In the field of embedded displays, Chip-on-Glass (COG) technology has become the preferred display solution for miniaturized electronic devices due to its highly integrated and thin design. COG LCD displays eliminate the need for an additional PCB circuit board by directly bonding the driver IC onto the glass substrate, significantly reducing module size, optimizing signal transmission efficiency, and lowering power consumption and electromagnetic interference. As the two core application branches of COG technology, graphic LCDs and character LCDs, with their flexible visual capabilities and simple and efficient text display capabilities, respectively, cover a wide range of applications from industrial control to consumer electronics, jointly building the application ecosystem of COG display technology.

COG Technology: Reshaping the Integrated Architecture of LCD Displays

The core breakthrough of COG technology lies in changing the installation method of the driver IC. Through anisotropic conductive film (ACF) bonding technology, the driver chip is directly fixed to the electrodes of the liquid crystal glass substrate, achieving seamless integration of the chip and the glass. This architectural design brings multiple technical advantages: First, it eliminates the need for a PCB carrier and connecting cables, significantly reducing the thickness of the display module, making miniaturization possible for portable devices; some COG LCD modules can have a thickness of only a few millimeters. Second, it shortens the signal path between the driver IC and the pixel array, effectively improving signal integrity, reducing transmission delay, and minimizing electromagnetic interference (EMI), thus meeting the working requirements of precision electronic equipment. Third, it simplifies the manufacturing process, reduces the number of welding steps and components, which improves product reliability and reduces BOM costs in mass production.

Compared with traditional COB (Chip-on-Board) technology, COG LCDs perform better in terms of thinness and stability, especially suitable for space-constrained scenarios; while COB is suitable for general industrial equipment due to its simple assembly and low maintenance costs. Currently, COG technology is deeply integrated with technologies such as IGZO-TFT backplanes and dynamic line frequency refresh, further breaking through power consumption bottlenecks and maintaining stable performance in a wide temperature range of -30℃ to 85℃, expanding its application boundaries in extreme environments.

Character COG LCDs: An Efficient Solution for Text Display

Character COG LCDs are designed specifically for displaying text and simple symbols. Their core feature is the use of fixed dot matrix units (typically 5×8 or 5×10 pixels) to form character cells. They can only display a preset ASCII character set, a small number of custom symbols, and simple icons, and cannot freely draw graphics. Common specifications include 16×2 and 20×4, meaning 16 or 20 characters per line, with 2 or 4 lines in total.  The module integrates dedicated controllers such as the HD44780, supporting parallel or serial interfaces for connection to microcontrollers, resulting in low programming difficulty and controllable integration costs.

In terms of technical advantages, character COG LCDs are characterized by "simplicity and efficiency": they have significantly low power consumption due to the small number of pixels and simple driving logic, with static power consumption reduced to microampere levels, making them suitable for smart instruments powered by button batteries; they offer a significant cost advantage, with manufacturing costs more than 30% lower than graphic LCDs, making them an ideal choice for cost-sensitive products; and they have strong interface compatibility, allowing for hardware interchangeability between different specifications of character COG LCDs, requiring only minor software adjustments for adaptation, greatly improving project development efficiency.

Their application scenarios are concentrated in devices that require precise transmission of text information, such as status displays in home appliances (coffee machines, thermostats), parameter reporting in industrial instruments, and information feedback in digital scales and audio equipment. In these scenarios, the clarity and stability of text information take precedence over visual expressiveness, and the technical characteristics of character COG LCDs perfectly match these requirements.

Graphic COG LCDs: A Versatile Performer for Flexible Visualization

Graphic COG LCDs break the limitations of character displays, employing a full-pixel independently controllable dot matrix architecture that allows for the free drawing of graphics, images, custom fonts, and complex interfaces. Core specifications include resolutions such as 128×64 and 240×128, with some high-resolution models supporting simple animations and full-color displays. They are equipped with graphic controllers such as the ST7565 and SSD1305, supporting flexible interfaces such as SPI and I²C, and can achieve dynamic display of complex images through frame buffer management, offering far superior visual performance compared to character LCDs.

In terms of technological evolution, graphic COG LCDs are upgrading towards high image quality and low power consumption: FFS/IPS optical technology achieves native contrast ratios of over 1500:1 and wide viewing angles, solving the problem of color shift at oblique angles; combining optical microcavity resonance technology and RGB pixel microstructure, high color gamut coverage is achieved without increasing physical resolution, providing a full-color solution for miniature devices; some 128×64 graphic COG LCDs operate at only 3.3V, combining thinness and low power consumption, with dimensions controllable within 48mm×37mm, suitable for handheld terminals, medical equipment, and other applications.

Thanks to their flexible visualization capabilities, graphic COG LCDs are widely used in portable medical devices (blood glucose meters, ECG monitors), in-car display terminals, industrial control human-machine interfaces, and smart wearable devices, clearly displaying complex content such as data curves, icon navigation, and Chinese character menus, becoming a core component of embedded devices requiring rich information display.

Differentiated Selection and Industry Trends of the Two Branches

The selection of character-type and graphic-type COG LCDs should be based on the core needs of the application scenario: if only text parameter display is required, and low cost and low power consumption are desired, the character type is the optimal choice; if a graphical interface, customized content, or complex information visualization is needed, the graphic type should be prioritized. From a technical parameter perspective, character-type LCDs excel in low cost, ease of integration, and long battery life; graphic-type LCDs have advantages in resolution, visual flexibility, and functional expandability, but the driving complexity and cost are relatively higher.

In the future, COG LCD display technology will show three major development trends: First, deeper technological integration, the popularization of IGZO-TFT and dynamic refresh technology will further reduce the power consumption of graphic COG LCDs, with static power consumption expected to drop to less than 1/5 of traditional solutions; second, full-color and miniaturization will proceed in parallel, and nanoscale inkjet printing technology will promote the mass production of high-PPI full-color COG LCDs, adapting to the upgrading needs of smart wearables and miniature medical devices; third, accelerated localization, leading manufacturers are building patent barriers through independent RISC-V architecture driver chips and optical microcavity technology research and development, and it is expected that the market size of Chinese standard graphic dot matrix COG LCDs will exceed 14.5 billion RMB by 2026.

Conclusion

COG LCD displays have reshaped the technological landscape of embedded displays with their integrated architecture, while the two main branches—character-based and graphic-based—meet the needs of simple text display and complex visualization, respectively, based on their differentiated positioning. From household appliances to precision industrial equipment, from portable medical terminals to intelligent in-car systems, COG LCDs have become an indispensable visual interface for electronic devices due to their thin, lightweight, low-power, and highly reliable characteristics. With continuous technological advancements, COG LCDs will continue to break through in power consumption control, image quality performance, and scene adaptability, providing solid support for the innovative development of the embedded industry.