Sensor

A sensor includes a detecting oscillator supported in such a manner that the detecting oscillator is allowed to oscillate; first and second electrodes; a detecting electrode facing the first and second electrodes; and signal supplying units configured to supply first and second AC signals respectively to the first and second electrodes. Either the first and second electrodes or the detecting electrode is provided on the detecting oscillator. The first and second AC signals respectively supplied to the first and second electrodes by the signal supplying units cause the detecting oscillator to be maintained at a neutral position for detection without being displaced when no physical quantity is input. When the detecting oscillator is displaced, an input physical quantity is detected on the basis of a signal corresponding to charges induced at the detecting electrode by the first and second AC signals supplied respectively to the first and second electrodes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sensor that detects a physical quantity, such as an angular velocity or an acceleration.

2. Description of the Related Art

Oscillation angular velocity sensors that use micro electro mechanical systems (MEMSs) have been proposed. In this type of angular velocity sensor, an oscillator is caused to perform a reference oscillation with a certain amplitude, and a Coriolis force that is generated upon input of an angular velocity is detected in the form of a displacement of oscillation of the oscillator. The oscillator must be designed so that the oscillator can readily oscillate in a direction for the reference oscillation and in a direction for detection. However, according to this scheme, the reference oscillation could cause oscillation in the direction for detection (a type of oscillation noise), and this might degrade the precision of a detection signal. In a scheme that has been proposed in view of this problem, an oscillator for reference oscillation (reference oscillator) and an oscillator for detection (detecting oscillator) are provided separately (this scheme is called the double-frame scheme).

As an example of a double-frame angular velocity sensor, in an angular velocity sensor proposed in U.S. Pat. No. 6,374,672, a donut-shaped reference oscillator supporting a disk-shaped detecting oscillator is caused to perform a reciprocating rotational oscillation, and the magnitude (maximum inclination) of oscillation caused by an angular velocity of the detecting oscillator provided inner to the reference oscillator is detected. According to this configuration, since it becomes easier to separate oscillation of the reference oscillator and oscillation of the detecting oscillator, the problem of degradation in the precision of a detection signal due to oscillation of the detecting oscillator caused by oscillation of the reference oscillator is alleviated.

In the angular velocity sensor described above, an angular velocity is detected on the basis of inclination of the detecting oscillator about a rotation axis for detection. The degree of inclination of the detecting oscillator can be recognized by detecting change in capacitance between a surface of the detecting oscillator and an opposing surface. More specifically, on a surface opposing the detecting oscillator (denoted by 70 in U.S. Pat. No. 6,374,672), detecting electrodes (denoted by 104 and 106 inFIG. 3of U.S. Pat. No. 6,374,672) having semicircular shapes are provided. The degree of inclination of the detecting oscillator can be detected by detecting capacitances between the detecting oscillator and the individual detecting electrodes.

FIGS. 12A to 12Cshow the configuration according to U.S. Pat. No. 6,374,672, in a simplified manner with the reference oscillator omitted.FIG. 12Ais a top view in which the vicinity of a detecting oscillator in a double-frame angular velocity sensor is shown as enlarged.FIGS. 12B and 12Care sectional views taken along line XIIB-XIIB perpendicularly to the sheet. InFIGS. 12A to 12C,401denotes a detecting oscillator,402denotes an upper electrode,403denotes a first lower electrode, and404denotes a second lower electrode. Furthermore,405denotes a left-half upper electrode,406denotes a right-half upper electrode,407denotes a lower supporting substrate,408denotes a rotation axis of the detecting electrode, and409denotes supports for the detecting oscillator401.

InFIG. 12A, the detecting oscillator401and the supports409are indicated by dotted lines, and the first lower electrode403and the second lower electrode404provided on the lower supporting substrate407are indicated by solid lines. The upper electrode402and a reference oscillation generator are not shown inFIG. 12A.

The detecting oscillator401has a disk-like shape, and is supported by the supports409from above and below as shown inFIG. 12A. The detecting oscillator401is designed so that the detecting oscillator401can readily perform a reciprocating rotational oscillation in a direction of an arrow R about the rotation axis408. The detecting oscillator401detects a Coriolis force on the basis of the magnitude of inclination of the detecting oscillator401. On the detecting oscillator401, the upper electrode402is provided. Hereinafter, it is assumed that the upper electrode402is composed of the left-half detecting electrode405and the right-half detecting electrode406on either side of the rotation axis408.

On the lower supporting substrate407facing the upper electrode402, the first lower electrode403and the second lower electrode404are provided. The first lower electrode403and the second lower electrode404are disposed line-symmetrically with respect to a center line (the rotation axis408) of the supports409for the detecting oscillator401.

Now, a case will be considered where the degree of inclination of the detecting oscillator401is detected on the basis of capacitances between the upper electrode402on the detecting oscillator401and the lower electrodes403and404on the lower supporting substrate407.

Next, a capacitance CL between the upper electrode402and the first lower electrode403inFIG. 12Bwill be considered. The capacitance CL can be considered as a combined capacitance of a capacitance C1between the left-half upper electrode405and the first lower electrode403and a capacitance C3between the right-half upper electrode406and the first lower electrode403. The distance between the left-half upper electrode405and the first lower electrode403is shorter than the distance between the right-half upper electrode406and the first lower electrode403. Thus, the capacitance C1is larger than the capacitance C3.

When the detecting oscillator401is inclined about the rotation axis408as shown inFIG. 12C, the distance between the detecting oscillator401and the first lower electrode403increases, and the distance between the detecting oscillator401and the second lower electrode404decreases. Since the capacitance CL is proportional to the electrode area and is inversely proportional to the distance between electrodes, the value of the capacitance C1decreases and the value of the capacitance C3increases. Since the capacitance C1is larger than the capacitance C3, the amount of decrease in the capacitance C1is larger than the amount of increase in the capacitance C3. Thus, the value of the combined capacitance CL decreases.

That is, it is possible to detect inclination of the detecting oscillator401by detecting an increase in the distance between the left-half detecting electrode405and the first lower electrode403on the basis of a decrease in the combined capacitance CL. A capacitance CR between the upper electrode402on the detecting oscillator401and the second lower electrode404on the lower supporting substrate407can be considered similarly as a combined capacitance of capacitances C2and C4.

In this specification, a state where no Coriolis force is exerted on a sensor so that the detecting oscillator401is not inclined, as shown inFIG. 12B, will be referred to as a “neutral position for detection”. The supports409for the detecting oscillator401are designed so as to form springs such that the detecting oscillator401can readily oscillate rotationally in response to even a small Coriolis force. Thus, the detecting oscillator204could be caused to oscillate by electrostatic attractive forces caused by signals applied for measurement of inclination of the detecting oscillator401. If the detecting oscillator401is displaced from the neutral position for detection and is caused to oscillate when no physical quantity to be detected is input as described above, then the stability of zero-point output of a detection signal is degraded and thereby sensitivity is degraded.

SUMMARY OF THE INVENTION

The present invention provides a sensor that can accurately detect a displacement such as inclination of a detecting oscillator with high sensitivity so that a physical quantity such as an angular velocity can be measured precisely.

A sensor according to the present invention includes a detecting oscillator supported in such a manner that the detecting oscillator is allowed to oscillate; first and second electrodes configured to receive application of alternating-current (AC) signals; a detecting electrode facing the first and second electrodes; and a signal supplying unit configured to supply first and second AC signals respectively to the first and second electrodes. Either the first and second electrodes or the detecting electrode is provided on the detecting oscillator. The first and second AC signals, respectively supplied to the first and second electrodes, cause the detecting oscillator to be maintained at a neutral position for detection without being displaced when no physical quantity is input. When the detecting oscillator is displaced, an input physical quantity is detected on the basis of a signal corresponding to charges induced at the detecting electrode by the first and second AC signals supplied respectively to the first and second electrodes.

The state described as “the detecting oscillator is maintained at the neutral position for detection” herein is not limited to a state where the detecting oscillator is maintained exactly at the neutral position for detection without being displaced, and covers a range where strictly the detecting oscillator is displaced from the neutral position for detection but still an expected precision of detection according to the present invention is maintained.

In the sensor according to the present invention configured as described above, when no physical quantity is input from outside, the first and second AC signals applied respectively to the first and second electrodes cause the detecting oscillator to be maintained at the neutral position for detection. When a physical quantity is input from outside, the physical quantity is measured using a displacement of the detecting oscillator from the neutral position for detection caused by the physical quantity. Thus, it is possible to accurately detect a displacement such as inclination of the detecting oscillator with high sensitivity, so that a physical quantity such as an angular velocity can be measured precisely.

DESCRIPTION OF THE EMBODIMENTS

In order to implement a sensor, e.g., an angular velocity sensor, that is capable of detecting a displacement such as a tilt of a detecting oscillator with high sensitivity, according to the present invention, attention is paid to signals applied to electrodes in order to detect capacitances that relate to the position of the detecting oscillator. That is, according to the present invention, a plurality of AC signals are used to detect capacitances.

First Embodiment

FIGS. 1A to 1Fare diagrams showing an angular velocity sensor according to a first embodiment.FIG. 1Ais a perspective view,FIG. 1Bis a sectional view taken perpendicularly to a substrate201along line IB-IB, andFIG. 1Cis a diagram showing layout of a first electrode (lower electrode)210and a second electrode (lower electrode)211on a lower supporting substrate208.

InFIGS. 1A to 1F,202denotes a reference oscillator,203denotes supports for the reference oscillator202,204denotes a detecting oscillator,205denotes supports for the detecting oscillator204,206denotes a reference oscillation generator,207denotes a spacer, and212denotes a detecting electrode (upper electrode). Furthermore,213denotes a driving signal supplying unit that supplies a driving signal to the reference oscillation generator206,214denotes a first signal supplying unit that supplies a first AC signal to the first electrode210, and215denotes a second signal supplying unit that supplies a second AC signal to the second electrode211. The first signal supplying unit214and the second signal supplying unit215constitute a signal supplying unit in this embodiment. Furthermore,216denotes an amount-of-charge measurement unit216that measures a physical quantity, namely, an angular velocity, on the basis of signals relating to charges induced at the detecting electrode212. These units213,214,215, and216are electrically connected individually to relevant parts via electrode pads (connection wires on the substrate201are not shown inFIG. 1A).

InFIG. 1C, only the first electrode210and the second electrode211provided on the lower supporting substrate208are shown by solid lines, and other parts are shown by dotted lines. InFIG. 1C, the detecting electrode212and the reference oscillation generator206are not shown.

In the configuration described above, the detecting oscillator204has a disk-like shape, and is supported by the reference oscillator202via a pair of supports205. On a bottom surface of the detecting oscillator204, the detecting electrode212having a circular shape is provided. The reference oscillator202has a donut shape, and is supported by the substrate201via four supports203provided at regular angular intervals. The substrate201is connected to the lower supporting substrate208via the spacer207. In a region on the lower supporting substrate208facing the detecting electrode212, the first electrode210and the second electrode211are provided.

The supports203for the reference oscillator202are designed so as to form springs such that reciprocating rotational oscillation of the reference oscillator202is most likely to occur in the direction of an arrow A about a rotation axis Z, which serves as a second rotation axis, while oscillation in other directions is inhibited. Thus, the reference oscillator202is caused by the reference oscillation generator206to perform a reciprocating rotational oscillation with the neutral position for detection as the center of oscillation (the origin of reference oscillation). The supports205for the detecting oscillator204, which is supported by the reference oscillator202in such a manner that oscillation is allowed, are designed so as to form springs such that reciprocating rotational oscillation of the detecting oscillator204is most likely to occur in the direction of an arrow C about a rotation axis Y, which serves as a first rotation axis, while oscillation in other directions is inhibited.

The reference oscillator202is caused to oscillate constantly in the direction of the arrow A about the rotation axis Z (this will be referred to as reference oscillation) by the reference oscillation generator206connected to the driving signal supplying unit213. The detecting oscillator204is supported by the reference oscillator202via the supports205so that the detecting oscillator204can perform a reciprocating rotational oscillation in the direction of the arrow A in synchronization with the reference oscillator202. At this time, the detecting oscillator204does not oscillate in the direction of the arrow C. When an angular velocity about the rotation axis X is input, a Coriolis force is exerted on the detecting oscillator204in the direction of the arrow C about the rotation axis Y. The Coriolis force causes the detecting oscillator204to perform a reciprocating rotational oscillation (this will be referred to as detecting oscillation) in the direction of the arrow C. Since the Coriolis force depends on the magnitude of the angular velocity, the magnitude of the angular velocity can be detected by detecting the magnitude of the detecting oscillation (the magnitude of inclination of the detecting oscillator204).

In this embodiment, the inclination of the detecting oscillator204is detected by measuring the capacitance between the first electrode210and the detecting electrode212and the capacitance between the second electrode211and the detecting electrode212. More specifically, a first AC signal301(shown inFIG. 2A) generated by the first signal supplying unit214is applied to the first electrode210, and a second AC signal302(shown inFIG. 2B) generated by the second signal supplying unit215is applied to the second electrode211.

The amount of charges electrostatically induced by the first AC signal301and the second AC signal302at the detecting electrode212is measured by the amount-of-charges measurement unit216. As the distances between the detecting electrode212and the first and second electrodes210and211decrease so that the capacitances increase from initial states (where no angular velocity about the rotation axis X is input), the amount of induced charges increases (as will be described later with reference toFIGS. 4A to 4DandFIGS. 5A to 5D). Conversely, as the distances between the detecting electrode212and the first and second electrodes210and211increase so that the capacitances decrease, the amount of induced charges decreases. The amount of induced charges is converted by the amount-of-charges measurement unit216into a detection signal in the form of a voltage or the like. On the basis of the detection signal, it is possible to accurately determine the magnitude of the inclination of the detecting oscillator204caused by a Coriolis force generated in response to input of an angular velocity, so that the angular velocity can be determined accurately.

The operations and advantages of providing a plurality of electrodes to which AC signals are applied will be further described.

FIGS. 2A and 2Bare graphs showing the first AC signal301and the second AC signal302applied to the first and second electrodes210and211in this embodiment.FIG. 2Cis a graph showing an electrostatic attractive force generated by the first and second AC signals301and302. InFIGS. 2A and 2Bshowing the first AC signal301and the second AC signal302, the horizontal axis represents time and the vertical axis represents the magnitude of the AC signal. InFIG. 2C, the horizontal axis represents time and the vertical axis represents the magnitude of the electrostatic attractive force. The potential in the case where no charges are induced at the detecting electrode212is used as an electrode reference potential Vr. The electrode reference potential Vr is determined according to a potential assigned to the detecting electrode212by the amount-of-charges measurement unit216.

The first AC signal301(shown inFIG. 2A) and the second AC signal302(shown inFIG. 2B) have the same frequency and mutually opposite phases with reference to the electrode reference potential Vr. Regarding electrostatic forces, it is possible to assume herein that only attractive forces are generated and repulsive forces are not generated. Thus, the forces exerted on the detecting oscillator204, having the detecting electrode212, by the supply of the first and second AC signals301and302to the first and second electrodes210and211can both be represented as shown inFIG. 2C. That is, by using the AC signals301and302, it is possible to exert attractive forces of the same magnitude on the detecting oscillator204from the first electrode210and the second electrode211at the same timing.

This is very advantageous to the implementation of an angular velocity sensor with high precision. According to this embodiment, it is possible to exert attractive forces of the same magnitude at the same timing on the detecting oscillator204from the first electrode210and the second electrode211individually, which are located on the left and right sides of the rotation axis of the detecting oscillator204. Thus, when no angular velocity is input, the detecting oscillator204is maintained at the neutral position for detection (the state shown inFIG. 1B, as defined earlier). Accordingly, the risk of the detecting oscillator204being caused to oscillate by the AC signals301and302is reduced considerably.

In order to maintain the detecting oscillator204at the neutral position for detection when no angular velocity is input, it is not necessary to apply AC signals of opposite phases as shown inFIGS. 2A and 2B, and alternatively, signals having the same frequency and having the same phase may be applied. Also in this case, it is possible to exert attractive forces of the same magnitude at the same timing on the detecting oscillator204from the first electrode210and the second electrode211.

For the purpose of comparison, a case will be considered where a signal shown inFIG. 3Ais applied to the first electrode210and a signal shown inFIG. 3Bis applied to the second electrode211. In this case, as shown inFIG. 3C, attractive forces F1and F2from the first electrode210and the second electrode211are exerted alternately on the detecting oscillator204. Thus, if the frequency of these signals applied to the first and second electrodes210and211is the same as the resonant frequency of the detecting oscillator204, such a driving force occurs that causes a reciprocating rotational oscillation of the detecting oscillator204about the rotation axis Y. Even if the frequency of the applied signals is not the same as the resonant frequency of the detecting oscillator204, a similar driving force occurs due to non-linear characteristics of the generated electrostatic attractive forces. The oscillation caused in this manner results in generation of a detection signal even when no angular velocity is input (i.e., the detecting oscillator204is not maintained at the neutral position for detection). This causes degradation in the performance of angular velocity detection.

As described above, according to this embodiment, attractive forces of the same magnitude are exerted simultaneously on the left and right sides of the detecting oscillator204, so that the detecting oscillator204is maintained at the neutral position for detection when no angular velocity is input. As a result, a reciprocating rotational oscillation about the rotation axis Y is not caused even when AC signals are applied. Thus, when no angular velocity is input, detection noises due to the AC signals301and302are not likely to occur. Accordingly, particularly in a case where an angular velocity is to be measured with high precision, it is possible to provide an angular velocity sensor in which the stability of output at a zero point of detection signal is achieved so that performance is improved significantly.

Furthermore, in capacitance-based detection, the magnitude of a detection signal for the same inclination of the detecting oscillator204increases as the electrodes210and211are provided closer to the detecting electrode212. At the same time, however, when the electrodes210and211are provided close to the detecting electrode212, electrostatic attractive forces exerted on the detecting oscillator204increase. That is, although the sensitivity of angular velocity detection improves, detection noises could occur due to oscillation of the detecting oscillator204caused by AC signals. In this embodiment, however, even when the electrodes210and211are provided close to the detecting electrode212, attractive forces are exerted precisely at the same time on the left and right sides of the detecting oscillator204, so that oscillation of the detecting oscillator204due to only the AC signals301and302is not likely to occur. Thus, in this embodiment, even if the first electrode210and the second electrode211are provided close to the detecting electrode212, it is possible to suppress detection noises while achieving improved detection sensitivity, so that an angular velocity can be detected with high precision. It is also advantageous in this respect to provide a plurality of electrodes to which AC signals are applied.

Furthermore, by increasing the magnitudes of the AC signals301and302, the magnitudes of detection signals for the same inclination of the detecting oscillator204can be increased. Also in this case, however, as the magnitudes of the AC signals301and302increase, electrostatic attractive forces exerted on the detecting oscillator204increase. That is, although the sensitivity of angular velocity detection improves, the detecting oscillator204is not maintained at the neutral position for detection, so that the possibility of occurrence of detection noises due to the detecting oscillator204being caused to oscillate by the AC signals301and302increases. However, also in this case, according to this embodiment, attractive forces are exerted precisely at the same time on the left and right sides of the detecting oscillator204, so that the detecting oscillator204is not likely to be caused to oscillate even if the magnitudes of the AC signals301and302are increased. That is, the detecting oscillator204is maintained at the neutral position for detection. Thus, even when the magnitudes of the applied AC signals301and302are increased, it is possible to suppress detection noises while improving detection sensitivity, so that an angular velocity can be detected with high precision. It is also advantageous in this respect to provide a plurality of electrodes.

Next, the operation of the amount-of-charges measurement unit216will be described.

The amount-of-charges measurement unit216detects the amount of change in charges electrostatically induced at the detecting electrode212by the first and second AC signals301and302individually applied to the first electrode210and the second electrode211. The principle of this detection will be described with reference toFIG. 1D,FIGS. 4A to 4D, andFIGS. 5A to 5D, in the context of the amount of change in charges induced at the detecting electrode212considered as being composed of a left-half detecting electrode217and a right-half detecting electrode218.

First, a case where the detecting oscillator204is not inclined will be described.FIG. 4Ashows change in the amount of charges Q1electrostatically induced at the left-half detecting electrode217by the first AC signal301applied to the first electrode210.FIG. 4Bshows change in the amount of charges Q2electrostatically induced at the right-half detecting electrode218by the first AC signal301.FIG. 4Cshows change in the amount of charges Q3electrostatically induced at the left-half detecting electrode217by the second AC signal302.FIG. 4Dshows change in the amount of charges Q4electrostatically induced at the right-half detecting electrode218by the second AC signal302. It is assumed here that the detecting oscillator204is maintained for a sufficiently long time without being displaced in relation to the AC signals301and302.

Since the left-half detecting electrode217is closer to the first electrode210than the right-half detecting electrode218, Q1is larger than Q2. Conversely, since the right-half detecting electrode218is closer to the second electrode211than the left-half detecting electrode217, Q4is larger than Q3. In this embodiment, the left-half detecting electrode217and the right-half detecting electrode218are provided symmetrically with respect to the rotation axis Y, and the first electrode210and the second electrode211are provided symmetrically with respect to the rotation axis Y. Thus, Q1is equal to Q4, and Q2is equal to Q3.

Furthermore, since the first AC signal301and the second AC signal302have opposite phases, the waveform of Q1and the waveform of Q4have mutually opposite phases, and the waveform of Q2and the waveform of Q3have mutually opposite phases. Thus, when the detecting oscillator204is not inclined, Q1and Q4cancel each other, and Q2and Q3cancel each other. Accordingly, the total amount of charges induced at the detecting electrode212becomes zero, so that no detection signal is output as a result.

Next, a case where the detecting oscillator204is inclined with its right side down as shown inFIG. 1Dwill be described.FIGS. 5A,5B,5C, and5D show changes in the amounts of charges Q1, Q2, Q3, and Q4in this case. It is assumed here that the inclination of the detecting oscillator204is maintained for a sufficiently long time without being displaced in relation to the AC signals301and302.

Compared with the case shown inFIGS. 4A to 4D, Q1decreases and Q4increases. Furthermore, since the waveforms of Q1and Q4have mutually opposite phases, a sum of the absolute value of the decrease in Q1and the absolute value of the increase in Q4is detected as a signal. Similarly, compared with the case shown inFIGS. 4A to 4D, Q2increases and Q3decreases. Since the waveforms of Q2and Q3have mutually opposite phases, a sum of the absolute value of the decrease in Q3and the absolute value of the increase in Q2is detected as a signal.

As described above, according to this embodiment, it is possible to directly detect the amount of charges induced at the detecting electrode212facing the electrodes210and211. That is, the amount of change in the capacitance between the electrodes210and211and the detecting electrode212facing the electrodes210and211can be detected directly by the amount-of-charges measurement unit216. Thus, the inclination of the detecting oscillator204can be detected with high sensitivity.

Furthermore, no detection signal is output when the detecting oscillator204is not inclined, and a detection signal proportional to inclination of the detecting oscillator204is output when the detecting oscillator204is inclined. Thus, it is possible to detect inclination in the vicinity of an inclination of 0 degrees of the detecting oscillator204with high sensitivity. This is particularly advantageous in an angular velocity sensor that has to detect small inclinations of the detecting oscillator204.

As described above, with the angular velocity sensor according to this embodiment, the degree of inclination of the detecting oscillator204can be detected with high sensitivity. That is, it is possible to provide an angular velocity sensor with high sensitivity and high precision.

Furthermore, let a reference potential for the first AC signal301be denoted by Vr1, a reference potential for the second AC signal302be denoted by Vr2, and a reference potential for the detecting electrode212be denoted by Vr. By setting different potentials as these potentials Vr1, Vr2, and Vr, it is possible to implement an angular velocity sensor with even higher sensitivity and precision. It is assumed here that the frequency of applied AC signals (carrier signals) is sufficiently higher than the resonant frequency of the detecting oscillator204.FIGS. 13A and 13Bshow the first and second AC signals301and302with reference to the reference potentials Vr1and Vr2, respectively.

When an angular velocity is input to the sensor, the detecting oscillator204performs a reciprocating rotational oscillation with a certain maximum inclination at a frequency of reference oscillation. When this oscillation occurs, the oscillation can be canceled out by adjusting the relationship among the reference potentials Vr1, Vr2, and Vr. The magnitude of an electrostatic attractive force exerted on the detecting oscillator204can be calculated from the relationship among the reference potentials Vr1, Vr2, and Vr at this time. Furthermore, the magnitude of a Coriolis force that has occurred can be determined from the magnitude of the electrostatic attractive force.

According to this method, an oscillation detector suffices to simply detect whether oscillation has occurred or not, and the electrostatic attractive force needed for cancelling out oscillation can be calculated from differences between reference potentials. Thus, the sensitivity and precision of detection are improved. Particularly, according to this embodiment, it is possible to generate an electrostatic attractive force for cancelling out oscillation without adding any component. Thus, it is possible to provide an angular velocity sensor with high sensitivity and high precision by a simple configuration.

Each of the reference potentials Vr1and Vr2is a certain DC component with an AC signal superposed thereon, and the reference potential Vr for the detecting electrode can be composed of only a DC component.FIGS. 13C,13D, and13E show the reference potentials Vr1, Vr2, and Vr, respectively. As shown inFIGS. 13C to 13E, the reference potentials Vr1, Vr2, and Vr have the same DC component. The AC components of the reference potentials Vr1and Vr2have a frequency corresponding to the frequency of reference oscillation and have mutually opposite phases. Thus, it is possible to generate an electrostatic attractive force according to a potential difference, needed to cancel oscillation of the detecting oscillator synchronized with reference oscillation.

Although the detecting electrode212is composed of a single part in the embodiment described above, the present invention is not limited to the embodiment described above. For example, the detecting electrode212may be divided into two parts individually corresponding to the first electrode210and the second electrode211. That is, two detecting electrodes217and218may be provided as shown in section inFIG. 1E. In this case, it is necessary to convert charges induced at the individual detecting electrodes217and218into voltage signals or the like and to add together the voltage signals or the like. With this configuration, it is possible to reduce the area of each detecting electrode, so that stray capacitance or the like can be reduced. This serves to reduce degradation of signals in the amount-of-charges measurement unit216.

Furthermore, although the electrodes210and211have semicircular shapes and the detecting electrode212has a circular shape in the embodiment described above, the present invention is not limited to the embodiment. Electrodes having various shapes, such as rectangular shapes, triangular shapes, or polygonal shapes, may be used. For example, the electrodes210and211may be shaped along the external shape of the detecting oscillator204, as shown in a top view inFIG. 1F. With this configuration, electrodes are disposed in regions associated with portions of the detecting oscillator204where displacement occurs most (i.e., in the vicinity of the periphery of the detecting oscillator204). Thus, it is possible to detect inclination of the detecting oscillator204effectively, and signal degradation due to stray capacitance or the like can be alleviated. Furthermore, although not shown, the detecting electrode212may be configured to have a donut shape. As described above, electrodes and detecting electrodes may be formed in regions on the detecting oscillator separated by a certain distance or longer from the first rotation axis and in regions facing the regions on the detecting oscillator.

Furthermore, although the detecting electrode212is provided on the detecting oscillator204and the electrodes210and211are provided in regions facing the detecting electrode212in the embodiment described above, the present invention is not limited to the embodiment. Alternatively, the electrodes210and211may be provided on the detecting oscillator204and the detecting electrode212may be provided in a region facing the electrodes210and211. In this case, by disposing the amount-of-charges measurement unit216on the lower supporting substrate208, the amount-of-charges measurement unit216can be provided close to the detecting electrode212. This serves to alleviate signal degradation caused by stray capacitance of wiring or the like.

Furthermore, although the reference oscillator202and the detecting oscillator204are provided separately in the embodiment described above, the present invention is not limited to the embodiment. That is, the reference oscillator202and the detecting oscillator204may be integrated together. In this case, the integrated oscillator is supported by springs of the same supports so that the oscillator can oscillate in two directions, namely, in a direction of reference oscillation and in a direction of detection oscillation. Thus, oscillation noise in the direction of detection oscillation, caused by reference oscillation, tends to occur. This oscillation noise translates to an error in detection of an angular velocity, thereby degrading detection precision of the sensor. More specifically, an angular velocity with a certain value is detected incorrectly even when the angular velocity is actually zero. This degrades the stability of sensor output.

However, with the scheme according to this embodiment, when the detecting oscillator is oscillating even though no angular velocity is input to the sensor, it is possible to cancel out the oscillation to achieve correction. Then, oscillation caused by an angular velocity as described earlier is canceled out on the basis of a difference between reference potential. Thus, an accurate angular velocity can be detected. Accordingly, it is possible to provide an angular velocity sensor having a simple configuration and in which performance degradation due to the effect of reference oscillation is alleviated.

At this time, an oscillation that occurs when no angular velocity is input may be corrected by measuring relationships between temperatures and values for correction at the time of shipping and using a sensor having a table representing the relationship together with a temperature sensor, or correction may be performed after shipping at an arbitrary time so that oscillation is suppressed.

Furthermore, a physical quantity sensor according to a seventh embodiment shown inFIG. 11and described later may be used. More specifically, it is possible to implement a sensor that detects a physical quantity exerted on a detecting electrode, in which outer portions of two reference oscillation generators having comb-shaped electrodes facing each other via a gap are used as first and second electrodes, and in which an entire oscillator including an inner portion is used as the detecting electrode.

These modifications can also be applied to embodiments described below as long as such modifications are structurally possible. For example, the modifications of using two detecting electrodes may be applied to embodiments described below other than an embodiment shown inFIGS. 8B and 8C.

In sum, in a sensor according to the present invention, first and second AC signals are supplied individually to first and second electrodes so that a detecting oscillator is maintained at the neutral position for detection, where the detecting oscillator is not displaced, and a physical quantity is detected on the basis of signals of charges induced at the detecting electrode when the detecting oscillator is displaced. Thus, a physical quantity sensor including a detecting oscillator, a plurality of electrodes, and a detecting electrode facing the plurality of electrodes so that a physical quantity can be detected according to the principle described above can be embodied as a sensor according to the present invention.

Second Embodiment

A second embodiment of the present invention will now be described. In an angular velocity sensor according to the second embodiment, shown inFIGS. 6A and 6B, a detecting electrode and electrodes to which AC signals are applied are all provided on the detecting oscillator204and the reference oscillators202and209. The configuration of the angular velocity sensor is otherwise the same as that in the first embodiment.FIG. 6Ais a perspective view, andFIG. 6Bis a sectional view taken perpendicularly to the substrate201along line VIB-VIB.

In this embodiment, the reference oscillator202is connected to the reference oscillator209via the spacer207such that the reference oscillator202and the reference oscillator209are integrated together. The first electrode210and the second electrode211are provided on the reference oscillator209facing the detecting electrode212. The configuration is otherwise the same as that in the first embodiment.

Now, the operation of this embodiment will be described. The spacer207and the reference oscillator209integrated with the reference oscillator202are caused to oscillate constantly in the direction of the arrow A about the rotation axis Z (reference oscillation) by the reference oscillator202together with the reference oscillator209. Furthermore, since the detecting oscillator204is supported by the reference oscillator202via the supports205, the detecting oscillator204performs a reciprocating rotational oscillation in the direction of the arrow A in synchronization with the reference oscillator202. The first electrode210and the second electrode211are provided on the reference oscillator209, and the detecting electrode212are provided on the detecting oscillator204. Thus, when reference oscillation occurs ideally, the positional relationships between the first electrode210and the detecting electrode212and between the second electrode211and the detecting electrode212are maintained perfectly.

When an angular velocity about the rotation axis X is input, a Coriolis force is exerted on the detecting oscillator204in the direction of the arrow C about the rotation axis Y. The principle of detection of the magnitude of an angular velocity based on the Coriolis force has been described earlier in relation to the first embodiment.

In the angular velocity sensor according to this embodiment, the detecting oscillator204performs the same reference oscillation as the reference oscillators202and209. With this configuration, even if some variation occurs in the oscillation of the reference oscillators202and209, mechanical contact between the detecting oscillator204, having the detecting electrode212thereon, and a member, having the first and second electrodes210and211thereon (the reference oscillator209in this embodiment), is substantially prevented. Thus, the detecting electrode212can be disposed close to the electrodes210and211. Accordingly, when the inclination of the detecting oscillator204is detected on the basis of capacitance, the inclination can be detected with high sensitivity.

Also in this embodiment, with AC signals used to detect capacitance, oscillation of the detecting oscillator204is inhibited. Thus, it is possible to precisely detect inclination with high stability of output. Particularly, when the detecting oscillator204and the reference oscillator209are provided close to each other in a configuration where the detecting oscillator204performs the same reference oscillation as the reference oscillators202and209, the angular velocity sensor becomes more susceptible to the effect of electrostatic attractive forces generated by AC signals. In this embodiment, however, with the operation of AC signals, the detecting oscillator204is maintained at the neutral position for detection. This serves to overcome the problem that the stability of output is degraded even though sensitivity is improved. That is, with the angular velocity sensor according to this embodiment, it is possible to detect an angular velocity with high sensitivity and high stability of output.

Third Embodiment

Next, a third embodiment of the present invention will be described. An angular velocity sensor according to the third embodiment differs from that according to the first embodiment in that the detecting electrode212is formed within the detecting oscillator204. The angular velocity sensor according to the third embodiment is configured otherwise the same as the angular velocity sensor according to the first embodiment.

FIG. 7shows the angular velocity sensor according to this embodiment.FIG. 7is a sectional view taken along a line perpendicular to the substrate201in this embodiment. InFIG. 7,219denotes an insulating film, and other reference numerals denote components corresponding to those in the first embodiment.

The detecting oscillator204has the insulating film219buried therein, and is insulated from other parts. A region of the detecting oscillator204surrounded by the insulating film219is used as the detecting electrode212. The detecting electrode212formed within the detecting oscillator204has a low resistance, and it is used as being equivalent to an electrode. From the detecting electrode212, charges induced at the detecting electrode212as described earlier can be extracted using a wire (not shown) on a top surface as shown inFIG. 7.

According to this configuration, it becomes readily possible to extract induced charges from the detecting electrode212on the front side of the sensor. This serves to increase design flexibility of the detecting oscillator204. Furthermore, since the sectional area of the detecting electrode212in the detecting oscillator204being regarded as a wire is very large, it is possible to alleviate signal degradation when the wire is extended from the detecting electrode212to the surface of the detecting oscillator204. When the feature of this embodiment is not employed, when signals are extracted through a wire from the surface of the detecting oscillator204where the detecting electrode212is provided, the signal could be degraded by a resistance due to the narrow width of the wire or stray capacitance due to the wire length.

Furthermore, according to this embodiment, without restriction regarding a wire, the shape of the detecting electrode212can be designed optimally for detection of inclination of the detecting oscillator204. Furthermore, it is readily possible to achieve insulation between a driving signal needed for the reference oscillation generator206and the detecting electrode212having very small induced charges. Thus, it is possible to alleviate degradation of a detection signal caused by a driving signal.

The structure in which the detecting electrode212is buried in the detecting oscillator204can be readily formed by forming a groove for burying the insulating film219in the detecting oscillator204and filling the groove with the insulating film219. Alternatively, a portion of the detecting oscillator204corresponding to the detecting electrode212may be removed, and the insulating film219may be formed in the periphery of the removed portion and then the removed portion may be filled with a conductive material to form the detecting electrode212. In this case, by choosing the material suitably, it is possible to increase the mass of the detecting oscillator204, which affects the sensitivity of angular velocity output. Accordingly, it is possible to extract a signal while further alleviating degradation of a detection signal in the detecting electrode212.

As described above, it is possible to form an electrode or a detecting electrode of a portion of a detecting oscillator insulated by an insulator from other portions. (An electrode can be formed in this manner in the case of a modification where the electrode is provided on a detecting oscillator). According to this embodiment, it is possible to provide an angular velocity sensor in which degradation of a detection signal attributable to a wire through which the detection signal is extracted from the detecting electrode212is alleviated.

Fourth Embodiment

A fourth embodiment shown inFIGS. 8A to 8Cdiffers from the first embodiment in that an electrostatic shield220is provided between the first electrode210and the second electrode211. The fourth embodiment is otherwise the same as the first embodiment.

FIG. 8Ashows a first type of angular velocity sensor according to this embodiment.FIG. 8Ais a sectional view taken perpendicularly to the substrate201. As shown inFIG. 8A, the electrostatic shield220is provided between the first electrode210and the second electrode211on the lower supporting substrate208so as to extend substantially along the direction of the rotation axis of the detecting oscillator204. The electrostatic shield220is formed with an appropriate height and along a length as long as or longer than the detecting electrode212and the electrodes210and211in the direction of the rotation axis. Furthermore, the electrostatic shield220is maintained at the same potential as the electrode reference potential Vr applied to the detecting electrode212. The electrostatic shield220may be formed of any metallic material having a conductivity suitable for an electrostatic shield, such as aluminum, stainless steel, or copper.

With the electrostatic shield220, the values of the capacitances C2and C3become very small. Thus, the inclination of the detecting oscillator204can be detected using the detecting electrode212purely on the basis of changes in the values of the capacitances C1and C4.

FIGS. 8B and 8Cshow a second type of angular velocity sensor according to this embodiment.FIG. 8Bis a sectional view, andFIG. 8Cis a top view. In the second type of angular velocity sensor, the detecting electrode212is replaced with a first detecting electrode217and a second detecting electrode218, and the detecting oscillator204has a through hole230between the detecting electrode217and the detecting electrode218. The through hole230extends with a suitable length along the direction of the rotation axis. The electrostatic shield220extends along a suitable length with a height larger than the height of the spacer207so that its upper portion extends into the through hole230. The width of the electrostatic shield220is chosen to be sufficiently smaller than the width of the through hole230so as not to interfere with reciprocating rotational oscillation of the detecting oscillator204. In this embodiment, the electrostatic shield220is extended inside the through hole of the detecting oscillator204, so that the values of the capacitances C2and C3can be reduced even further.

With the angular velocity sensor according to this embodiment, the inclination of the detecting oscillator204can be detected directly in the form of changes in the values of the capacitances C1and C4. Thus, the inclination of the detecting oscillator204can be detected even more precisely.

Fifth Embodiment

Next, a fifth embodiment will be described with reference toFIGS. 9A and 9B. The fifth embodiment differs from the first embodiment in that third and fourth electrodes are provided. The fifth embodiment is otherwise the same as the first embodiment.

FIGS. 9A and 9Bare sectional views of an angular velocity sensor according to this embodiment. InFIGS. 9A and 9B,221denotes an upper supporting substrate,222denotes a third electrode,223denotes a fourth electrode, and224denotes a second detecting electrode. In this embodiment, in addition to the components of the first embodiment, the upper supporting substrate221, the third electrode222, the fourth electrode223, and the second detecting electrode224are additionally provided as components. The first electrode210and the third electrode222, and the second electrode211and the fourth electrode223are provided so as to be individually plane-symmetrical with respect to a center plane extending in an intra-plane direction of the detecting oscillator204. The detecting electrode212is provided on a lower surface of the detecting oscillator204, and the second detecting electrode224is provided on an upper surface of the detecting oscillator204. On the upper supporting substrate221, the third electrode222and the fourth electrode223are provided. The upper supporting substrate221is connected to the substrate201via the spacer207.

In this embodiment, from the signal supplying unit described earlier, the first AC signal301is applied to the first electrode210and the fourth electrode223, and the second AC signal302is applied to the second electrode211and the third electrode222.

According to this embodiment, the detecting oscillator204receives equal attractive forces from above and below at the same timing. Thus, compared with the case where attractive forces are applied from only one direction, oscillation of the detecting oscillator204caused by the AC signals301and302is further inhibited. Thus, the detecting oscillator204is maintained at the neutral position for detection when no angular velocity is input. As a result, occurrence of detection noises can be suppressed further. This serves to improve precision of detection particularly when an angular velocity is to be detected precisely.

Furthermore, when the detecting oscillator204is inclined as shown inFIG. 9B, the first electrode210becomes closer to the detecting electrode212and the fourth electrode223becomes closer to the second detecting electrode224. On the other hand, the second electrode211becomes remoter from the detecting electrode212and the third electrode222becomes remoter from the second detecting electrode224. At this time, the same AC signal301is being applied to the first electrode210and the fourth electrode223. Thus, waveforms representing change in the amount of charges induced at the detecting electrode212by the first electrode210and change in the amount of charges induced at the second detecting electrode224by the fourth electrode223have the same phase, and have amplitudes larger than amplitudes in the case where the detecting oscillator204is not inclined.

On the other hand, the second electrode211and the third electrode222receives the same second AC signal302. Thus, waveforms representing change in the amount of charges induced at the detecting electrode212by the second electrode211and change in the amount of charges induced at the second detecting electrode224by the third electrode222have the same phase and have amplitudes smaller than the amplitudes in the case where the detecting oscillator204is not inclined.

Thus, when the detecting oscillator204is displaced, charges are induced at the detecting electrode212by the first and second AC signals301and302individually supplied to the first and second electrodes210and211, and charges are induced at the second detecting electrode224by the first and second AC signals301and302individually supplied to the fourth electrode223and the third electrode222. The sensor according to this embodiment detects an acceleration as a physical quantity on the basis of signals corresponding to these induced charges.

The charges induced at the detecting electrode212and the second detecting electrode224are added together, and the sum is converted by the amount-of-charges measurement unit216into a detection signal in the form of a voltage or the like. Accordingly, sensitivity is substantially doubled compared with the first embodiment.

With the angular velocity sensor according to this embodiment, it is possible to detect an angular velocity with improved sensitivity and output stability.

Although the embodiments described above relate to angular velocity sensors having a reference oscillator and in which a detecting oscillator performs a reciprocating rotational oscillation, the present invention can be applied to a simple physical quantity sensor, such as an angular velocity sensor, including only a detecting oscillator, or to a physical quantity sensor, such as an angular velocity sensor or an acceleration sensor, in which a detecting oscillator performs a reciprocating translational oscillation.

The features of this embodiment are also applicable to a configuration in which the electrodes210,211,222, and223are integrated with the reference oscillator202, as shown inFIG. 9C.

Sixth Embodiment

Next, an angular velocity sensor according to a sixth embodiment will be described with reference toFIGS. 10A and 10B. The sixth embodiment differs from the first embodiment in that no reference oscillator is provided and only a detecting oscillator is provided. The sixth embodiment is otherwise the same as the first embodiment.

FIGS. 10A and 10Bshow the angular velocity sensor according to this embodiment.FIG. 10Ais a perspective view, andFIG. 10Bis a sectional view taken along line XB-XB perpendicularly to a substrate300. InFIGS. 10A and 10B,300denotes a substrate,304denotes a detecting oscillator,305denotes supports for the detecting oscillator304,307denotes a spacer,308denotes a lower supporting substrate,310denotes a first electrode (lower electrode),311denotes a second electrode (lower electrode), and312denotes a detecting electrode (upper electrode).

The description regarding the first and second AC signals301and302given with reference toFIGS. 2A to 2C, the description regarding charges induced at the detecting oscillator304given with reference toFIGS. 4A to 4DandFIGS. 5A to 5D, and the principle of detection of inclination of the detecting oscillator304, described in the context of the first embodiment, also apply in this embodiment. In this embodiment, the magnitude of a physical quantity such as an angular velocity about an axis of rotational oscillation of the detecting oscillator304is detected by detecting the magnitude of inclination of the detecting oscillator304caused by a force applied about the axis due to the physical quantity.

According to this embodiment, it is possible to implement a physical quantity sensor with high precision that can measure the inclination of the detecting oscillator304with high sensitivity.

Seventh Embodiment

Next, a physical quantity sensor according to a seventh embodiment, such as an acceleration sensor, will be described with reference toFIG. 11. In this embodiment, a reference oscillator is not provided, and only a detecting oscillator that is capable of performing a reciprocating translational oscillation is provided.

FIG. 11is a perspective view of the physical quantity sensor according to this embodiment. InFIG. 11,351denotes a substrate,354denotes a detecting oscillator that is capable of performing a reciprocating translational oscillation in the direction A, which also functions as a detecting electrode,355denotes supports for the detecting oscillator354,360denotes a first comb-shaped electrode,361denotes a second comb-shaped electrode,364denotes an insulator for forming an electrode in the substrate351, and370and371denote comb-shaped electrode portions of the detecting electrode (detecting oscillator)354facing the comb-shaped electrodes360and361via gaps.

Also in this embodiment, the description regarding the first and second AC signals301and302given with reference toFIGS. 2A to 2C, the description regarding charges induced at the detecting oscillator354given with reference toFIGS. 4A to 4DandFIGS. 5A to 5D, and the principle of detection of inclination of the detecting oscillator354, described in the context of the first embodiment, also apply in this embodiment. Compared with the sixth embodiment, the detecting electrode and electrodes in this embodiment have different forms and layout, but the principle of operation is the same. According to this embodiment, the magnitude of a physical quantity such as an acceleration in the direction of translational oscillation of the detecting oscillator354is detected by detecting the magnitude of displacement of the detecting oscillator354caused by a force applied to the detecting oscillator354due to the physical quantity.

According to this embodiment, it is possible to implement a physical quantity sensor with high precision that can measure a translational displacement of the detecting oscillator354with high sensitivity.

This application claims the benefit of Japanese Application No. 2007-119641 filed Apr. 27, 2007, which is hereby incorporated by reference herein in its entirety.