TFA sensor
TFA sensors are electrical circuits based on CMOS - ASICs , which are used as optical sensors, e.g. B. Imagers can be used. The name is derived from the English term "thin film on asic".
construction
By vapor deposition of a thin layer of amorphous silicon , an optically active multiple layer, which represents a photodiode , is produced on a previously manufactured ASIC . This makes the ASICs extremely sensitive to light. The TFA technology enables a particularly cost-effective production of powerful image sensors and is at the same time well suited for the integration of pixel electronics for the realization of intelligent image sensors. It goes back to the invention of the multispectrophotodiode at the University of Siegen and the further developments by the former company Silicon Vision .
Applications
There is currently no global supplier of commercial TFA image sensors in the patented NIPIN layer sequence, which is necessary for color reception. The technology as such (amorphous hydrogenated silicon (aSi: H) on CMOS sensors) is used successfully in X-ray sensors. A simply structured thin layer (NIP) is used for monochrome images.
Awards
For the invention of the TFA sensors, M. Böhm of the University of Siegen was awarded the Phillip Morris Prize in 1996.
advantages and disadvantages
In contrast to conventional technologies, such as B. CCDs , the TFA technology enables a 3D integration of photo detectors and image preprocessing in the ASIC. This allows - with the same functionality - a larger number of pixels, since only one pixel is required for all colors, but the 3 colors must be read out one after the other, which increases the required exposure time.
The materials used as the TFA layer allow a much higher dynamic than z. B. with CCDs or pure CMOS sensors.
By using two process steps and process technologies, the two components can be optimized more easily independently of one another, since the optically active TFA layer can be optimized along specific optical boundary conditions.
Due to the use of amorphous silicon as a light-sensitive layer, however, these sensors are sensitive to the Staebler-Wronski effect . Similar to crystal defects in a solid semiconductor crystal , amorphous silicon also has a large number of structural defects in the form of open bonds (so-called "dangling bonds"). Although these are usually saturated by hydrogen atoms, even in the visible light range, some photons have sufficient energy to break these silicon-hydrogen bonds. As the amount of radiation increases, the leakage current of the sensors increases. This can lead to strong light sources "burning in".
Web links
Individual evidence
- ↑ Digital image sensors Prof. Dr. Markus Bohm. 1996 Laureate. Philip Morris Foundation, accessed July 19, 2019 .