Low noise SQUID sensors and electronics

As a worldwide leader for high performance SQUID electronics, low-noise SQUID sensors, customized SQUID systems, and magnetic measurement, our partners- PTB and Magnicon are developing ultra- low noise -SQUIDs Array Amplifier (SSA) chips and electronics readout system.

At the link below you can find some useful information about related materials and latest products. If you have any questions or suggestions, please feel free to contact them.

Readout of SQUID sensors with small dimensions

SQUID sensor with dimensions in the nanometer/micrometer range can achieve a very low flux noise. Due to the small size the SQUID inductance L and the shunt capacitance C are both low, in contrast to common SQUID sensors:

SΦ ~ 2L ⋅ 16 kBT (LC)1/2M ,

At T = 4.2 K, inductances of a few pH and capacitances of a few hundreds of fF lead to a very low spectral flux noise of √SΦ< 0.05 µΦ0/√Hz. In general the flux to voltage transfer coefficient VΦ of a single SQUID is not sufficient for direct readout with a room temperature preamplifier. A common approach to overcome this is a readout in a two-stage configuration using a SQUID preamplifier [1].


Fig. 1. Readout in two-stage configuration. A nanoSQUID as first stage is readout by a SQUID series array (SSA) as amplifier.

To enhance the overall transfer coefficient a gain GΦ between nanoSQUID flux ΦΝ and preamplifier SQUID flux ΦPre is required:

GΦ = ϑΦPre / ϑΦN >> 1.

For this purpose we developed a SQUID series array (SSA) [2] as amplifier with a low spectral current noise of √SI,SSA< 10 pA/√Hz at 4.2 K. This array consists of 16 SQUIDs with a total input inductance LIn,SSA < 3 nH.


Fig. 2. Physical layout of a SSA chip with two independent channels.

The SSA chip comprises input filter to avoid radiofrequency interference and bias resistors ranging from 0.2 mΩ to 200 mΩ;. The value of the bias resistor could be selected by wire bond.

The SSA are available by Magnicon, Hamburg, Germany:

  1. D. Drung, "SQUID Electronics," The SQUID Handbook, Weinheim, Wiley-Verlag, p. 148, 2004
  2. D. Drung, C. Aßmann, J. Beyer, A. Kirste, M. Peters, F. Ruede, and Th. Schurig, "Highly sensitive and easy-to-use SQUID sensors," IEEE Transactions on Applied Superconductivity, vol. 17, no. 2, pp. 699-704, 2007