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|About us - Our History|
State-of-the-Art Silicon Radiation Detectors
|– The Beginning|
A Quantum Step in Performance
|– The Next Step|
|– Today’s Situation|
|State-of-the-Art Silicon Radiation Detectors – The Beginning
The start of the development of silicon radiation detectors within the Max-Planck-Gesellschaft was stimulated by G. Lutz – one of the later founders of the MPG HLL – in the early eighties by the need of fast and radiation hard position resolving tracking detectors for fixed target experiments in high energy physics research.
This need was falling on fertile soil at the Technische Universität München based in Garching next to Munich: The development of a planar process, derived from the upcoming microelectronics industry, was transformed towards a fabrication process for detectors.
The NA11 and NA32 fixed target experiments at CERN (1982-96) were the first ones using silicon detectors fabricated by the planar process for precise particle tracking. They were exhibiting spatial resolution in the range between two micrometers and five micrometers.
The reconstruction of the decay vertices of charmed hadrons was leading to a lifetime measurement of unprecedented accuracy. At that time the sensitive detector areas were in the scale of square centimetres and the associated readout electronics of a few hundred channels were filling racks of electronics. Since then the use of silicon radiation detectors became very popular in many fields of basic research: Today the largest high energy physics experiments to date, ATLAS and the CMS detector at the Large Hadron Collider (LHC), make use of approximately 300 m² of silicon detectors.
But also outside of particle physics silicon radiation detectors have marked a gigantic triumph: In astrophysics they are used as spectroscopic imagers, in materials sciences as X-ray detectors for fluorescent light, in synchrotron radiation research as high speed X-ray counters, in Gamma ray applications in medicine and astrophysics as high sensitive light detectors for the readout of scintillation light.
|A Quantum Step in Performance and Complexity – The Next Step
ESA’s XMM-Newton satellite project demanded a challenging large X-ray imager. It became evident that the production of wafer scale defect free novel silicon detectors needed such a well-defined cleanroom environment that it even exceeded the possibilities of microelectronics industry.
In 1990 the technology was transferred to the former premises of the Fraunhofer - Institut für Festkörpertechnologie, based in the Pasing district of Munich. A 250 m² cleanroom of class-10 to class-100 was rented and equipped with fabrication tools for ultra high resistivity float zone silicon.
The existing technology was upgraded to four inch wafer size for a fully double sided process. In addition to semiconductor fabrication technology a test area with test benches for the ATLAS strip and pixel detectors was built and an X-ray test facility for the XMM pnCCDs was installed. The simulation and layout tools were upgraded and the implementation of a process data base system for quality assurance and control was realized.
G. Lutz and L. Strüder took over the leadership of the MPG HLL. They successfully realized the implementation of a 36 cm² pnCCD for XMM – being still the world’s largest direct converting X-ray CCD.
In 1999 we started the evaluation of the upgrade from four inch wafer size (100mm) to 150 mm. This step was motivated by new projects in need of monolithic detectors larger than six by six square centimeter, the maximum for 100mm format with a diagonal of approximately 8.5 cm.
|Optimum Conditions – Today’s Situation
In 2000 we finished our second facility transfer to the Neuperlach section of Munich on-site the Siemens campus. A 600 square meter Class-1 cleanroom was commissioned and qualified in 2001. Again this change of facility was a tremendous step forward in process technology which can be expressed in the following way:
In Garching the thermal leakage current per square centimeter – a probe for the quality of the fabrication process – was about 1 nA, in Pasing about 0.5 nA on 280 μm thick detectors. In Neuperlach we routinely achieve 0.1 nA per square centimeter but on 500 μm thick depleted silicon wafers. The smallest structures were going from 3 μm to 2 μm in Pasing. At present they are going to 1.5 μm.
With our present process technology we are well prepared to realize upcoming projects seen on the horizon up to 2020.
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