1. What is a TMR sensor IC?
A TMR sensor IC integrates a TMR sensor element and a signal processing circuit. A TMR sensor element is a magnetic sensor element using the Tunnel Magneto-Resistance effect (TMR effect). The TMR effect at room temperature was discovered by Professor Terunobu Miyazaki at Tohoku University in 1995. Unlike conventional Hall or AMR sensor elements, a TMR sensor element is a new magnetic sensor technology that is less susceptible to temperature changes, has extremely high magnetic sensitivity and high resistance.
The high magnetic sensitivity and high resistance of TMR sensor elements have made it possible to manufacture magnetic sensor ICs with low power consumption and high accuracy.
The TMR sensor IC will find application in a wide range of devices from consumer products with limited power supply capacity to industrial and automotive equipment that demand high-accuracy control.
2. Operating principle of a TMR sensor element
To get a better understanding of how a TMR sensor element works, it is helpful to explain the magneto-resistance effect (MR effect).
The MR effect is a phenomenon where resistance changes with changes in a magnetic field. It is a phenomenon that occurs in magnetic materials (for example, iron, nickel or cobalt). The characteristics of the MR effect vary with how the interior of the magnetic material was magnetized.
A TMR sensor element is configured from an extremely thin nanometer level nonmagnetic insulation layer sandwiched between two ferromagnetic layers. Electrons tunnel from one ferromagnetic layer into the other via insulation layer. This is a quantum mechanical phenomenon.
Resistance decreases when the magnetization direction of the two ferromagnetic materials is parallel and increases when it is antiparallel.
The MR ratio (the rate of change in resistance depending on the state of a magnetic field) in TMR junctions can reach more than 100% in production. In lab conditions, levels upwards of 1,000% have been achieved.
3. TMR sensor IC configuration
The TMR sensor IC supplies current to the built-in TMR sensor element, amplifies the potential difference of its element and processes the signal in internal circuits to output a signal depending on the magnetic flux density.
The table and figure below show the internal configuration of an ultra-low power consumption TMR sensor IC.
|TMR sensor element||Resistance changes with the magnetic field (magnet)|
|Gain amplifier||The potential difference is amplified in response to the resistance of the TMR sensor element.|
|Control circuit||This circuit sets intermittent control of circuit and the operating conditions of the circuit.|
|Comparator with hysteresis||Controls output, outputs “H” or “L” depending on magnetic flux density.|
4. TMR sensor IC types
There is a great variety of TMR sensor ICs for different applications. The following is a list of major examples of TMR sensor IC types: the TMR linear sensor (analog or digital output), a sensor that obtains an output signal proportional to the intensity of a magnetic field; the TMR switch sensor (digital output) that obtains ON/OFF signals; the TMR angle sensor that obtains an output signal in response to the rotation angle of a magnet; the TMR current sensor that obtains an output signal in response to the amount of current flowing through a conductor and other sensors.
TMR Switch Sensor IC Detection Methodology
A TMR switch sensor IC detects the presence of magnetic fields, fields that have a north (N) and south (S) pole. There are three types of TMR switch sensor ICs. A “unipolar detection” IC detects the N pole or S pole. An “omnipolar detection” IC detects both N and S poles without making a distinction. A “bipolar latch detection” IC alternately detects N poles and S poles.
Select the detection methodology that best suits the application you intend to use it for. ABLIC Inc. currently mass-produces omnipolar TMR sensor ICs.
For this method, only one magnetic field pole (north or south) is detected, and on/off operation is performed according to the magnetic flux density to output a high or low level signal.
For this method, both magnetic field poles (north and south) are detected, and on/off operation is performed according to the magnetic flux density to output a high or low level signal.
For this method, both magnetic field poles (north and south) are detected in alternation, and on/off operation is performed according to the magnetic flux density and polarity to output a high or low level signal.
ABLIC’s TMR sensor IC
|TMR sensor IC||Webshop|