Fabrication and Characterization of magnetometer for space applications FATJON QEJVANAJ Doctoral Thesis in Physics School of Information and Communication Technology KTH Royal Institute of Technology Stockholm, Sweden 2016 ii ISBN 978-91-7595-982-5 KTH School of Information and TRITA-ICT 2016:15 Communication Technology SE-164 40 Stockholm SWEDEN Akademisk avhandling som med tillstånd av Kungliga Tekniska Hög- skolan framlägges till offentlig granskning för avläggande av teknologie doktorsexamen i Fysik fredagen den 10 juni 2016 klockan 13:00 i Sal C, Electrum, Kungl Tekniska Högskolan, Isafjordsgatan 26, Kista. ©Fatjon Qejvanaj, June 2016 Tryck: Universitetsservice US-AB, Stockholm, 2016 Abstract The present rapid increase in the number of space missions demands a de- crease in the cost of satellite equipment, but also requires the development of instruments that have low power consumption, low weight, and small size. Anisotropic magnetoresistance (AMR) sensors can answer these needs on account of their small size, weight, and power consumption. AMR sensors also produce lower noise than either giant magnetoresistance (GMR) or tun- nel magnetoresistance (TMR) devices and are thus more suitable for space applications. The type of AMR sensor developed in this study was a Planar Hall Effect Bridge (PHEB) sensor. The FM layer was also coupled with an AFM layer in order to fix the internal magnetization of the FM layer. One technique that was employed in order to meet the low-noise require- ment was to make the FM layer thicker than has previously been attemp- ted. In doing so, the exchange bias field between the AFM layer and the FM layer is no longer high enough to bias the thicker FM layer, so in order to correct this unwanted effect, the material stack was upgraded to two AFM– FM interfaces. With this configuration, it became possible to increase the exchange field by up to 60%. Stronger exchange bias leads to a thicker FM layer and so to lower noise in the device performance. Another strategy that was used to lower the resistance of the device was to implement an NiFeX alloy instead of the standard NiFe. NiFeX consists of an alloy of NiFe and Cu, Ag, or Au; the last of these is known to have very low resistivity. This solution leads to a significant lowering of the device’s resistance. A re- cent technological advance used to fabricate devices with lower resistance is to deposit a multilayer of AFM–FM. Keyword: AMR, Magnetic sensor, Ferromagnetic, Antiferromagnetic, NiFe, IrMn, exchange bias. iii Sammanfattning Då antalet rymduppdrag snabbt ökar fordras lägre kostnader för satelli- tutrustning och det blir nödvändigt att utveckla instrument med låg ener- giförbrukning, låg vikt och liten storlek. Framtagandet av en magnetisk sensor baserad på AMR överensstämmer väl med dessa krav genom sin ringa storlek, vikt och strömförbrukning. AMR- sensorer uppvisar också lägre brus än sensorer baserade på GMR och TMR vilket gör dem mer användbara för rymdtillämpningar. AMR-sensorn som utvecklats i denna studie är en s.k. Planar Hall Effect Bridge-sensor (PHEB). Det ferromagnetiska skiktet (FM) har dessutom kom- binerats med ett AFM skikt för att fixera den interna magnetiseringen av FM-skiktet. För att kunna uppfylla kravet på lågt brus behövdes FM skiktet göras tjock- are än vad som någonsin gjorts tidigare. Därigenom blir dock det magnet- iska utbytesfältet mellan AFM skiktet och FM skiktet inte tillräckligt starkt för att förspänna ett så tjockt FM skikt, så för att korrigera denna oönskade effekt har materialstacken uppgraderats till två AFM-FM-gränssnitt. Med denna konfiguration var det möjligt att öka det magnetiska utbytesfältet upp till 60%. Ett starkare utbytesfält medger ett tjockare FM lager vilket ger sensorn bättre brusprestanda. En annan strategi som använts för att sänka resistansen hos sensorn var införandet av NiFeX-legeringar istället för standardlegeringen NiFe. NiFeX är en legering mellan NiFe och endera av Cu, Ag eller Au, varav den sista är känd för att ha en mycket låg resistiv- itet. Den här lösningen leder till en signifikant sänkning av sensorernas resistans. Ytterligare en tekniska förbättring som använts för att nå lägre resistans var att införa multipla skikt av AFM-FM. Med denna konfiguration var det möj- ligt att tillverka sensorer med ett totalt sett ännu tjockare FM-skikt med bibe- hållen uniform inre magnetisering. v vi Contents Contents vii Symbols and acronyms ix Publication list xii Author´s Contribution to the Publications xiii Acknowledgments xvi 1 Introduction 1 2 Magnetometers in space 3 2.1 Magnetism . 3 2.1.1 Earth’s magnetic field . 4 2.1.2 Ferromagnetism . 5 2.1.3 Antiferromagnetism . 5 2.2 AMR . 6 2.3 Planar Hall effect sensors . 6 2.3.1 Exchange bias . 7 2.3.2 Sensitivity . 8 2.3.3 Noise . 8 2.3.4 Detectivity . 9 I Fabrication and characterization methods 11 3 Methods and techniques 13 vii viii CONTENTS 3.1 Sputter deposition . 13 3.2 Lift-off lithography . 13 3.3 Gamma ray irradiation . 15 3.4 Probe station and project magnet . 15 3.5 Noise setup . 16 4 PHEB fabrication 19 4.1 Sensing layer fabrication . 19 4.2 Contact pad and corners . 19 4.3 PCB integration . 21 4.4 Sensitivity characterization . 22 4.5 Noise characterization of the integrated circuits . 23 II PHEB development 25 5 Double bias PHEB 27 5.1 Characterization of materials . 28 5.2 Double and single bias . 29 5.3 Double bias PHEB . 31 6 NiFeX PHEB 33 6.1 Characterization of NiFeX . 34 6.2 NiFeX and 100% NiFe . 35 7 IrMn/NiFe multilayer PHEB 39 7.1 Characterization of IrMn/NiFe multilayer . 39 7.2 IrMn/NiFe single and multilayer . 42 8 PHEB irradiation 47 8.1 Characterization of irradiated PHEB . 48 9 Conclusion 51 Bibliography 53 Symbols and acronyms ix x CONTENTS Table 1 Σ Sensitivity AFM Antiferromagnetic Ag Silver AGM Alternating Gradient Magnetometer AMR Anisotropic magnetoresistance Au Gold Cu Copper D Detectivity EB Exchange bias Fe Iron FM Ferromagnetic H Magnetic field Ir Iridium M Magnetization Mn Manganese MS Saturation magnetization Ni Nickel PHE Planar Hall effect PHEB Planar Hall effect bridge PSD Power spectral density SNR Signal-to-noise ratio TID Total irradiation dose RS Sheet resistance Publication list List of papers included in the thesis Paper 1: F. Qejvanaj, M. Zubair, A. Persson, S. M. Mohseni, V. Fallahi, S. R. Sani, S. Chung, T. Le, F. Magnusson, and J. Åkerman, “Thick Double-Biased IrMn/NiFe/IrMn Planar Hall Effect Bridge Sensor,” IEEE Trans. Magn., vol. 50, no. 11 (2014) Paper 2: F. Qejvanaj, H. Mazraati and S. Jiang A. Persson, S. R. Sani, S. Chung, F. Magnusson, and J. Åkerman, “Planar Hall Effect Bridge Sensor with NiFeX,” IEEE Trans. Magn., vol. 51, no. 11 (2014) Paper 3: F. Qejvanaj, H. Mazraati, S. M. Mohseni, V. Fallahi, S. Jiang, S. Chung, F. Magnusson, and J. Åkerman, “Order of magnitude increase in AMR sensor layer thickness throughmulti-interface exchange biasing”, Manuscript Paper 4: F. Qejvanaj, H. Mazraati, S. M. Mohseni, S. Jiang, S. Chung, A. Isernia, F. Magnusson, and J. Åkerman, “A PHEB magnetometer with record thick multiexchange-biased sensor layer”, Manuscript Paper 5: F. Qejvanaj, H. Mazraati, S. M. Mohseni, S. Jiang, S. Chung, F. Magnusson, and J. Åkerman, “Gamma radiation hardness of PHEB magnetometers”, Manuscript xi xii CONTENTS List of papers not included in the thesis Paper 1: B. Bruhn, F. Qejvanaj, T. Gregorkiewicz, and J. Linnros, “Temporal correl- ation of blinking events in CdSe/ZnS and Si/SiO2 nanocrystals ”, "Physica B: Condensed Matter ", vol. 453, pages. 63 - 67, (2014) Paper 2: B. Bruhn, F. Qejvanaj, I. Sychugov and J. Linnros, “Blinking Statistics and Excitation-Dependent Luminescence Yield in Si and CdSe Nanocrystals”, The Journal of Physical Chemistry C, vol. 118, no. 4, (2014) Author´s Contribution to the Publications Paper 1: Most of the planning and experimental work, evaluation and writing. Paper 2: Most of the planning and experimental work, evaluation and writing. Paper 3: Most of the planning and experimental work, evaluation and writing. Paper 4: Most of the planning and experimental work, evaluation and writing. Paper 5: Most of the planning and experimental work, evaluation and writing. xiii Acknowledgments During this time that I worked to my thesis I had the opportunity to be in- spired by many great people that made me grow in knowledge but also as a person. I´d like to thanks all the people that I meet and spend this time of my life. I´ll be always grateful to all of you. Fist of all, I´d like to express my gratitude to my supervisor Professor Johan Åkerman for this immense opportunity that he gave me. Thanks to Johan, I learned how to organize my work, from the beginning ideas to writing the finial report. I learned how to do scientific research and how to collaborated and work with other people. Thanks Johan for these years, I´ll be forever grateful. Special thanks to my industrial co-supervisor Fredrik Magnusson for his presence and motivation during all my PhD studies. Fredrik has been al- ways encouraging and motivating during the time spent together. He teach- ing many valuable lesson on how to work in a company environments. Fre- drik, tack så mycket för dessa oförglömliga år. Many thanks to my co-supervisor Professor Majid Mohseni for his teaching and his support. His knowledge was very important for my growth from the start until the end of my PhD. Thanks to Dr Sunjea Chung for being al- ways present when I needed help. Thanks for Dr. Sohrab Sanni for is teach- ing he has been valuable person to as for advice. I´d like to acknowledge all the members of the Applied Spintronics group as well.