Miniature Magnetic Sensors

Magnetic sensors are widely used in nearly all engineering and industrial sectors, including high-density magnetic recording, navigation, target detection, anti-theft systems, non-destructive testing, magnetic labeling, space research, and bio-magnetic measurements in the human body. Miniature magnetic sensors with high sensitivity are particularly advantageous in biomedical and specialized industrial applications. Amongst the various extant magnetic sensors, Micro-Electro-Mechanical System (MEMS) and Giant Magneto impedance (GMI) sensors have the ability to sense low levels of magnetic field in the order of 10 millitesla as well as the space to be further miniaturized. In this thesis, MEMS and GMI sensors are studied in detail both theoretically and experimentally. Multiphysics analyses have been developed to provide a path to further investigate these two types of sensors for various sensor configurations. Several prototype units are successfully developed, fabricated and tested to verify the validity of these models. MEMS reed sensors consist of tri-layer beams of Au/Ni/Au. The actuation of these sensors is initiated by the magnetic force to maintain the continuity of magnetic field streamlines. The Ni layer is deployed as the main magnetic core, and the gold layers are used to enhance the contact quality of the switches. In this work, a unique fabrication process is developed that significantly reduces the number of masking and lithography steps. As well, a detailed finite element method is presented to study the behavior of these sensors and to optimize the device performance. The FEM study considers various magnetic environments, providing a performance map for the sensors. Having a performance map is essential for a system's operation and for tracking its operational behavior. The study also considers the effects of various device formations and packaging for these types of sensors. The generated magnetic force is observed to be much higher than the required mechanical force for device actuation. The GMI sensors exhibit many advantages over their conventional counterparts. In particular, thermal stability and high sensitivity make GMI sensors attractive candidates for a wide range of applications. The GMI sensors are based on concepts different from those for conventional giant magneto resistance (GMR) sensors. GMI sensors have been under active research only in the past decade. In this thesis, thin film multilayer GMI sensors are realized using microfabrication technology. The fabricated sensors are tri-layers of Co73Si12B15 /Au./ Co73Si12B15 The thin film GMI sensors are studied in detail using FEM simulation, and several sensors are developed, fabricated and tested to work in the millitesla range. A post-processing step is proposed to optimize the performance of GMI sensors and to enhance their magnetic sensitivity. The post-processing characterization shows that annealing the devices with a specific annealing cycle has the optimal effect of enhancing the magnetic characteristics of CoSiB. The sensors are treated with this post-processing recipe, demonstrating a considerable increase in their magneto impedance (MI) ratio. The research has made a contribution to establishing the engineering foundation toward the development of low-cost miniature GMI magnetic sensors for low field intensity applications

Development and characterization of sensors fabricated from polymer based magnetoelectric nanocomposites

Tese de Doutoramento em Engenharia Electrónica e de ComputadoresSensors are increasingly used in many applications areas, integrated in structures, industrial machinery, or in the environment, contributing to improve the society level of well-being. It is expected that sensorization will play on of the most relevant roles in the fourth industrial revolution, and allow, together with mechanization and informatization, a full automation. Particularly, magnetic sensors allow measurements, without physical contact, of parameters such as direction, presence, rotation, angle, or current, in addition to magnetic field. In this way, for most applications, such sensors offer a safe, noninvasive and non-destructive measurement, as well as provide a reliable and almost maintenance-free technology. Industry demands for smaller, cheaper and low-powered magnetic sensors, motivating the exploration of new materials and different technologies, such as polymerbased magnetoelectric (ME) composites. These composites are flexible, versatile, lightweight, low cost, easy to model in complicated shapes, and typically involve a lowtemperature fabrication process, being in this way, a solution for innovative magnetic sensor device applications. Therefore, the main objective of this thesis is the development of polymer-based ME sensors to be incorporated into technological devices. Thus, the ME effect is increasingly being considered an attractive alternative for magnetic field and current sensing, being able to sense static and dynamic magnetic fields. In order to obtain a wide-range ME response, a nanocomposite of Tb0.3Dy0.7Fe1.92 (Terfenol-D)/CoFe2O4/poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) was produced and their morphological, piezoelectric, magnetic and magnetoelectric properties investigated. The obtained composites reveals a high piezoelectric response (≈-18 pC∙N- 1) that is independent of the weight ratio between the fillers. In turn, the magnetic properties of the composites are influenced by the composite composition. It was found that the magnetization saturation values decrease with increasing CoFe2O4 content (from 18.5 to 13.3 emu∙g-1) while the magnetization and coercive field values increase (from 3.7 to 5.5 emu∙g-1 and from 355.7 to 1225.2 Oe, respectively) with increasing CoFe2O4 content. Additionally, the films show a wide-range dual-peak ME response at room temperature with the ME coefficient increasing with increasing weight content of Terfenol-D, from 18.6 mV∙cm-1∙Oe-1 to 42.3 mV∙cm-1∙Oe-1. The anisotropic ME effect on a Fe61.6Co16.4Si10.8B11.2 (FCSB)/poly(vinylidene fluoride) (PVDF)/FCSB laminate composite has been used for the development of a magnetic field sensor able to detect both magnitude and direction of ac and dc magnetic fields. The accuracy (99% for both ac and dc sensors), linearity (92% for the dc sensor and 99% for the ac sensor), sensitivity (15 and 1400 mV∙Oe-1 for the dc and ac fields, respectively), and reproducibility (99% for both sensors) indicate the suitability of the sensor for applications. A dc magnetic field sensor based on a PVDF/Metglas composite and the corresponding readout electronic circuits for processing the output ME voltage were developed. The ME sensing composite presents an electromechanical resonance frequency close to 25.4 kHz, a linear response (r2=0.997) in the 0–2 Oe dc magnetic field range, and a maximum output voltage of 112 mV (ME voltage coefficient α33 of ≈30 V∙cm-1∙Oe-1). By incorporating a charge amplifier, an ac–rms converter and a microcontroller with an on chip analog-to-digital converter (ADC), the ME voltage response is not distorted, the linearity is maintained, and the ME output voltage increases to 3.3 V (α33effective=1000 V∙cm-1∙Oe-1). The sensing device, including the readout electronics, has a maximum drift of 0.12 Oe with an average total drift of 0.04 Oe, a sensitivity of 1.5 V∙Oe-1 (15 kV∙T-1), and a 70 nT resolution. Such properties allied to the accurate measurement of the dc magnetic field in the 0–2 Oe range makes this polymerbased device very attractive for applications, such as Earth magnetic field sensing, digital compasses, navigation, and magnetic field anomaly detectors. A dc current sensor device based on a ME PVDF/Metglas composite, a solenoid, and the corresponding electronic instrumentation were developed. The ME sample exhibits a maximum α33 of 34.48V∙cm-1∙Oe-1, a linear response (r2=0.998) and a sensitivity of 6.7 mV∙A-1. With the incorporation of a charge amplifier, a precision ac/dc converter and a microcontroller, the linearity is maintained (r2=0.997), the ME output voltage increases to a maximum of 2320 mV and the sensitivity is increased to 476.5 mV∙A-1. Such features indicate that the fabricated ME sensing device is suitable to be used in non-contact electric current measurement, motor operational status checking, and condition monitoring of rechargeable batteries, among others. In this way, polymer-based ME composites proved to be suitable for magnetic field and current sensor applications.Os sensores estão a ser cada vez mais utilizados em diversas áreas, integrados em estruturas, máquinas industriais ou projetos ambientais, contribuindo para melhorar o nível de bem-estar e eficiência da nossa sociedade. Espera-se que a “sensorização” contribua decisivamente para a quarta revolução industrial, e que permita, em conjunto com a mecanização e a informatização, uma completa automação. Em particular, os sensores magnéticos permitem medir parâmetros como a direção, presença, rotação, ângulo ou corrente, para além do campo magnético, tudo isto sem qualquer contacto físico. Assim, para a maioria das aplicações, estes sensores oferecem uma medição segura, não invasiva e não destrutiva, para além de garantirem uma tecnologia confiável e de escassa manutenção. A indústria procura e exige sensores magnéticos mais pequenos, mais baratos e de baixo consumo, daí a motivação para explorar novos materiais e diferentes tecnologias, tais como os compósitos magnetoelétricos (ME) baseados em polímeros. Estes compósitos são flexíveis, versáteis, leves, de baixo custo, fáceis de se modelar em formas complexas e tipicamente envolvem um processo de fabricação a baixa temperatura, constituindo uma solução fiável e de qualidade para os sensores magnéticos. É da constatação deste potencial que surge este estudo e o objetivo desta tese: o desenvolvimento de sensores ME de base polimérica. O efeito ME é cada vez mais considerado como uma alternativa credível para a medição de campo magnético e da intensidade da corrente elétrica, podendo detetar campos magnéticos estáticos e dinâmicos. De modo a obter uma gama mais alargada de resposta ME, produziram-se nanocompósitos de Tb0.3Dy0.7Fe1.92 (Terfenol-D)/CoFe2O4/poli(fluoreto de vinilideno trifluor-etileno) (P(VDF-TrFE) e as suas propriedades morfológicas, piezoelétricas, magnéticas e magnetoelétricas foram investigadas. Os compósitos obtidos revelam uma elevada resposta piezoelétrica (≈-18 pC∙N-1) que é independente da percentagem de cada material magnetoestrictivo. Por sua vez, as propriedades magnéticas são influenciadas pela composição dos compósitos. Verificou-se que a magnetização de saturação diminuí com o aumento da percentagem de CoFe2O4 (de 18.5 para 13.3 emu∙g-1) enquanto que a magnetização e o campo coercivo aumentam (de 3.7 para 5.5 emu∙g-1 e de 355.7 para 1225.2 Oe, respetivamente) com o aumento da percentagem em massa de CoFe2O4. O efeito ME anisotrópico num compósito Fe61.6Co16.4Si10.8B11.2 (FCSB)/ poli(fluoreto de vinilideno) (PVDF)/FCSB laminado foi utilizado para desenvolver um sensor de campo magnético capaz de detetar tanto a magnitude como a direção de campos magnéticos ac e dc. A exatidão (99% para ambos os sensores ac e dc), linearidade (92% para o sensor dc e 99% para o ac), sensibilidade (15 e 1400 mV∙Oe-1 para o sensor dc e ac, respetivamente) e reprodutibilidade (99% para ambos os sensores) indicam a aptidão destes sensores para aplicações avançadas. Desenvolveu-se ainda um sensor de campo magnético dc baseado num compósito ME de PVDF/Metglas, bem como a correspondente eletrónica de leitura para processar a tensão de saída ME. O compósito ME apresenta uma ressonância eletromecânica de aproximadamente 25.4 kHz, uma resposta linear (r2=0.997) para uma gama de campos magnéticos dc entre 0–2 Oe e uma tensão de saída máxima de 112 mV (coeficiente ME α33≈30 V∙cm-1∙Oe-1). Ao incorporar um amplificador de carga, um conversor ac–rms e um microcontrolador com um conversor analógico-digital (ADC), a tensão ME não é distorcida, a linearidade manteve-se e a tensão ME aumentou para 3.3 V (α33efectivo=1000 V∙cm-1∙Oe-1). O sensor, incluindo a eletrónica de leitura, obteve um desvio máximo de 0.12 Oe com um desvio total médio de 0.04 Oe, uma sensibilidade de 1.5 V∙Oe-1 (15 kV∙T-1) e 70 nT de resolução. Tais propriedades aliadas à medida exata do campo magnético dc entre 0–2 Oe tornam este dispositivo indicado para aplicações como sensores de campo magnético terrestre, compassos digitais, navegação e detetores de anomalia no campo magnético. Foi ainda possível desenvolver e otimizar um sensor de corrente baseado num compósito ME de PVDF/Metglas, num solenoide e na correspondente eletrónica de instrumentação. A amostra ME exibe um α33 máximo de 34.48V∙cm-1∙Oe-1, uma resposta linear (r2=0.998) e uma sensibilidade de 6.7 mV∙A-1. Com a incorporação de um amplificador de carga, um conversor ac/dc de precisão e um microcontrolador, a linearidade manteve-se, a tensão ME aumentou para um máximo de 2320 mV e a sensibilidade subiu para 476.5 mV∙A-1. Estas propriedades tornam este sensor ME apropriado para a medição de corrente elétrica sem contato, para a verificação do estado de funcionamento de motores e para monitorização da condição de baterias recarregáveis, entre outros. Concluindo-se deste modo que os compósitos de ME com base em polímeros provaram ser adequados para aplicações na medição de campos magnéticos e intensidade de corrente elétrica

Direct and Non-Invasive Monitoring of Battery Internal State Via Novel GMI-IDT Magnetic Sensor

Efficient battery management systems (BMSs) in rechargeable battery-based systems require precise measurements of various battery parameters including state of charge (SOC), state of health (SOH) and charge capacity. Presently, SOC, charge capacity and SOH can only be indirectly inferred from long-term measurement of current, open circuit voltage (OCV), and temperature using multiple sensors. These techniques can only give an approximation of SOC and often require knowledge of the recent battery history to prevent excessive inaccuracy.To improve the performance of the BMS, an alternative method of monitoring the internal state of Li-ion batteries is presented here. Theoretical analysis of Li-ion batteries has indicated that the concentration of active lithium ions in the cathode is directly related to the magnetic susceptibility of the electrode materials. While charging/discharging, due to the change in the oxidation and/or spin state of metal atoms, the magnetic moment in the cathode varies. This indicates the potential for directly probing the internal state of the Li-ion batteries during charging/discharging by monitoring the changes in magnetic susceptibility via an appropriately designed magnetic sensor. In this research, a highly sensitive micromagnetic sensor design is investigated consisting of a single interdigital transducer (IDT) shunt-loaded with a magnetically sensitive Giant Magnetoimpedance (GMI) microwire. This design takes advantage of the coupling of the impedance characteristics of the GMI microwire to the IDT transduction process. The initial GMI-IDT sensor design is further developed and modified to maximize sensitivity and linearity. The sensor can detect magnetic field in the range of 900 nT and minute changes less than 1 μT when operated at or near its peak sensitivity. In addition, an appropriate procedure for preconditioning the GMI wire is developed to achieve sensor repeatability. Furthermore, using the identified optimum geometry of the experimental setup, the proposed sensor is implemented in monitoring the internal state of two types of Li-ion cells used in electric vehicles (EVs). The initial characterization results confirm that the GMI-IDT sensor can be used to directly monitor the charge capacity of the investigated Li-ion batteries. Other possible applications also include energy storage for renewable energy sources, and portable electronic devices

3D Self‐Assembled Microelectronic Devices: Concepts, Materials, Applications

Modern microelectronic systems and their components are essentially 3D devices that have become smaller and lighter in order to improve performance and reduce costs. To maintain this trend, novel materials and technologies are required that provide more structural freedom in 3D over conventional microelectronics, as well as easier parallel fabrication routes while maintaining compatability with existing manufacturing methods. Self‐assembly of initially planar membranes into complex 3D architectures offers a wealth of opportunities to accommodate thin‐film microelectronic functionalities in devices and systems possessing improved performance and higher integration density. Existing work in this field, with a focus on components constructed from 3D self‐assembly, is reviewed, and an outlook on their application potential in tomorrow's microelectronics world is provided

Orthogonal fluxgate type magnetic microsensors with wide linear operation range

This thesis presents a study on the development of microfabricated fluxgate type magnetic sensors operating within a wide linear operation range. Fluxgate type magnetic sensors are powerful devices due to their high sensitivity, low offset, and high temperature stability. Unfortunately, their linear operation range is limited, since an attempt to increase the linear range also increases the power dissipation of the sensor for the traditionally used parallel fluxgate configuration. In this study, microfabricated fluxgate sensors with wide linear operation range and low power dissipation are developed with the use of the orthogonal fluxgate configuration and a closed magnetization path for the excitation. In the scope of this work, three different fluxgate microsensor structures suitable for operation within a wide linear range are developed, fabricated, and characterized. The sensor structures are named as: rod type orthogonal macro fluxgate sensor, rod type orthogonal micro fluxgate sensor, and ring type micro fluxgate sensor. All of the structures have a CMOS compatible fabrication process flow. Furthermore, the rod type micro sensor and the ring type micro sensor are fabricated by using only standard thin film deposition and photolithography techniques, enabling batch fabrication of these sensor structures. All of the structures use planar sensing coils and an electroplated FeNi core. Apart from the design and development of the sensor, the FeNi electroplating process is intensively investigated since this process directly affects the performance of the sensors. The rod type orthogonal macro fluxgate sensor uses a 20 µm diameter gold bonding wire as the excitation rod, and a 10 µm thick FeNi core electroplated over the bonding wire. The AC current passing through the excitation rod creates a periodical excitation field in the radial direction, which is always perpendicular to the external magnetic field to be detected along the core. With this sensor, the idea of increasing the linear operation range without increasing the power dissipation by using a closed magnetization path and the orthogonal structure is verified. By using a 200 mA-peak sinusoidal excitation current at 100 kHz, passing through the low resistance excitation rod, a linear operation range of ±2.5 mT is reached with a 0.5 mm long core, whereas the linear range is ±250 µT with a 4 mm long core. The rod type orthogonal micro fluxgate sensor presents a modified version of the macro sensor, which can be fabricated in wafer level with standard deposition and photolithography techniques. For this sensor, the excitation rod is formed with an electroplated layer of copper which is sandwiched between two FeNi layers forming the ferromagnetic core. The cross-sectional dimensions of the excitation rod and the core are 8 µm × 2 µm, and 16 µm × 10 µm, respectively. The sensor operates with 100 mA-peak sinusoidal excitation current at 100 kHz, and the linear operation range for different sensors having 0.5, 1, and 2 mm long cores are 1100, 410, and 160 µT, respectively. The linear operation range is independent of the excitation conditions for current peaks larger than 100 mA, which is required to saturate the core, and operating frequencies lower than 200 kHz, where the skin effect is not dominant. The sensitivity, perming, the equivalent magnetic noise density, and the power dissipation of the 0.5 mm long sensor are 102.8 µV/mT, 7.1 µT, 268 nT/√Hz @ 1 Hz, and 10 mW, respectively for the given excitation conditions. The noise analysis showed that the noise of the sensor increases with decreasing sensor dimensions. The ring type micro fluxgate sensor has a core composed of cascaded planar 2 µm thick FeNi rings which can be fabricated in a single electroplating step, increasing the control of the magnetic properties of the core. The excitation rod passes through the middle of the FeNi rings as a sewing thread, providing a planar circular excitation loop. The angle between the excitation field and the external magnetic field changes according to the position on the ring, which leads to a partially orthogonal partially parallel fluxgate operation mode. The tests of the sensors showed that the maximum operating frequency is extended to 1 MHz level, which is due to the thinner FeNi layer. A sinusoidal current with 180 mA-peak at 1 MHz is used for the excitation of the sensors. A linear operation range of 2 mT and a sensitivity of 730 µV/mT is reached with a 4-ring structure, with the rings having 22 µm and 38 µm inner and outer radius, respectively. The comparison of the developed sensors with the previously reported state of the art sensors show that the first microfabricated fluxgate sensors having a wide linear operation range and low power dissipation are realized as an accomplishment of this work. All the sensors are CMOS compatible, and a sensor system can be realized by using the metallization layers of a CMOS process for producing the sensing coils, and fabricating the cores on wafers as a post process

Ferromagnetic Composite Wire Inductors

Ph.DDOCTOR OF PHILOSOPH

Scattering of microwaves by a passive array antenna based on amorphous ferromagnetic microwires for wireless sensors with biomedical applications

Co-based amorphous microwires presenting the giant magnetoimpedance effect are proposed as sensing elements for high sensitivity biosensors. In this work we report an experimental method for contactless detection of stress, temperature, and liquid concentration with application in medical sensors using the giant magnetoimpedance effect on microwires in the GHz range. The method is based on the scattering of electromagnetic microwaves by FeCoSiB amorphous metallic microwires. A modulation of the scattering parameter is achieved by applying a magnetic bias field that tunes the magnetic permeability of the ferromagnetic microwires. We demonstrate that the OFF/ON switching of the bias activates or cancels the amorphous ferromagnetic microwires (AFMW) antenna behavior. We show the advantages of measuring the performing time dependent frequency sweeps. In this case, the AC-bias modulation of the scattering coefficient versus frequency may be clearly appreciated. Furthermore, this modulation is enhanced by using arrays of microwires with an increasing number of individual microwires according to the antenna radiation theory. Transmission spectra show significant changes in the range of 3 dB for a relatively weak magnetic field of 15 Oe. A demonstration of the possibilities of the method for biomedical applications is shown by means of wireless temperature detector from 0 to 100 degrees C

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)