Mitigating Sensor Cracking using the Interposer Strategy in the ATLAS ITk Strip Detector

Abstract

This paper introduces the strategy of using an interposing layer to mitigate thermal-stress-induced fracturing of silicon sensors in ATLAS ITk Strip modules. This strategy involves a change in the module design in which layers of soft adhesive and a kapton separator, known as an interposer, are added to the module stack-up to decouple thermal stresses. This paper discusses the interposer design and its implementation in the ATLAS ITk Strip barrel, including material tests to validate the additional components, the development of new processes to integrate the new layers into the module assembly workflow, results from design validation and quality control testing of prototype interposed modules, and studies indicating that the new design significantly reduces the thermal stress experienced by the sensor. Tests of prototype support structures loaded with interposed modules have shown no sensor fractures in the relevant temperature range for operation in ATLAS, resulting in the adoption of the interposer strategy as the primary sensor cracking mitigation in the ATLAS ITk Strip barrel.