Results of tests of three-dimensionally integrated chips bonded to sensors

The VIPIC1 readout integrated circuit was designed for X-ray Photon Correlation Spectroscopy experiments that are typically performed using mono-energetic (8 keV) X-rays at a synchrotron radiation facility. The device is a pixel detector with sparsification and parallel readout from the groups, yielding high timing resolution. Recent improvements in bonding alignment of wafers resulted in deliveries of 3D bonded wafers. The stacks, bonded with both the Cu-Cu thermo-compression method and the Cu DBI bonding method, yielded operational devices that have been tested. Chips (with a pixel pitch of $80~\mu\hbox{m}$ ) were also bonded to silicon pixelated sensors (with a pixel pitch of $100~\mu\hbox{m}$ ) and the assemblies were exposed to X-ray sources for the first time. The paper focuses on the test results, including the calibrated noise (ENC) and the conversion gain. The noise measured corresponded to $39~\hbox{e}^ {- }$ and $70~\hbox{e}^ {- }$ , respectively for the readout channels that were not connected and connected to the sensor diodes. The conversion gain varied from 43 to $52~\mu\hbox{V/e}^ {- }$ as a function of the bias current in the front-end block. Essentially all the pixels on a small prototype were operational.