LTPO Displays: What will OLED be like in the iPhone 13? Parsing

Most recently, the famous analyst Ming-Chi Kuo shared new information about the upcoming Apple smartphones, which will be released this year.

Let’s see what he promised us:

  • less bangs,
  • more battery,
  • ditching Lightning in favor of MagSafe in a generation
  • LTPO screen with support for 120Hz frequency.

So stop! What else is LTPO? How is it different from what is now? Is this some new screen technology?

First, let’s remember what two main types of screens are. In principle, there are OLED and LCD screens, that is, screens based on organic light-emitting diodes, which are themselves light sources, and screens based on liquid crystals, where the LEDs act only as a backlight.

It is important to understand here that, in principle, the type of screens is not so important as the fact that any screen is a complex layered structure.

Besides the diodes or color filters themselves, there are many other important parts. It turns out to be such a modern sandwich. Using a complex set of combinations, these screens are printed layer by layer.

And the very procedure for printing modern screens, in fact, is based on the same technologies as the creation of modern processors, for example, lithography, chemical and physical vapor deposition, plasma-chemical etching, and many others! These are hundreds of the most complex and very precise operations. In general, this is a topic for a separate video, let’s talk about screens here!

Just look at the complex that Applied Materials offers to its customers for creating flexible OLED screens! Pay attention – to the person, he is here for the scale.

And despite the fact that fundamentally different physical processes are behind OLED and LCD screens, there are similar areas in their design. Let’s take a look at the picture. See the TFT patch in the picture.

Nostalgia rolls over, because this is the same acronym popular in the 2000s, which was used in advertising for all TFT LCD screens. So, in fact, these TFTs are also present in modern OLED screens.

In decoding, this means Thin-Film Transistor or Thin Film Transistor. This is a layer of transistors that are used in different types of screens for different purposes – in LCDs to control the polarization of crystals, and in OLED displays, they are responsible for turning on and off each specific LED.

In simple terms, these are small switches that control the flow of current to each pixel. Without transistors, we wouldn’t even be able to just turn the pixels on and off on the screen! And these transistors are controlled by separate special controllers.

Transistors must have one important parameter – for example, in LCD screens they must be transparent or, in the case of OLED panels, either transparent or completely absorbing light to avoid image artifacts! And this changes the materials from which they are made, which radically changes the technology of their production!

So, if you think that a TFT layer is something very simple, then this is not at all the case. Modern displays are a very complex device and engineers, and scientists are fighting to improve every aspect, not only the pixels themselves, but also, for example, response speed, energy efficiency. Look at the cross-sectional photo taken with an electron microscope.

But for comparison, the structure of the transistor in old TFT screens!

Any modern smartphone with OLED screens and even many LCD displays uses the so-called LTPS transistor layer, which means Low Temperature PolySilicon or low temperature polycrystalline silicon. This is the semiconductor material from which the transistor channel is made, the place through which current flows when the transistor is on. Transistors based on polycrystalline silicon are used in the TFT layer and in general in any modern smartphone with OLED screens.

The LPTS production process includes many subtleties. But the main thing is a special temperature treatment, which makes it possible to obtain silicon with a certain crystal size.

This structure, in turn, increases the mobility of electrons, which makes it possible to increase the pixel density per inch, that is, increases the screen resolution! In addition, energy efficiency is increased. But there is a problem, the frequency is limited to 60Hz and cannot be dynamic. This is due to design constraints because current flows out of the transistor relatively slowly. And to increase to 120 Hz or more, manufacturers are forced to integrate special chips that consume a lot of power. They deal with the control of transistors in the TFT layer. That is, the gain from high electron mobility is lost when we talk about high frequencies!

This is where we come in LTPO or Low-Temperature Polycrystalline Oxide titer. In fact, it is a combination of two technologies: LPTS, which we talked about above, and IGZO.

This is a special modified type of transistors, where an additional transistor from a different material is used. To the polysilicon transistor is added a special neighboring one made of India, Zinc and Gallium Oxide, or IGZO – Indium gallium zinc oxide.

It turns out to be a very complex structure, just look at the sectional diagram of the green pixel of an OLED screen. And there are millions of them on the screen!

And what has been achieved using the combination of LTPS and IGZO technologies?

One advantage is noise reduction, which improves the accuracy of the use of screens. Noise can occur due to the low leakage rate, but immediately it happens faster.

But the main thing is energy efficiency. Is it estimated that the savings will be up to 15 percent due to the significantly lower current? required to turn on the transistor! And as we remember – the screen is one of the most voracious places on our phone! The difference will be significant.

And the last is frequency. Due to the use of Oxide, it becomes possible to both lower the screen frequency to 1 Hz and increase it to more than 144 Hz. This is all due to the low leakage current through the transistor. And this can be done without the use of special amplification controllers. All this happens smoothly and depending on what you are doing with your device right now. In general, manufacturers have found a middle ground!

And the most interesting thing is that such screens are already in use. Samsung began to install LTPO screens in their smartphones starting with the Galaxy Note20, they are also in the new flagships of the company. Also similar displays are used by OnePlus and OPPO with their devices.

And Apple itself tried out the LTPO technology several years ago. They’ve been using them in their Apple Watch since the fourth generation to be able to drop the refresh rate down to 1Hz to save the watch’s already small battery. So, without loud announcements, they began to use a new generation of transistors in screens!

In general, everything is as usual – Apple takes the best from the world of technology and installs it into its devices! Looking forward to 120Hz in the new iPhone 13 … And now you will know why iPhone and Samsung have the best screens on the market and are able to work with adaptive frequency.

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