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Sub-kelvin current amplifier using a DC-SQUID
Physica B 284}288 (2000) 2117}2118
Sub-kelvin current ampli"er using a DC-SQUID Kimmo Kinnunen *, Antti NuottajaK rvi , Sami PoK yhoK nen , Jukka Pekola , Arttu Luukanen, Heikki SipilaK , Ilkka Suni, Jorma Salmi, Heikki SeppaK , Mikko Kiviranta Department of Physics, University of Jyva( skyla( , P.O. Box 35, FIN-40351 Jyva( skyla( , Finland Metorex International Oy, Nihtisillankuja 5, FIN-02631 Espoo, Finland VTT Electronics, P.O. Box 1101, FIN-02044 VTT, Finland VTT Automation, P.O. Box 1304, FIN-02044 VTT, Finland
Abstract We have set up a system where a low-noise DC-SQUID is used as a current ampli"er. The SQUID output is read using a wide band electronics unit based on the noise cancellation scheme. The SQUID has been installed in a compact Nanoway PDR50 dilution refrigerator, and superconducting transitions of Ti/Au thermometer strips for X-ray calorimeter applications have been measured. We can operate at 100 mK using a SQUID with Pd shunt resistors. Noise and bandwidth results of the setup are presented. 2000 Elsevier Science B.V. All rights reserved. Keywords: SQUID; Ampli"er; Cryogenic detectors
We are developing transition-edge sensors (TES) utilizing electrothermal feedback (ETF) [1] for X-ray calorimeter and far-infrared bolometer applications. Absorbed radiation causes changes in the current through a detector which are measured using a sensitive SQUID current ampli"er. We use a new version of the low-noise DC-SQUID from VTT [2] in which the shunt resistors are made of Pd instead of Mo. This allows us to install the SQUID close to the detector which is operated at about 100 mK. The SQUID is read out using a wideband (1 MHz) electronics unit designed at VTT that utilizes the noise cancellation scheme [3]. The SQUID was originally designed for neuromagnetometric use and the electronics was designed assuming operation within the range of one #ux quantum, which corresponds to a current of 2.5 lA at the input coil of the SQUID. Since the currents required to operate our detector in the ETF mode are larger than that, we had to modify our electronics unit somewhat to allow closed-loop operation over a wider range.
* Corresponding author. E-mail address: [email protected]." (K. Kinnunen)
Furthermore, we have to use a transformer between the detector and the SQUID input coil because the input coil is not #oating. The transformer also helps us to step down the current seen by the input coil, but on the other hand it brings extra noise and reduces the resolution of the system. With the transformer the sensitivity is 24 lA/U . With some further modi"cations of the elec tronics we plan to use a 1 : 1 transformer. The SQUID is installed inside a small superconducting box which is connected to the mixing chamber of a He/He dilution refrigerator and our sample stage is attached directly underneath the box. A twisted pair of superconducting wire is fed inside a thin superconducting tube from the sample stage into the shield. The advantage of this setup is that we can minimize the stray inductance of coupling leads between the SQUID and the detector by keeping the wiring short (about 50 mm). A schematic view of our setup is presented in Fig. 1. The SQUID is voltage biased and it is used to measure current changes through the detector. The electronics unit provides a stable bias voltage for the detector which can be digitally controlled by the user. Fig. 2 shows a measured signal from a 5.9 keV X-ray source. The detector used in the measurement was a
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 3 0 1 8 - 5
2118
K. Kinnunen et al. / Physica B 284}288 (2000) 2117}2118
Fig. 1. Measurement setup. The electronics unit is at room temperature, R at 4 K, and all the rest shown sits at 100 mK.
400 lm;400 lm Ti/Au bilayer TES with a Bi absorber on top, its normal state resistance was 0.8 ) and the bias leads were made of Nb. This particular detector was not very good because it had a ¹ of 550 mK, so the noise is ! quite high due to the high temperature. The bath temperature was 476 mK and the bias current 135 lA. More details about our detectors can be found in Ref. [4]. In preliminary noise measurements with the transformer input open, the noise #oor of our system was found to be about 3 kU /(Hz. The noise spectrum shows a high noise level at low frequencies due to mechanical vibrations from pumping lines and a poor superconducting shield. We expect to improve the performance in the future. Frequency response was #at at least up to 650 kHz, where we tested the electronics, but it can be tuned up to 1 MHz.
Fig. 2. One of the "rst observed X-ray pulses.
Acknowledgements This work has been supported by the European Space Agency (ESTEC contract No. 12835/98/NL/SB).
References [1] K.D. Irwin, G. Hilton, D. Wollman, J. Martinis, J. Appl. Phys. 83 (1998) 3978. [2] H. SeppaK , M. Kiviranta, A. Satrapinski, L. GroK nberg, J. Salmi, I. Suni, IEEE Trans. Appl. Supercond. 3 (1993) 1816. [3] M. Kiviranta, H. SeppaK , IEEE Trans. Appl. Supercond. 5 (1995) 2146. [4] A. Luukanen, H. SipilaK , K. Kinnunen, A. NuottajaK rvi, J. Pekola, in these Proceedings (LT-22), Physica B 284}288 (2000).
Sub-kelvin current ampli"er using a DC-SQUID Kimmo Kinnunen *, Antti NuottajaK rvi , Sami PoK yhoK nen , Jukka Pekola , Arttu Luukanen, Heikki SipilaK , Ilkka Suni, Jorma Salmi, Heikki SeppaK , Mikko Kiviranta Department of Physics, University of Jyva( skyla( , P.O. Box 35, FIN-40351 Jyva( skyla( , Finland Metorex International Oy, Nihtisillankuja 5, FIN-02631 Espoo, Finland VTT Electronics, P.O. Box 1101, FIN-02044 VTT, Finland VTT Automation, P.O. Box 1304, FIN-02044 VTT, Finland
Abstract We have set up a system where a low-noise DC-SQUID is used as a current ampli"er. The SQUID output is read using a wide band electronics unit based on the noise cancellation scheme. The SQUID has been installed in a compact Nanoway PDR50 dilution refrigerator, and superconducting transitions of Ti/Au thermometer strips for X-ray calorimeter applications have been measured. We can operate at 100 mK using a SQUID with Pd shunt resistors. Noise and bandwidth results of the setup are presented. 2000 Elsevier Science B.V. All rights reserved. Keywords: SQUID; Ampli"er; Cryogenic detectors
We are developing transition-edge sensors (TES) utilizing electrothermal feedback (ETF) [1] for X-ray calorimeter and far-infrared bolometer applications. Absorbed radiation causes changes in the current through a detector which are measured using a sensitive SQUID current ampli"er. We use a new version of the low-noise DC-SQUID from VTT [2] in which the shunt resistors are made of Pd instead of Mo. This allows us to install the SQUID close to the detector which is operated at about 100 mK. The SQUID is read out using a wideband (1 MHz) electronics unit designed at VTT that utilizes the noise cancellation scheme [3]. The SQUID was originally designed for neuromagnetometric use and the electronics was designed assuming operation within the range of one #ux quantum, which corresponds to a current of 2.5 lA at the input coil of the SQUID. Since the currents required to operate our detector in the ETF mode are larger than that, we had to modify our electronics unit somewhat to allow closed-loop operation over a wider range.
* Corresponding author. E-mail address: [email protected]." (K. Kinnunen)
Furthermore, we have to use a transformer between the detector and the SQUID input coil because the input coil is not #oating. The transformer also helps us to step down the current seen by the input coil, but on the other hand it brings extra noise and reduces the resolution of the system. With the transformer the sensitivity is 24 lA/U . With some further modi"cations of the elec tronics we plan to use a 1 : 1 transformer. The SQUID is installed inside a small superconducting box which is connected to the mixing chamber of a He/He dilution refrigerator and our sample stage is attached directly underneath the box. A twisted pair of superconducting wire is fed inside a thin superconducting tube from the sample stage into the shield. The advantage of this setup is that we can minimize the stray inductance of coupling leads between the SQUID and the detector by keeping the wiring short (about 50 mm). A schematic view of our setup is presented in Fig. 1. The SQUID is voltage biased and it is used to measure current changes through the detector. The electronics unit provides a stable bias voltage for the detector which can be digitally controlled by the user. Fig. 2 shows a measured signal from a 5.9 keV X-ray source. The detector used in the measurement was a
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 3 0 1 8 - 5
2118
K. Kinnunen et al. / Physica B 284}288 (2000) 2117}2118
Fig. 1. Measurement setup. The electronics unit is at room temperature, R at 4 K, and all the rest shown sits at 100 mK.
400 lm;400 lm Ti/Au bilayer TES with a Bi absorber on top, its normal state resistance was 0.8 ) and the bias leads were made of Nb. This particular detector was not very good because it had a ¹ of 550 mK, so the noise is ! quite high due to the high temperature. The bath temperature was 476 mK and the bias current 135 lA. More details about our detectors can be found in Ref. [4]. In preliminary noise measurements with the transformer input open, the noise #oor of our system was found to be about 3 kU /(Hz. The noise spectrum shows a high noise level at low frequencies due to mechanical vibrations from pumping lines and a poor superconducting shield. We expect to improve the performance in the future. Frequency response was #at at least up to 650 kHz, where we tested the electronics, but it can be tuned up to 1 MHz.
Fig. 2. One of the "rst observed X-ray pulses.
Acknowledgements This work has been supported by the European Space Agency (ESTEC contract No. 12835/98/NL/SB).
References [1] K.D. Irwin, G. Hilton, D. Wollman, J. Martinis, J. Appl. Phys. 83 (1998) 3978. [2] H. SeppaK , M. Kiviranta, A. Satrapinski, L. GroK nberg, J. Salmi, I. Suni, IEEE Trans. Appl. Supercond. 3 (1993) 1816. [3] M. Kiviranta, H. SeppaK , IEEE Trans. Appl. Supercond. 5 (1995) 2146. [4] A. Luukanen, H. SipilaK , K. Kinnunen, A. NuottajaK rvi, J. Pekola, in these Proceedings (LT-22), Physica B 284}288 (2000).