum dots color-conversion. For each type of display with uniform RGB chip size, our simulation results indicate that there exists an optimal LED chip size, which leads to 30–40% power saving. We then extend our model to analyze difffferent RGB chip sizes, and fifind that with optimized chip sizes an additional 12% average power saving can be achieved over that with uniform chip size.

Micro-LED displays with high peak luminance, true dark state, high resolution, wide color gamut and long lifetime are emerging as next-generation displays. Two approaches are commonly used to achieve full color: red/green/blue (RGB) subpixels and blue-LED pumped color-conversion. In the fifirst scheme, RGB micro-LED chips are fabricated from difffferent semiconductor materials, according to their lattice constants and energy band gaps. For examples, red LEDs are typically fabricated by growing AlGaInP epilayers on GaAs substrates, while green and blue LEDs are produced by depositing InGaN epilayers on sapphire substrates. In such a RGB display panel, millions of micro-LED chips are transferred from the corresponding semiconductor wafers to the display substrate through mass transfer processes. In the color-conversion scheme, we can use UV or blue LEDs to excite the down-conversion materials, such as quantum dots (QDs) or phosphors. These color- conversion materials can be fabricated by inject printing or photolithography. These micro- LED displays have found potential applications in ultra-large size and seamlessly tiled video walls, 75-inch modular TVs, medium-size sunlight readable vehicle displays, smart watches, and high-resolution-density microdisplays for augmented reality and virtual reality, just to name a few.

In addition to above-mentioned properties, low power consumption is always desirable for micro-LED display to compete with its counterparts such as liquid crystal displays (LCDs) and organic LED (OLED) displays. Especially for a mobile display, its operating time is governed by the battery capacity. Thus, power consumption is a critical issue for all mobile display devices. Although TVs and desktop monitors are usually connected to wall plugs, low power consumption helps to save the ecosystem.

In this paper, we evaluate the power consumption of both types of micro-LED displays, including RGB chips and blue LEDs pumped color conversion, under difffferent ambient lighting conditions. First, we evaluate the power consumption of uniform LED chip size, i.e. RGB subpixels having the same chip size, as the baseline for comparison. The optimum LED chip sizes corresponding to the lowest power consumption for three applications: smartphones, laptop computers, and TVs, are analyzed. For TV applications, the LED chip size studied ranges from 5 µm to 50 µm. The optimal LED chip size is found to be 16 µm for the RGB type and 20 µm for the color conversion type. At the optimal chip size, the power saving can reach 30–40%. Next, we extend our model to evaluate RGB subpixels with difffferent chip sizes. Through the same optimization procedures, our proposed micro-LED display with difffferent RGB chip sizes further reduces ~ 12% average power consumption than that with uniform LED chip size. 

Fig1

From Equation 2, we find the luminance ambient reflectance of red, green and blue subpixels is  6.83%, 16.73%, and 2.88%, respectively. Because the ambient light is reflected in the emission area but  is absorbed in the black matrix region, the luminance ambient reflectance is proportional to the  aperture ratio of the micro-LED display. The relationship between aperture ratio and luminance  ambient reflectance of color conversion micro-LED display is shown in Figure 8.