Pixel Size

Pixel size refers to the actual physical dimensions of each pixel on the focal plane array of an infrared detector chip, i.e., the real-world length and width represented by a single pixel. The unit is usually micrometers (μm). Common specifications include 8 μm, 12 μm, 17 μm, and 25 μm. As one of the core parameters of an infrared detector, pixel size directly affects the volume, cost, and imaging performance (such as resolution and field of view) of infrared thermal imaging modules.

Evolution of Pixel Size

With the widespread application of infrared thermal imaging technology in fields such as security, industrial inspection, and consumer electronics, there is a growing market demand for more compact systems and higher resolution. This has driven continuous reduction in the pixel size of detectors. The pixel size has evolved from earlier standards of 45 μm, 30 μm, and 25 μm to smaller dimensions such as 17 μm, 15 μm, 12 μm, 10 μm, and 8 μm. Research and development efforts are now even exploring pixel sizes beyond these dimensions.

Why Are Pixel Sizes Becoming Smaller?

• Optical Miniaturization: For an unchanged detector resolution and field of view, reducing the pixel size facilitates the miniaturization of optical systems. Smaller pixels allow for the use of lenses with a shorter focal length and a smaller aperture, which significantly reduces the volume, weight, and cost of the optical components. This drives the development of thermal imaging systems toward lighter and more compact designs.

• Higher Resolution and Wider Field of View: Under the premise of an identical focal plane array size, smaller pixels increase the total number of pixels (i.e., higher resolution). When combined with a suitable optical system, this higher pixel density can also enable a wider field of view, thereby expanding the observational coverage.

• Improved Spatial Resolution: At the same observation distance, smaller pixels improve spatial resolution, allowing the system to detect finer details of targets.

• Better Long-Distance Detection: For a target of the same size, a large-format detector array employing smaller pixels can extend the identification distance, thereby improving long-range detection capabilities.
  

Note: Pixel size cannot be reduced indefinitely. As it approaches the wavelength of the infrared radiation (e.g., approximately 10 μm in the LWIR band), diffraction effects will significantly degrade the image quality. Therefore, practical applications require a comprehensive consideration of system needs and physical constraints to select a pixel size that is both reasonable and optimal.

Pixel Size Calculation

Pixel Size Calculation

Pixel Size (μm) = [Sensor Size (mm) / Sensor Resolution (pixels)] × 1000

For a rectangular sensor with an aspect ratio of a:b, pixel size is typically calculated separately for the horizontal and vertical directions:

Horizontal Pixel Size (μm) = [Horizontal sensor size (mm) / Horizontal resolution (pixels)] × 1000
Vertical Pixel Size (μm) = [Vertical sensor size (mm) / Vertical resolution (pixels)]× 1000

Selection of Pixel Size

1. Application Requirements

• For high resolution (e.g., precision inspection, remote sensing imaging) or wide field of view (e.g., security monitoring, automotive night vision), smaller pixel detectors are preferred.

• In cases where long detection distance is not critical, but cost efficiency is important (e.g., civilian temperature measurement), detectors with larger pixel sizes may be more suitable.
  

2. Balancing Performance and Cost

• Smaller pixels improve resolution and field of view but require more complex chip manufacturing processes and higher costs.

• Larger pixels have more mature processes and lower cost, but may limit system performance. Trade-offs should be made according to practical needs.

3. Compatibility with Optical System and Sensitivity

• Pixel size must be compatible with the focal length and field of view of the infrared optical lens to prevent issues such as blurring or inefficient field coverage.

Note: the same process, reducing pixel size may decrease the photosensitive area of each pixel, potentially reducing detector sensitivity—especially in the long-wave infrared band. Thus, sensitivity requirements should be carefully considered in the selection process.