THERMAL SENSORS BACKGROUND FACTS

The purpose of this article is to provide additional background information regarding the type of sensor used in the Bering Optics thermal scopes and to assist with better understanding of the thermal detectors’ attributes and core's difference. This document is current for Apr-12-2021.

THERMAL SENSORS HISTORICAL BACKGROUND FACTS

In the last few years, thermal imaging devices were rapidly developed for commercial applications, thanks to the availability of inexpensive uncooled detectors. Modern detectors are usually made of three different materials: Amorphous Silicon (A-Si), Vanadium Oxide (VOx) or Barium Strontium Titanate (BST), where each has their own benefits.

The VOx and BST technologies were developed in 1978-79. At that time the Vanadium Oxide technology was controlled by the US military. Without going into details, in later years VOx and A-Si technologies outperformed BST.

The A-Si technology was developed in the mid 90's in Europe as a more affordable alternative technology, where a thin layer of Amorphous Silicon was used to coat the microbolometer instead of Vanadium Oxide. The big advantage of using Amorphous Silicon was that A-Si detectors could be fabricated in a silicon foundry, which is a less expensive process, but less thermal sensitive material.

The A-Si technology that came out of Europe was labeled as inferior simply for the reason that it did not fit the already established standard for detector material, originally used by the US military.

Going past the historical facts, the paragraph below will compare the VOx and A-Si sensors and outline their advantages and disadvantages.

VOx vs. A-Si

VOx detectors are more sensitive and have better NETD (Noise Equivalent Temperature Difference). Therefore, they can "see" the smaller differences of temperature apart, which is important in thermal imaging application.
VOx detectors have higher current running through them with the same voltage as A-Si, which is lowering "thermal noise".
When investing in a thermal imaging system, the end user should be sure the device will save its capabilities for many years. As detecting material, A-Si outperforms VOx in terms of lifework time (typically 15 years without desensitization) versus VOx material which is facing desensitization after 10 years of usage.
Being less sensitive, A-Si detectors are more stable to perform in high temperature conditions which makes them more in demand in industrial sectors and in firefighting applications.
Both, VOx and A-Si detectors can be produced with pixels as small as 12 microns making one not superior or inferior to another in this regard.

CONCLUSION

There is a high degree of flexibility in configuring the design of the thermal imaging systems to meet the specific performance requirements and offer differentiated products to end-users especially for outdoor and tactical applications. Only an optimal combination of multiple factors is essential in providing the ability to "see" a clear thermal pattern image combined with the best detection and recognition distances. Some factors influencing this optimal combination are: Lens material (Ge is the best), aperture and F-number, detector technology and material (VOx is the most sensitive), the size of microbolometers (12um pixel pitch provides more magnification than 17um, but less FOV), ROIC, NUC algorithm (the combo of automatic and manual controls are the best), MEMS process, Image processing software, firmware features, display resolution, menu options and production effectiveness.

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