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Quantum Materials and Devices

Summary:

Quantum coherent materials have become important in magnetic sensors as well as information processing technology. For magnetic sensors, spin-based transport in metals and across tunnel barriers is important because it can increase the signal to noise and reduce the power. These devices have applications in a wide variety of fields, ranging from sensing to imaging. We have developed large (256 element) arrays and systems to make forensic copies of magnetic tapes for data migration and authenticity analysis. In the area of quantum computing, we are developing crystalline tunnel junctions that will improve quantum state visibility and measurements. We are also working to improve the coherence of these devices by developing low-loss dielectrics.

Description:

NIST has become a world leader in the area of high sensitivity magnetic field sensors. To achieve this, we have explored spintronic devices, including anisotropic magneto-resistive (AMR) and tunneling magneto-resistive (TMR) devices. With the AMR devices, we have developed tape read heads that have many sensing elements. These devices are designed to operate at DC, and are used to image magnetic tapes. The system that we built was delivered to the FBI and is currently in the process of being validated for use on analog audio tape evidence. The TMR devices are targeted towards low noise field sensors and are integrated with a flux concentrator. We have reached noise levels better than one millionth of the Earth’s magnetic field, with a dynamic range allowing us to run them in an un-shielded environment. These devices are very low power and are targeted towards geological and exploratory work.

For the quantum computing work, we have been developing superconducting devices using a novel approach to making a tunnel barrier. Traditionally these tunnel junctions use convenient amorphous, thermal oxide barriers because the thickness is easily controllable and they tend to be pin-hole free. However, it has been shown that they have energy-absorbing defects at random frequencies due to their amorphous nature. Therefore, we developed a process to grow epitaxial tunnel junctions. This is challenging because the tunnel current depends exponentially on the barrier thickness, and epitaxial barriers require high temperatures to crystallize. We worked around these issues using precision, ultra-high vacuum molecular beam epitaxy (MBE) growth and lattice matched, superconducting rhenium films on sapphire substrates. We are the first to be able to fabricate, characterize, and successfully integrate them into devices. In addition, the performance of the devices improved significantly, enabling us to use optical lithography rather than e-beam.

Major Accomplishments:

  • Developed low-noise magnetic field sensors
  • Developed magnetic imaging arrays and a system for conducting forensic analysis of magnetic tapes using this technology
  • First implementation of epitaxial Josephson junction
  • Demonstrated that epitaxial Josephson junctions reduce the number of detrimental splittings in a qubit
One second of audio in a cassette tape imaged using the 256-sensor array.
One second of audio in a cassette tape imaged using the 256-sensor array.

Start Date:

January 1, 1997

End Date:

ongoing

Lead Organizational Unit:

pml

Facilities/Tools Used:

  • UHV Surface Science chamber: Auger electron spectroscopy (CMA), Low temperature Omicron STM/AFM, LEED, RHEED, 3 sputter, e-beam, and effusion sources, ion mill, plasma source, atomic H source.
  • PPMS with low field VSM
  • 3” wafer, 6-source UHV sputter deposition chamber (Lesker) with heated substrate (600 C), RHEED, oxidation.
  • 3” wafer, 3-source HV UHV sputter deposition (PVD) with heated substrate (800 C), Al effusion source, oxidation, RHEED.
  • Noise characterization facilities for magnetic and superconducting systems.
  • Veeco - DI 3000 AFM/MFM
  • Circuit board prototyper capable of RF circuit boards fabrication.
  • Access to clean room fabrication – pattern generator, mask aligner, lithography tools (spin coaters, developers), metallization tools and CVD reactors for SiOx and SiN, deep reactive ion etch (with MEMS capability), critical point dryer, e-beam lithography, and other associated facilities.

Staff:

David Pappas

Related Programs and Projects:

Contact

David Pappas
(303) 497-3374

325 Broadway
Boulder, CO 80305-3328