CN102279373A - Uniaxially electrostatic-driven sensor for weak magnetic field measurement - Google Patents

Abstract

The invention provides a single-axis electrostatic drive weak magnetic field measurement sensor, which includes an insulating base, a pair of electrostatic drive electrodes, two pairs of input and output electrodes, a GMR sensitive element, two identical magnetic field line concentrators, a micro-cantilever beam, and a modulation film. Electrodes are plated on the insulating base and shallow grooves are etched. The GMR sensitive element and the two magnetic force line concentrators are all fixed on the surface of the insulating base, and the central axes of the three are in a straight line. The micro-cantilever beam is made of conductive silicon wafer, including the base and the cantilever. The base is fixed on the insulating base, the base is connected to the cantilever, and the lower surface of the upturned end of the cantilever is prepared with a modulation film; the vertical distance between the modulation film and the GMR sensitive element is 8-15 microns. The weak magnetic field measuring sensor provided by the present invention has larger modulation depth, higher resolution and simple structure and process.

Description

A Single-axis Electrostatically Driven Weak Magnetic Field Measurement Sensor

technical field

The invention relates to the technical field of sensors, in particular to sensors for weak signals, and in particular to a single-axis magnetic sensor for measuring weak magnetic fields.

Background technique

Weak magnetic field measurement is widely used in geomagnetic navigation, target detection, geological exploration, biomedicine and other fields. At this stage, there are many types of sensors used for weak magnetic field measurement, mainly including fluxgate sensors, optical pump magnetic sensors, proton magnetic sensors, optical fiber magnetic sensors, giant magnetoresistive magnetic sensors, and GMR (Giant Magnetoresistive, giant magnetoresistance) Magnetic sensors, etc. Among them, the GMR magnetic sensor is made based on microelectronics technology. Compared with other types of magnetic sensors, it has the characteristics of small size, low power consumption, and easy mass production.

In 1988, the experimental groups led by French scientist Albert Fert and German scientist Peter Grunberg independently discovered the GMR effect successively. Among them, the experimental group of Albert Fert found that the resistance value of the iron-chromium multilayer film changed sharply in a weak magnetic field, and described this phenomenon Named "GMR effect", and Peter Grunberg's group also found a similar experimental phenomenon in the iron-chromium-iron three-layer antiferromagnetic thin film structure. Since then, the research on the GMR effect has been carried out in full swing, and new structures with the GMR effect have emerged continuously, and the structure with the GMR effect is also called a GMR sensitive element. With the deepening of research, it is found that the higher the magnetic field sensitivity of the GMR sensitive element, the greater the noise, especially the 1/f noise, and the 1/f magnetic noise which depends on the internal magnetic structure cannot pass the conventional electrical modulation method It is this that limits the improvement of the resolution of the GMR magnetic sensor.

In recent years, a lot of research has been carried out abroad on how to effectively suppress the 1/f noise of GMR sensitive elements. Among them, the technical solution to suppress the 1/f noise of GMR sensitive elements by using micromechanical structures to drive magnetic thin films to modulate the measured low-frequency weak magnetic field is the most feasible. Alan S.Edelstein of U.S. Army Laboratory, etc. successively obtained 4 related U.S. national patents (patent numbers: US6670809, US7046002, US7185541, US7195945) between 2003 and 2007. The common features of the technical solutions described in these patents are : Firstly, the magnetic field line concentrator is prepared on the micro-mechanical structure, and then the micro-mechanical structure and the magnetic field line concentrator are driven to vibrate at high frequency together by means of electrostatic drive, and the magnetic field magnification of the magnetic field line concentrator changes periodically accordingly. At this time, it is in the magnetic field line concentrator The GMR sensitive element in the sensor gap can detect a high-frequency modulated magnetic field to be measured. Although this type of technical solution can effectively suppress the 1/f noise of GMR sensitive elements and significantly improve the low-frequency magnetic field resolution of GMR magnetic sensors, its structure is relatively complicated, and the manufacturing process involves deep reactive ion etching technology and insulating silicon technology. The process is time-consuming and labor-intensive, and the cost is high. In addition, the modulation depth is also low (about 14%), which is not conducive to further improving the magnetic field resolution.

Contents of the invention

The invention will provide a weak magnetic field measurement sensor with large modulation depth, high resolution and simple structure and process.

The technical solution of the present invention is: a single-axis electrostatic drive weak magnetic field measurement sensor, including an insulating substrate, a pair of electrostatic drive electrodes, two pairs of input and output electrodes, GMR sensitive elements, two identical magnetic field line concentrators, and a micro-cantilever beam , modulation film. The insulating base adopts a glass sheet with surface polishing, and two pairs of input and output electrodes and a pair of electrostatic driving electrodes are plated on the insulating base; a shallow groove is etched in the center of the insulating base, and one end of the shallow groove extends to the edge of the insulating base; One pole is plated in the shallow groove and extends to the edge of the insulating substrate, and the other pole is electrically connected to the micro-cantilever beam. The GMR sensitive element is in the shape of a thin strip, and there is a transverse gap in the center of its upper surface. Each magnetic flux concentrator has a "concave" groove at one end, and the width of the "concave" groove is slightly wider than that of the GMR sensitive element. Both the GMR sensitive element and the two magnetic force line concentrators are fixed on the surface of the insulating base, and the two ends of the GMR sensitive element are respectively located in the "concave" groove of the magnetic force line concentrator, and the GMR sensitive element and the two magnetic force line concentrators are among the three Axes are aligned. The two pairs of input and output electrodes are respectively connected to the two pairs of input and output electrodes of the GMR sensitive element. The micro-cantilever beam is made of conductive silicon wafer, including the base and the cantilever. The base is fixed on the insulating base, the base is connected to the cantilever, the cantilever is located directly above the electrostatic driving electrode in the shallow groove, and there are a number of damping holes on the cantilever; the free end of the cantilever is upturned, and there are two aligning A modulation film of soft magnetic material with high magnetic permeability is prepared between the two alignment holes on the lower surface of the upturned end; the modulation film is facing the gap of the GMR sensitive element, and the shape of the modulation film is the same as the surface shape of the gap. The vertical distance from the GMR sensitive element is determined according to actual needs, usually 8-15 microns.

The beneficial effects of the present invention are: adopting the modulation method that the modulation film vibrates directly above the GMR sensitive element can make the vibration amplitude of the modulation film relatively large, so the modulation depth obtained is relatively large (the simulation experiment proves that it is greater than 40%). The modulation of the membrane makes the weak DC magnetic field a high-frequency alternating magnetic field at the GMR sensitive element, which suppresses the 1/f noise of the GMR element, and the weak magnetic field is amplified at the GMR sensitive element by using a magnetic force line concentrator, so that the magnetic sensor can measure The resolving power is greatly improved (the simulation experiment proves that the improvement is two orders of magnitude); the structure of the micro-cantilever beam is simple, the manufacture is convenient, and the manufacturing cost of the sensor is effectively reduced.

Description of drawings

Fig. 1 is a schematic structural view of a single-axis electrostatic drive weak magnetic field measurement sensor provided by a specific embodiment of the present invention;

Fig. 2 is a schematic diagram of an insulating substrate in a specific embodiment of the present invention;

Fig. 3 is a schematic diagram of the assembly structure of the strip-shaped magnetic field line concentrator and the GMR sensitive element in a specific embodiment of the present invention;

Fig. 4 (a) is the top view of the micro-cantilever beam in a certain embodiment of the present invention;

Fig. 4 (b) is the bottom view of the micro-cantilever beam in a certain embodiment of the present invention;

Fig. 4(c) is a side view of the micro-cantilever in a specific embodiment of the present invention.

1-base, 2-cantilever, 3-modulating membrane, 4-step 1, 5-damping hole, 6-step 2, 7-alignment hole, 8-insulation base, 9-shallow groove, 11-a and 11 -b-electrostatic driving electrode pair, 12-a and 12-b-input and output electrode pair one, 13-a and 13-b-input and output electrode pair two, 14-GMR sensitive element, 15-magnetic flux concentrator, 16- Gap, 17 - microcantilever.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

Fig. 1 is a schematic structural view of a single-axis electrostatically driven weak magnetic field measurement sensor provided by a specific embodiment of the present invention. As shown in the figure, this specific embodiment includes an insulating substrate 8, a pair of electrostatic drive electrodes 11-a and 11-b, two pairs of input and output electrodes 12-a and 12-b, 13-a and 13-b, GMR sensitive Element 14, two identical magnetic field line concentrators 15, micro-cantilever beam 17, modulation film 3 (see Fig. 4). The insulating base 8 adopts a glass sheet with surface polishing, and the glass sheet is coated with two pairs of input and output electrodes 12-a and 12-b, 13-a and 13-b, and a pair of electrostatic driving electrodes 11-a and 11-b; A shallow groove 9 is etched in the center of the insulating substrate 8, and one end of the shallow groove extends to the edge of the insulating substrate; the electrode 11-b of the electrostatic driving electrode is plated in the shallow groove 9, and the electrode 11-a of the electrostatic driving electrode is electrically connected to the micro-cantilever beam 17 . The GMR sensitive element 14 is in the shape of a thin strip, and there is a transverse gap 16 (see Figure 3) in the center of its upper surface; one end of each magnetic flux concentrator 15 has a "concave" groove, and the width of the "concave" groove is more sensitive than GMR. The element 14 is slightly wider (see Fig. 3); the GMR sensitive element 14 and the two magnetic field line concentrators 15 are all fixed (such as being bonded with epoxy resin) on the surface of the insulating base 8, and the two ends of the GMR sensitive element 14 are respectively located at In the "concave" groove of a magnetic flux concentrator 15, the central axes of the GMR sensitive element 14 and the two magnetic flux concentrators 15 are in a straight line (see FIG. 3 ). The two pairs of input and output electrodes are respectively connected to the two pairs of input and output electrodes of the GMR sensitive element 14 . The base 1 of the micro-cantilever beam 17 is fixed (such as bonding with epoxy air resin or low-temperature bonding) on the insulating substrate 8, the base 1 is connected to the cantilever 2, and the cantilever 2 is directly above the shallow groove 9; There are several damping holes 5 (see Figure 4(b)); the free end of the cantilever 2 is upturned (see Figure 4(a)), that is, the end away from the base is upturned; two alignment holes 7 are opened at the upwarped end A modulation film 3 made of a soft magnetic material with high permeability is prepared between the two alignment holes 7 on the lower surface of the upturned end (see Fig. 4 (c)); Above, the shape of the modulation film 3 is the same as the surface shape of the gap 16, and the vertical distance between the modulation film 3 and the GMR sensitive element 14 is usually 8-15 microns as required.

Fig. 2 is a schematic diagram of an insulating substrate in a specific embodiment of the present invention. As shown in the figure: the insulating base 8 is made of polished glass, and its shape is not limited to the rectangle shown in Figure 2; the central photoetching of the insulating base 8 has a shallow groove 9, and its shape is not limited to the "T" shape shown in Figure 2 , the 11-b electrode that can accommodate the electrostatic drive electrode in the shallow groove 9 meets the requirements. The corrosion solution is glass corrosion solution such as dilute hydrofluoric acid. The corrosion depth is determined according to the required electrostatic force. The greater the required electrostatic force, the greater the corrosion depth. The shallower; the 11-a pole of the electrostatic driving electrode is composed of two small electrodes; the shape and specific position of the input and output electrode pairs 12-a and 12-b, 13-a and 13-b are not limited as shown in Figure 2, It only needs to be able to be electrically connected to the GMR sensitive element 14; all electrode pairs on the insulating substrate 8 are prepared by sputtering (or vacuum evaporation, electroplating, etc.) conductive film layers (gold, aluminum, copper, etc.), and then photoetching and etching forming.

Fig. 3 is a schematic diagram of the assembly structure of the magnetic field line concentrator and the GMR sensitive element in a specific embodiment of the present invention. As shown in the figure: the GMR sensitive element 14 adopts commercially available products (such as AA002-02 of NVE), the GMR sensitive element 14 is in the shape of a thin strip, and there is a transverse gap 16 in the center of the upper surface; Made of magnetic material (such as NiFe, CoZrNb, etc.), its shape is rectangular (or trapezoidal, etc.), and one end has a "concave" groove; The ends are embedded in the "concave" grooves of the two magnetic flux concentrators 15, and the central axes of the three are in a straight line.

Fig. 4(a) to Fig. 4(c) are the top view, bottom view and side view of the micro-cantilever beam in a specific embodiment of the present invention. As shown in the figure: the micro-cantilever beam 17 is made of a silicon chip through a micro-machining process, including a base 1 and a cantilever 2 . The base 1 is not limited to the "concave" shape, any shape that satisfies the support of the cantilever 2 can be used. The base 1 is connected to the cantilever 2; the cantilever 2 has several damping holes 5 along the length direction, and the number of damping holes can be 3 to 5 The free end of the cantilever 2 is upturned, and there is a step 6 at the upturned end, and two alignment holes 7 are opened at the upturned end of the cantilever 2; a modulation film 3 is prepared between the two alignment holes 7 on the lower surface of the upturned end of the cantilever 2 Modulating film 3 is made of high magnetic permeability soft magnetic material (such as NiFe, CoZrNb, etc.), and is rectangular along the axis direction of cantilever 2. The preparation method is to electroplate (or vacuum evaporation, sputtering) on the lower surface of the upturned end of cantilever 2 earlier. Radiation, etc.) a layer of high permeability soft magnetic material film, and then formed by photolithography and etching process.

When in use, connect a pair of electrostatic drive electrodes to an external excitation circuit to make the cantilever work in a resonant state; a pair of input and output electrodes are connected to an external constant voltage source (or current source), and a pair of input and output electrodes are connected to an external detection Circuit connection, the size of the weak magnetic field can be obtained according to the measured value of the external detection circuit.

Claims (2)

1. A weak magnetic field measurement sensor driven by uniaxial electrostatics, comprising an insulating base (8), a pair of electrostatic drive electrodes (11-a, 11-b), two pairs of input and output electrodes (12-a and 12-b, 13-a and 13-b), GMR sensitive element (14), two identical magnetic field line concentrators (15), micro-cantilever beam (17), modulation film (3), it is characterized in that, described insulating substrate (8 ) adopts a glass sheet with surface polishing, and two pairs of input and output electrodes and a pair of electrostatic drive electrodes are plated on the insulating base (8); a shallow groove (9) is etched in the center of the insulating base (8), and one end of the shallow groove (9) extends To the edge of the insulating substrate (8); one pole of the electrostatic drive electrode (11-a, 11-b) is plated in the shallow groove (9), and extends to the edge of the insulating substrate (8), and the other pole is connected to the micro-cantilever beam (17) Electrically connected; the GMR sensitive element (14) is in the shape of a thin strip, and there is a transverse gap (16) in the center of its upper surface; one end of each magnetic field line concentrator (15) has a "concave" groove, "concave" The width of the "shaped groove is slightly wider than the GMR sensitive element (14); the GMR sensitive element (14) and the two magnetic flux concentrators (15) are all fixed on the surface of the insulating base (8), and the two ends of the GMR sensitive element (14) Respectively located in the "concave" shaped groove of the magnetic flux concentrator (15), these three central axes of the GMR sensitive element (14) and the two magnetic flux concentrators (15) are in a straight line; two pairs of input and output electrodes are respectively connected to the GMR sensitive element ( 14) two pairs of input and output electrodes are connected; the micro-cantilever beam (17) is made of conductive silicon wafer, including the base (1) and the cantilever (2); the base (1) is fixed on the insulating base (8), and the base (1) Connect the cantilever (2), the cantilever (2) is located directly above the electrostatic driving electrode plated in the shallow groove (9), and a number of damping holes (5) are opened on the cantilever (2); on the free end of the cantilever (2) The upturned end is provided with two alignment holes (7), and a modulated film (3) of soft magnetic material with high magnetic permeability is prepared between the two alignment holes (7) on the lower surface of the upturned end; the modulated film ( 3) Facing the gap of the GMR sensitive element (14), the shape of the modulation film (3) is the same as the surface shape of the gap (16) of the GMR sensitive element (14). 2. The single-axis electrostatically driven weak magnetic field measurement sensor according to claim 1, characterized in that the vertical distance between the modulation film (3) and the GMR sensitive element (14) is in the range of 8 to 15 microns.

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