The silicon microbolometer: the basic building block

Amorphous silicon forms the basic building block of ULIS thermal imaging sensors. First developed over thirty years ago, the silicon microbolometer—an infrared imaging sensor that converts infrared radiation into visible images—has reached maturity.
The technology is today used in a broad range of commercial and military applications like thermography (temperature measurement), night vision, surveillance, firefighting, search and rescue, and home energy audits.

ULIS, a leading provider of infrared imaging sensors, uses amorphous silicon microbolometer technology (aSi). Amorphous silicon offers four major advantages:

Sharp images of moving objects

Amorphous silicon microbolometers are characterized by a small thermal time constant (≤ 10 ms). Therefore, they are less sensitive to the smearing effect that often appears when fast-moving objects are imaged; they can also be operated at a higher frame rate.
Amorphous silicon reduces the time needed to obtain an image once the camera has been turned on. Because the sensor does not need to be heated or cooled to reach operating temperature, it works virtually instantaneously. In military applications, this shorter time-to-image can save lives.

Low power consumption

Operating power consumption is a critical issue for any handheld electronic device. ULIS’ uncooled focal plane arrays require much less energy than other uncooled sensors. As an example, a 160 x 120 sensor requires only 40 mW at a frame rate of 50 Hz; the power requirements for 640 x 480 and 1024 x 768 sensors are equally low at less than 150 mW and 170 mW, respectively. Amorphous silicon’s temperature behavior leads to easier TEC-less focal plane operation, reducing system power consumption.

Solar immunity design

All uncooled microbolometers react similarly when the IR camera is pointed directly at the sun: pixels pick up the sun's image and a temporary signal offset occurs, slowly decreasing after exposure and producing a ghost image. However, ULIS amorphous-silicon-based sensors allow the problem to be corrected automatically for quality images, even after direct sun exposure and even with high-intensity or long exposures.
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Competitive pricing and lower total cost of ownership

Because the composition of amorphous silicon presents no variations, pixel temperature behaviors are identical. For TEC-less systems, this reduces system calibration time drastically, making system production more cost-effective.

Performance specifications of ULIS infrared imaging sensors
- High sensitivity to infrared radiation: extremely accurate
- Fast response time: capable of producing images at a high frame rate
- Small pixel size: compact and cost-effective
- Several array sizes available: VGA/16, VGA/4, VGA, XGA
- Designed for use in demanding environments: MIL STD 810/883