Infrared (IR) or thermal imaging sensors, traditionally used in defence, are increasingly being introduced in civilian sectors with the rise of new commercial and high volume markets such as automotive, surveillance, thermography, medical diagnosis, environmental sensing and IR imaging in smartphones. The market size in 2018 is around 1M units for the civil market and only 0.1 million units for the defence market. In the case of smartphones, the market size 1s expected to rise to 9.8M units in 2021.
It is believed that thermal imaging will play a key role in turning self-driving vehicles into consumer products. This trend created a cost-driven market in favour of uncooled infrared imaging systems. Unlike their cooled counterparts, which operate based on photo-generation and collection of electrons and holes, uncooled IR detectors sense the temperature change due to the absorption of IR radiation.
The cooled detectors offer higher performance (higher resolution and signal-to-noise ratio, faster response) at a higher cost due to the need for cryogenic cooling. On the other hand, uncooled detectors offer cost effective solutions targeting the competitive low-end high-volume user market. Among uncooled detectors such as thermopiles, pyroelectric, and microbolometers, the latter are the most popular for infrared imaging purposes offering high resolution. Microbolometers are made of temperature-sensitive resistance materials, such as vanadium oxide for forming an electronic image. Their resolution in the scene temperature is on the order of 20 mK. However, the complexity of the readout integrated circuit and the need for the thermal leg structures to be electrically.