Advanced MTJ Sensory Devices for Industrial and Healthcare Applications

  • Yousof Mashraei

Student thesis: Doctoral Thesis


Magnetic sensors are deployed in many applications such as automotive, consumer electronics, navigation and data storage devices. Their market’s growth is driven by demands of higher performance; primarily to assist in the advancement of the Internet of Things (IoT) and smart systems. Challenging obstacles of miniaturization and power consumptions must be overcome. A leading sensor that has the potential to accelerate the development is the magnetic tunnel junction (MTJ) devices. Corrosion causes catastrophic consequences for industries. Preventive measures could save up to 35% of annual corrosion-related costs. An advanced corrosion sensing technique is developed based on iron nanowires. The iron nanowires are magnets which lose their magnetization when corroded. Their magnetization loss is monitored using sensitive MTJ sensor. Combined, the nanowires and the MTJ sensor realize a highly integrated sensor concept that enables corrosion sensing with an ultra-low power consumption of less than 1 nW, a sensitivity of 0.1 %/min, a response time of 30 minutes and an area of 128 μm2. Surgical tool development is accelerating in the healthcare sector. Cardiac catheterization specifically is a minimally invasive surgery that relies heavily on x-ray imaging and contrast dyes. A flexible tri-axis MTJ sensor is developed to help minimizing the need for x-ray imaging during the procedure. The flexible sensor can bend to a diameter of 500 μm without compromising the performance and can endure over 1000 bending cycles without fatigue. Three flexible sensors are mounted onto the tip of a 3 mm cardiac catheter, realizing a novel sensor-on-tube (SOT) tri-axis sensor concept. The sensor has a high sensitivity of 9 Ω/° and an MR ratio of 29%. It weighs 16 μg only, adds 5 μm to the catheter’s diameter and a total size 300 μm2. The prototype system estimated the heading angle with an RMS error value of 7° and tracked the orientation of the sensor with an acceptable accuracy. However, the sensor has a misalignment issue caused by the manual placement of the sensors. A high precision tool is needed for the assembly, and any further misplacement -within a reasonable margin of error- could be corrected by calibration algorithms.
Date of AwardMay 2019
Original languageEnglish (US)
Awarding Institution
  • Computer, Electrical and Mathematical Sciences and Engineering
SupervisorJurgen Kosel (Supervisor)


  • Corrosion
  • Magnetic Tunnel Junction
  • Catheterization
  • Triaxial Sensor
  • Nanowires

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