Chip-On-Glass (COG) vs. Chip-On-Board (COB)
Overview:
Unlike conventional LCD modules, Chip-On-Glass (COG) displays are designed without a printed circuit board (PCB). Instead, the LCD driver/controller is directly bonded to the glass substrate of the display. This configuration enables COG displays to be more compact, cost-effective, and highly customizable compared to traditional LCD modules.
COG Displays
COG LCDs are constructed from two pieces of polarised glass. One side of the glass is treated with a polymer that forms grooves aligned with the polarizing film. A liquid crystal material is then applied to the grooved side of one glass layer, aligning the crystals with the grooves. The second glass layer is placed on top, groove-side inward and perpendicular to the first, forming a grid-like row and column layout.
The driver/controller IC is mounted directly onto the glass by bonding the IC’s gold bumps to the indium tin oxide (ITO) tracks on the display surface. This direct mounting approach eliminates the need for a bezel or PCB, allowing for ultra-thin profiles.
Key Features of COG Displays:
- Supports 5×8 dot matrix characters or monochrome graphic icons (customizable)
- High brightness with low power consumption
- Ultra-thin profiles—can be as thin as 2mm without a bezel
- Built-in font support with four font tables in character-type COG modules
- Highly cost-effective solution
Graphic COB LCDs
Graphic LCD modules based on Chip-On-Board (COB) construction are available in STN and FSTN variants and come in a range of pixel resolutions (e.g., 240×128 = 240 pixels wide by 128 pixels high). These displays use a passive matrix structure and a dot matrix layout, capable of rendering both text and bitmap-style graphics.
Unlike character displays, graphic LCDs require detailed input for each pixel, offering greater flexibility and image complexity at the cost of increased data handling.
Character COB LCDs
Character-based COB LCD modules are also monochrome passive matrix displays, featuring built-in, pre-programmed font tables. They are available in standard formats, ranging from 1 line × 8 characters up to 4 lines × 40 characters, and are often compatible with vacuum fluorescent display (VFD) module replacements.
Each display consists of a fixed number of character cells per row. These cells are populated using characters from the internal font tables—e.g., assigning a capital letter “A” to row 1, cell 1.
Available in:
- STN or FSTN types
- Standard sizes and character formats
- Ideal for simple text-based interfaces