Search

The ATLAS and CMS experiments will both replace their entire tracking systems for operation at the HL-LHC in 2026. This will include a significantly larger pixel systems, for example, for ATLAS approximately 15 m 2 . To keep the tracker material budget low it is crucial to minimize the mass of the pixel modules via thinning both the sensor and readout chip to about 150 μm each. The bump yield of thin module assemblies using solder based bump bonding can be problematic due to wafer bowing during solder reflow at high temperature. A new bump-bonding process using backside compensation on the readout chip to address the issue of low yield will be presented. The objective is to compensate dynamically the stress of the front side stack by adding a compensating layer to the backside of the wafer. A SiN and Al:Si stack has been chosen for the backside layer. The bow reducing effect of applying a backside compensation layer will be demonstrated using the FE-I4 wafer. The world's first results from assemblies produced from readout wafers thinned to 100 μm with a stress compensation layer are presented with bond yields close to 100% measured using the FE-I4 readout chip. [ABSTRACT FROM AUTHOR]

A new approach to photo detection using pixel Hybrid Photon Detectors (pixel-HPD's) has been adopted for the LHCb-RICH detector. These devices use a hybrid pixel detector inside an evacuated photo tube providing high-precision, low noise detection of Cherenkov radiation. The approach takes advantage of modern CMOS technology offering many advantages over more traditional techniques. These advantages include extremely high sensitivity, low noise and fast readout. A major technological challenge was the encapsulation of a hybrid pixel detector inside a photo detector tube. The fabrication of the HPD tube involves packaging of the pixel detector assembly onto a ceramic carrier to form the photo-anode and the subsequent bake out of the pixel anode under vacuum. Both processes involve high temperatures. A fine pitch solder bump-bonding technique, which is compatible with the manufacture of hybrid photo detectors, has been developed. The technology and the tests used for qualifying the new process for pixel-HPD production are described. More than 40 pixel detector assemblies have been produced with almost all showing <1% of missing pixels. A number of assemblies were baked out using temperature cycles identical to those used for pixel-HPD manufacture. None of the assemblies demonstrated any degradation. SEM photos clearly indicate the reliability of the process. 10 pixel-HPD tubes have been produced using this new bump-bonding process and those behave according to expectations. The pixel-HPD is the first of a new generation of photo detector tubes suitable for RICH and other visible photon sensing applications. [ABSTRACT FROM AUTHOR]