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Display Technology

TFT

Highlights

A TFT-LCD (Thin Film Transistor – Liquid Crystal Display) is a technology of flat panel display

» A TFT-LCD is comprised of some basic components:

1. A Backlight Source (Light-Emitting Diode aka LED, Cold Cathode Fluorescent Lamp aka CCFL)

2. A bottom polarizing film (Linear Polarizer) and Color Filter which are pattered specific to each display

3. Thin-Film Transistor

4. Bottom Glass patterned with ITO for electrical circuitry

5. Liquid Crystal Fluid (Twisted Nematic aka TN typically, or STN Super Twisted Nematic)

6. Top Glass patterned with ITO and Top Polarizer (Linear type) offset from the bottom polarizer by specific angles.

7. Edge-mounted LCD driver chipsets.

8. The entire structure is most-

How It Works

1. Light is generated from a backlight source, typically LED. Light is generated as close to white spectrum.

2. Light is polarized (linear) from the bottom polarizer.

3. Driver ICs will logically control to activate pixels on or off.

» Inactive LCD pixels will not 'twist' light

» Active pixels will twist light about the horizontal plane of the glass (around a vertical axis)

4. Light through a pixel that is inactive will be blocked due to the offset of top and bottom polarization. While light through a pixel that is activated is twisted to pass through the top polarizer to be observed.

5. Color is added through a color filter to all sub-pixels (R,G,B)

MVATFT

Highlights

A MVA-TFT (Multi-Domain Vertical Alignment – Thin-Film Transistor) is a specific type of TFT-LCD technology.

» An MVA-TFT is comprised similar to a standard TFT-LCD with a few notable exceptions:

1. Polarization of a standard TFT-LCD are Linear Polarizers. This is for both creating optimal contrast and also for function of which light is viewed. MVA-TFT through some differences in process is able to use a Circular- type Polarizer which have more symmetrical viewing performance.

2. Liquid Crystal within the LCD panel will rotate about a different axis. MVA will process the fluid to rotate around the horizontal axis which is referred to as vertical alignment since the fluid will rotate in the same direction as passing light.

»Additional description of fluid rotation: TFT-LCD is like a Merry-Go-Round Carousel while MVA-TFT is like a Ferris Wheel.

How It Works

1. Light is generated from a backlight source, typically LED. Light is generated as close to white spectrum.

2. Driver ICs will logically control to activate pixels on or off.

» Inactive LCD pixels will block light

» Active pixels will open with the direction of the light to let it pass through.

3. Top Circular polarization is added to enhance contrast

4. Color is added through a color filter to all sub-pixels (R,G,B)

OLED

Highlights

A PMOLED (Passive-Matrix Organic Light Emitting Diode) is a type of flat panel display.

»Construction of a PMOLED Display:

Construction of a PMOLED Display:

1. PMOLED displays contain a layer of glass with ITO for electrical circuitry

2. Thin-deposits of semi-conductive materials.

» A P-type material

» An N-Type material

» An emissive layer material

» Metallic compounds top and bottom.

3. A layer of glass or metal for bottom encapsulation (non-viewed side).

4. A circular top polarizer to keep ideal viewing contrast.

5. Desiccant(s) and a seal enclosing the two layers of glass together.

Notable Technology of PMOLED

1. Each individual sub-pixel of a PMOLED display functions much like familiar LED components such that light is emitted from the material.

2. A PMOLED display multiplexes the power to each sub-pixel through a driver/controller chip mounted on the edge of the display glass.

» Size and resolution are limited since power is multiplexed through the driver IC and applied to the rows with a duty-cycle.

» Power efficiency and brightness are more difficult to achieve as the size and resolution of the panel is increased.

3. Materials in PMOLED are solid-state and are temperature independent in both optical (contrast and brightness) performance and pixel response time.

4. PMOLED are lower resolution and smaller size and format designs due to drive structure limitations. They are ideal for cost-sensitive applications and more simplistic architecture for small format sizes.

5. Unlike Passive-LCD, Passive-OLED technology is capable of frame rates suitable for video if required due to the fast pixel response of the technology.

How they work.

1. Rows and columns of P & N materials are layered and connected through metallic compounds to the ITO.

2. Electrons and holes through the P & N materials combine in the emissive layer producing light.

3. The color (wavelength) of light can be controlled by doping the emissive layer material.

4. Full-color designs can be achieved by designing each sub-pixel natively as red, green, and blue emission (most common architecture). This deposition is called 3-process since each substrate must have a deposit for each color independently. 

STN-LCD

Highlights

A STN-LCD (Super Twist Nematic – Liquid Crystal Display) is a mature technology of flat panel display

»A STN-LCD is comprised of some basic components:

1. A Backlight Source (Light-Emitting Diode aka LED, Cold Cathode Fluorescent Lamp aka CCFL)

2. A bottom polarizing film (Linear Polarizer)

3. Bottom Glass patterned with ITO for electrical circuitry

4. Liquid Crystal Fluid (Twisted Nematic aka TN typically, or STN Super Twisted Nematic)

5. Top Glass patterned with ITO and Top Polarizer (Linear type) offset from the bottom polarizer by specific angles.

6. Edge-mounted LCD driver chipsets.

Notable Technology of STN LCD

1. Fluid response of LCD is slow, so STN displays are not capable of full motion video frame rates. LCD may vary from 2 to 5 frames per second, while video is typically in the 20-30 fps range. If Video is desired, please refer to TFT-LCD technology.

2. STN LCD is only currently still available in monochromatic formats. Polarization may allow for various color schemes including blue background (negative), black background (negative), silver/gray background (positive). Also, pixel colors can vary from the color of backlighting (negative type designs) or black (FSTN) and navy blue (STN).

3. STN and TN technology will also imply some variations in operation/storage temperature and temperature response. Please consult your sales and display documentation to ensure the performance is suitable and configured ideally.

4. Temperature compensation may be required as contrast and response will vary with temperature.

How It Works

1. Light is generated from a backlight source, typically LED. Backlighting can be in any color desired and available. Popular colors include white, blue, yellow, green, orange, and amber. Existing tooling of the LED backlight for various colors will vary by display.

2. Light is polarized (linear) from the bottom polarizer.

3. Driver ICs will logically control to activate pixels on or off.

a. Inactive LCD pixels will not 'twist' light

b. Active pixels will twist light about the horizontal plane of the glass (around a vertical axis)

4. Light through a pixel that is inactive will be blocked due to the offset of top and bottom polarization. While light through a pixel that is activated is twisted to pass through the top polarizer to be observed.

AMOLED

Highlights

An AMOLED (Active-Matrix Organic Light Emitting Diode) is a type of flat panel display most similar to PMOLED, but with technology also used in TFT-LCD displays

Construction of a AMOLED Display:

1. AMOLED Displays are similar to PMOLED in most ways including material deposition. The layer sequence of AMOLED may vary from PMOLED due to manufacturing process.

2. Notable additions in AMOLED is the addition of a thin-film transistor layer (TFT).

3. Driver/Controllers also will vary from PMOLED due to the variance in power drive circuitry.

Notable Technology of AMOLED

1. AMOLED's most significant benefit is the separation of power from logic circuitry. Each sub-pixel of the display will contain both Anode, Cathode, and logical connections.

2. Power is more efficiently used on AMOLED since the power is not multiplexed through the driver and brightness is achieved at a lower power drive.

3. AMOLED technology is capable of scaling to larger panel sizes and higher resolutions with this separation of power circuitry.

How they work.

1. Light emission is produced the same as PMOLED using P & N type materials and layers.

2. Power circuitry operates such that a backplane voltage is created and available to each sub-pixel and capacitors at each sub-pixel can keep pre-charge levels necessary such that logical controls can operate quickly for high-resolution panels.

3. Logic circuitry is similar to a TFT-LCD with RGB-TTL interface and when a pixel is activated it will trigger a transistor at each pixel to activate. This activation will also trigger transistors for the power circuits to pass Anode/Cathode power to the P & N type materials inside the panels.

4. Light is emitted at each sub-pixel. System memory passing through logical circuits can activate an entire bitmap of pixels to produce a full color image. With proper frame rates of images both animation or video can be produced.

 
Technology STN-LCD TFT-LCD MVA-TFT PMOLED AMOLED
Polarization Linear Linear Circular Circular Circular
Emmission Various Various Transmissive Emissive Emissive
Backlight Yes or No Yes Yes N/A N/A
Color Filter No Yes Yes N/A N/A
Viewing Cone  Skew Skew Symmetrical Symmetrical Symmetrical
Viewing Angles  OK Good Great Best Best
Thickness  Various Thin Thin Ultra-Thin  Ultra-Thin 
Contrast OK Good Better Best Best
Sunlight Reading  Varies (Backlight)  Varies (Backlight)  Better (Backlight)  OK (Brightness)  Varies (Brightness) 
Temperature Dependent Dependent Dependent Independent Independent