- Email: [email protected]
Hamamatsu APD for CMS ECAL: quality insurance
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
Hamamatsu APD for CMS ECAL: quality insurance D. Bailleuxa, I. Britvitchb,1, K. Deitersc, R. Egelanda, B. Gilberta, J. Grahla, Q. Ingramc, A. Kuznetsovb,1, E. Lestera, Y. Musienkob,2, D. Renkerc, S. Reucroftb, R. Rusacka, T. Sakhelashvilic, A. Singovskia,*, J. Swainb a
University of Minnesota, Minneapolis, MN, USA b Northeastern University, Boston, USA c Paul Scherrer Institute, Villigen, Switzerland
Abstract The Hamamatsu Photonics S8148 large area Avalanche Photo Diodes (APD) were designed for the crystal electromagnetic calorimeter of the CMS setup at LHC in a close collaboration of Hamamatsu Photonics and CMS APD group (PSI, Northeastern University and University of Minnesota). All essential parameters of these devices are controlled by the producer and are fairly stable during the mass production, except the radiation hardness. To insure 99.9% reliability of APDs in the radiation hard environment of LHC, the CMS APD group had to invent a dedicated screening procedure. The details of this procedure and some results of the screening are discussed. r 2003 Elsevier B.V. All rights reserved. Keywords: Photodetector; Silicon; Electromagnetic calorimeter
1. Introduction The Avalanche Photo Diodes (APD) [1–4] (ECAL) were requested by CMS electromagnetic calorimeter for three major reasons. First, operation in a strong magnetic field excluded use of any type of PMT. Second, the relatively low scintillation efficiency of the PbWO4 crystals required photo detector with internal amplification and small nuclear counter effect. And third, the radiation environment required device with re-
duced sensitivity to ionising and neutron irradiations [4]. Practically, all these requirements were satisfied by Hamamatsu Photonics in the design of the S8148 APD [1,2], developed in the collaboration with the CMS APD group. The only parameter which cannot be guaranteed by the producer is the radiation hardness.
2. S8148 radiation damage *Corresponding author. Tel.: +41-22-767-1674; fax: +4122-767-8940. E-mail address: [email protected] (A. Singovski). 1 On leave from IHEP, Protvino, Russia 2 On leave from INR, Troitsk, Russia
Study of the radiation effects on S8148 APD performed by the CMS APD group together with Hamamatsu Photonics shows that first, irradiation by neutrons results in a linear increase of the dark current with dose and does not cause a significant
0168-9002/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.11.102
ARTICLE IN PRESS D. Bailleux et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
change of such APD parameters as breakdown and operation voltages, quantum efficiency, capacitance etc. [3] and second, irradiation by gammas creates a relatively small increase in the dark current but some of the irradiated APDs show a dramatic increase of the low frequency noise and/or significant decrease of the breakdown voltage. The second effect leads to the calorimeter cell failure and such APD must be rejected. Detailed R&D on APD radiation damage by photons performed by Hamamatsu Photonics and CMS APD group has shown that: 1. APD damage by ionising particles is a surface effect. This can be due to point-like dielectric defects in the high electric field region (Fig. 1); 2. The APDs susceptible to damage by ionising radiation could only partially be identified and removed by Hamamatsu. 3. Irradiation of APDs by 1:2 MeV photons from a 60 Co source does not change any parameters of the ‘‘healthy’’ APDs, except a slight rise of the dark current and noise, which can be largely annealed by heating APD to 80 for 4 weeks.
623
3. Screening The APD screening consists of the following steps: 1. irradiation of all APDs ð0:5 MradÞ with 60 Co gamma source (at PSI); 2. measurement of breakdown voltage ðVb Þ and dark current ðId ðV ÞÞ of all irradiated APDs 1 day after irradiation (at PSI); 3. measurement of noise for 4 gain values M ¼ 1; 50, 150, 300 before annealing (at CERN APD Lab); 4. annealing of all APDs in the oven (for 4 weeks at T ¼ 80 C; at CERN APD Lab); 5. measurement of Vb ; Id ðV Þ after annealing and ageing (at CERN APD Lab); 6. rejection of potentially non-reliable APDs: ones showing * shift of Vb more than 5 V; * high dark current, * high noise.
Hence, it was found relevant to apply the APD screening procedure to insure radiation hardness.
(a)
(b)
Point - like surface defect
Region with high transversal electric field
Fig. 1. (a) schematic of the APD structure; (b) APD breakdown: light is emitted from the point where current is high because dielectric is broken by irradiation. Picture is taken by Hamamatsu Photonics.
Fig. 2. CMS APD acceptance and quality control procedure.
ARTICLE IN PRESS 624
D. Bailleux et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
The flowchart of the CMS ECAL APD quality control procedure is shown of the Fig. 2.
4. APD quality control It was found finally that the output control made by Hamamatsu Photonics is sufficient to ensure sufficient APD quality and stability of all parameters during mass production. The CMS APD group is performing a detailed measurement of about 1% sample of the delivered APDs, one APD per production wafer. In addition, about 1% of APDs are extracted after the third step of the screening procedure (before annealing) and irradiated with neutrons from the 252 Cf source in University of Minnesota to the dose of 1013 neutrons=cm2 :
dVb_psi; Vb_original - Vb after Co irradiation
5. Screening results The screening procedure was applied so far to about 70k APDs. The rejection rate is about 7%. The typical rejection plot is shown at Fig. 3. APDs showed a large shift of the breakdown voltage after irradiation were rejected (pink squares). Fig. 4 shows the APD rejection by reason. The noise after irradiation is the most efficient rejection criterion, as it could be expected. The ‘‘BAD position’’ rejection means that if for the given position on the given production wafer more than 30% APDs are rejected, the other APDs from the same position are rejected as well. The screening efficiency was tested by sending the sample of APDs, accepted by screening to the same procedure again. No one of 225 APDs was rejected.
All rejected
45.00 35.00 25.00 15.00 5.00 -5.00 68840
6. Conclusions 69840
70840
71840
72840
The Hamamatsu Photonics S8148 APD fit well to the CMS ECAL photodetector specification. All essential APD parameters are stable during production, as shown by the sampling tests
73840
Fig. 3. Change of the breakdown voltage for one of the production batch. APDs with shift of Vb > 5 V are rejected.
BAD_position Id/M_cern
Reason of rejection
Id_cern Vb_cern Noise Id/M_psi Id_psi Vb_psi Id/M_Ham Vb_ham 0
0.5
1
1.5
Fig. 4. The APD rejection statistics, sorted by reason.
2
2.5
ARTICLE IN PRESS D. Bailleux et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
performed by CMS APD group. The dedicated screening procedure efficiently select radiation tolerant APDs.
References [1] K. Dieters, et al., Nucl. Instr. and Meth. A 461 (2001) 574.
625
[2] Q. Ingram, et al., Proceedings of EPS International Conference of High Energy Physics, Budapest, 2001; PrHE-hep2001/256. [3] J. Grahl, et al., Proceedings of the 10th International Conference on Calorimetry in particle Physics, Pasadena, USA, World Scientific, Singapore, 2003, p. 231. [4] J. Grahl, et al., Nucl. Instr. and Meth. A 504 (2003) 44.
Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
Hamamatsu APD for CMS ECAL: quality insurance D. Bailleuxa, I. Britvitchb,1, K. Deitersc, R. Egelanda, B. Gilberta, J. Grahla, Q. Ingramc, A. Kuznetsovb,1, E. Lestera, Y. Musienkob,2, D. Renkerc, S. Reucroftb, R. Rusacka, T. Sakhelashvilic, A. Singovskia,*, J. Swainb a
University of Minnesota, Minneapolis, MN, USA b Northeastern University, Boston, USA c Paul Scherrer Institute, Villigen, Switzerland
Abstract The Hamamatsu Photonics S8148 large area Avalanche Photo Diodes (APD) were designed for the crystal electromagnetic calorimeter of the CMS setup at LHC in a close collaboration of Hamamatsu Photonics and CMS APD group (PSI, Northeastern University and University of Minnesota). All essential parameters of these devices are controlled by the producer and are fairly stable during the mass production, except the radiation hardness. To insure 99.9% reliability of APDs in the radiation hard environment of LHC, the CMS APD group had to invent a dedicated screening procedure. The details of this procedure and some results of the screening are discussed. r 2003 Elsevier B.V. All rights reserved. Keywords: Photodetector; Silicon; Electromagnetic calorimeter
1. Introduction The Avalanche Photo Diodes (APD) [1–4] (ECAL) were requested by CMS electromagnetic calorimeter for three major reasons. First, operation in a strong magnetic field excluded use of any type of PMT. Second, the relatively low scintillation efficiency of the PbWO4 crystals required photo detector with internal amplification and small nuclear counter effect. And third, the radiation environment required device with re-
duced sensitivity to ionising and neutron irradiations [4]. Practically, all these requirements were satisfied by Hamamatsu Photonics in the design of the S8148 APD [1,2], developed in the collaboration with the CMS APD group. The only parameter which cannot be guaranteed by the producer is the radiation hardness.
2. S8148 radiation damage *Corresponding author. Tel.: +41-22-767-1674; fax: +4122-767-8940. E-mail address: [email protected] (A. Singovski). 1 On leave from IHEP, Protvino, Russia 2 On leave from INR, Troitsk, Russia
Study of the radiation effects on S8148 APD performed by the CMS APD group together with Hamamatsu Photonics shows that first, irradiation by neutrons results in a linear increase of the dark current with dose and does not cause a significant
0168-9002/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.11.102
ARTICLE IN PRESS D. Bailleux et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
change of such APD parameters as breakdown and operation voltages, quantum efficiency, capacitance etc. [3] and second, irradiation by gammas creates a relatively small increase in the dark current but some of the irradiated APDs show a dramatic increase of the low frequency noise and/or significant decrease of the breakdown voltage. The second effect leads to the calorimeter cell failure and such APD must be rejected. Detailed R&D on APD radiation damage by photons performed by Hamamatsu Photonics and CMS APD group has shown that: 1. APD damage by ionising particles is a surface effect. This can be due to point-like dielectric defects in the high electric field region (Fig. 1); 2. The APDs susceptible to damage by ionising radiation could only partially be identified and removed by Hamamatsu. 3. Irradiation of APDs by 1:2 MeV photons from a 60 Co source does not change any parameters of the ‘‘healthy’’ APDs, except a slight rise of the dark current and noise, which can be largely annealed by heating APD to 80 for 4 weeks.
623
3. Screening The APD screening consists of the following steps: 1. irradiation of all APDs ð0:5 MradÞ with 60 Co gamma source (at PSI); 2. measurement of breakdown voltage ðVb Þ and dark current ðId ðV ÞÞ of all irradiated APDs 1 day after irradiation (at PSI); 3. measurement of noise for 4 gain values M ¼ 1; 50, 150, 300 before annealing (at CERN APD Lab); 4. annealing of all APDs in the oven (for 4 weeks at T ¼ 80 C; at CERN APD Lab); 5. measurement of Vb ; Id ðV Þ after annealing and ageing (at CERN APD Lab); 6. rejection of potentially non-reliable APDs: ones showing * shift of Vb more than 5 V; * high dark current, * high noise.
Hence, it was found relevant to apply the APD screening procedure to insure radiation hardness.
(a)
(b)
Point - like surface defect
Region with high transversal electric field
Fig. 1. (a) schematic of the APD structure; (b) APD breakdown: light is emitted from the point where current is high because dielectric is broken by irradiation. Picture is taken by Hamamatsu Photonics.
Fig. 2. CMS APD acceptance and quality control procedure.
ARTICLE IN PRESS 624
D. Bailleux et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
The flowchart of the CMS ECAL APD quality control procedure is shown of the Fig. 2.
4. APD quality control It was found finally that the output control made by Hamamatsu Photonics is sufficient to ensure sufficient APD quality and stability of all parameters during mass production. The CMS APD group is performing a detailed measurement of about 1% sample of the delivered APDs, one APD per production wafer. In addition, about 1% of APDs are extracted after the third step of the screening procedure (before annealing) and irradiated with neutrons from the 252 Cf source in University of Minnesota to the dose of 1013 neutrons=cm2 :
dVb_psi; Vb_original - Vb after Co irradiation
5. Screening results The screening procedure was applied so far to about 70k APDs. The rejection rate is about 7%. The typical rejection plot is shown at Fig. 3. APDs showed a large shift of the breakdown voltage after irradiation were rejected (pink squares). Fig. 4 shows the APD rejection by reason. The noise after irradiation is the most efficient rejection criterion, as it could be expected. The ‘‘BAD position’’ rejection means that if for the given position on the given production wafer more than 30% APDs are rejected, the other APDs from the same position are rejected as well. The screening efficiency was tested by sending the sample of APDs, accepted by screening to the same procedure again. No one of 225 APDs was rejected.
All rejected
45.00 35.00 25.00 15.00 5.00 -5.00 68840
6. Conclusions 69840
70840
71840
72840
The Hamamatsu Photonics S8148 APD fit well to the CMS ECAL photodetector specification. All essential APD parameters are stable during production, as shown by the sampling tests
73840
Fig. 3. Change of the breakdown voltage for one of the production batch. APDs with shift of Vb > 5 V are rejected.
BAD_position Id/M_cern
Reason of rejection
Id_cern Vb_cern Noise Id/M_psi Id_psi Vb_psi Id/M_Ham Vb_ham 0
0.5
1
1.5
Fig. 4. The APD rejection statistics, sorted by reason.
2
2.5
ARTICLE IN PRESS D. Bailleux et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 622–625
performed by CMS APD group. The dedicated screening procedure efficiently select radiation tolerant APDs.
References [1] K. Dieters, et al., Nucl. Instr. and Meth. A 461 (2001) 574.
625
[2] Q. Ingram, et al., Proceedings of EPS International Conference of High Energy Physics, Budapest, 2001; PrHE-hep2001/256. [3] J. Grahl, et al., Proceedings of the 10th International Conference on Calorimetry in particle Physics, Pasadena, USA, World Scientific, Singapore, 2003, p. 231. [4] J. Grahl, et al., Nucl. Instr. and Meth. A 504 (2003) 44.