Kuen-Lin Chen

Integrated high-TC radio frequency superconducting quantum interference device using SrTiO3 bicrystal substrate resonators

In contrast to the previous high-TC radio frequency (rf) superconducting quantum interference device (SQUID) magnetometer, in which the rf SQUID is placed face to face with the substrate resonator, a simple integrated washer-type rf SQUID magnetometer based on a single SrTiO3 bicrystal substrate resonator is designed and fabricated in this work. The magnetometer combines the rf SQUID, flux focusing, and resonator into a single chip. This integrated washer-type rf SQUID magnetometer offers a superior advantage in integrating the device to a scanning SQUID detection system in which the distance between the sample and SQUID can be minimized.

Superconducting-quantum-interference-device array magnetometers with directly coupled pickup loop and serial flux dams

In this work, we studied the engineering of high-transition-temperature superconductor Josephson junctions and superconducting quantum interference device (SQUID) by using step-edge or the bicrystal grain-boundary technologies. Serial Josephson junctions and bare SQUID array reveal high quality device characteristics. A high-Tc SQUID magnetometer exhibiting magnetic field sensitivity of 33fT∕Hz1∕2 in the white regime and 80fT∕Hz1∕2 at 1Hz was demonstrated by incorporating the flux dams and serial SQUID into the pickup loop of magnetometer. Furthermore, we demonstrate the opening of the flux dams by applying an external magnetic field to induce a current higher than the critical current of the serial flux dams. We show that the serial flux dams effectively suppress the low frequency 1∕f-like noises.

High-Tc superconducting quantum interference devices: Status and perspectives

In this paper, an overview of the current status of high-Tc superconducting quantum interference devices (SQUIDs), from device engineering to biomagnetic applications, is given. The authors offer a description of the current status of SQUID sensors, challenges encountered, and the solution of fabricating SQUID sensors with low flux noises. The current challenge that we face is to fabricate high-Tc SQUIDs that are not only more reproducible than the current technology but also capable of providing a high IcRn product and fabricating SQUID with high yield. Improvement of flux noises and fabrication yield in the integrated multichoices directly coupled SQUID magnetometer or gradiometer with series SQUID array are presented. High-Tc SQUID magnetometers exhibiting magnetic field sensitivity of ∼30–50fT∕Hz1∕2 or better at 100Hz was demonstrated by incorporating serial SQUID into the pickup loop of the magnetometers. New technologies currently being developed and applications for high-Tc SQUIDs are addressed.

Multifunctional design of high-transition-temperature directly coupled superconducting-quantum-interference-device magnetometers on a chip

We have designed four multifunctional high-transition-temperature directly coupled superconducting-quantum-interference-device (SQUID) magnetometers on a 10×10mm2 SrTiO3 bicrystal substrate. Each magnetometer is composed of two serial bare SQUIDs. These magnetometers can be connected to four kinds of first-order electronic planar gradiometers or two kinds of second-order electronic planar gradiometers by using analog subtracting electronic circuits. The noise spectra of each magnetometer, two first-order electronic planar gradiometers, and a second-order planar gradiometer were measured. We measured the small magnetic signal generated from a double D coil to show that this design could supplement the deficiency of a magnetometer.

Fabrication and Properties of High-

We have successfully fabricated YBCO Josephson junctions and SQUIDs with variable thickness bridges. The variable-thickness bridges of YBCO thin film were fabricated by photolithography and Focused ion beam mill. The Josephson effects of variable thickness bridges were obtained in a 80 nm-thick-film of high-Tc YBa2Cu3Oy. The Shapiro steps were observed in single junction in the gigahertz range from 3.02 to 14.64 GHz. The voltage-current and voltage-field characteristics were measured in SQUID magnetometer. The SQUID shows a peak-to-peak voltage swing of 1.5 μV at 70 K. The properties of one junction and SQUID magnetometer have been investigated.

T_{\rm c}

The dual first-order planar gradiometers of high transition temperature (high-Tc) superconducting quantum interference devices (SQUIDs) were designed and fabricated on a 10×10 mm2 SrTiO3 bicrystal substrate. Each gradiometer consists of four bare SQUIDs which are connected to two symmetric pickup loops. Any two of the SQUIDs can be connected in series to obtain better performance. In this study, by selecting the coupling direction of SQUID, a balance resolution of 0.08% was achieved. And, a second-order electronic planar gradiometer was composed of these two first-order gradiometers. Experimental data showed that the noise performance of the second-order electronic planar gradiometer composed of two planar first-order gradiometers can reach 15 μΦ0/Hz1/2 at 1 kHz in an unshielded environment, which is comparable to the noise level of a magnetometer in a shielded environment.

YBCO Josephson Junction and SQUID With Variable Thickness Bridges by Focused Ion Beam

The instantaneous switch-off of the gas precursors during the ramp-down cycle in a spike ramp process is demonstrated to be an effective method to enhance the reliability of rapid thermal oxide. Due to the slow ramp-down rate (60/spl deg/C-90/spl deg/C/s) of a rapid thermal process, the oxidation during the slow ramp-down cycle may produce the inferior oxide, especially for ultrathin oxide. To avoid the oxidation in the slow ramp-down cycle, the oxidation precursor (oxygen) is switched off during the ramp-down cycle. The reliability of resulting oxide without oxidation during the ramp-down cycle is enhanced as compared with the conventional oxide, which is still oxidized during the ramp-down cycle.

Characterization of dual high transition temperature superconducting quantum interference device first-order planar gradiometers on a chip

A gate-voltage-controlled high transition temperature direct current superconducting quantum interference device (high-Tc dc SQUID) magnetometer was fabricated to study how the electric field effect affects the device’s voltage-flux and voltage-current characteristics. The magnetometer consists of a monolithic YBa2Cu3O7−δ superconducting film and bicrystal junctions covered by a polymethylmethacrylate film as the gate insulator. It was found that the magnetic flux modulated voltage swing of the SQUID magnetometer varies by 48% when the gate voltage is changed from −1.9 to 9.5 V. The variation in voltage swing is attributed to the change of effective capacitance in grain-boundary junctions.

Reliability improvement of rapid thermal oxide using gas switching

Silicon dioxide dots are deposited on the Si cap layers of self-assembled Ge dots using a liquid phase deposition method. The Si capping layer directly above the Ge dots has a tensile strain, while the Si cap on the wetting layer is not strained. The tensile strain can enhance the silicon dioxide nucleation and deposition on Si surface, and SiO2 dots are directly formed on the top of Ge dots with the SiO2 wetting layers between the dots. The step height and base width of the dots increase with the deposition time. A metal-oxide-semiconductor photodetector is fabricated using the liquid-phase-deposited oxide, and has a responsivity of 0.08 mA/W at 1550 nm.

Tunable high transition temperature superconducting quantum interference device magnetometer with gate-voltage-controlled bicrystal junctions

We have fabricated a high-T/sub c/ electronic planar gradiometer composed of dc SQUIDs on a 10 mm /spl times/ 10 mm SrTiO/sub 3/ bicrystal substrate. The SQUIDs were patterned in a single-layer YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film which is prepared by pulsed laser deposition. The outputs of the magnetometers are added and subtracted by analog electronic circuits to form the gradiometer. These magnetometers could be used to construct two sets electronic planar first-order gradiometers or an electronic planar second-order gradiometer, which could measure the elements /spl part/B/sub z///spl part/x and /spl part/B/sub z///spl part/y or /spl part//sup 2/B/sub z///spl part/x/spl part/y, respectively. The noise spectra of each magnetometer and a first-order electronic planar gradiometer were measured.