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ATLAS Insertable B-Layer (IBL) and DBM detectors

The IBL detector consists of 14 staves with 20 modules on each stave. For the first time not only standard planar silicon sensors have been used but as well the novel 3D silicon sensor technology. On each stave 8 modules at both end of the stave are made of these 3D sensors. A picture of a 3D single chip module can be seen in Fig. 1. To cope with the increased radiation damage and higher occupancies at this small radius a new FE-chip, FE-I4, have been developed. This chip is with roughly 2 x 2 cmmuch larger than its predecessor FE-I3 and required special treatment during the bump bonding to the sensor becasue of it very low target thickness of 150 µm. FE-I4 features 336 times 80 pixel with a pixel cell size of 50 times 250 µm2 and is fabricated in 130 nm CMOS technology. The 26,880 pixel per chip stores the hit data now inside the pixel matrix until the trigger signal arrives and send their data with 160 MBit/s per chip to the central ATLAS readout system.  

During the IBL development and production our main contributions were the chip development and its testing as well as the module production and testing. In total 50% of the roughly 750 built modules were assembled and tested in Bonn.


Fig. 1: Photograph of single chip IBL module consisting of one FE-I4 chip, one 3D silicon sensor and the module flex inside a handling frame.


In addition to the IBL a second detector has been added to the ATLAS Pixel Detector during the LS1 in 2013/14. The Diamond Beam Monitor (DBM) consists of 8 small tetelscopes installed around the beam pipe in forward and backward direction roughly at pseudorapitities between 3.2 to 3.5 as shown in Fig. 2. Each telescope uses 3 hybrid pixel detector modules based on one FE-I4 pixel chip bump bonded to a CVD diamond sensor. The modules are pointing to the IP of ATLAS to allow for a precise bunch to bunch luminosity measurement and beam spot monitor. Diamond is an ideal sensor material for this kind of application. It can be opeated in this high radiation environment even without or only limited cooling needs because of its complete lack of leakage current in comparision to silicon. The DBM for the first time operates a sizeable number of diamond pixel detectors inside a particle physics experimentlike ATLAS. Due to problems during the production of the diamond pixel modules only 6 out of the 8 telescopes are made of diamond. The other 2 telescopes use standard planar silicon sensors similar to the IBL double chip modules. The readout of the DBM telescopes are fully integrated in the ATLAS IBL readout and share all components like opto-link and off detector readout systems. Our contribution to the DBM was the bump bonding of the diamond sensors to the FE-I4 and the testing of the assembled modules.



Fig. 2: Installation of the DBM telescopes inside the ATLAS Pixel Detector volume.


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