X-FAB releases new isolation class, reducing chip size

Engineered to support more compact and efficient single-photon avalanche diode (SPAD) implementations, this new isolation class facilitates tighter functional integration, improved pixel density, and higher fill factor – resulting in a smaller chip area.

SPADs are crucial components in a wide range of emerging applications, including LiDAR for autonomous vehicles, 3D imaging, depth sensing in AR/VR systems, quantum communication and biomedical sensing. X-FAB already offers several SPAD devices built on its 180nm XH018 platform, with active areas ranging from 10µm to 20µm. This includes a near-infrared optimised diodefor elevated photon detection probability (PDP) performance.

To enable high-resolution SPAD arrays, a compact pitch and elevated fill factor are necessary. The newly released module ISOMOS1, a 25V isolation class module, allows for significantly more compact transistor isolation structures, eliminating the need for an additional mask layer and aligning perfectly with X-FAB’s other SPAD variants.

The advantages of this enhancement are evident when comparing SPAD pixel layouts. In a typical 4x3 SPAD array with 10x10µm² optical areas, the adoption of the new isolation class enables a ~25% reduction in total area and boosts fill factor by ~30% compared with the previously available isolation class. With carefully optimised pixel design, even greater gains in area efficiency and detection sensitivity are achievable.

X-FAB’s SPAD solution has been widely used in applications that require direct Time-of-Flight, such as smartphones, drones, and projectors. This new technological advancement directly benefits these applications in which high-resolution sensing with a compact footprint is essential. It enables accurate depth sensing in multiple scenarios, including industrial distance detection and robotics sensing, for instance, by protecting the area around a robot and avoiding collisions when robots are working as cobots. Beyond increasing performance and integration density, the new isolation class opens up opportunities for a broader range of SPAD-based systems requiring low-noise, high-speed single-photon detection within a compact footprint.

“The introduction of a new isolation class in XH018 marks an important step forward for SPAD integration. It enables tighter layouts and better performance, while allowing for more advanced sensing systems to be developed using our proven, reliable 180 nanometer platform," said Heming Wei, Technical Marketing Manager for Optoelectronics, X-FAB.