Enhanced X-FAB process variant boosts photodiode responsiveness

The specialist foundry, X-FAB Silicon Foundries, has made augmentations that have extended the scope of its XS018 180 nm sensor process, meaning that it is now able to offer a photodiode-specific process core module.

While the company’s XS018 process had been mainly focused on the fabrication of multi-pixel CMOS image sensors, this new module is dedicated to photodiode fabrication.

With this module, X-FAB can now offer customers six different photodiode options. These cover wavelengths from ultra-violet (UV) right through to near-infra-red (NIR). The diverse operational parameters of the photodiodes means that they can be aligned with various customer application requirements.

The new X-FAB photodiodes are capable of delivering best-in-class UV sensitivity, attaining 40% quantum efficiency (QE) in the UVA band, 50-60% QE in the UVB band and over 60% QE in the UVC band. In relation to NIR, significant performance improvements have also been witnessed. At 850 nm the photodiodes have 17% greater QE than legacy devices based on the original XH018 process, and at 905 nm there is a 5% QE increase witnessed. With a QE of approximately 90%, the human eye response option is highly suited to ambient light sensing applications.

A unique feature means that photodiode responsivity can be stipulated, via specifying the size of the metal aperture. The output current of the photodiode is thereby scalable between full current and no current – in order that any differences caused by filtering can be compensated for. In turn, this helps to simplify the accompanying amplification circuitry for photodiode arrays.

Other enhancements include a 10% increase in the fill factor compared to devices based on the earlier XH018 generation. Through this, devices can be created that will respond to lower light levels, or the size of the die can be reduced in order to save space.

“Through ongoing investment, X-FAB has built up strong optoelectronic credentials. Among the proof points of this is the fact that over 20% of mobile phone handsets manufactured worldwide feature an ambient light sensor that was produced by us,” said Luigi Di Capua, VP of Product Marketing at X-FAB. “Thanks to the advances we have announced in relation to our photodiode offering, we will now be better positioned to address client demands for proximity sensing, spectral analysis and optical distance/triangulation measurement solutions.”

The six photodiodes are available as of now, through the “my X-FAB” customer portal.