How Micro-LEDs Work

How Micro-LEDs work

 

Before I describe how Micro-LEDs work, let us start by defining the Light-emitting diodes (LED). Diodes are passive electric components whose function is to allow a unidirectional flow of current. However, LED is a special kind of diode that produces light. Today, there so many light colors that LED produces which was not the case several years ago. LEDs are common today and you might use one today in your house or one of your electronic devices. Today, the primary use of LED is to produce light in houses, streets, and in your TV

What is micro-LED

Micro-LED is simply the normal LED but now miniaturized to microscopic size. They are surprisingly very good at emitting light and thought to rival the current Organic light-emitting diodes (OLED) displays on the market today. The pictures are of quality that rivals those produced by the OLED themselves. The micro-LED do not possess the downside the comes with the OLED.

OLED  tends to degrade with time which is not the case with the micro-LED. So, your micro-LED display will emit the maximum amount of light even when exposed to environmental factors without degrading. If you remember the plasma screens, you might also have realized when an image stayed on the screen for long, it got burnt on the screen. This does not happen when using micro-led. This makes them very useful for gamers and other sports. This also means that the manufacturers will not need to worry about the lifespan of displays used on smartwatches, smartphones,  or even billboards. The current displays degrade with time and have to be replaced soon.

And how comes there are close to zero micro-LED screens in the market? You should know that it has been a problem to manufacture display screens using the micro-LED. Firstly, they are very small, microscopic. Secondly, they need to be perfectly aligned lest you get uneven colors. This has been a challenge even when using robots.

Therefore, the chances of having a micro-LED screen in the market are very narrow. But no need to worry, the current LED available in the market offers desirable performance. Though they have some drawbacks, they are far cheaper than plasma tv and OLED tv. We did an article on how plasma tv display work already.

History of micro-LED

How Micro-LEDs work topic would be exhaustively covered if I leave its history uncovered. Research on inorganic micro-LED started earlier than 2000 by researchers from the Texas tech university. By that time they were at Kansa state university. After they announced success in positively creating the micro-LED based on the indium gallium nitride, several other researchers have engaged in research and development of the same concept. The micro-LED has found numerous uses today include the creation of brighter and more power-efficient display screens. The other application is an on-chip LED ( whether using DC or AC) to solve the issue that exists between infrastructure that uses high voltages and the low voltage LED. Additionally, the technology has been explored for use in visible light communications.

Initial developments

The first micro-LED arrays were driven passively and s were the micro display. It was only in 2011 that the first actively driven video-capable micro-LED was created.  It was VGA  format and it was an InGaN micro-LED. This was achieved by combining the IC hybrid assembly and the complementary metal-oxide semiconductors. The year that followed, Sony leased the first micro LED TV which was prohibitively expensive.

How are micro-LEDs made?
flip-chip method

Many methods are there that can be used to make micro-LED displays. The first method is the flip-chip method. Here the LED is manufactured on the traditional sapphire substrate. The traditional method is used to deposit the transistor arrays and the solder bumps on silicon wafers. The metallization process is highly useful when using this method. The many LEDs are bonded to the silicon substrate using ovens. This is the method that is used when creating virtual reality headsets.   This method has some of its disadvantages. Firstly, the sizes of the pixel are limited. Secondly, the accuracy when placing the LED is wanting. Thirdly, there is a need for cooling so that the display does not break or warp because LED temperatures and those of silicon are different. Finally, the method is very costly which makes the final product very expensive as well.

Use of silicon substrate

The second method to use involves having the micro-LED bonded to an integrated circuit layer on the silicon substrate. The material used as a bonding agent is then removed using a suitable method used in semiconductor manufacturing. The major problem here is that each of the micro LEDs has to be tested individually and the faulty ones to be replaced. The method used to replace the defective micro-LED is the laser lift-off equipment. The bond between the micro-LED and the substrate is weakened and the LED is removed. The pick and place machine of very high accuracy is used for this process. It is a process that takes a very long time. Mass transferring micro LED to the silicon substrate takes 18 days for a smartphone screen. So, the process has to be hastened to increase their production.

As of  2021, there are more than 100 companies that are involved in the research and development of micro-LED panels. The researchers are exploring micro-LED as an alternative to the current LED and OLED panels.

HOW LED are used in your tv or phone as a display

Now let us dig into what brought us here, how micro-LEDs work. There are LED display screens and there are LCD screens that use LED as the source of backlight. Today, there are limited full LED screens but numerous LED backlight LCD screens. Let us take a look at how the LED is used before we venture into the micro-LED.

Your television is thin, light and very big. So, your screen is divided into various components. The components include a backlight, light polarizer, LCD panel, and finally a second light polarizer. If the first polarizer performs horizontal polarization, the second polarizer performs vertical polarization.

Source of backlight

LED produces a very bright white light. The light passes through the polarizer which eliminates all other electric fields except the vertical or horizontal depending on the first polarizer. In the LCD panel, there are electrons and liquid crystals.  The electrodes pass current to each cell selectively. When the liquid crystals receive current, they distort the already polarized light wave. The amount of distortion is proportional to the amount of current each liquid crystal in the cell receives. If a cell receives no current, the polarized light passes the crystals unaltered.

Light polarization

Once the light leaves the cell to the second polarizer, the higher the distortion the light received in the cell, the higher the amount of light that passes through the second polarizer. If no distortion took place (because a cell received not current), no light can pass through the second polarizers. Hence a dark pixel.

Now, the color of the image you see on your screen comes after the light passes through the second polarizer to the RGB filter. Once the light is filtered this way, a final image is displayed on your screen.

 

Now you see, your LED tv set is just an LCD tv apart from the source of backlight. LCDs use either of these two methods as a source of the backlight; CCFLs or the LED. The latter is highly favored because they are power efficient and they allow very thin displays to be made. Furthermore, LEDs are cheaper to make.

The first micro-LED

Samsung has hyped the market some days ago when it introduced the first micro-led tv for demonstration purposes. The Samsung displayed a variety of colorful images such as the towering cityscapes and shining gems. It was a 110-inch screen.

If such a screen was an LCD type, it would have serious problems such as off-angle fading, crushing, or even blooming. Such image qualities would be very difficult to achieve even with local dimming for an LCD screen. An OLED screen might also have an impress close to those.

According to ZDNet a micro-LED screen of such size would cost $ 150,000 in south Korean and it is likely to the same price in the USA. The closest tv to this one in terms of quality, size, and the price is the LG SIGNATURE Z9 88 inch Class 8K Smart OLED TV. It goes for $ 30,000.

High cost and difficulty

It goes without saying that the major electronic manufacturers think micro-LED is the next big thing when it comes to displaying technology. After Apple, Inc. acquired the micro-LED develop luxury, people started to anticipate an apple product that features this technology.

Despite its impressive performance, this technology is still in its development phase. Producing micro-LED displays is very difficult and very expensive than even the OLED. How micro-LEDs work require them to be packed accurately in high densities per area.

Will the micro-LED replace OLED

As of now and probably the next five years,  OLED is the king of the display technology jungle. The reason behind this is that despite their high cost of production, OLEDs are cheaper and easier to produce compared to micro-LED displays.

So, even though the “the wall” from Samsung was both inspiring and breathtaking, it remains unaffordable for many people who are middle and lower class. This is likely to change soon through research and developments.

If, however, the cost and the process of producing the micro-LED screens goes down, the OLED might be phased out just the Plasma tv and the cathode ray tube tv. Micro LED has advantages that rival OLED by far especially when it comes to quality and longevity.

Even though tv might take a long time to catch up on the use of micro-LED, mobile phones, and other small screen displays might be quite to take up the technology.

There is the likelihood that, just the Apple adopted the OLED on its iPhones and other products, it might also be quick to adopt micro-LED once they are deemed viable. Micro LEDs are very viable for filmmaking.

Mini LED vs Micro LED

Before we are done with how micro-LEDs work, let us compare them with min LEDs. The mini LEDs are quite small, they are smaller than the average LED we use today. These diodes are as big as 0.008 inches while the normal size LED is about 0.04 inches. Their small size means they are high LED density on a given area.  And what is the advantage of this you ask? Well, do you remember we had spoken about dimming in our previous article on how LED tv display? When you have several LEDs in a small area, it offers hundreds of dimming zone for better contrast. Now you know.

Premium models have more dimming zones compared to other models. So, when the number of dimming zone increases, each zone becomes smaller and the backlight is more tightly controlled. The bright regions become better the dark regions become deeper and there is a less haloing effect.

What should you do now?

Now that you know how micro-LEDs work, should you go for them or not? Do not be afraid to go for an OLED tv if you want to. Just like the micro-LED, OLEDs are still under research and development and they might prove to offer better performance in the future.  If Micro LED will be too expensive to manufacture, it might never be commercially available like many other technologies today.

 

 

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Micro-LED vs OLED