Cross-Coupling First-Order Gradient Superconducting Quantum Interference Device for Current Sensing

Abstract

High sensitivity and low noise of superconducting quantum interference devices make them ideal for reading the minute changes in resistance of a transition-edge sensor, which occurs when it absorbs energy or power. A series of first-order gradient, cross-coupling octagonal SQUIDs specifically tailored for use in TES were developed and fabricated for the advantage of lower parasitic capacitance compared with the overlap-coupling ones. It is obtained that a lower screening parameter and increased shunt resistance per junction lead to a higher flux-to-voltage transfer coefficient. This enhancement significantly boosts detection sensitivity and effectively minimizes noise contributions from electronics operating at room temperature. The low-temperature measurement results of the sample with an input coil of 3.5 turns indicate that a small device current white noise of 4.8 pA/√Hz, a device flux white noise of 1.1 μΦ₀/√Hz, and an optimal flux-to-voltage transfer coefficient of 338.2 μV/Φ₀ are achieved. The bandwidth of a SQUID current sensor with a smaller inductance of the input coil and a larger shunt resistance exceeds 10 MHz. SQUID current sensors, featuring octagonal structures with the first-order gradient cross-coupling, exhibit low flux noise, low current noise, and a high flux-to-voltage transfer coefficient, which can satisfy the requirements of TES applications.