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Project Details
Funding Scheme : General Research Fund
Project Number : 704911
Project Title(English) : Low-frequency noise study on junction geometry of magnetic tunnel junction (MTJ) sensors for enhancing sensitivity 
Project Title(Chinese) : 基於提高磁隧道結傳感器靈敏度及其幾何尺寸對低頻噪聲影響的研究 
Principal Investigator(English) : Dr Pong, Philip Wing Tat 
Principal Investigator(Chinese) :  
Department : Department of Electrical and Electronic Engineering
Institution : The University of Hong Kong
E-mail Address : ppong@eee.hku.hk 
Tel :  
Co - Investigator(s) :
Prof Dahlberg, E. Dan
Dr Shull, Robert
Panel : Physical Sciences
Subject Area : Physical Sciences
Exercise Year : 2011 / 12
Fund Approved : 473,333
Project Status : Completed
Completion Date : 11-4-2014
Project Objectives :
Objectives The goal of this project is to carry out systematic experimental studies on the influence of junction geometry (junction area, oxide barrier thickness, and magnetic free-layer thickness) on MTJ low-frequency (0.1 Hz to 100 kHz) noise which were not explored before. The specific aims are: 1. To calculate the influence of junction geometry on magnetic tunnel junction (MTJ) noise based on the theoretical noise model, and then determine the design of experimental samples. 2. To investigate experimentally the dependence of low-frequency noise of MTJs on junction area and compare with the calculation. 3. To investigate experimentally the dependence of low-frequency noise of MTJs on thickness of insulating oxide barrier and compare with the calculation. 4. To investigate experimentally the dependence of low-frequency noise of MTJs on thickness of magnetic free layer and compare with the calculation. 5. To develop a MTJ sensor prototype that provides the minimized noise level with optimized junction geometry based on the research outcomes from objectives 2, 3, and 4.
Abstract as per original application
(English/Chinese):
Realisation of objectives: 1. All the project objectives have been achieved. 2. As suggested by the RGC Panel Member in the previous progress report, we have now completed the analysis of the experimental results. We have written up and published these experimental results in the journal paper "Comprehensive noise characterization of magnetic tunnel junction sensors for optimizing sensor performance and temperature detection" published in the SCI journal "Materials Research Innovations" and also presented these experimental results in the International Conferences of Asian Union of Magnetics Societies (IcAUMS) 2014.
Summary of objectives addressed:
Objectives Addressed Percentage achieved
1.To calculate the influence of junction geometry on magnetic tunnel junction (MTJ) noise based on the theoretical noise model, and then determine the design of experimental samples. Yes100%
2.To investigate experimentally the dependence of low-frequency noise of MTJs on junction area and compare with the calculation. Yes100%
3.To investigate experimentally the dependence of low-frequency noise of MTJs on thickness of insulating oxide barrier and compare with the calculation. Yes100%
4.To investigate experimentally the dependence of low-frequency noise of MTJs on thickness of magnetic free layer and compare with the calculation. Yes100%
5.To develop a MTJ sensor prototype that provides the minimized noise level with optimized junction geometry based on the research outcomes from objectives 2, 3, and 4. Yes100%
Research Outcome
Major findings and research outcome: As suggested by the RGC Panel Member in the previous progress report, all the analysis of the experimental results were completed and published in the journal paper "Comprehensive noise characterization of magnetic tunnel junction sensors for optimizing sensor performance and temperature detection" published in the SCI journal "Materials Research Innovations" and also presented these experimental results in the International Conferences of Asian Union of Magnetics Societies (IcAUMS) 2014. Major research outputs: 5 peer-reviewed journal papers (3 on experimental results, 2 on theoretical calculation results) 6 papers presented in recognized international conferences 3 PhD students trained and graduated Major findings: 1. We have investigated the influence of junction geometry on the noise spectrum of a magnetic tunnel junction (MTJ) sensor. The fluctuation of the MTJ sensor was extracted from the micromagnetic simulation result. A noise analysis program was written in MATLAB to carry out fast fourier transform on the fluctuation to obtain the noise spectrum. The effect of the junction geometry, particularly the edge effect, was found to have significant influence on the noise performance of the sensor. 2. We carried out noise measurement on them to find out its relation between noise and junction area. The measurement experiments have been completed, and we completed the analysis of all the experimental results. Further physical insights on how junction area should be optimized to minimize the sensor noise were obtained. 3. We carried out noise measurement on them to find out its relation between noise and insulating oxide barrier. The measurement experiments have been completed, and we completed the analysis of all the experimental results. Further physical insights on how thickness of insulating oxide barrier should be optimized to minimize the sensor noise were obtained. 4. We carried out noise measurement on them to find out its relation between noise and magnetic free layer. The measurement experiments have been completed, and we completed the analysis of all the experimental results. Further physical insights on how thickness of magnetic free layer should be optimized to minimize the sensor noise were obtained. 5. We have made significant progress on optimizing the junction geometry. We have applied what we have learned from objectives 2, 3, and 4 in fabricating optmized MTJ sensors.
Potential for further development of the research
and the proposed course of action:		 For the past 20 years, magnetic sensors have found enormous applications in many aspects. Detection of ultralow magnetic fields between 1 femtoTesla to about 100 picoTesla has significant practical applications in weapon detection and biomedical imaging. Magnetoresistive thin film sensors are a very promising candidate for this purpose because they are low-cost, low-power, and portable. Learning from the results of this GRF research project, there are good reasons to believe that this type of sensor technology can be pushed into the 1 picoTesla regime by using magnetic tunnel junctions (MTJs) because MTJs have a large magnetoresistance (MR) and they can be made with low noise. We should move on to work on the ultimate fabrication of the ultrasensitive MTJ magnetic field sensors with 1 picoTesla sensitivity at low frequency.
Layman's Summary of
Completion Report:		 The research outcomes of this project created great impact in pushing forward the frontier of scientific knowledge on low-frequency noise and advancing spintronic magnetic sensor technology on noise reduction. The mechanisms of electronic 1/f noise and magnetic 1/f noise have been revealed. This study sheds light on the unknown 1/f noise mechanism and completes the theoretical model. The research results also provide clear design guidance for reducing sensor noise level and improving sensor sensitivity by fine-tuning the MTJ junction geometry.
Research Output
Peer-reviewed journal publication(s)
arising directly from this research project :
(* denotes the corresponding author)
Year of
Publication		 Author(s) Title and Journal/Book Accessible from Institution Repository
2013 T. Zeng, Y. Zhou, K. W. Lin, P. T. Lai, and P. W. T. Pong*  IEEE Transactions on Magnetics vol. 49, page. 3121 (2013)  No 
2012 T. Zeng , Y. Zhou , K. W. Lin , P. T. Lai , and P. W. T. Pong*  IEEE Transactions on Magnetics Vol. 58, page 2831, (2012)  No 
2012 Z. Q. Lei, T. Zeng, G. Feng, P. J. Chen, P. T. Lai, and Philip W. T. Pong*  IEEE Transactions on Magnetics vol. 48, page. 3712 (2012)  No 
2012 Z. Q. Lei,L. Li,G. J. Li,C. W. Leung,J. Shi,C. M. Wong,K. C. Lo,W. K. Chan,C. S. K. Mak,S. B. Chan,N. M. M. Chan,C. H. Leung,P. T. Lai,and P. W. T. Pong*  Journal of Applied Physics vol. 111, page. 07E505 (2012)  No 
C. Zheng, X. Li, R. D. Shull, P. J. Chen and P. W. T. Pong*  Comprehensive noise characterisation of magnetic tunnel junction sensors for optimising sensor performance and temperature detection, Materials Research Innovations, 2015, vol. 19, issue S3, p. S53 - S57  No 
Recognized international conference(s)
in which paper(s) related to this research
project was/were delivered :
Month/Year/City Title Conference Name
01/2013/Chicago Thermal stability of magnetic tunnel junction sensors with Conetic alloy  12th Joint MMM/Intermag Conference 2013 
01/2013/Chicago Detection of 10-nm superparamagnetic iron oxide nanoparticles using exchange-biased GMR sensors in Wheatstone bridge  12th Joint MMM/Intermag Conference 2013 
04/2011/Taipei Detection of iron oxide magnetic nanoparticles using magnetic tunnel junction sensors with Conetic alloy  IEEE International Magnetics Conference 2011 
07/2013/Taichung Thermal Stability of CoFe/Al2O3/CoFe Magnetic Tunnel Junction Sensors  International Symposium on Advanced Magnetic Materials and Applications, Taichung, Taiwan, 2013 
07/2013/Taichung Optimizing Conetic Magnetic Tunnel Junction Sensors by Plasma Oxidation and Insert Layer  International Symposium on Advanced Magnetic Materials and Applications, Taichung, Taiwan, 2013 
10/2014/Haikou Comprehensive noise characterisation of magnetic tunnel junction sensors for optimising sensor performance and temperature detection  International Conferences of Asian Union of Magnetics Societies 2014 
Other impact
(e.g. award of patents or prizes,
collaboration with other research institutions,
technology transfer, etc.):
  SCREEN ID: SCRRM00542