The Fractal ASIC series of the IGNITE project: CMOS 28-nm technology for high-precision 4D-tracking

The IGNITE project intends to develop technical solutions for the next generation of trackers at colliders, with special attention to the inner tracking systems, where extreme particle fluxes will be reached. The project is implementing an integrated module, comprising sensor, electronics, and fast readout, aimed at fast 4D-tracking. System pixels are required to have pitch around 50 $\mu \mathrm{m}$ and time resolution below 50 ps on the full chain (sensor to data readout). In the present paper we present measurement results concerning the performance of the first-born prototype ASIC (Ignite-0), which explores circuital solutions for high-performance Analog Front End and Time-to-Digital Converter circuits (time resolution below 30 ps). Such prototype structures have been tested before being integrated in a new design, featuring a 64x64 pixel matrix for the readout of pixelated sensors. Such device, having $55 \ \mu \mathrm{m}$ pixel pitch and named Ignite-64, has been recently submitted. The subsequent and final ASIC of the project, presently under preparation, will have a larger matrix of $256 \times 256$ pixels, $45 \ \mu \mathrm{m}$ pitch, while keeping time resolution of 30 ps and a power consumption density below $1.5 \mathrm{~W} / \mathrm{cm}^{2}$. All the IGNITE devices are designed following an approach which we named Fractal Design. It relies on vertical integration and allows covering large areas with fully scalable structures.