Yongsheng Tang, Xingbo Gao, Shilin Shen, Aqiang Liu
Chengdu Leapchip Microelectronics Co., Ltd., Chengdu, Sichuan 610000, China
Abstract: With the continuous advancement of electronic information technology, Micro LED display technology has emerged as a cutting-edge solution. This technology offers numerous advantages, including low power consumption, high resolution, miniaturization, and fast response speed, making it widely applicable in fields such as visible light communication, medical detection, and spatial displays. Driver ICs play a crucial role in Micro LED display systems and are essential to the development of the technology. This paper analyzes the display principles and structural characteristics of Micro LED, outlines its technical advantages, and explores the application of driver ICs within Micro LED display technology for reference.
Keywords: Micro LED; Driver IC; Display Technology
At present, China’s display technology is steadily improving, and users are placing higher demands on display screens. Against this backdrop, displays are gradually evolving toward greater integration, miniaturization, and high-definition resolution, and are widely used across various devices such as augmented reality (AR) equipment, tablets, televisions, smartphones, and data projectors. From the early development of LCD to today’s Micro LED, display technology has progressed over several decades. Each type of display technology has its own advantages and plays a vital role in different industries. LCD technology, for instance, offers a long lifespan and low cost, but it also has drawbacks such as limited flexibility and contrast, making it more suitable for industries where high display precision is not a critical requirement. In contrast, Micro LED technology offers superior resolution, excellent compatibility, and high brightness, making it an ideal choice among current display technologies.
1. Display Principles and Structure of Micro LED
1.1 Display Principles of Micro LED
Micro LED is a miniaturized, arrayed, and thin-film electronic device based on the LED structure. Essentially, a Micro LED is a type of LED chip that shares the same light-emitting mechanism as conventional LEDs. It can be viewed as a PN junction capable of photoelectric conversion. In practical applications, when a forward voltage is applied from the P side to the N side, the built-in electric field is disrupted, enhancing the diffusion of charge carriers. Holes in the P region move toward the N region, while electrons in the N region move toward the P region. In the space charge region, electrons and holes recombine, releasing energy in the form of photons and ultimately producing light. Micro LED converts electrical energy into light energy with a simplified process and higher conversion efficiency.
1.2 Structure of Micro LED
The traditional Micro LED chip adopts a “wire-bonded” upright structure. However, with the development of lift-off and epitaxial growth technologies, vertical and flip-chip structures have gradually emerged. In upright-structured Micro LED chips, both the P electrode and N electrode are located on the same side of the chip, causing the current to spread outward after being injected. This structure uses wire bonding, with bonding pads present on the surface for pressure welding. However, the metal electrodes can partially block light emission. As the size of the Micro LED decreases, this light blockage becomes more significant, thereby affecting luminous efficiency. Additionally, the chip base typically uses a sapphire substrate, which offers poor heat dissipation. Heat can only be expelled through the pins, leading to accumulation and negatively impacting device performance, ultimately reducing optical output power. In flip-chip structured Micro LED chips, current is injected through flip-chip soldering. An insulating thermally conductive filler is inserted between the metal and substrate contact points, significantly improving heat dissipation. In vertical-structured Micro LED chips, the two electrodes are placed on opposite sides of the chip, allowing current to flow vertically through the epitaxial layer. This prevents lateral current crowding, reduces heat buildup, and improves thermal management. However, in small-sized screens with higher resolution and smaller pixel dimensions, the bonding process becomes more challenging. At present, flip-chip structured Micro LEDs are more widely used due to their advantages in integration, scalability, and simplified manufacturing.
2. Advantages of Micro LED Display Technology
2.1 Superior Image Quality
At a constant power level, Micro LED displays can achieve higher brightness—typically in the range of 2000 to 4000 cd/m²—because they are not affected by optical blockers or polarizing filters. Additionally, Micro LED screens offer a half-power viewing angle greater than 170°, and when combined with high dynamic range (HDR) technology and surface blackening techniques, they deliver ultra-high contrast and premium HDR visual performance.
2.2 High Energy Efficiency
Traditional LCD display technology has a light transmittance of only about 5%, resulting in low optical efficiency. In contrast, Micro LED is a self-emissive display technology using red, green, and blue light sources, and is not restricted by light transmittance. Under the same brightness, the theoretical power consumption of Micro LED displays is 90% lower than that of LCDs. Furthermore, LED chip materials are mature and efficient in converting electricity into light, and the theoretical power consumption of Micro LED is only about 50% that of OLED technology.
2.3 Long Lifespan
Micro LED uses inorganic semiconductor materials as its light source, which are highly stable and have a long lifespan. Compared to quantum dot materials and OLED organic light-emitting semiconductors, Micro LED has inherent advantages in aging resistance, water and oxygen resistance, and thermal durability.
2.4 Extremely High Resolution
Due to their microscopic size, Micro LED chips are well-suited for building high-resolution displays. While current manufacturing processes still present challenges, Micro LED technology has demonstrated the potential to quickly break through performance barriers and achieve ultra-fine resolutions in a relatively short development cycle.
3. Characteristics of the Driver IC
The driver IC is a critical component of the LED lighting system. It integrates multiple elements—such as resistors, comparators, regulators, and power transistors—and enables the control of LED driving current by adjusting external resistors, ensuring the brightness meets desired levels. The main characteristics of the driver IC include:
(1) DC Control: By employing constant-current driving, the driver IC eliminates current fluctuations caused by forward voltage variations, thereby maintaining consistent brightness.
(2) High Efficiency: Typically, power efficiency is defined as the ratio of output power to input power. For Micro LED driver ICs, efficiency is measured as the ratio of LED output power to input power, resulting in relatively high energy efficiency.
(3) PWM Dimming: When the duty cycle is 50%, applying full current yields 50% brightness. At this point, the PWM (Pulse Width Modulation) frequency exceeds 100 Hz. The driver IC is capable of handling PWM frequencies up to 50 kHz.
(4) Overvoltage Protection: In constant current mode, the driver IC can provide overvoltage protection for the operating current. Regardless of the load conditions, it ensures a stable output current.
(5) Load Disconnection: In the event of a power failure, the driver IC can disconnect the LED from the power supply via its load disconnection feature, preventing potential damage or malfunction.
4. Application of Driver ICs in Micro LED Display Technology
4.1 Driver IC Parameters
Micro LED is known for its high-definition image quality, long lifespan, and exceptional energy efficiency, making it a focal point across various industries. Numerous manufacturers are actively investing in Micro LED research and development. While significant progress has been made in integration processes, there is still substantial room for improvement. Researchers have recently achieved breakthrough innovations in driver IC architecture by adopting advanced integration schemes. One such advancement involves the use of Mini-LVDS (Low Voltage Differential Signaling) to enable high-speed data transmission. Additionally, circuit design has been streamlined to support a more unified and efficient display control solution.
Typical parameters of commonly used driver ICs are shown in Table 1.
Table 1. Protection IC Parameters
| Parameter | MP26A | MP31A | MP22A | MP22AK |
|---|---|---|---|---|
| Overvoltage Detection Value /V | 4.275 | 4.275 | 4.310 | 4.310 |
| Undervoltage Detection Value /V | 2.4 | 2.3 | 2.3 | 2.3 |
| Overcurrent Detection Value /V | 0.15 | 0.10 | 0.13 | 0.13 |
| Overcurrent Detection Delay /s | 1.00 | 1.00 | 0.25 | 0.25 |
| Maximum Self-consumption Current /μA | 6.0 | 6.0 | 6.0 | 6.0 |
| Package | TEP–5L | TEP–5L | TEP–5L | TEP–5L |
| Continuous Overcurrent Capacity /A | 1.5 | 1.5 | 1.5 | 1.5 |
Driver ICs offer rapid switching speeds, typically activating within just 20 nanoseconds. They feature high current gain, with a maximum gain reaching up to 200%, and maintain excellent current accuracy, with current deviation not exceeding ±1.0%. By adopting a row-column integrated driving design, they can effectively support arbitrary scanning applications across 1 to 90 rows. A single IC is capable of controlling up to 120×90 pixels, supporting 16-bit input data buffering and outputting based on grayscale levels. Through the use of grayscale clocking technology, overall system electromagnetic interference (EMI) is minimized. Furthermore, the integration of dynamic power-saving modules and open-LED detection enhances the overall integration level of the driver IC, resulting in better display performance and delivering advantages such as reduced useless power consumption, black-screen energy saving, and dynamic energy optimization.
4.2 Functional Modules
The chip adopts ball grid array (BGA) packaging technology, allowing the bottom surface of the device to serve as the connection interface. Compared with other packaging methods, this technique offers lower thermal resistance and inductance, along with higher pin density. The use of different packaging technologies to increase the number of pins not only enhances the level of chip integration but also improves high-speed performance. In the driver IC, the low-voltage differential signal input interface is mLVDS IN, while the output interface is mLVDS OUT. These interfaces offer key advantages, including lower power consumption, faster transmission speeds, and simplified circuit structure. The GPLL module serves as a phase-locked loop (PLL) unit that processes the received clock signal and optimizes grayscale clock generation. The timing control module handles the sequencing of chip signals and integrates specific display algorithms to continuously optimize visual performance. The display data processing unit is responsible both for displaying image data and for conducting data detection and correction. The row scanning driver module supports flexible scanning across 1 to 90 rows and allows for various scanning configurations. The constant current driving module supports a wide range of current outputs and uses per-channel tuning technology to independently calibrate each channel, thereby ensuring current accuracy.
4.3 Application Performance
4.3.1 Chip Power Consumption
By adopting a common-cathode driving architecture, external resistors are not required, and the constant current output current can be configured through internal registers, thereby reducing overall chip power consumption.
4.3.2 Current Accuracy
With per-channel calibration, each output channel can be fine-tuned individually. Current variation between channels and across ICs is minimal, with channel current deviation within ±1.0% and IC-to-IC current deviation also within ±1.0%. Variations in the LED’s forward voltage have minimal impact on the output current.
4.3.3 Communication Efficiency
Mini LVDS, a high-speed serial interface, connects with the timing controller and column driver without generating significant electromagnetic interference. It provides high bandwidth for the display system. Integrating Mini LVDS into the chip simplifies the transmission path and significantly improves data transfer efficiency.
4.3.4 Row-Column Integrated Driving
Micro LED driver chips have moved beyond the traditional separation of row and column drivers by adopting an integrated row-column architecture. In this design, constant current (column) drivers and row drivers are combined within a single chip, avoiding cross-board color inconsistencies and high-brightness coupling issues. This results in a smaller pitch, simplified circuit design, and higher integration. The chip features 180 row output channels and 360 constant current (column) drivers, achieving a highly integrated design with reduced footprint. High integration also lowers power consumption during chip operation, enhancing overall energy efficiency. During the chip design phase, higher scan frequencies and additional functional modules—such as blanking and coupling circuits—are included to improve grayscale performance at low current levels. Through the use of unified serial data and pulse width control, the signal can be precisely managed, ensuring optimal compatibility between the driver IC and LED pixels, ultimately delivering superior image display quality.
5. Conclusion
In summary, Micro LED display technology offers numerous advantages, including vibrant color reproduction, high brightness, wide dynamic range, and the ability to illuminate individual pixels. By minimizing pixel pitch to the micron level, the overall display structure becomes thinner and lighter, aligning with modern development trends. While the future of Micro LED displays is promising, the technology still faces several challenges. Key areas such as mass transfer processes and color conversion methods require further improvement, with many technical bottlenecks yet to be overcome. Among these, driver circuit design plays a particularly critical role. Therefore, focused research on Micro LED display driver IC technology is essential. Advancing the capabilities of driver ICs will be pivotal in driving innovation and accelerating breakthroughs in Micro LED display technology.
