A scanning SQUID microscope with 200 MHz bandwidth

Abstract

We developed a scanning DC SQUID microscope with novel readout electronics capable of wideband sensing RF magnetic fields from 50 to 200 MHz and simultaneously providing closed-loop response at kHz frequencies. To overcome the 20 MHz bandwidth limitation of traditional closed-loop SQUIDs, a flux-modulated closed loop simultaneously locks the SQUID quasi-static flux and flux-biases the SQUID for amplification of the RF flux up to  0 /4 in amplitude. Demodulating the SQUID voltage with a double lock-in technique yields a signal representative of both the amplitude and phase of the RF flux. This provides 80 dB of a linear dynamic range with the flux noise density of 4  0 /Hz at 200 MHz for YBa 2 Cu 3 O 7 bi-crystal SQUID at 77 K. We describe the electronics performance and present images for RF magnetic field of the travelling wave in a coplanar waveguide, the standing wave in an open-circuited microstrip, and a surface mounted device antenna.

Multi-terminal multi-junction dc SQUID for nanoscale magnetometry

“…This means that the horizontal extent of φ max a (i 2 ) should be at least 1/2. Since the critical-state phase differences satisfy ϕ c1 = −π/2 for i 2 = a 2 + a 1 , ϕ c1 = ϕ c2 = π/2 for i 2 = a 2 − a 1 and ϕ c2 = −π/2 for i 2 = −(a 2 + a 1 ) we can find, using (15) and (16), that the horizontal extent of φ max a (i 2 ) is 1/2+β L a 1 /4 when i 2 > a 2 −a 1 and 1/2+β L a 2 /4 when i 2 ≤ a 2 − a 1 . As shown in Fig.…”

“…Superconducting quantum interference devices (SQUIDs) are very sensitive sensors of magnetic field [1][2][3][4][5][6][7][8][9][10][11] and in recent years are widely used for nanoscale magnetic sensing and for scanning magnetic microscopy [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Scanning SQUIDs are commonly fabricated using planar lithographic techniques and often include integrated pickup and feedback coils, which allow flux biasing the SQUID near its optimal working point using a flux-locked loop (FLL) [10].…”

Electrically Tunable Multiterminal SQUID-on-Tip

“…In recent years, there has been a growing effort to develop and apply nanoscale magnetic imaging tools to address the rapidly evolving fields of nanomagnetism and spintronics. These include magnetic force microscopy (MFM), , magnetic resonance force microscopy (MRFM), − nitrogen vacancy (NV) center sensors, − scanning Hall probe microscopy (SHPM), − X-ray magnetic microscopy (XRM), and micro- or nanosuperconducting quantum interference device (SQUID)-based − scanning microscopy (SSM). − Scanning micro- and nanoscale SQUIDs are of particular interest for magnetic imaging due to their high sensitivity and large bandwidth. , The two main technological approaches to the fabrication of scanning SQUIDs are based on planar lithographic methods ,,− and on self-aligned SQUID-on-tip (SOT) deposition. ,, …”

Precision Magnetometers for Aerospace Applications: A Review

“…SQUID (Superconducting QUantum Interference Device) magnetometers [ 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 ] consist of a superconducting loop split by one or two Josephson junctions (essentially, nonlinear inductors) [ 100 , 101 ], as illustrated in Figure 6 .…”

“…The current circulating in the superconducting loop, and the corresponding voltage drop across the Josephson junction(s), are sensitive to the magnetic flux threading the loop. SQUID magnetometers offer high magnetic field sensitivity (sub-fT/Hz 1/2 [ 97 , 102 ]), high dynamic range (they can operate in the Earth’s magnetic field [ 92 , 94 ]), a large range of spatial resolutions (down to the nanometer scale [ 103 , 107 ]), and broad bandwidth operation (DC to GHz [ 104 ]). To achieve superconductivity, the SQUID needs to be operated in a cryogenic environment; this incurs large operating costs and is usually incompatible with low SWaP applications.…”