Radiation tolerant sensors for the ATLAS pixel detector
Radiation tolerant sensors for the ATLAS pixel detector
Radiation tolerant sensors for the ATLAS pixel detector
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and <strong>the</strong> 5 disks in each <strong>for</strong>ward direction. The<br />
modules <strong>for</strong> <strong>the</strong> B-layer are needed about 2 years<br />
later allowing a separate production and <strong>the</strong> use of<br />
<strong>the</strong> MCMD-technology, which will be optimized<br />
according to <strong>the</strong> special B-layer requirements, e.g.<br />
300 mm long cells. One important option is to have<br />
equal-sized <strong>pixel</strong> cells all over <strong>the</strong> sensor without<br />
elongated and ganged <strong>pixel</strong> as <strong>the</strong> cell geometry is<br />
not dictated by <strong>the</strong> read-out chip and also <strong>the</strong><br />
implementation ofbricked <strong>pixel</strong>s would easily be<br />
possible without any additional cross-talk caused<br />
by routing in one metal layer. These will improve<br />
<strong>the</strong> spatial resolution in this important layer <strong>for</strong><br />
<strong>the</strong> impact parameter measurement and <strong>the</strong><br />
b-tagging. There<strong>for</strong>e, <strong>the</strong> starting sensor wafer<br />
production will be <strong>for</strong> tiles <strong>for</strong> <strong>the</strong> outer modules<br />
which will be built with a flex hybrid. The wafer<br />
layout has been finalized according to <strong>the</strong> results<br />
of<strong>the</strong> prototype studies. The design of<strong>the</strong> <strong>pixel</strong><br />
cells is shown in Fig. 7, with <strong>the</strong> bias-grid structure<br />
in <strong>the</strong> middle and <strong>the</strong> passivation opening <strong>for</strong><br />
bump bonding on <strong>the</strong> o<strong>the</strong>r side ofeach <strong>pixel</strong>.<br />
Besides three tiles <strong>for</strong> <strong>the</strong> <strong>ATLAS</strong> <strong>pixel</strong> <strong>detector</strong><br />
modules, <strong>the</strong> wafer will contain six single chip<br />
devices and a number oftest structures <strong>for</strong> quality<br />
control. According to <strong>the</strong> Quality Assurance plan,<br />
part of<strong>the</strong> control measurement will have already<br />
been per<strong>for</strong>med by <strong>the</strong> vendors, but <strong>the</strong>se measurements<br />
and additional tests will be per<strong>for</strong>med<br />
by <strong>the</strong> <strong>ATLAS</strong> institutes.<br />
6. Conclusions<br />
R. Wunstorf / Nuclear Instruments and Methods in Physics Research A466 (2001) 327–334 333<br />
With <strong>the</strong> knowledge of<strong>the</strong> radiation effects in<br />
silicon <strong>detector</strong>s as a good starting point, <strong>the</strong><br />
Fig. 7. Design of<strong>the</strong> <strong>pixel</strong> sensor cell <strong>for</strong> <strong>the</strong> <strong>ATLAS</strong> <strong>pixel</strong> <strong>detector</strong>.<br />
<strong>ATLAS</strong> <strong>pixel</strong> collaboration began in 1996 to<br />
develop silicon <strong>pixel</strong> <strong>sensors</strong> capable ofsurviving<br />
<strong>the</strong> harsh radiation environment at <strong>the</strong> LHC. To<br />
reach this challenging goal, a dual-track strategy<br />
was followed. Besides <strong>the</strong> studies concerning <strong>the</strong><br />
sensor design and prototyping within <strong>the</strong> <strong>ATLAS</strong><br />
<strong>pixel</strong> collaboration, <strong>the</strong> investigations of<strong>the</strong><br />
radiation hardness ofsilicon were done within<br />
<strong>the</strong> ROSE collaboration. The result is an n + –in–n<br />
<strong>pixel</strong> sensor with moderated p-spray using oxygen<br />
diffused silicon. Indispensable to <strong>the</strong> quality<br />
control during production is <strong>the</strong> implemented bias<br />
grid, which enables measurements of<strong>the</strong> I2V<br />
characteristic with two contacts and prevents<br />
problems due to missing bumps during operation.<br />
Acknowledgements<br />
These important results <strong>for</strong> <strong>the</strong> <strong>ATLAS</strong> Experiment<br />
could not have been achieved without <strong>the</strong><br />
considerable engagement of<strong>the</strong> members of<strong>the</strong><br />
<strong>ATLAS</strong> Pixel Collaboration and <strong>the</strong> ROSE<br />
collaboration and <strong>the</strong>ir cooperation. There<strong>for</strong>e,<br />
<strong>the</strong> acknowledgement goes to all who participated<br />
in <strong>the</strong> sensor design, <strong>the</strong> sensor measurements, <strong>the</strong><br />
irradiations, <strong>the</strong> testbeam runs and <strong>the</strong> logistics,<br />
sending <strong>the</strong> <strong>sensors</strong> on time to <strong>the</strong> different places.<br />
References<br />
[1] <strong>ATLAS</strong> Collaboration, <strong>ATLAS</strong> Pixel Detector Technical<br />
Design Report, CERN/LHCC/98-13, Geneva, 1998.<br />
[2] <strong>ATLAS</strong> Collaboration, <strong>ATLAS</strong> Inner Detector Technical<br />
Design Report, CERN/LHCC/97-16 and CERN/LHCC/<br />
97-17, Geneva, 1997.