Summer School for Buyers: OLED Displays

As technology evolves, the bill of material (BOM) on new products change along with them. For the procurement department, that translates, often, into new product lines, new vendors, and a variety of supply chain changes. In this four-part series, we’ll do a quick recap of how Organic Light Emitting Diode (OLED) technology works and how the technology has and will evolve to help buyers get up to speed without getting an engineering degree.

To get started, let’s look at where the technology has been.

Types of flat panel display

Flat panel display technology is divided into two types: non-emissive display, which requires an external light source and emissive display, which produces its own light organically. Thin-film transistor (TFT) LCD is a non-emissive and older display technology which requires an external light source to work, while OLED is considered an emissive display technology that does not require a backlight because each pixel provides its own illumination. OLED has three self-emitting phosphorescent organic compounds: red, green, and blue. An OLED display utilizes the emissive phenomenon of three-color phosphorescent organic compounds combined with electrons emitted from positive anode and negative cathode particles.

Evolution of OLED

OLED technology, depending on driver scheme, falls into one of two categories: passive-matrix (PM) OLED and active-matrix (AM) OLED. PM OLED technology drives the display to emit light by placing voltages into both vertical and horizontal axes of light- emitting diodes arrayed on the screen and producing light at the point of their intersection.

PM OLED, a simple structure with low manufacturing cost, is challenging to produce a high-quality larger-format screen because the larger screen size causes an exponential increase in power consumption. This causes a sharp decline in battery life and device availability. As a result, PM OLED technology typically can be found in small form-factor displays such as wearable devices like smartwatches and wrist-based fitness trackers.

To compensate for the drawbacks of PM OLED, AM OLED has emerged as an ideal technology for smartphone screens and other medium and larger displays, including in automotive and consumer applications such as large-screen televisions. AM OLED is ideal for these applications because each light-emitting diode has a built-in thin-film transistor to individually control each and every light-emitting diode, which eliminates the need for a display backlight. This, in turn, reduces power consumption and enables thinner form factor devices.

Advantages of OLED

OLED has various advantages thanks to its self-emissive characteristics. In terms of color gamut, liquid crystal displays (LCD) cannot produce its own light, which is why it requires a backlight at the back of the display, and the light emitted from the backlight passes through liquid crystal and a color filter, resulting in loss of color purity. However, AM OLED’s self-emissive characteristic, which is not susceptible to color purity loss, can achieve near “true to life” color representation. AM-OLED also consumes less power than LCD. Since each pixel itself emits light individually to display color, no pixel is turned on to represent black color. By contrast, the backlight is “always on” in an LCD screen, which does not allow for a “true black” color.

Without a backlight, light leakage does not occur, which enables a high contrast ratio, making OLED more suitable for mobile device readability in outdoor settings. And with no backlight required, OLED smartphones can be made thinner than LCD-based models, which allow for thinner and possibly lighter mobile products, and enables more space for a larger battery, which means more usage of the device between recharging. Furthermore, OLED is more comfortable on the eyes as its self-emissive mechanism is known to emit less hazardous blue light in the wavelength of 415nm to 455nm (up to 50% less than LCD), which can damage the retina.

OLED also offers fast response time, which enables “blur free” motion, which means clearer boundaries of moving objects without video screen delay. This feature meets the fast response time requirement of HMD (Head Mounted Displays) used in VR/AR, as well as various display applications including TV, tablet, smartphone, and an expected wide range of other applications.

These other applications will take advantage of the flexible display capabilities of OLED, which can be folded, rolled or bent. This will play a key role in the growing and highly-competitive mobile market, where differentiated design is critical for success. Since flexible AM OLED display successfully entered mass production in 2013, products in various form factors have been launched and the design freedom OLED enables will enable even more innovation in the years to come.

Applications with OLED

Since the first AM OLED product entered mass production in 2007, OLED display has been used in various applications. Initially, OLED had a high unit price, and due to some technical constraints, it was adopted only for an external display of mobile devices such as MP3 players. However, after the launch of AM OLED Samsung’s Galaxy S in 2010, use in the smartphone market has grown rapidly. AM OLED displays grew in earnest with a corresponding increase in demand for OLED DDICs.

In addition, the first AM OLED tablet PC, Samsung’s Galaxy Tab 7, arrived in 2012. This was an indication that OLED display had moved beyond smartphones and was becoming widely adopted for various mobile IT devices. Around the same time, portable gaming devices and digital cameras also started to adopt AM OLED displays, broadening the range of applications for OLED DDIC. OLED displays now are appearing in other consumer electronics products such as HMD for VR/AR applications.

 Paul Kim, vice president of marketing, Standard Products Group, MagnaChip Semiconductor Corp., co-authored this article. Kim became vice president of marketing, Standard Products Group in December 2015. He joined MagnaChip in August 2011 and served as vice president of Display Design, Display Solutions Division. Prior to joining MagnaChip, Kim served as principal engineer of SOC & Display Driver IC Design Group of Samsung Electronics, where he worked from 1994 to 2010. Kim holds B.S degree in Electrical Engineering from Inha University, Korea.

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