Micronas Two New Hall Effect Sensors

In the field of position detection in automotive and industrial applications, more and more sensor functions are required. The accuracy and stability of sensors in harsh environments must continue to increase. Position detection applications on throttle valves, clutches or steering wheels must be implemented as precisely as possible. For short-range (6-mm upper limit) or small-angle (60-degree upper limit) measurement applications, existing one-dimensional linear Hall sensors can be used. But for larger angles, you need to use a new technology. To this end, Micronas has developed two new Hall-effect sensor product lines, HAL36xy and HAL38xy.

For the first time, the above-mentioned products use so-called "vertical Hall films". We have worked closely with the Fraunhofer Institute for Integrated Circuits (FhG IIS) to develop these Hall elements for the new Micronas process. Micronas authorized the application of a pixel cell pixel technology called "Hall-in-One" and applied it to the HAL 36xy/HAL 38xy series. These sensor families include seven different products and thus cover a wide range of applications ranging from clutch position or neutral detection to steering wheel angle measurement.

Micronas was the first manufacturer of Hall effect sensors to successfully introduce sensors using "vertical Hall technology" into automotive applications.

Previously, angle measurements could only be achieved with integrated flux concentrators or complex dual-column AMR (anisotropic magnetoresistive) sensors, which can now be accomplished with a standard CMOS process. In contrast to AMR technology, vertical hole technology enables the measurement of angles up to 360° and linear distances with a single product. The main advantage of the program developed by Micronas is the use of so-called "pixel cell" pixels. It consists of two vertical Hall plates and a horizontal Hall plate. With pixel cell pixels, three magnetic field subvectors can be measured at one point. The lines of magnetic force parallel to the sensor surface are measured by vertical Hall plates, and the lines of magnetic force perpendicular to the sensor surface are measured by horizontal Hall plates.

The HAL36xy uses only two vertical Hall plates Bx and By, while the HAL38xy uses horizontal Hall plates and one of the vertical Hall plates. Depending on the sensor type, the customer can select the desired combination of Hall plates. Bx and Bz are active, or By and Bz are active. In addition, two output signal formats (pulse width modulation or analog signal) can be selected.

The ideal application for the HAL36xy series is angle measurements up to 360°, such as steering wheel angle measurements. For this purpose, a radially magnetized magnet (see Fig. 2) is mainly used and it is driven parallel to the sensor surface. The two vertical Hall plates are placed perpendicular to each other, generating both sine and cosine signals. The sensor automatically calculates the arc tangent value and converts it to an analog or digital output signal.

The output signal and the measured angle are directly proportional. Based on the arc tangent analysis, the change of the air gap and the magnet temperature of the magnet has little effect on the re-measurement method. These sensors are designed to operate over the temperature range of –40°C to 170°C (die temperature) and provide a variety of diagnostic functions. The sensor's own self-test is performed on the first energized rotating circle to ensure that the sensor line is functioning properly. The sensor can detect an overvoltage or undervoltage condition and indicate it in the output signal. The user can also define the applied magnetic field strength range. If the magnetic field strength exceeds a specific range, the sensor can display an error signal. This range can be defined and programmed by the user. The programming of the sensor is achieved through a user-friendly graphical interface software tool.

The HAL38xy with vertical and horizontal Hall plates is mainly used for linear displacement applications and the measurement distance can be 50% longer than the magnet length. With a magnet with a length of 10 mm, a distance greater than or equal to 15 mm can be measured. In this application, an axially magnetized magnet moves parallel to the sensor surface (Figure 3). Longer distances can be measured with a suitable magnet.

In traditional single-dimension measurement sensor applications, the magnet length must be designed to be 30% longer than the measured displacement. The relatively increased cost of using two-dimensional sensors can therefore easily be offset by the savings of expensive magnetic materials. Therefore, while improving performance, it also achieves cost advantages.

Another possible application of the HAL38xy is the measurement of the angle at the axis. A radially magnetized magnet is fixed on the shaft and rotates on the sensor side. If the two magnetic arctangent calculations provide an ideal sine cosine correlation curve, the arctangent can provide a linear relationship to the angle. This is not achievable in all applications. The ideal shaft angle measurement setting can only be achieved with special magnets. If you use a conventional magnet, you need to perform linearization after the arctangent calculation. To accomplish this task, the HAL38xy and HAL36xy provide 32-point calibration to linearize the output signal.

The fact that other sensor manufacturers are also trying to use vertical Hall technology (for example, simple products such as Hall switches) proves the attractiveness of this technology. Micronas implemented the vertical Hall sensor technology early on and is now the market leader in this field. With the introduction of next-generation direct angle sensors, Micronas will expand its lead in the market. The new generation of products will have further improved angle measurement performance, provide higher measurement accuracy, lower flux density lower limit, so that the product can be used in a much weaker magnetic field.