Drift of magnetic sensitivity of smart hall sensors due to moisture absorbed by the IC-package

Ausserlechner, Udo; Motz, Mario; Holliber, Michael

doi:10.1109/icsens.2004.1426198

Cited by 20 publications

(11 citation statements)

References 3 publications

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“…As sensor elements one can use horizontal Hall plates (HHall) [9,10] or MAGFETs [11]. The main advantage is the mature technology of HHalls, where the problems of offset [12] and mechanical stress [13,14] are solved. Another advantage is the differential sensing principle, which is robust against background magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

“…The magnetic sensitivity of Hall plates depends on the sum of in-plane stress components ∝ (1 + P 12 (σ xx + σ yy )), with P 12 ≈ 45%/GPa [14]. The current which supplies the Hall plates is defined by resistors, which suffer from piezo-resistivity of about −24%/GPa in the case of generally used n-doped resistors [14]. Thus the Hall output signals have a sensitivity to mechanical stress of roughly 69%/GPa.…”

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confidence: 99%

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A Theory of Magnetic Angle Sensors With Hall Plates and Without Fluxguides

Ausserlechner¹

2013

PIER B

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Abstract-Magnetic angle sensors detect the angular position of a permanent magnet attached to a rotating shaft. The magnet is polarized diametrically to the rotation axis. No soft magnetic flux guides are present. The semiconductor die is placed on and orthogonal to the rotation axis. There are two kinds of systems: (i) perpendicular systems detect the field components perpendicular to the rotation axis, and (ii) axial systems detect the component parallel to the rotation axis. The former use magneto-resistive sensors or vertical Hall effect devices; the latter use Hall plates. This paper focuses on axial systems, derives their conceptual limitations, and compares them with perpendicular systems. An optimized system and optimum shapes of magnets are reported. Angle errors due to assembly tolerances of magnet and sensor versus shaft are explained. It is proven that assembly tolerances of optimized axial systems give three times larger errors than perpendicular systems.

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

A Theory of Magnetic Angle Sensors With Hall Plates and Without Fluxguides

Ausserlechner¹

2013

PIER B

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“…This, over the intended temperature range, leads to thermal offset drift. The series expansion of (7) in combination with a resistor mismatch μ according to (10) leads to…”

Section: Temperature Coefficient Mismatchmentioning

confidence: 99%

“…Variations of the temperature cause a change of magnetic sensitivity via the temperature dependent mobility and Hall scattering factor [8]. Moreover, a change of the environmental conditions of packaged Hall sensors, i.e., temperature, humidity [9], [10], and cyclic loads [11] lead to a change of the package stress and consequently lead to a change of the sensitivity [5], [12]. An optimized assembly process can help to decrease the stress-related sensitivity drift of Hall sensors [13], [14].…”

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confidence: 99%

Package Stress Monitor to Compensate for the Piezo-Hall Effect in CMOS Hall Sensors

Huber¹,

Schott²,

Oliver

2013

IEEE Sensors J.

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Package-induced stress changes the sensitivity of planar Hall plates via the piezo-Hall effect. In this paper, we present a novel stress sensor that allows us to compensate for this undesired mechanical cross-sensitivity. The new CMOScompatible sensor is based on a Wheatstone bridge built of eight appropriately arranged n-and p-doped piezoresistors. The differential output signal V bridge of the sensor is proportional to the sum of in-plane normal stresses σ x x +σ yy with the sensitivity S bridge,σ = ∂ V bridge / V bias /∂ σ x x + σ yy = −0.047GPa −1 . Doping concentrations larger than 10 19 cm −3 for both the n-and p-type resistors are used to minimize the parasitic resistor mismatch due to the junction field effect. Simultaneously, the highly doped resistors keep the relative thermal cross-sensitivity of the sensor as small as 74 ppm K −1 . In contrast to conventional sensor rosettes, the new sensor has the advantage of offering a differential output signal. The measured signal is successfully used to decrease the stress-impact on the sensitivity of CMOS Hall sensors by a factor of five.

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“…Yet, we believe that the dominant contribution comes from varying moisture content of the mold compound: at high ambient humidity the moisture diffuses into the mold compound thereby increasing its volume, and reducing the strong compressive stress on the die [8] which, in turn, increases the magnetic sensitivity of the Hall probe. A strong argument for this theory is the good reproducibility of this drift after subsequent drying and soaking periods [9]. Although, in principle, it seems possible to reduce this kind of moisture drift by optimized mold compounds, there is no economically viable solution in sight.…”

Section: Introductionmentioning

confidence: 99%

Compensation of the Piezo-Hall Effect in Integrated Hall Sensors on (100)-Si

2007

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Silicon Hall sensors are known to suffer from a long-term drift in the magnetic sensitivity between 1% and 4%, depending on the degree of moisture in the mold compound of the package. This drift is mainly caused by changes of mechanical stress exerted by the plastic package onto the die. We present a system, which continuously measures the relevant stress components, estimates the sensitivity drift, and corrects for it digitally. An individual precalibration versus temperature is necessary to achieve the required level of accuracy. Results from laboratory characterization with pressure cells and lifetime drift during qualification runs show that this system can keep the drift of magnetic sensitivity well below 1%.

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Drift of magnetic sensitivity of smart hall sensors due to moisture absorbed by the IC-package

Cited by 20 publications

References 3 publications

A Theory of Magnetic Angle Sensors With Hall Plates and Without Fluxguides

A Theory of Magnetic Angle Sensors With Hall Plates and Without Fluxguides

Package Stress Monitor to Compensate for the Piezo-Hall Effect in CMOS Hall Sensors

Compensation of the Piezo-Hall Effect in Integrated Hall Sensors on (100)-Si

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