Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2001-02-06
2003-07-08
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C428S692100, C338S03200R
Reexamination Certificate
active
06590389
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor thin film magnetic sensor and production method thereof.
DESCRIPTION OF BACKGROUND ART
Magnetic sensors, such as a magnetic resistance device or a Hall device, using a compound semiconductor thin film with a high electron mobility, such as InSb, are capable of detecting a static magnetic field, and are capable of detecting a rotational angle or speed even at a high or low rotational speed. Therefore, such sensors are widely used as magnetic sensors for small-sized DC motors.
However, InSb has a problem that it is difficult to meet the strict requirements of the recently expanding applications of magnetic sensors. For example, a magnetic sensor using InSb has a high sensitivity and exhibits very good characteristics in the vicinity of room temperature. However, since resistance of a magnetic sensing part greatly depends on temperature, at low temperatures of, below −40° C., a magnetic sensor using InSb becomes liable to pick up electrical noises due to considerable increase in resistance of the device. Further, at high temperatures exceeding 120° C. increases in drive current because of a large decrease in device resistance results in driving difficulty. That is, InSb has a maximum temperature variation rate of resistance of −2%/° C., thus having a high temperature dependence. The temperature variation rate &bgr;
R
of resistance is determined by the following equation:
Temperature variation rate &bgr;
R
(%/° C.)=(1/R)dR/dT×100.
In the present invention, a small temperature variation of resistance generally means a small value of the temperature variation rate &bgr;
R
(%/° C.).
Recently, magnetic sensors are widely used as non-contact sensors, and the application fields of such sensors is expanding. In such the recently expanding application field of magnetic sensors, as compared with prior art applications, requirements are increasing for using magnetic sensors as non-contact sensors even under conditions of lower temperatures or higher temperatures. In general, the temperature range at which the magnetic sensor is driven tends to be expanding. In the application of small-sized motors used in the conventional VTR or personal computers, the magnetic sensor has been sufficient if it is usable in a temperature range in the vicinity of room temperature, for example, in the range of about −20 to 80° C. (drive temperature range of substantially 100° C.). However, in a non-contact magnetic sensor for an automobile or an industrial non-contact magnetic sensor which is expected to be expanding in demand, use in the temperature range of −50° C. to 150° C. (drive temperature range of substantially 200° C.) is actually required.
Because InSb has a high temperature dependence with a temperature variation rate that is negative, an InSb sensor has a high resistance at a low temperature, and a low resistance at a high temperature. If the temperature changes from −50° C. to +150° C., resistance at −50° C. is 28 to 30 times (54 times when the temperature variation rate of resistance is −2%) as high as resistance at +150° C. As a result, variation of self resistance in effect becomes a variation of input resistance of the magnetic sensor, and as a result, at high temperatures, a breakdown or the like due to eddy current is generated, a higher drive input current becomes required, and in a small-sized integrated drive circuit, stable drive of the device becomes difficult. That is, a complex, expensive drive circuit is required.
Further, at low temperatures, device resistance becomes very high, which results in a strong influence of stray magnetic noise or causes misoperation due to noise As a result, the magnetic sensor is usable only in very limited cases, and its merit as a non-contact sensor, hasp not been sufficiently utilized.
When such a magnetic sensor, a power supply for driving the magnetic sensor, and a control circuit of the magnetic sensor for amplifying the magnetic field detection output are attempted to be realized in a small size, at a low cost, and with high performance, such a temperature dependence of resistance due to the material is a great problem. For example, a maximum ratio of resistance at −50° C. and resistance at 150° C. must be within 15 times in absolute value.
The present invention has been made for solving the above-described problems of the prior art magnetic sensors, and an object of the present invention is to provide a magnetic sensor that is capable of operating with a simple drive circuit with a high sensitivity, a small temperature dependence, and in a wide temperature range. A further object of the present invention is to provide a magnetic sensor that is capable of being driven in the range of −50° C. to 150° C. with high reliability and capable of being driven by a small-sized, low-cost control circuit. More specifically, an object of the present invention is to provide a high sensitivity, high reliability magnetic sensor that is small in change of input resistance of the magnetic sensor between a low temperature (for example, −50° C. which is a required lower limit temperature) and a high temperature (for example, 150° C. which is a required higher limit temperature).
Further, in driving the magnetic sensor in a wide temperature range from low to high temperatures, a large thermal stress is exerted through a package of the magnetic sensor, and a passivation technology for protecting the magnetic sensing part from a new thermal stress is necessary, and meeting such a requirement is also an object of the present invention.
SUMMARY OF THE INVENTION
The inventors have investigated composition, thin film formation, doping and the like of a compound semiconductor thin film having a high electron mobility which is capable of producing a high sensitivity magnetic sensor and also investigated matching with a control circuit. In particular, as a result of investigating temperature dependence of device resistance or device resistance change at low and high temperatures, a thin film with a high electron mobility capable of suppressing temperature variation of input resistance of the magnetic sensor to a small value and a production method thereof have been found. As a result, the inventors have found a magnetic sensor with a small temperature variation of resistance.
Further, in driving the magnetic sensor in a wide temperature range from low to high temperatures, a large thermal stress is exerted through a package of the magnetic sensor. However, by forming on the magnetic sensing part an intermediate layer of a dielectric III-V group compound semiconductor having the same properties as III-V group compound semiconductor constituting the magnetic sensing part, a passivation technology for protecting the magnetic sensing part from thermal stress is exerted directly from the inorganic passivation layer (protective layer). As a result, a magnetic sensor structure capable of driving in a wide temperature range and with a high reliability has been found.
Further, it has been found that when temperature variation of input resistance of the magnetic sensor is within a predetermined range, the sensor can be driven by a small-sized control circuit in a wide temperature range.
Still further, a small-sized digital output magnetic sensor apparatus and a production method thereof have been found, which magnetic sensor apparatus combines a high sensitivity magnetic sensor as a magnetic sensing part using a compound semiconductor thin film providing a high mobility satisfying such requirement, with a small-sized control circuit for such a magnetic sensor, which is capable of outputting an output proportional to magnetic field detection signal and a plurality of signals corresponding to detection or non-detection of magnetic field
That is, a magnetic sensor according to the teachings of the present invention comprises a magnetic sensor having an In
x
Ga
1−x
As
y
Sb
1−y
(0<x≦1, 0≦y≦1) thin film layer f
Okada Ichiro
Okamoto Atsushi
Shibasaki Ichiro
Yoshida Takashi
Asahi Kasei Kogyo Kabushiki Kaisha
Snow Walter E.
LandOfFree
Magnetic sensor, magnetic sensor apparatus, semiconductor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic sensor, magnetic sensor apparatus, semiconductor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic sensor, magnetic sensor apparatus, semiconductor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3022808