LCD is a mature display technology. OLED has appeared in many phones and TVs. Micro LED is a newer display technology that offers improved visual performance.
LCD
Liquid crystal display (LCD). An LED display in this context refers to an LCD that uses LED light-emitting diodes as the backlight source. The following summarizes the working principle of TFT LCD.
Advantages
- Low cost and long lifespan: LCD manufacturing is mature, with lower production difficulty and cost compared to OLED, and generally longer lifetime.
- No flicker: The backlight is an independent white LED backlight panel, which can effectively avoid screen flicker.
- High perceived sharpness: For the same resolution, LCD can appear sharper than OLED.
Disadvantages
- Higher power consumption: LCD requires an additional backlight, so devices tend to be thicker and consume more power than OLED designs.
- Lower contrast: LCD cannot turn off the backlight at the pixel level; black is produced by blocking backlight with liquid crystal molecules, which can result in a grayish appearance.
OLED
Organic light-emitting diode (OLED) uses organic semiconductor and luminescent materials that emit light when driven by an electric field. Under an applied field, holes from the anode and electrons from the cathode move into the hole transport and electron transport layers, respectively, and migrate to the emissive layer. When they meet in the emissive layer, excitons are formed and excite luminescent molecules, which then emit visible light.
Advantages
- Self-emissive pixels: Each pixel emits light independently, enabling thinner displays.
- Lower power and flexibility: OLEDs eliminate the need for a separate backlight, color filter, and some LCD structures, reducing power consumption and enabling flexible displays.
- High contrast and vivid colors: Because pixels can be turned fully off, blacks are deeper and overall color saturation and brightness can be higher.
- Faster response: OLED pixel response is faster than that of LCD.
Disadvantages
- Burn-in risk: OLED screens are more susceptible to image retention and burn-in.
- Blue emitter lifetime: Blue OLED materials typically have shorter lifetimes than other colors.
- Visible flicker and color shift: PWM-driven dimming and color biases can produce noticeable flicker and color shifts, which may cause eye discomfort during long-term use.
- Pixel density considerations: For the same resolution, some OLED implementations can appear less sharp than LCD.
Micro LED
Micro LED, also referred to as μLED, denotes LED chips with sizes smaller than 100 um. Like conventional LEDs, micro LEDs are self-emissive. RGB micro LED chips form individual pixels for display applications.
Advantages
- Fast response, high brightness, wide viewing angle, good color performance, and long lifetime.
- Self-emissive with no backlight required, enabling thin, compact, and energy-efficient displays.
Manufacturing challenges
- Mass transfer technology: Miniaturizing LEDs and assembling them at wafer scale requires advanced wafer-level processes.
- Chip processing: For micro LEDs that retain the substrate, dicing and cutting are major challenges. As chip size decreases, die yield tends to fall.
- Driver IC technology: Micro LED operation uses very low currents. Traditional driver ICs may perform poorly at low currents, causing poor grayscale performance and uneven brightness; some pixels may appear dim or not light at all.
- Testing and repair: Micro LED electrode dimensions are often smaller than probe tips, preventing conventional probe-based testing methods.
