Final Report Summary - SENPIMAG (A novel technology for ultra sensitive reliable integrated magnetic sensors: a new era in magnetic detection)
During last century research on magnetic sensors has been very active. Despite this continuous interest, from the point of view of impact in industry and society there have not been major advances other than SQUID, flux gate, Hall effect or AMR sensors, all of them already in use decades ago.
Therefore the aim of this project was to develop a new technology of magnetic sensors. Specifically it aimed to develop a new technology that can improve all the important characteristics of a magnetic sensor at the same time and in absolute value: ultra-high sensitivity, micron or even nano-size scale, low cost, high reliability, broad frequency range, very low power consumption and easy fabrication process.
This new technology is based on interfacing a magnetostrictive magnetic material and a piezoelectric that will act as a sensor element. The sensor head is made by the ferromagnetic material grown on top of the piezoelectric sensor and the electric contacts that read the voltage induced in the piezoelectric. The head is placed in the middle of two current lines that create the driving AC magnetic field. This field is magnetizing periodically the magnetostrictive material in the direction perpendicular to the measuring axis. The voltage induced in the piezoelectric will be double frequency (2f) of the frequency of the driving field (low noise configuration). An external field will change the amplitude of this 2f output. No coils are required for detection.
The sensitivity obtained so far is not as good as expected. There are three main reasons for that. Firstly, the piezoelectric approach could not be realised during the project. A piezoelectric reading should be much more sensitive than the piezoresistive reading. SINTEF is now able to deposit PZT films over Si wafer and they can produce cantilevers from those structures. Some partners within the consortium will collaborate in the future to achieve this approach.
Secondly, the magnetic material drops slightly in performance when deposited over the device (instead over an ultra-flat Si wafer). Some more optimisation will be required.
Thirdly, the magnetic material has a magnetostriction of 30 ppm. At the moment UPM is working on developing soft magnetic films with larger magnetostriction, based on their results. The sensor is even, so it cannot detect the direction of the field unless is biased. Many applications do not require the detection of the direction of field, but rather the amplitude or even just the presence of magnetic field. For applications requiring the detection of the direction of the field, the sensor would have to be biased with a permanent magnet. The consortium expect to address most of these issues in the future.
An ultra-sensitive integrated magnetic sensor is something of major socio-economical interest. Magnetic detection is involved in plenty of the aspects of our modern lives, from detection of metals for security purposes to control and navigation. Improving the performance of a magnetic sensor is always welcome. But most important of all in terms of social impact are the potential applications in which the actual magnetic sensors cannot fulfil the requirements. One of the focuses is medical application where the magnetic fields are in the range of pT. Here, an integrated and extremely sensitive magnetic sensor would be largely interesting. Other point of interest is the identification of vehicles or labels. This could increase the security in big shopping areas or airports for instance.
Providing the expected impact in industry and society, the good perspectives for economic development are quite significant, especially for companies working in magnetic field detection. Our intention to protect the IPR emerging from this project and work with partner organisations to the commercialisation of the technology. The most clear potential applications are vehicles guidance and 'Yes / no magnetic detection', which are fields of extremely importance with the increase of technologic devices in final products.
Therefore the aim of this project was to develop a new technology of magnetic sensors. Specifically it aimed to develop a new technology that can improve all the important characteristics of a magnetic sensor at the same time and in absolute value: ultra-high sensitivity, micron or even nano-size scale, low cost, high reliability, broad frequency range, very low power consumption and easy fabrication process.
This new technology is based on interfacing a magnetostrictive magnetic material and a piezoelectric that will act as a sensor element. The sensor head is made by the ferromagnetic material grown on top of the piezoelectric sensor and the electric contacts that read the voltage induced in the piezoelectric. The head is placed in the middle of two current lines that create the driving AC magnetic field. This field is magnetizing periodically the magnetostrictive material in the direction perpendicular to the measuring axis. The voltage induced in the piezoelectric will be double frequency (2f) of the frequency of the driving field (low noise configuration). An external field will change the amplitude of this 2f output. No coils are required for detection.
The sensitivity obtained so far is not as good as expected. There are three main reasons for that. Firstly, the piezoelectric approach could not be realised during the project. A piezoelectric reading should be much more sensitive than the piezoresistive reading. SINTEF is now able to deposit PZT films over Si wafer and they can produce cantilevers from those structures. Some partners within the consortium will collaborate in the future to achieve this approach.
Secondly, the magnetic material drops slightly in performance when deposited over the device (instead over an ultra-flat Si wafer). Some more optimisation will be required.
Thirdly, the magnetic material has a magnetostriction of 30 ppm. At the moment UPM is working on developing soft magnetic films with larger magnetostriction, based on their results. The sensor is even, so it cannot detect the direction of the field unless is biased. Many applications do not require the detection of the direction of field, but rather the amplitude or even just the presence of magnetic field. For applications requiring the detection of the direction of the field, the sensor would have to be biased with a permanent magnet. The consortium expect to address most of these issues in the future.
An ultra-sensitive integrated magnetic sensor is something of major socio-economical interest. Magnetic detection is involved in plenty of the aspects of our modern lives, from detection of metals for security purposes to control and navigation. Improving the performance of a magnetic sensor is always welcome. But most important of all in terms of social impact are the potential applications in which the actual magnetic sensors cannot fulfil the requirements. One of the focuses is medical application where the magnetic fields are in the range of pT. Here, an integrated and extremely sensitive magnetic sensor would be largely interesting. Other point of interest is the identification of vehicles or labels. This could increase the security in big shopping areas or airports for instance.
Providing the expected impact in industry and society, the good perspectives for economic development are quite significant, especially for companies working in magnetic field detection. Our intention to protect the IPR emerging from this project and work with partner organisations to the commercialisation of the technology. The most clear potential applications are vehicles guidance and 'Yes / no magnetic detection', which are fields of extremely importance with the increase of technologic devices in final products.
