Production process
Technology Excursus Hall and TMR Effect
The function of a Hall sensor is based on the physical principle of the Hall effect, named after its discoverer Edwin Herbert Hall (1855-1938): When a magnetic field acts perpendicularly on a current-carrying conductor, an electrical voltage is generated across the direction of current flow (Hall voltage). In the Hall effect, the electrons of a current impressed in the Hall element are deflected by the magnetic field from their original direction of flow to the edge of the sensitive element by the Lorentz force. This creates a potential difference in the element: the so-called Hall voltage. This voltage is proportional to the field strength of the magnetic field and the current strength of the impressed current. By exploiting this proportionality, a wide range of applications is possible. For example, the strength of an external magnetic field can be determined. Current measurements are also possible, since every current-carrying conductor generates a magnetic field around itself. This magnetic field can now be used for (indirect) measurement of the current strength. Since the Hall effect is most pronounced in semiconductors, a small plate of semiconductor material is used as the Hall element.
The component of the magnetic flux perpendicular to the chip surface is measured. In a conventional Hall sensor, the required evaluation electronics are integrated on the chip in addition to the Hall plate. Field lines that penetrate the Hall element perpendicularly generate a proportional electrical voltage that is processed by a digital signal processor and converted into a usable output format.
TDK-Micronas is the center for magnetic field sensor technology within the TDK Group. In addition to the Hall-effect sensors mentioned above, our focus is also on marketing TDK's TMR sensors, which are based on the so-called magnetoresistive effect (MR). Here, a change in the magnetic field leads to a change in electrical resistance. A magnetic quantity can therefore be used to derive an electrical quantity that can be easily measured. TMR is again a special form of MR technology. In TMR technology, the so-called tunnel effect ensures a much greater change in resistance as soon as a magnetic field is applied (TMR, Tunnel Magneto Resistance). TMR sensors therefore offer the advantage of higher sensitivity and accuracy.
TMR technology is based on a quantum mechanical effect. In our case, this is manifested in a stack of magnetic material separated in the middle by an electrical insulator - the so-called tunnel barrier. The direction of magnetization of the free layer depends on the external magnetic field. The direction of the fixed layer remains unchanged. The resistance of the TMR element is proportional to the relative angle between the free and fixed layers.
Operating principle of TMR technology
Within TDK's Sensor Systems Business Group, there are other sensor manufacturers, such as InvenSense, Tronics or TDK Electronics, which complete TDK's extensive sensor portfolio with their sensors based on other sensor technologies, for example for measuring pressure, temperature or sound.