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Planar technology was introduced in 1982, which led to the rapid progress in development of the silicon detectors. Among others, strip detectors were invented and matched to meet the requirements of the Large Hadron Collider (LHC) developed at The European Organization for Nuclear Research (CERN). Main advantages were lower noise, smaller capacitance, room working temperature, easier production, reduced cooling requirements and larger area coverage. [1;3]
Strip silicon radiation detectors
Theory and design
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Silicon detectors consist of n type material while having p type aluminium strips on the surface which are separated by a thin insulator. At the same time there is an electric field between the p strips and the n type material. When a radiation particle passes the detector, silicon atoms are ionized and free electrons leave these atoms with an electron vacancy (holes). After they reach the p type strip they are collected and then create a charge on the aluminium strip which is possible to be measured with special electronics.
Orava et al (2007) proposes a new type of the strip silicon detector (Figure 2) which implements cross-connected short strips interlaced by long strips. The main advantage is that better measuring resolution is achieved, which requires much less accuracy [3].
Figure 2. Layout of the single sided stereo angle silicon strip detector. Reprinted from Orava et al (2007)[3,227].
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Furthermore, detector is designed in a way that every second strip is long while short strips are crossing them which helps to register particles at better angles to the surface of the sensor. Consequently, the high efficiency and proper special resolution are achieved. [3].
Development in Finland
VTT Technical Research Centre of Finland has been developing strip silicon radiation detectors for many years. What is more, VTT have been closely working with CERN which conducts the most important experiments on particle physics in the world.
Wafer is a very thin slice of silicon crystal which is used to produce the actual detectors. The production line at VTT can make wafers up to 200 mm in diameter using planar technology. Furthermore, the thickness of the strip detectors is only 150 μm or 300 μm which can be implemented for different bias configurations. Area of the detectors is from 5 x 5 cm2 to 1 x 1 cm2. Interestingly, the modern fabrication techniques such as etching, planarization, lithography and bonding are applied. The most important thing is that leakage currents of the detectors are under few nanoamperes, which makes it acceptable for radiation detection. [2].
Conclusion
References
Rehak, P. ; Brookhaven Nat. Lab., Upton, NY, USA. Silicon radiation detectors [online]. Nuclear Science Symposium Conference Record, 2003 IEEE (Volume:5 ); 19-25 Oct. 2003, 2492-2497.
URL:
http://ieeexplore.ieee.org.ezproxy.metropolia.fi/stamp/stamp.jsp?tp=&arnumber=1352629
Accessed 18 February 2013.
Virolainen, T. ; Kamarainen, V. ; Ji, F. ; Garcia, F. ; Orava, R. ; van Remortel, N. ; Santala, M. Silicon radiation detector development at VTT [online]. Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE (Volume:2 ); Oct. 26 2007-Nov. 3 2007, 1494-1497.
URL:
http://ieeexplore.ieee.org.ezproxy.metropolia.fi/stamp/stamp.jsp?tp=&arnumber=4437282
Accessed 18 February 2013.
Huhtinen, M. ; Res. Inst. for High Energy Phys., Helsinki, Finland ; Orava, R. ; Pimia, M. ; Tuuva, T. Single sided stereo angle silicon strip detector [online]. Nuclear Science, IEEE Transactions on (Volume:40 , Issue: 4 ); Aug 1993, 227-229.
URL:
http://ieeexplore.ieee.org.ezproxy.metropolia.fi/stamp/stamp.jsp?tp=&arnumber=256575
Accessed 18 February 2013.