Impact of double-layer metal routing on silicon strip sensor performance

Abstract

In 2020, the CMS detector will suffer from higher radiation dose of the upgraded High-Luminosity LHC. The CMS Tracker has to be upgraded to be radiation harder and to reduce its material budget. In this work, new optional design of the CMS silicon strip sensor is tested, where the Pitch Adapter (PA) was integrated into the sensor’s structure via the second-metal-layer routing. The PA, which is made of glass with metal routing on top, is used as an interface between the silicon strip sensor and the readout chip. Incorporating the PA to the sensor helps reducing the material budget of the CMS Tracker and allows a flexible design of a smaller sensor. The test sensors are parts of the HPK campaign of the CMS Tracker collaboration. There are regions on the sensors with and without double metal (DM) routing, and regions with different double metal routing lengths. The effects of the double-layer metal routing on charge collection and signal to noise ratio (S/N) are investigated in this work. The experimental parts were done at Brown University. The quality of the test sensors were checked by electrical properties measurements. The signal measurements were made before and after irradiation with 800-MeV proton, to the fluence comparable to that of the upgraded LHC. No significant difference on charge collection and S/N between different regions were observed. The charge sharing between two consecutive strips (one strip with DM and other strip without DM) further confirms this conclusion.