MEMS DEVICE
A MEMS gyroscope is disclosed herein, wherein the MEMS gyroscope comprised a magnetic sensing mechanism and a magnetic source that is associated with the proof-mass. The magnetic sensing mechanism comprises multiple magnetic field sensors that are designated for sensing the magnetic field from a magnetic source so as to mitigate the problems caused by fabrication.
This US utility patent application claims priority from co-pending US utility patent application “A HYBRID MEMS DEVICE,” Ser. No. 13/559,625 filed Jul. 27, 2012, which claims priority from U.S. provisional patent application “A HYBRID MEMS DEVICE,” filed May 31, 2012, Ser. No. 61/653,408 to Biao Zhang and Tao Ju. This US utility patent application also claims priority from co-pending US utility patent application “A MEMS DEVICE,” Ser. No. 13/854,972 filed Apr. 2, 2013 to the same inventor of this US utility patent application, the subject matter of each of which is incorporated herein by reference in its entirety.
TECHNICAL FIELD OF THE DISCLOSUREThe technical field of the examples to be disclosed in the following sections is related generally to the art of operation of microstructures, and, more particularly, to operation of MEMS devices comprising MEMS magnetic sensing structures.
BACKGROUND OF THE DISCLOSUREMicrostructures, such as microelectromechanical (hereafter MEMS) devices (e.g. accelerometers, DC relay and RF switches, optical cross connects and optical switches, microlenses, reflectors and beam splitters, filters, oscillators and antenna system components, variable capacitors and inductors, switched banks of filters, resonant comb-drives and resonant beams, and micromirror arrays for direct view and projection displays) have many applications in basic signal transduction. For example, a MEMS gyroscope measures angular rate.
A gyroscope (hereafter “gyro” or “gyroscope”) is based on the Coriolis effect as diagrammatically illustrated in
The MEMS gyro is a typical capacitive MEMS gyro, which has been widely studied. Regardless of various structural variations, the capacitive MEMS gyro in
Current capacitive MEMS gyros, however, are hard to achieve submicro-g/rtHz because the capacitance between sensing electrodes decreases with the miniaturization of the movable structure of the sensing element and the impact of the stray and parasitic capacitance increase at the same time, even with large and high aspect ratio proof-masses.
Therefore, what is desired is a MEMS device capable of sensing angular velocities and methods of operating the same.
SUMMARY OF THE DISCLOSUREIn view of the foregoing, A MEMS gyroscope is disclosed, the MEMS gyrioscope comprising: a mass-substrate, comprising: a movable prof-mass; and a magnetic source attached to the proof-mass such that the magnetic source is capable of moving with the proof-mass; and a sensor substrate below the mass-substrate, comprising: a magnetic sensing mechanism for detecting a magnet field from the magnetic sensor, wherein the magnetic sensing mechanism is static relative to the magnetic source, wherein the magnetic sensing mechanism further comprising: a plurality of signal sensors associated with said magnetic source for detecting a magnetic field from said magnetic source; and a reference sensor disposed in the vicinity of the signal sensors for detecting a background magnetic signal such that the detections of the signal sensors use the detection of the reference sensor as a reference.
In another example, a wafer assembly is disclosed herein, comprising: a mass wafer comprising a plurality of mass dies, each mass die comprising: a movable prof-mass; and a magnetic source attached to the proof-mass such that the magnetic source is capable of moving with the proof-mass; and a sensor wafer comprising a plurality of sensor dies, each sensor die comprising: a magnetic sensing mechanism for detecting a magnet field from the magnetic sensor, wherein the magnetic sensing mechanism is static relative to the magnetic source, wherein the magnetic sensing mechanism further comprising: a plurality of signal sensors associated with said magnetic source for detecting a magnetic field from said magnetic source; and a reference sensor disposed in the vicinity of the signal sensors for detecting a background magnetic signal such that the detections of the signal sensors use the detection of the reference sensor as a reference.
Disclosed herein is a MEMS gyroscope and method of using the same for sensing an angular velocity, wherein the MEMS gyroscope utilizes a magnetic sensing mechanism. It will be appreciated by those skilled in the art that the following discussion is for demonstration purposes, and should not be interpreted as a limitation. Many other variations within the scope of the following disclosure are also applicable. For example, the MEMS gyroscope and the method disclosed in the following are applicable for use in accelerometers.
Referring to
The magnetic sensing mechanism (114) in this example comprises a magnetic source 116 and magnetic sensor 118. The magnetic source (116) generates a magnetic field, and the magnetic sensor (118) detects the magnetic field and/or the magnetic field variations that is generated by the magnetic source (116). In the example illustrated herein in
Other than placing the magnetic source on/in the movable proof-mass (1112), the magnetic source (116) can be placed on / in the sensor substrate (120); and the magnetic sensor (118) can be placed on/in the proof-mass (112).
It is also noted that the MEMS gyroscope illustrated in
The MEMS gyroscope as discussed above with reference to
Alternatively, the proof-mass can be driven by magnetic force, an example of which is illustrated in
Referring to
The magnetic source (114) of the MEMS gyroscope (106) illustrated in
The conductive wire (142) can be implemented in many suitable ways, one of which is illustrated in
The magnetic sensor (118) illustrated in
The reference sensor (150) and the signal sensor (152) preferably comprise magneto-resistors, such as AMRs, giant-magneto-resistors (such as spin-valves, hereafter SV), or tunneling-magneto-resistors (TMR). For demonstration purpose,
In examples wherein the spacer (158) is comprised of a non-magnetic conductive layer, such as Cu, the magneto-resistor (118) stack can be configured into a CIP structure (i.e. spin-valve, SV), wherein the current is driven in the plane of the stack layers. When the spacer (158) is comprised of an oxide such as Al2O3, MgO or the like, the magneto-resistor stack (118) can be configured into a CPP structure (i.e. TMR), wherein the current is driven perpendicularly to the stack layers.
In the example as illustrated in
The top and bottom pin layers (154 and 162, respectively) preferably have different blocking temperatures. When the free layer (156) is “freed” from being pinned by the top pin layer (154), the reference layer (160) preferably remains being pinned by the bottom pin layer (162). Alternatively, when the free layer (156) is still pinned by the top pin layer (154), the reference layer (160) can be “freed” from being pinned by the bottom pin layer (162). In the later example, the reference layer (160) can be used as a “sensing layer” for responding to the external magnetic field such as the target magnetic field, while the free layer (156) is used as a reference layer to provide a reference magnetic orientation.
The different blocking temperatures can be accomplished by using different magnetic materials for the top pin layer (154) and bottom pin layer (162). In one example, the top pin layer (154) can be comprised of IrMn, while the bottom pin layer (162) can be comprised of PtMn, vice versa. In another example, both of the top and bottom pin layers (154 and 162) may be comprised of the same material, such as IrMn or PtMn, but with different thicknesses such that they have different blocking temperatures.
It is noted by those skilled in the art that the magneto-resistor stack (118) is configured into sensors for sensing magnetic signals. As such, the magnetic orientations of the free layer (156) and the reference layer (160) are substantially perpendicular at the initial state. Other layers, such as protective layer Ta, seed layers for growing the stack layers on substrate 120 can be provided. It is further noted that the magnetic stack layers (118) illustrated in
In some applications, multiple magnetic sensing mechanisms can be provided, an example of which is illustrated in
By using the different blocking temperatures of the sensors as discussed above with reference to
With reference to
At time T1, the wire remains OFF and the signal sensor can be at any state. When the reference sensor is stabled at the “Lock” state (e.g. finishes “locking” the state of its free layer), the wire is set to the ON state at time T2, by driving current with pre-defined amplitude through the wire so as to generate magnetic field. The current can be DC or AC. After the magnetic field generated by the wire is stabilized, the signal sensor can be set to the ON state. Setting the signal sensor to the ON state can be accomplished by raising the temperature of the pin layer used for pinning the free layer of the signal sensor above its blocking temperature so as to free the free layer. A current is driven through the signal sensor so as to measure its magneto-resistance.
After the signal sensor finished the measurement, it locks its instant state at time T3 by for example, lowering the temperature of its top pin layer (used for pinning the free layer) below its blocking temperature such that the free layer is magnetically coupled to (thus pinned by) the top pin layer. The signal sensor at this state is referred to as the “Lock” state.
When the signal sensor finishes its locking at time T3, the reference sensor and the signal sensor can output their measurements to so to obtain the magnetic field from the magnetic source attached to the proof-mass, thus extract the information of the movement of the proof-mass.
The reference sensor and the signal sensor can be connected by a Wheatstone bridge, or can be connected directly to an amplifier or other electrical circuits to obtain the target magnetic field, which not be detailed herein.
In the example discussed above, the reference sensor and/or the signal sensor can be configured to “lock” the status (e.g. the detected magnetic signal). This locking capability can be accomplished in many ways. In the following, such locking capability will be discussed with reference to signal sensor, and the reference sensor can be implemented in substantially the same ways.
In one example, the signal sensor can be configured to be comprised of a storage layer that comprises a ferromagnetic layer. The storage layer is connected to electrical leads such that electrical current can be applied through the storage layer. When current is applied, the storage layer is heated, and its temperature can be elevated.
The material, as well as the geometry (e.g. the thickness) of the storage layer can be configured such that at the elevated temperature above a threshold temperature, such as the Currie temperature, the storage layer is capable of being magnetized by the target magnetic signal so as to accomplish the detection of the target magnetic signal. When the temperature of the storage layer is dropped to a temperature below the threshold temperature, the storage layer “freezes” its magnetization states so as to accomplish its “locking” operation.
Referring to
The coercivity of a magnetic thin-film (layer) also varies with its thickness, as diagrammatically illustrated in
In addition to utilizing the temperature dependence of coercivity of a ferromagnetic layer, a magnetic coupling structure can be utilized to accomplish the “locking” process, as illustrated in
For example, when it is desired to detect the target magnetic field signal, the signal sensor may elevate its temperature above the blocking temperature TB by for example, applying current through the free layer (172) and/or the pining layer (170). The free layer (172) is thus “freed” and can be used for picking up the target magnetic field signal. When it is desired for the signal sensor to lock its detection, for example, after the detecting the target magnetic signal, the signal sensor can decrease its temperature below the blocking temperature TB. At a temperature below TB, the free layer (172) is magnetically pinned by the pinning layer (172). The magnetic states of the free layer (172), which corresponds to the target magnetic field signal, is thus “frozen” in the free layer (172).
In the above discussion, a magnetic sensing mechanism is provided for detecting the magnetic field from the magnetic source of the proof-mass. However, the magnetic source and the magnetic sensors are in different substrates, such as the mass-substrate 108 and sensor substrate 110 as shown in
Regardless of various relative position arrangements, the mass-substrate (108) and sensor substrate 110 (as illustrated in
The above problem caused by wafer misalignment can be solved by increasing the accuracy of the alignment during the wafer assembly, which however, is extremely hard with present fabrication technologies. This disclosure provides an alternative approach to remedy the misalignment. Referring to
With the multiple magnetic sensors provided at the pre-determined different locations, such as A, B, and C, the problem caused by the misalignment during the wafer assembly can be mitigated, if not eliminated. For example, the magnetic source (146) is expected to be at location A and associated with magnetic sensor 118. After the wafer assembling, the magnetic source may be in the vicinity of position B or C due to assembling misalignment. Magnetic sensor 118 in this situation may not be optimal for detecting the magnetic field from the magnetic source 146. However, magnetic sensor 182 (for position B) or 184 (for position C) can be used for effectively detecting the magnetic field from the magnetic source (146). In this way, the problem caused by misalignment during wafer assembling can be mitigated or eliminated.
The magnetic sensors (118, 182, and 184) each have a reference sensor and a signal sensor as discussed in the above sections. Alternatively, the magnetic sensors each can be comprised of a signal sensor, such as those discussed above with reference to
In another example, a reference sensor can be provided for multiple signal sensors, as illustrated in
The reference sensor (152) can be placed at any suitable locations within an area in which the associated signal sensors are disposed. For example, reference sensor 152 can be placed in the vicinity of signal sensor 118, 150, or 184. However, it is preferred that the reference sensor (152) is at a location that is as close to the geometric center of the associated signal sensors as possible. Alternatively, the reference sensor (152) can be at a location that is as close to a symmetric center to which the associated signal sensors are substantially symmetric. By such configuration, the reference sensor (152) is capable of providing a substantially “uniform reference signal” to all associated signal sensors. If the reference sensor (152) is disposed too far away such that the reference signal provided by such reference sensor (152) may not be suitable for all signal sensors.
The MEMS gyroscope as discussed above can be fabricated on a wafer level. For example, as illustrated in
Wafer 190 is a magnetic sensor wafer with a plurality of magnetic sensing mechanisms formed thereon. Wafer 190 can be of any size and shape as desired as wafer 186. Wafer 190 is comprised of a material that is suitable for forming the desired magnetic sensors. Multiple dies are formed in wafer 190, such as die 192. And each die comprises a desired magnetic sensing mechanism as discussed in above sections.
The mass-wafer (186) and the magnetic sensor wafer 190 are assembled into a wafer assembly as illustrated in
Referring to
It will be appreciated by those of skilled in the art that a new and useful MEMS gyroscope has been described herein. In view of the many possible embodiments, however, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative only and should not be taken as limiting the scope of what is claimed. Those of skill in the art will recognize that the illustrated embodiments can be modified in arrangement and detail. Therefore, the devices and methods as described herein contemplate all such embodiments as may come within the scope of the following claims and equivalents thereof. In the claims, only elements denoted by the words “means for” are intended to be interpreted as means plus function claims under 35 U.S.C. §112, the sixth paragraph.
Claims
1. A MEMS gyroscope, comprising:
- a mass-substrate, comprising: a movable prof-mass; and a magnetic source attached to the proof-mass such that the magnetic source is capable of moving with the proof-mass; and
- a sensor substrate below the mass-substrate, comprising: a magnetic sensing mechanism for detecting a magnet field from the magnetic sensor, wherein the magnetic sensing mechanism is static relative to the magnetic source, wherein the magnetic sensing mechanism further comprising: a plurality of signal sensors associated with said magnetic source for detecting a magnetic field from said magnetic source; and a reference sensor disposed in the vicinity of the signal sensors for detecting a background magnetic signal such that the detections of the signal sensors use the detection of the reference sensor as a reference.
2. The MEMS gyroscope of claim 1, wherein the magnetic source comprises a conductive wire to which current can be applied so as to generate a magnetic field.
3. The MEMS gyroscope of claim 1, wherein the magnetic source comprises a magnetic nanoparticle.
4. The MEMS gyroscope of claim 2, wherein conductive wire has a length along a length of at least one of the plurality of magnetic sensing mechanisms.
5. The MEMS gyroscope of claim 2, wherein at least one of the plurality of magnetic sensors comprises a giant-magnetic-resistor.
6. The MEMS gyroscope of claim 2, wherein at least one of the plurality of magnetic sensors comprises a spin-valve structure.
7. The MEMS gyroscope of claim 2, wherein at least one of the plurality of magnetic sensors comprises a tunnel-magnetic-resistor.
8. The MEMS gyroscope of claim 2, wherein at least one of the magnetic sensors comprises magnetic pickup coil that is an element of a fluxgate.
9. The MEMS gyroscope of claim 2, wherein the magnetic sensors each has a geometric length and a width, wherein the geometric lengths of the magnetic sensors are substantially parallel, and are substantially parallel to the length of the conductive wire.
10. The MEMS gyroscope of claim 2, wherein at least one of the magnetic sensors comprises a reference sensor and a signal sensor pair.
11. A wafer assembly, comprising:
- a mass wafer comprising a plurality of mass dies, each mass die comprising a movable prof-mass; and a magnetic source attached to the proof-mass such that the magnetic source is capable of moving with the proof-mass; and
- a sensor wafer comprising a plurality of sensor dies, each sensor die comprising: a magnetic sensing mechanism for detecting a magnet field from the magnetic sensor, wherein the magnetic sensing mechanism is static relative to the magnetic source, wherein the magnetic sensing mechanism further comprising: a plurality of signal sensors associated with said magnetic source for detecting a magnetic field from said magnetic source; and a reference sensor disposed in the vicinity of the signal sensors for detecting a background magnetic signal such that the detections of the signal sensors use the detection of the reference sensor as a reference.
12. The wafer assembly of claim 11, wherein the magnetic source comprises a conductive wire to which current can be applied so as to generate a magnetic field.
13. The wafer assembly of claim 11, wherein the magnetic source comprises a magnetic nanoparticle.
14. The wafer assembly of claim 12, wherein conductive wire has a length along a length of at least one of the plurality of magnetic sensing mechanisms.
15. The wafer assembly of claim 12, wherein at least one of the plurality of magnetic sensors comprises a giant-magnetic-resistor.
16. The wafer assembly of claim 12, wherein at least one of the plurality of magnetic sensors comprises a spin-valve structure.
17. The wafer assembly of claim 12, wherein at least one of the plurality of magnetic sensors comprises a tunnel-magnetic-resistor.
18. The wafer assembly of claim 12, wherein at least one of the magnetic sensors comprises magnetic pickup coil that is an element of a fluxgate.
19. The wafer assembly of claim 12, wherein the magnetic sensors each has a geometric length and a width, wherein the geometric lengths of the magnetic sensors are substantially parallel, and are substantially parallel to the length of the conductive wire.
20. The wafer assembly of claim 12, wherein at least one of the magnetic sensors comprises a reference sensor and a signal sensor pair.
Type: Application
Filed: Jul 6, 2013
Publication Date: Jan 30, 2014
Inventors: Biao Zhang (Hinsdale, IL), Tao Ju (Beijing)
Application Number: 13/936,145
International Classification: G01C 19/56 (20060101); B81B 5/00 (20060101);