Development of ultra-low magnetic field sensors with magnetic tunnel junctions

Philip W.T. Pong, John E. Bonevich, William F. Egelhoff

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Scopus citations


The discovery of tunneling magnetoresistance (TMR) has enhanced the magnetoresistance (MR) ratio from the giant magnetoresistance (GMR) regime of around 10% to over 400% at room temperature. A combination of magnetic tunnel junctions with high magnetoresistance ratio and soft magnetic layers enables the development of ultra-low magnetic field sensor with sensitivity down to the scale of picoTesla. A magnetic field sensor with such high sensitivity would have important applications in biomedicine, information storage, and remote sensing such as higher resolution images for cardiograph and magnetic resonance imaging and thus earlier detection of abnormal health condition; higher hard-disk density; and remote sensing of metallic objects. We have constructed an automated four-probe electrical measurement system for measuring TMR of magnetic tunnel junctions with high throughput, enabling us to optimize the properties of the devices. Magnetron sputtering is used to deposit thin films with thickness ranged from angstroms to nanometers. Photolithography and ion plasma etching are applied to pattern the devices. The devices have a range of size from 10 μm × 10 μm to 80 μm × 80 μm. The device is composed of the bottom electrode, free soft magnetic layer, insulating oxide layer, pinned layer, pinning layer, and top electrode. The magnetization of the free layer can be rotated by the external magnetic field which in turn changes the resistance of the device and provide the sensing capability. The system structure, design consideration, fabrication process, and preliminary experimental results are discussed and presented in this paper.

Original languageEnglish (US)
Title of host publicationNanoengineering
Subtitle of host publicationFabrication, Properties, Optics, and Devices IV
StatePublished - 2007
Externally publishedYes
EventNanoengineering: Fabrication, Properties, Optics, and Devices IV - San Diego, CA, United States
Duration: Aug 27 2007Aug 30 2007

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


ConferenceNanoengineering: Fabrication, Properties, Optics, and Devices IV
Country/TerritoryUnited States
CitySan Diego, CA

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


  • Magnetic field sensor
  • Magnetic tunnel junction
  • Soft magnetic layer
  • Tunneling magnetoresistance
  • Wheatstone bridge


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