Screen 101 - Digitizer, Glass, Touch screen... What are the correct terms?

Posted on 07 Jan 11:35
We often see people referring to the screen and its components with so many different names that it has created a general confusion in our industry. People don't understand the terms digitizer, touch panel, touch screen, glass and so forth... and the truth is we all had a learning curve. So let’s start with some term definitions going from a full assembly to the glass. If you are interested into LCD Refurbishing, this is a most read for you!
Screen Assembly - Screen with plastic frame glued to it. This could have or not have the plastic attachments that hold the front camera and proximity sensor in place. 
Screen - As basic as it might look, these smartphone screens have a lot more technology in them than most electronics we have at home. They are as complex as the inside of the phone and the perfect complement for our iPhones, Samsungs, and other Smartphones. 
The iPhone screen basic layers are the following from the back to the front:
  • Backlight
  • LCD
  • Digitizer
  • Polarizer
  • OCA
  • Glass
Samsung screens do not have a backlight because they use OLED technology instead of LCD technology but they are essentially the same layers (we still need light and a display panel). So the term screen for us is when all these layers are bonded together. 
Backlight - Light that shines through the layers for us to be able to see the information displayed on the LCD.
LCD - Abbreviation for Liquid Crystal Display. These are display panels that do not emit their own light. They work by either letting light go trough or blocking it.
*Fun note: LCDs have three sub-pixels, one green, one red, one blue. Each one of these sub pixels have 256 shades depending on the voltage applied. That is how we can see a nice screen full of color!
OLED (for Samsung phones) - It stands for Organic Light Emitting Diode. Basically the Emitting part is made of an organic compound which responds to different voltages. That is why for this technology we do not need a backlight.
Digitizer - It is a clear capacitance sensing layer able to capture analog signals (our finger movements in our case or our nose if it is cold outside and have gloves on) and covert them to digital signals (present or not present, zeros and ones) for our phone to understand.
You can think of it as a grid and each node (points where horizontal and vertical lines meet) as a data point. Each node has a coordinate” and based on that coordinate a location on the display is known. All these  nodes are sending a zero to the phone until our finger triggers it and then it sends a one. Inside of our smartphones there is an Integrated Circuit (IC) in charge of processing all this information. 
This digitizer is a film. A very thin clear film. This thin film is glued to the glass or to the LCD depending on the device model. Older model devices have the digitizer on the glass, but in newer devices it comes bonded with the LCD.
Polarizer - It is a film that translates the information from the LCD to our eyes. When this layer is off all we can see it is a very bright light coming through the LCD.
OCA - Optically Clear Adhesive is the glue used to primarily adhere the glass (part A) to the rest of the other components at this point in the process (part B). It is common to call part B LCD at this point in the process. 
Glass - The very top layer of our screen. Nothing high tech here just treated coated glass.
Wow! We got a little technical there. Lets review some of the other terms not addressed yet.
Touch Screen - As mentioned above, older smartphones (remember the iPhone 3G and 3GS?) came with the digitizer bonded to the glass. This was not bonded to the LCD (part B) so most likely that is where that term came from. Modern smartphones come in one piece and that touch screen is now part of the screen.
Touch Panel - This is back when Apple decided to use an actual panel as digitizer. It was not a film but a thick hard layer that powered the touch capabilities in our iPhone 4 and 4s. The layers on the iPhone 4 and 4s screens are as follow: Backlight, LCD, Polarizer, OCA, Touch Panel, OCA, Glass.
Hopefully by now it is clear why this process is called LCD Refurbishing. Not clear yet? Well... We can replace every other single layer in the screen but the LCD!
If you have any questions or terms not mentioned here please comment below!