Direct-coupled micro-magnetometer with Y-Ba-Cu-O nano-slit SQUID fabricated with a focused helium ion beam

Abstract

Direct write patterning of high-transition temperature (high-TC) superconducting oxide thin films with a focused helium ion beam is a formidable approach for the scaling of high-TC circuit feature sizes down to the nanoscale. In this letter, we report using this technique to create a sensitive micro superconducting quantum interference device (SQUID) magnetometer with a sensing area of about 100 × 100 μm2. The device is fabricated from a single 35-nm thick YBa2Cu3O7−δ film. A flux concentrating pick-up loop is directly coupled to a 10 nm × 20 μm nano-slit SQUID. The SQUID is defined entirely by helium ion irradiation from a gas field ion source. The irradiation converts the superconductor to an insulator, and no material is milled away or etched. In this manner, a very narrow non-superconducting nano-slit is created entirely within the plane of the film. The narrow slit dimension allows for maximization of the coupling to the field concentrator. Electrical measurements reveal a large 0.35 mV modulation with a magnetic field. We measure a white noise level of 2 μΦ0/Hz1∕2. The field noise of the magnetometer is 4 pT/Hz1∕2 at 4.2 K.

Direct-Write Ion Beam Irradiated Josephson Junctions

“…The helium ion beam offers great control over junction properties and uniformity which broadens the applications of ion irradiated junctions. Furthermore, direct writing of YBCO can also be utilized to combine junctions with nanowires [12] and nanostructured SQUIDs [15]. HI-JJ fabrication requires less process steps than prior-art techniques and can easily be scaled to a wafer process.…”

“…Recently, our group demonstrated that by confining the irradiated region to sub-10nm dimensions with a finely focused helium ion beam (FHIB) that we can dramatically affect the electrical properties of ion irradiated Josephson devices. Specifically, ion irradiated junctions were demonstrated with insulating tunnel barriers, no excess current, and very high resistance (R N ) [12]- [15].…”

Ultrasensitive Magnetic Field Sensors for Biomedical Applications

“…The limit of detectivity of the dc SQUID can be of the order of 1 fT/√Hz [45][46][47] in a frequency range of magnetic field from dc to GHz [48]. The maximum possible detection limit is achieved for millimeter-sized sensors [49], but further miniaturization of SQUID magnetometers to a micro-or nano-meter size is followed by a reduction in sensitivity [50,51]. The schematic image of a common sensing element of the dc SQUID magnetometer is presented in Figure 3.…”

Nano-patterning of cuprate superconductors by masked He+ ion irradiation: 3-dimensional profiles of the local critical temperature

“…Another noncontact method has been recently demonstrated employing a focused He + beam. Josephson junctions in thin YBCO bridges are fabricated by irradiating narrow stripes with the focused 30 keV ion beam of a helium ion microscope that is scanned over the sample surface [24,25,26,27]. Since no mask is used this method offers great flexibility and sub-10 nm resolution [27], but can be only applied to very thin HTSC films due to penetration depth limitations of the available ion energy.…”