Silicon strip prototypes for the ATLAS Upgrade tracker of the HL-LHC

We present the development of a low mass, highly modular structure for the strip tracker region of the upgraded ATLAS detector of the HL-LHC. The design of this double-sided structure, called “stavelet”, has been modified with respect to the baseline design in order to reduce significantly the amount of material, keeping the same electrical and thermal performances of previous single-sided stave prototypes. The aluminium shielding layers of the bus tapes that constitute the power and data traces have been removed, allowing an effective reduction of the percentage radiation length approximately equal to 15 % with respect to the previous prototypes. A new co-curing process for the bus tapes and carbon fibre facings has been investigated. In this process, the bus tapes are embedded in between the carbon fibre facings, acting as an effective shielding for the sensor modules. Precision mechanical assembly tools have also been developed, allowing for controlled placement and gluing of the silicon modules onto the stavelet core. Two different LV powering distributions (serial and DC-DC) are implemented in the stavelet prototype, one on each side. The layout of the different components and construction procedure of the double-sided stavelet will be described. Detailed surface metrology, thermal, and electrical results of the different components and of the final stavelet prototype will be also presented.