MEMS DEVICE AND A METHOD OF USING THE SAME
A method of using a MEMS gyroscope is disclosed herein, wherein the MEMS gyroscope comprised a magnetic sensing mechanism. A magnetic field is generated by a magnetic source, and is detected by a magnetic sensor. The magnetic field varies at the location of the magnetic sensor; and the variation of the magnetic field is associated with the movement of the proof-mass of the MEMS gyroscope. By detecting the variation of the magnetic field, the movement and thus the target angular velocity can be measured.
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 US 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 method of measuring an angular velocity by using a MEMS gyroscope, the method comprising: moving a proof-mass of the MEMS gyroscope in a driving mode using a magnetic driving mechanism; measuring a background magnetic signal using a reference magnetic sensor; storing the measurement from the reference magnetic sensor; generating a target magnetic field that is associated with a movement of a proof-mass of the MEMS gyroscope; activating a signal magnetic sensor for measuring the background magnetic signal and the generated target magnetic signal; comparing the measurements from the reference and signal magnetic sensors so as to obtain the target magnetic field; and extracting the angular velocity from the target magnetic field.
A method of detecting a target angular velocity, comprising: providing a MEMS gyroscope that comprises a movable proof-mass, a magnetic source, and a magnetic sensor, wherein the proof-mass is capable of moving in response to the target angular velocity under the Coriolis effect, and wherein the magnetic source is capable of generating a magnetic field that varies with the movement of the proof-mass, and wherein the magnetic sensor is capable of detecting the magnetic field from the magnetic source; detecting a background magnetic signal using a reference sensor; storing the detected background magnetic signal by the reference sensor; moving a proof-mass of the MEMS gyroscope in a driving mode using a magnetic driving mechanism; generating the magnetic field by the magnetic source; detecting a variation of the magnetic field by the magnetic sensor; and extracting the angular velocity from the variation of the magnetic field.
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 FIG. 9 are what is often referred to as “bottom pin” configuration in the field of art. In other examples, the stack can be configured into what is often referred as “top pinned” configuration in the field of art, which will not be detailed herein.
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 Th 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).
The MEMS gyro with the above discussed status locking mechanism can be operated in many ways for detecting the target angular velocity, an example of which is diagramed in
A detecting time period from time To to time T comprises a ΔTtarget, and may or may not comprise ΔTref. In examples wherein ΔTref exists, ΔTref can be at any time location between detecting time period from time To to time T. In particular, ΔTref can be at the beginning of the detecting time period. In another example, ΔTref can be at the immediate front of ΔTtarget. In an alternative example, ΔTtarget can be immediately followed by ΔTtarget. The detecting time period from T0 to T may also comprise one or more delay time periods ΔTdelay, and the delay time period(s) can be at any time location in the time period from T0 to T, as shown in
When the signal sensor completes the measurement, it may lock its measurement by entering into a lock state, even though it is not required. After both of the reference and signal sensors complete their measurement, the measurement results from the reference and signal sensors can be compared (step 184) so as to extract the target magnetic field. The movement of the proof-mass, and thus the target angular velocity can be determined.
After obtaining the target magnetic field at step 184, it is determined if the entire measurement is finished (step 186). If so, the measurement process can be stopped. Alternatively, the reference and signal sensors can be set, for example, to their initial states for the next measurement (step 188). If the entire measurement is not finished (e.g. according to the scheme shown in
In addition to the scheme shown in
In some examples, a measurement scheme can be divided into multiple sections and each section may have different schemes, an example of which is illustrated in
It will be appreciated by those of skilled in the art that a new and useful MEMS gyroscope and a method of operating the same have 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 method of measuring an angular velocity by using a MEMS gyroscope, the method comprising:
- moving a proof-mass of the MEMS gyroscope in a driving mode using a magnetic driving mechanism;
- measuring a background magnetic signal using a reference magnetic sensor;
- storing the measurement from the reference magnetic sensor;
- generating a target magnetic field that is associated with a movement of a proof-mass of the MEMS gyroscope;
- activating a signal magnetic sensor for measuring the background magnetic signal and the generated target magnetic signal;
- comparing the measurements from the reference and signal magnetic sensors so as to obtain the target magnetic field; and
- extracting the angular velocity from the target magnetic field.
2. The method of claim 1, wherein the step of measuring the background magnetic signal comprises:
- raising the temperature of the reference magnetic sensor above a blocking temperature of the reference sensor such that the reference sensor is capable of detecting the background magnetic field signal.
3. The method of claim 2, wherein the reference sensor comprises a free layer for detecting the background magnetic field signal, wherein the free layer is magnetically pinned by an antiferromagnetic layer when the temperature is blow the blocking temperature.
4. The method of claim 2, wherein the step of generating the magnetic field comprises:
- driving a current through a conductive wire so as to generating the magnetic field.
5. The method of claim 4, wherein the magnetic sensor comprises a spin-valve structure.
6. The method of claim 4, wherein the magnetic sensor comprises a tunneling-magneto-resistor structure.
7. A method of detecting a target angular velocity, comprising:
- providing a MEMS gyroscope that comprises a movable proof-mass, a magnetic source, and a magnetic sensor, wherein the proof-mass is capable of moving in response to the target angular velocity under the Coriolis effect, and wherein the magnetic source is capable of generating a magnetic field that varies with the movement of the proof-mass, and wherein the magnetic sensor is capable of detecting the magnetic field from the magnetic source;
- detecting a background magnetic signal using a reference sensor;
- storing the detected background magnetic signal by the reference sensor;
- moving a proof-mass of the MEMS gyroscope in a driving mode using a magnetic driving mechanism;
- generating the magnetic field by the magnetic source;
- detecting a variation of the magnetic field by the magnetic sensor; and
- extracting the angular velocity from the variation of the magnetic field.
8. The method of claim 7, wherein the step of measuring the background magnetic signal comprises:
- raising the temperature of the reference magnetic sensor above a blocking temperature of the reference sensor such that the reference sensor is capable of detecting the background magnetic field signal.
9. The method of claim 8, wherein the reference sensor comprises a free layer for detecting the background magnetic field signal, wherein the free layer is magnetically pinned by an antiferromagnetic layer when the temperature is blow the blocking temperature.
10. The method of claim 8, wherein the step of generating the magnetic field comprises:
- driving a current through a conductive wire so as to generating the magnetic field.
11. The method of claim 8, wherein the magnetic sensor comprises a spin-valve structure.
12. The method of claim 8, wherein the magnetic sensor comprises a tunneling-magneto-resistor structure.
Type: Application
Filed: Jul 5, 2013
Publication Date: Jan 30, 2014
Inventors: BIAO ZHANG (Hinsdale, IL), TAO JU (Beijing)
Application Number: 13/935,558