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Gain stabilization and noise minimization for SiPMs at cryogenic temperatures
Nuclear Inst. and Methods in Physics Research, A (
)
–
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Gain stabilization and noise minimization for SiPMs at cryogenic temperatures P. Achenbach *, M. Biroth *, W. Lauth, A. Thomas Institut für Kernphysik, Johannes Gutenberg-Universität, Mainz, Germany
a r t i c l e
i n f o
Keywords: Silicon photomultiplier (SiPM MPPC) Cryogenic temperature Liquid nitrogen Liquid helium
a b s t r a c t The performance of solid-state photon detectors such as avalanche photodiodes or silicon photomultipliers (SiPMs) is strongly affected by temperature. Important device characteristics for the detection of low light levels or single photons are photon detection efficiency, dark noise, and gain. In the present work the C-series SiPMs from SensL was characterized in cryogenic environments. At 77 K the SiPMs proved to be an excellent choice for single photon detection and an operation point with minimum noise contributions was found. At 4 K the performance was degraded, exhibiting a smaller gain and a larger noise. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Single photon detection with solid-state devices such as avalanche photodiodes (APDs) or silicon photomultipliers (SiPMs) is affected considerably by temperature. There are many contributing and mutually interacting effects, especially if the temperature is reduced below conventional operating ranges, which is for many applications somewhere near −60 ◦ C. Extreme temperature environments are reached in liquid nitrogen at 77 K and liquid helium at 4 K. First, the characteristics of a solid-state device will continue to follow familiar trends from the conventional temperature range. However, at some temperatures, different effects start influencing the characteristics. These depend on: ∙ Type of the photon detection device (PIN, APD, SiPM, . . . ), ∙ Materials, geometry, dimensions, and other design, characteristics of the device (structure of microcells, trenches, quenching resistors, . . . ), ∙ Doping concentrations and other properties of the basic semiconductor material, ∙ Design of the circuit, the contacts, the connections, and the packaging. The lower limit for the operating temperature is typically determined by the ionization energy of the dopants, that produce the charge carriers in the device. If the temperature is too low, the dopants will not be sufficiently ionized and there will be insufficient carriers, resulting in a condition called freeze-out. For example, in Si the dopant ionization
energy is 𝜖Si ∼ 0.05 eV and the freeze-out occurs at 𝑇FO ∼ 40 K, while in Ge 𝜖Ge ∼ 0.01 eV and 𝑇FO ∼ 20 K. There are additional effects that allow devices to be operated below their freeze-out temperature. On the other hand, there are effects that prevent operation even before the device is cooled to the freeze-out temperature. Finally, it is not sufficient for a particular solid-state device to produce signals in a certain temperature environment, but also a stable and reliable operation is required. In typical applications, the internal gain should be stabilized and the photodetector noise minimized, for example by controlling the bias voltage. The controlled operation of solid-state devices much below the freeze-out temperature is not only experimentally very challenging, but also theoretically most complex [1–5]. 2. Measurement and analysis of charge spectra at cryogenic temperatures The studied SiPM devices were of type MicroFC-30035-SMT from SensL [6], with 3 mm × 3 mm active area and 35 μm small microcells, resulting in a total of 4774 microcells per SiPM. Devices were illuminated by a pulsed diode through an optical fiber. For the tests at cryogenic temperatures the SiPM were directly immersed in the liquids. Details of the experimental setups can be found in Refs. [2,7]. Fig. 1 shows typical charge spectra taken at room temperature, in liquid nitrogen, and in liquid helium. The fitting of the charge distributions was performed with the model presented in Ref. [2]. The fit
* Corresponding authors.
E-mail addresses: [email protected] (P. Achenbach), [email protected] (M. Biroth). https://doi.org/10.1016/j.nima.2017.10.080 Received 23 October 2017; Received in revised form 24 October 2017; Accepted 26 October 2017 Available online xxxx 0168-9002/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: P. Achenbach, et al., Gain stabilization and noise minimization for SiPMs at cryogenic temperatures, Nuclear Inst. and Methods in Physics Research, A (2017), https://doi.org/10.1016/j.nima.2017.10.080.
P. Achenbach et al.
Nuclear Inst. and Methods in Physics Research, A (
)
–
and crosstalk probability at different overvoltages. The resolving power was highest at liquid nitrogen temperature as seen by the small width of the peaks. The gain as a function of bias voltage is shown in Fig. 2 for the different temperatures. A linear dependence was preserved even at 77 K and 4 K. The breakdown voltage 𝑈BD was observed to decrease from room temperature to liquid nitrogen temperature, but to increase again at liquid helium temperature. At liquid helium temperature the microcell capacitance extensively dropped and a minimum overvoltage of 1−2 V was required for photon detection. The capability to resolve neighboring peaks in the spectra was quantified by the resolving power, 𝑅, and was determined from the gain and the gain fluctuations. Fig. 3 shows 𝑅 at liquid nitrogen temperature in dependence of the overvoltage 𝛥𝑈 = 𝑈BIAS − 𝑈BD . The maximum resolving power was found to be 𝑅 ∼ 557 ± 21 peaks. This remarkable result is a consequence of a good pixel-to-pixel uniformity and negligible contributions of electronic noise and dark counts. At room temperature the resolving power is compromised by the dark noise rate and afterpulse probability, so that 𝑅 decreased with increasing overvoltage already above 𝛥𝑈 ≥ 1.7 V and the maximal resolving power was 𝑅 = 57 ±9. At 4 K this number was reduced further to 𝑅 = 11 ±1. It should be emphasized that good resolving powers cannot be achieved at the lowest temperatures. It is assumed that this behavior is due to significant changes in the silicon properties in the temperature range 𝑇 < 100 K.
Fig. 1. Charge spectra of SensL Series-C devices at temperatures of 297, 77, and 4 K. The count rates were normalized and fits were performed to extract the SiPM characteristics. The peak resolving power was highest at liquid nitrogen temperature. Data were taken at overvoltages with the highest resolving power. The spectrum at 77 K was taken only up to signals from 10 fired pixels, where the dynamic range of the data acquisition system ended.
3. Conclusion The Series-C SiPM devices from SensL were characterized at liquid nitrogen and liquid helium temperatures and found to be well performing. At 77 K the devices proved to be an excellent choice for single photon detection and an operation point with minimum noise contributions was found, much improved as compared to room temperature. At 4 K the performance was degraded, exhibiting a smaller gain and a larger noise. It is assumed that the observed phenomena are related to the temperature dependent properties of silicon such as the change in charge carrier generation, transport and multiplication in the electric fields.
Fig. 2. Gain of a SensL Series-C device as a function of bias voltage. A linear dependence was preserved even at 77 K and 4 K as shown by the fit lines. The breakdown voltage 𝑈BD was observed to decrease from room temperature to liquid nitrogen temperature, but to increase again at liquid helium temperature. The slope of the gain with bias voltage was also observed to be significantly different at 4 K.
Acknowledgments This work was supported in part by the Federal State of RhinelandPalatinate and the Deutsche Forschungsgemeinschaft (DFG grant no. SFB1044) with the Collaborative Research Center 1044. References [1] G. Collazuol, et al., Studies of silicon photomultipliers at cryogenic temperatures, Nucl. Instrum. Methods Phys. Res. A 628 (2011) 389–392. [2] M. Biroth, P. Achenbach, E. Downie, A. Thomas, Silicon photomultiplier properties at cryogenic temperatures, Nucl. Instrum. Methods Phys. Res. A 787 (2015) 68–71. [3] N. Dinu, A. Nagai, A. Para, Studies of MPPC detectors down to cryogenic temperatures, Nucl. Instrum. Methods Phys. Res. A 787 (2015) 275–279. [4] A. Cardini, D. Brundu, V. Fanti, A. Lai, A. Loi, Operation of silicon photomultipliers at liquid helium temperature, in: Proceedings of the IEEE Nuclear Science Symposium and Medical Imaging Conference, Seattle, WA, USA, 8–15 Nov. 2014, pp. 1–6. [5] P. Achenbach, M. Biroth, E. Downie, A. Thomas, On the operation of silicon photomultipliers at temperatures of 1–4 kelvin, Nucl. Instrum. Methods Phys. Res. A 824 (2016) 74–75. [6] SensL C-Series Datasheet, SensL Technologies, Cork, Ireland, 2015 Rev. 2.1. [7] M. Biroth, P. Achenbach, E. Downie, A. Thomas, A low-noise and fast pre-amplifier and readout system for SiPMs, Nucl. Instrum. Methods Phys. Res. A 787 (2015) 185–188.
Fig. 3. Resolving power to separate individual peaks in the charge spectra of SensL SeriesC devices at liquid nitrogen temperature as a function of overvoltage. The optimal biasing of the device was achieved at 𝛥𝑈 ≈ 3 V. The resolving power was determined from fits to the charge spectra.
parameters were used to determine characteristic device parameters like relative photon detection efficiency (PDE), gain, microcell capacitance,
2
Please cite this article in press as: P. Achenbach, et al., Gain stabilization and noise minimization for SiPMs at cryogenic temperatures, Nuclear Inst. and Methods in Physics Research, A (2017), https://doi.org/10.1016/j.nima.2017.10.080.
)
–
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Gain stabilization and noise minimization for SiPMs at cryogenic temperatures P. Achenbach *, M. Biroth *, W. Lauth, A. Thomas Institut für Kernphysik, Johannes Gutenberg-Universität, Mainz, Germany
a r t i c l e
i n f o
Keywords: Silicon photomultiplier (SiPM MPPC) Cryogenic temperature Liquid nitrogen Liquid helium
a b s t r a c t The performance of solid-state photon detectors such as avalanche photodiodes or silicon photomultipliers (SiPMs) is strongly affected by temperature. Important device characteristics for the detection of low light levels or single photons are photon detection efficiency, dark noise, and gain. In the present work the C-series SiPMs from SensL was characterized in cryogenic environments. At 77 K the SiPMs proved to be an excellent choice for single photon detection and an operation point with minimum noise contributions was found. At 4 K the performance was degraded, exhibiting a smaller gain and a larger noise. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Single photon detection with solid-state devices such as avalanche photodiodes (APDs) or silicon photomultipliers (SiPMs) is affected considerably by temperature. There are many contributing and mutually interacting effects, especially if the temperature is reduced below conventional operating ranges, which is for many applications somewhere near −60 ◦ C. Extreme temperature environments are reached in liquid nitrogen at 77 K and liquid helium at 4 K. First, the characteristics of a solid-state device will continue to follow familiar trends from the conventional temperature range. However, at some temperatures, different effects start influencing the characteristics. These depend on: ∙ Type of the photon detection device (PIN, APD, SiPM, . . . ), ∙ Materials, geometry, dimensions, and other design, characteristics of the device (structure of microcells, trenches, quenching resistors, . . . ), ∙ Doping concentrations and other properties of the basic semiconductor material, ∙ Design of the circuit, the contacts, the connections, and the packaging. The lower limit for the operating temperature is typically determined by the ionization energy of the dopants, that produce the charge carriers in the device. If the temperature is too low, the dopants will not be sufficiently ionized and there will be insufficient carriers, resulting in a condition called freeze-out. For example, in Si the dopant ionization
energy is 𝜖Si ∼ 0.05 eV and the freeze-out occurs at 𝑇FO ∼ 40 K, while in Ge 𝜖Ge ∼ 0.01 eV and 𝑇FO ∼ 20 K. There are additional effects that allow devices to be operated below their freeze-out temperature. On the other hand, there are effects that prevent operation even before the device is cooled to the freeze-out temperature. Finally, it is not sufficient for a particular solid-state device to produce signals in a certain temperature environment, but also a stable and reliable operation is required. In typical applications, the internal gain should be stabilized and the photodetector noise minimized, for example by controlling the bias voltage. The controlled operation of solid-state devices much below the freeze-out temperature is not only experimentally very challenging, but also theoretically most complex [1–5]. 2. Measurement and analysis of charge spectra at cryogenic temperatures The studied SiPM devices were of type MicroFC-30035-SMT from SensL [6], with 3 mm × 3 mm active area and 35 μm small microcells, resulting in a total of 4774 microcells per SiPM. Devices were illuminated by a pulsed diode through an optical fiber. For the tests at cryogenic temperatures the SiPM were directly immersed in the liquids. Details of the experimental setups can be found in Refs. [2,7]. Fig. 1 shows typical charge spectra taken at room temperature, in liquid nitrogen, and in liquid helium. The fitting of the charge distributions was performed with the model presented in Ref. [2]. The fit
* Corresponding authors.
E-mail addresses: [email protected] (P. Achenbach), [email protected] (M. Biroth). https://doi.org/10.1016/j.nima.2017.10.080 Received 23 October 2017; Received in revised form 24 October 2017; Accepted 26 October 2017 Available online xxxx 0168-9002/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: P. Achenbach, et al., Gain stabilization and noise minimization for SiPMs at cryogenic temperatures, Nuclear Inst. and Methods in Physics Research, A (2017), https://doi.org/10.1016/j.nima.2017.10.080.
P. Achenbach et al.
Nuclear Inst. and Methods in Physics Research, A (
)
–
and crosstalk probability at different overvoltages. The resolving power was highest at liquid nitrogen temperature as seen by the small width of the peaks. The gain as a function of bias voltage is shown in Fig. 2 for the different temperatures. A linear dependence was preserved even at 77 K and 4 K. The breakdown voltage 𝑈BD was observed to decrease from room temperature to liquid nitrogen temperature, but to increase again at liquid helium temperature. At liquid helium temperature the microcell capacitance extensively dropped and a minimum overvoltage of 1−2 V was required for photon detection. The capability to resolve neighboring peaks in the spectra was quantified by the resolving power, 𝑅, and was determined from the gain and the gain fluctuations. Fig. 3 shows 𝑅 at liquid nitrogen temperature in dependence of the overvoltage 𝛥𝑈 = 𝑈BIAS − 𝑈BD . The maximum resolving power was found to be 𝑅 ∼ 557 ± 21 peaks. This remarkable result is a consequence of a good pixel-to-pixel uniformity and negligible contributions of electronic noise and dark counts. At room temperature the resolving power is compromised by the dark noise rate and afterpulse probability, so that 𝑅 decreased with increasing overvoltage already above 𝛥𝑈 ≥ 1.7 V and the maximal resolving power was 𝑅 = 57 ±9. At 4 K this number was reduced further to 𝑅 = 11 ±1. It should be emphasized that good resolving powers cannot be achieved at the lowest temperatures. It is assumed that this behavior is due to significant changes in the silicon properties in the temperature range 𝑇 < 100 K.
Fig. 1. Charge spectra of SensL Series-C devices at temperatures of 297, 77, and 4 K. The count rates were normalized and fits were performed to extract the SiPM characteristics. The peak resolving power was highest at liquid nitrogen temperature. Data were taken at overvoltages with the highest resolving power. The spectrum at 77 K was taken only up to signals from 10 fired pixels, where the dynamic range of the data acquisition system ended.
3. Conclusion The Series-C SiPM devices from SensL were characterized at liquid nitrogen and liquid helium temperatures and found to be well performing. At 77 K the devices proved to be an excellent choice for single photon detection and an operation point with minimum noise contributions was found, much improved as compared to room temperature. At 4 K the performance was degraded, exhibiting a smaller gain and a larger noise. It is assumed that the observed phenomena are related to the temperature dependent properties of silicon such as the change in charge carrier generation, transport and multiplication in the electric fields.
Fig. 2. Gain of a SensL Series-C device as a function of bias voltage. A linear dependence was preserved even at 77 K and 4 K as shown by the fit lines. The breakdown voltage 𝑈BD was observed to decrease from room temperature to liquid nitrogen temperature, but to increase again at liquid helium temperature. The slope of the gain with bias voltage was also observed to be significantly different at 4 K.
Acknowledgments This work was supported in part by the Federal State of RhinelandPalatinate and the Deutsche Forschungsgemeinschaft (DFG grant no. SFB1044) with the Collaborative Research Center 1044. References [1] G. Collazuol, et al., Studies of silicon photomultipliers at cryogenic temperatures, Nucl. Instrum. Methods Phys. Res. A 628 (2011) 389–392. [2] M. Biroth, P. Achenbach, E. Downie, A. Thomas, Silicon photomultiplier properties at cryogenic temperatures, Nucl. Instrum. Methods Phys. Res. A 787 (2015) 68–71. [3] N. Dinu, A. Nagai, A. Para, Studies of MPPC detectors down to cryogenic temperatures, Nucl. Instrum. Methods Phys. Res. A 787 (2015) 275–279. [4] A. Cardini, D. Brundu, V. Fanti, A. Lai, A. Loi, Operation of silicon photomultipliers at liquid helium temperature, in: Proceedings of the IEEE Nuclear Science Symposium and Medical Imaging Conference, Seattle, WA, USA, 8–15 Nov. 2014, pp. 1–6. [5] P. Achenbach, M. Biroth, E. Downie, A. Thomas, On the operation of silicon photomultipliers at temperatures of 1–4 kelvin, Nucl. Instrum. Methods Phys. Res. A 824 (2016) 74–75. [6] SensL C-Series Datasheet, SensL Technologies, Cork, Ireland, 2015 Rev. 2.1. [7] M. Biroth, P. Achenbach, E. Downie, A. Thomas, A low-noise and fast pre-amplifier and readout system for SiPMs, Nucl. Instrum. Methods Phys. Res. A 787 (2015) 185–188.
Fig. 3. Resolving power to separate individual peaks in the charge spectra of SensL SeriesC devices at liquid nitrogen temperature as a function of overvoltage. The optimal biasing of the device was achieved at 𝛥𝑈 ≈ 3 V. The resolving power was determined from fits to the charge spectra.
parameters were used to determine characteristic device parameters like relative photon detection efficiency (PDE), gain, microcell capacitance,
2
Please cite this article in press as: P. Achenbach, et al., Gain stabilization and noise minimization for SiPMs at cryogenic temperatures, Nuclear Inst. and Methods in Physics Research, A (2017), https://doi.org/10.1016/j.nima.2017.10.080.