Displacement measurement apparatus for microstructure and displcement measurement method thereof

A displacement measurement apparatus for a microstructure according to the present invention measures a displacement of the microstructure having a fixed portion electrode including a first electrode and a second electrode and a movable portion electrode located oppositely to the fixed portion electrode. A bias generating circuit applies a bias signal to between the first electrode and the movable portion electrode so that influence of a noise signal on a detection signal picked up from between the second electrode and the movable portion electrode may be reduced. A C/V converting circuit converts a capacitance change that is picked up from between the second electrode and the movable portion electrode into a voltage. A detecting circuit detects a displacement of the movable portion electrode based on the voltage.

TECHNICAL FIELD

The present invention relates to a displacement measurement apparatus for a microstructure, such as an acceleration sensor and an angular velocity sensor, and a displacement measurement method thereof.

BACKGROUND OF THE INVENTION

In recent years, multiaxis acceleration sensors and angular velocity sensors using MEMS (Micro Electro Mechanical System), for example, as microstructures are widely used in various fields such as airbags for cars. Various tests are performed to such microstructures to measure a sensor output etc.

A test method for a MEMS sensor is described in United States Patent Application Publication No. US 2007/0080695. In United States Patent Application Publication No. US 2007/0080695, an input signal is provided from an input signal generator for a fixed electrode that constitutes one electrode of capacitors of the MEMS sensor. An output signal outputted from a movable electrode that constitutes the other electrode is provided for a detection system. The MEMS sensor is vibrated by a vibration exciter. The detection system measures a resonance frequency, a constant of spring and a damping constant, etc.

In the test method described in United States Patent Application Publication No. US 2007/0080695, an external displacement source causes a test system to be complicated and high in cost. Especially, in the case of multiaxis acceleration sensors and multiaxis angular velocity sensors, necessity of displacing the sensors in respective detection axis directions causes a structure of the external displacement source to be more complicated. Further, the external displacement source displaces a movable portion indirectly via a supporting member of the microstructure and a supporting portion of the movable portion of the microstructure. Consequently, an impact time, intensity and phase applied to the movable portion cannot be controlled precisely. Therefore, measurement accuracy is not high.

Characteristics of the microstructure needs to be measured in a state that the microstructure is formed on a wafer. Although a measurement method for one MEMS sensor is described in United States Patent Application Publication No. US 2007/0080695, a measurement method for a MEMS sensor formed on a wafer is not described in United States Patent Application Publication No. US 2007/0080695. If the external displacement source, such as a vibration exciter etc. described in United States Patent Application Publication No. US 2007/0080695, displaces the wafer, the entire wafer is displaced from the outside. Then a probe contacting a surface of a pad vibrates. Consequently, there is a problem that a contact resistance varies during a measurement or an electric contact can not be achieved.

On the other hand, in a method that a movable electrode is electrostatically driven by application of bias between the movable electrode and a fixed electrode opposite to the movable electrode without using the external displacement source, afflux of the applied bias signal to a detection circuit as noise causes the measurement to be inaccurate.

A main object of the present invention is to provide a displacement measurement apparatus for a microstructure and a displacement measurement method thereof where no external displacement source is necessary and characteristics of a microstructure can be measured accurately.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, a displacement measurement apparatus for a microstructure having a fixed electrode including a first electrode and a second electrode and a movable electrode opposed to the fixed electrode includes:

a bias generator that applies a bias signal to the first electrode and the movable electrode; and

a detector that detects a displacement of the movable electrode based on a first detection signal obtained from the second electrode and the movable electrode.

According to the first aspect of the present invention, the bias signal is applied to the first electrode and the movable electrode, and the first detection signal is picked up from the second electrode and the movable electrode. Namely, an electrode that the bias signal is applied to and an electrode that the detection signal is picked up from are separated. For this reason, the bias signal commingling into the second electrode can be reduced. Therefore, it is possible to measure characteristics of a microstructure accurately without using external displacement source.

In accordance with a second aspect of the invention, a displacement measurement method for a microstructure having a fixed electrode including a first electrode and a second electrode and a movable electrode opposed to the fixed electrode includes the steps of:

applying a bias signal to the first electrode and the movable electrode;

extracting a first detection signal from the second electrode and the movable electrode; and

detecting a displacement of the movable electrode based on the first detection signal.

According to the second aspect of the present invention, the bias signal is applied to the first electrode and the movable electrode, and the first detection signal is picked up from the second electrode and the movable electrode. Namely, an electrode that the bias signal is applied to and an electrode that the detection signal is picked up from are separated. For this reason, the bias signal commingling into the second electrode can be reduced. Therefore, it is possible to measure characteristics of a microstructure accurately without using external displacement source.

In accordance with a third aspect of the invention, a displacement measurement method for a microstructure having a fixed electrode and a movable electrode opposed to the fixed electrode, the method comprising the steps of applying a bias signal to the fixed electrode and the movable electrode; and

picking up a detection signal from the fixed electrode and the movable electrode so as to detect a displacement of the movable electrode;

wherein the bias signal is not applied while picking up the detection signal.

According to the third aspect of the present invention, in a case the microstructure as a measuring object has only one fixed electrode, it is possible to measure characteristics of the microstructure accurately without using external displacement source.

DETAILED DESCRIPTION OF INVENTION

FIG. 1is a block diagram showing a displacement measurement apparatus for a microstructure of preferable embodiment of the present invention. InFIG. 1, a microstructure1, for example, is an acceleration sensor that detects an acceleration when velocity is applied from outside. The microstructure1includes a fixed portion electrode4including a first electrode2and a second electrode3, and a movable portion electrode5located oppositely to the fixed portion electrode4. In the microstructure1, the movable portion electrode5and the fixed portion electrode4are horizontally located. The movable portion electrode5is displaced by a bias signal applied to between the first electrode2of the fixed portion electrode4and the movable portion electrode5. A displacement signal is picked up as a detection signal from between the second electrode3of the fixed portion electrode4and the movable portion electrode5. Such microstructures1are formed in large numbers on a wafer that is not shown in the figures.

Incidentally, the microstructure1shown inFIG. 1is one example of an acceleration sensor where the direction to which the movable portion electrode5is displaced by the bias signal and the direction to which the movable portion electrode5is displaced by applying an acceleration are identical.

When the bias signal is applied to between the first electrode2and the movable portion electrode5from a bias generating circuit20that operates as a bias signal applying means, the movable portion electrode5displaces. A capacitance change according to the displacement is picked up from between the second electrode3of the fixed portion electrode4and the movable portion electrode5, and then the detection signal is provided to a C/V converting circuit30. The C/V converting circuit30converts the capacitance change into a voltage change, then outputs the voltage change to a detecting circuit40. The detection circuit40outputs a measurement signal according to the voltage change. The C/V converting circuit30and the detection circuit40operate as a detecting means, a synchronous detecting means and a first and second signal extracting means.

FIG. 2AandFIG. 2Bshow a structure of a microstructure shown inFIG. 1.FIG. 2Ais an illustrated plan view, andFIG. 2Bis a cross-sectional view taken along the line IIB-IIB ofFIG. 2A. An oxidized insulating film11is formed on a substrate10shown inFIG. 2B. The microstructure1is formed on the oxidized insulating film11.

Specifically, the movable portion electrode5shown inFIG. 1includes a weight portion51of the movable portion electrode, a plurality of pectinate electrodes52of the movable portion, a plurality of pectinate electrodes53of the movable portion, movable springs54and55, and anchor portions56and57inFIG. 2AandFIG. 2B. The weight portion51of the movable portion electrode connects to the pectinate electrodes. The plurality of pectinate electrodes52of the movable portion extend in a pectinate form in one direction that is orthogonal to a longitudinal direction of the weight portion51of the movable portion electrode. The plurality of pectinate electrodes53of the movable portion extend in another direction. The movable springs54and55support both ends of the weight portion51of the movable portion electrode. The anchor portions56and57fix the movable springs54and55. Although the anchor portions56and57are fixed on the oxidized insulating film11, the movable springs54and55, the weight portion51of the movable portion electrode and the plurality of pectinate electrodes52and53of the movable portion are not fixed on the oxidized insulating film11. Therefore, the movable springs54and55, the weight portion51of the movable portion electrode and the plurality of pectinate electrodes52and53of the movable portion resonate when velocity is increased.

The first electrode2and the second electrode3of the fixed portion electrode4are respectively located separately, and are formed on the oxidized insulating layer11so that the movable portion electrode5is located between the fixed portion electrodes. The first electrode2includes a pectinate portion21of the fixed portion that is located between the plurality of pectinate electrodes52of the movable portion extending from one side of the weight portion51of the movable portion electrode of the movable portion electrode5. The second electrode3includes a pectinate portion31of the fixed portion that is located between the plurality of pectinate electrodes53of the movable portion extending from the other side of the weight portion51of the movable portion electrode of the movable portion electrode5.

Intervals between the pectinate portions21and the pectinate electrodes52of the movable portion are arranged to be wide in an upper side and narrow in a lower side. To the contrary, intervals between the pectinate portions31and the pectinate electrodes53of the movable portion are arranged to be narrow in an upper side and wide in a lower side. Capacitance value between two electrodes is greater when distance between the two electrodes is narrower. In case of the same distance change, the capacitance value changes greater when the initial distance between the two electrodes is narrower. Therefore, the capacitance value change between the pectinate portions21and the pectinate electrodes52is dominantly effected by the distance change between the two electrodes in the lower side. To the contrary, the capacitance value change between the pectinate portions31and the pectinate electrodes53is dominantly effected by the distance change between the two electrodes in the upper side.

When acceleration is applied to the longitudinal direction of the weight portion51of the movable portion electrode, and therefore the weight portion51of the movable portion electrode and the pectinate electrodes52and53of the movable portion are displaced for the paper-based upper direction, the capacitance value between the pectinate portions21and the pectinate electrodes52of the movable portion increases, the capacitance value between the pectinate portions31and the pectinate electrodes53of the movable portion decreases, and vice versa. Monitoring a difference of the capacitance values of the both sides makes it possible to monitor the displacement of the movable portion due to inertial force, namely an indicator of the acceleration. This is the operation of the microstructure1as an acceleration sensor.

A bias applying pad22is formed on one end of the first electrode2. A detecting electrode32is formed on one end of the second electrode3. A movable portion electrode pad58is formed on an anchor portion57of the movable portion electrode5. A probe of a probe card that is not shown in figures contacts these pads22,32and58, and then applies the bias signal or takes out the detection signal.

A bias output outputted from the bias generating circuit20shown inFIG. 1is inputted to the bias applying pad22and the movable portion electrode pad58. Then bias is applied to the pectinate portions21and the pectinate electrodes52of the movable portion. A signal input terminal of the C/V converting circuit is connected to the detecting electrode32and the movable portion electrode pad58. When the bias signal is applied to between the first electrode2and the movable portion electrode5, the movable portion electrode5displaces, capacitance between the second electrode3and the movable portion electrode5changes, and the detection signal according to the displacement of the movable portion electrode arises.

FIG. 3AandFIG. 3Bshow a structure of a pseudo-microstructure1athat is used when a noise element is detected.FIG. 3Ais an illustrated plan view, andFIG. 3Bis a cross-sectional view taken along the line IIIB-IIIB ofFIG. 3A. The pseudo-microstructure1ais provided separately from the microstructure1shown inFIG. 2AandFIG. 2B. The pseudo-microstructure1ahas the same structure and is located in the same positional relationship. The only difference is that a pseudo-weight portion51aand pseudo-pectinate electrodes52aand53aof movable portion are fixedly formed on the oxidized insulating film11. In the pseudo-weight portion51a, a pseudo-movable portion electrode5adoes not displace even though the bias signal is applied to between the first electrode2and the pseudo-movable portion electrode5a.Because a leakage element of the bias signal arises at the second electrode3via the pseudo-movable portion electrode5a, the leak element of the bias signal can be picked up from the second electrode3as a noise element.

FIG. 4AandFIG. 4Bare waveform charts showing a bias voltage of an alternating current signal and a capacitance change between the second electrode3and the movable portion electrode5. The bias voltage of an alternating current signal is applied to between the first electrode2and the movable portion electrode5. The capacitance change between the second electrode3and the movable portion electrode5is included in a detection signal taken out from between the second electrode3and the movable portion electrode5.

Next, a description will be given of the operation of the measurement apparatus for the microstructure in one embodiment of the present invention. The bias generating circuit20outputs an alternating bias signal “a” in which electric voltage temporally changes as shown inFIG. 4A. The bias generating circuit20applies the alternating bias signal “a” to between the first electrode2of the fixed portion electrode4and the movable portion electrode5. Then, The bias generating circuit20electrostatically drives the movable portion electrode5forcefully by electrostatic attractive force with desired displacement. At this time, the capacitance between the pectinate portion31and the pectinate electrodes53of the movable portion that are opposed with each other changes. The C/V converting circuit30converts a capacitance change “b” of a capacitance shown inFIG. 4Binto a voltage change. The detecting circuit40detects a displacement amount based on the voltage change.

Here, as shown inFIG. 4AandFIG. 4B, the capacitance change “b” is picked up while the alternating bias signal “a” is applied. In other words, the detecting circuit40simultaneously detects the displacement amount of the movable portion electrode5while the bias generating circuit20applies the alternating bias signal “a”.

Incidentally, the alternating current may be a signal in which electric voltage temporally changes, such as a sign-wave signal, a square wave signal and a triangular-wave signal. In this case, driving the movable portion electrode5at a resonance frequency of an expansion and contraction movement of the movable springs54and55of the movable portion electrode5makes it possible to obtain the displacement of the movable portion more efficiently.

As described above, it is possible to apply the bias signal to between the first electrode2and the movable portion electrode5, and to pick up the capacitance change of the movable portion electrode5from between the second electrode3and the movable portion electrode5. Therefore, separating an electrode that the bias signal is applied to and an electrode that the detection signal is picked up from makes it possible to reduce the bias signal commingling into the movable portion device, and to measure characteristics of a microstructure accurately without using external displacement source.

Further, separating an electrode that the bias signal is applied to from an electrode that the detection signal is picked up from enables the detecting circuit40to detect the displacement amount of the movable portion electrode5while the bias generating circuit20applies the bias signal. For this reason, it is not necessary to adopt a method, for example, that the detecting circuit40starts detecting the displacement amount after the bias generating circuit20has stopped applying the bias signal. Namely, it is not necessary to switch the application of the bias signal and the start of the detection as just described. Therefore, a time lag that is required for switching can be reduced, resulting in reducing time for detecting the displacement amount totally.

However, because a noise element “c” is contained in a signal that is observed after performing the CV-conversion of the capacitance change “b” shown inFIG. 4B, a precise measurement cannot be performed. Here, the noise element “c” arises from the alternating bias signal “a” that is applied to between the first electrode2and the movable portion electrode5commingling into the second electrode3via the movable portion electrode5. Therefore, a description will be given of a method for detecting the true displacement signal of the movable portion electrode5with eliminating the noise content “c” from the capacitance change “b”.

The bias generating circuit20and the C/V converting circuit30are connected to the pseudo-microstructure1ashown inFIG. 3AandFIG. 3Binstead of the microstructure1shown inFIG. 2AandFIG. 2B. The bias generating circuit20outputs the alternating bias signal and applies the bias voltage “a” shown in theFIG. 4Ato between the first electrode2and the pseudo-movable portion electrode5a. However, the pseudo-movable portion electrode5adoes not displace because the weight portion51aof the movable portion electrode of the pseudo-movable portion electrode5aand the pectinate electrodes52aand53aof movable portion are fixed onto the oxidized insulating film11. The alternating bias signal “a” leaks to the second electrode3as the noise element “c” via the pseudo-movable portion electrode5a. This noise element is converted into the voltage by the C/V converting circuit30. Then a voltage value of the noise element is detected by the detecting circuit40. Subtracting the noise element “c” from the converted voltage value of the capacitance change “b” detected by the above-mentioned microstructure1makes it possible to detect a converted voltage value of the capacitance change that does not contain the noise content “c”. Accordingly, the true displacement signal of the movable portion electrode5can be detected.

In this way, detecting the noise element commingling into the second electrode3in advance and subtracting the noise content from the converted voltage of the detected capacitance change “b” make it possible to detect the true displacement signal of the movable portion electrode5. Therefore, characteristics of the microstructure1can be measured accurately.

FIG. 5AandFIG. 5Bare waveform charts for explaining an embodiment in which white-noise is employed as a random signal. The bias generating circuit20generates a bias signal of white-noise shown inFIG. 5A, and applies a bias voltage “d” to the first electrode2. The white-noise is noise that ranges through a wide frequency band with uniform energy. When the white-noise is applied as the bias signal to between the first electrode2and the movable portion electrode5, the movable portion electrode5resonates by consuming its own resonance frequency element included in the white-noise signal. The C/V converting circuit30converts a capacitance change “e” that arises between the second electrode3and the movable portion electrode5shown inFIG. 5Binto a voltage. The detecting circuit40analyzes the frequency element based on the voltage change provided from the C/V converting circuit30. This enables the detecting circuit40to detect the resonance frequency and its amplitude.

Here, as shown inFIG. 5AandFIG. 5B, the capacitance change “e” is picked up while the alternating bias signal “d” is applied. In other words, the detecting circuit40simultaneously detects the resonance frequency and its amplitude while the bias generating circuit20applies the bias voltage “d”.

According to this embodiment, because the detection signal becomes a signal in which the resonance frequency of the microstructure is emphasized due to the employment of the white-noise as the bias signal, frequency characteristic arising from the resonance can be obtained. This enables a measurement of a resonance frequency and a measurement of a Q-value with a good S/N ratio. Q-value is an index showing a sharpness of a resonance peak.

Further, separating an electrode that the bias signal is applied to from the electrode that the detection signal is picked up from enables the detecting circuit40to detect the displacement amount of the movable portion electrode5while the bias generating circuit20applies the bias signal. For this reason, it is not necessary to adopt a method, for example, that the detecting circuit40starts detecting the displacement amount after the bias generating circuit20has stopped applying the bias signal. Namely, it is not necessary to switch the application of the bias signal and the start of the detection as just described. Therefore, a time lag that is required for switching can be reduced, resulting in reducing time for detecting the displacement amount totally.

FIG. 6AtoFIG. 8Bare waveform charts for explaining an embodiment in which a bias signal is applied until a movable portion electrode5starts moving and the application of the bias signal is stopped after the movable portion electrode5has started moving.

The bias generating circuit20generates a direct current bias signal having a predetermined voltage as shown inFIG. 6A, and applies the bias voltage “f” to between the first electrode2and the movable portion electrode5. This keeps the movable portion electrode5forcefully displaced. At a time0, the direct current bias signal is changed to 0 or another level. The movable portion electrode5loses its forced power when the level of the direct current signal has changed. The movable portion electrode5that lost its forced power starts freely oscillating so as to restore its position by restoring force of movable springs54and55that are components of the movable portion electrode5. Because an oscillation of the movable portion electrode5is damped as time advances, a capacitance change “g” between the movable portion electrode5and the second electrode3is damped as shown inFIG. 6B. The detecting circuit40analyzes the freely-oscillating waveform from the time0when the application of the direct current bias signal stopped based on the voltage change converted by the C/V converting circuit30. Further, the detecting circuit40measures the capacitance change and detects a resonance frequency, a damping characteristic or Q-value.

Here, as shown inFIG. 6AandFIG. 6B, the capacitance change “g” is picked up simultaneously with starting to apply the bias voltage “f”. (However, a zero capacitance change “g” is picked up during a period from the start of the bias application to the time0.) In other words, the detecting circuit40starts detecting the resonance frequency, the damping characteristic or the Q-value simultaneously with the bias generating circuit20starting to apply the bias voltage “f”. For this reason, a time lag to the start of the detection can be reduced in comparison with a method that the detecting circuit40starts detecting the resonance frequency, etc. after the bias generating circuit20has stopped applying the bias signal at the time0.

In contrast to the employment of the direct current bias voltage as the bias signal in the explanation ofFIG. 6AandFIG. 6B, an alternating current bias voltage is employed inFIG. 7AandFIG. 7B. Application of the alternating current bias voltage stops after the movable portion electrode5has started moving at the time0. Specifically, the bias generating circuit20generates the alternating current bias signal, and applies a bias voltage “h” to between the first electrode2and the movable portion electrode5shown inFIG. 7A. In this occasion, such an alternating current bias signal should preferably be selected that has a frequency that resonates the movable portion electrode5at an expected resonance frequency.

The bias generating circuit20changes the bias voltage “h” of the alternating current bias signal to 0V or another certain level of direct current at a time0after the application of the alternating current bias signal has stopped. The movable portion electrode5keeps oscillating according to the bias voltage while the alternating current bias signal is being applied to between the first electrode2and the movable portion electrode5. However, the movable portion electrode5loses its forced power when the application of the bias voltage stops. The movable portion electrode5that lost its forced power starts freely oscillating so as to restore its position by restoring force of movable springs54and55. Finally, the movable portion electrode5finishes its free oscillation with its oscillation damped. The detecting part40detects a capacitance change “i” shown inFIG. 7Bfrom the time the bias is applied to the time the free oscillation is finished through the time0. Further, the detecting circuit40analyzes the freely-oscillating waveform from the time0, measures the capacitance change and detects a resonance frequency, a damping property and Q-value.

Here, as shown inFIG. 7AandFIG. 7B, the capacitance change “i” is picked up simultaneously with starting to apply the bias voltage “h”. (However, a zero capacitance change “i” is picked up during a period from the start of the bias application to the time0.) In other words, the detecting circuit40starts detecting the resonance frequency, the damping property and the Q-value simultaneously with the bias generating circuit20starting to apply the bias voltage “h”. For this reason, a time lag to the start of the detection can be reduced in comparison with a method that the detecting circuit40starts detecting the resonance frequency, etc. after the bias generating circuit20has stopped applying the bias signal at the time0.

FIG. 8AandFIG. 8Bshow an embodiment in which a 1 (one) pulse bias signal is applied until the movable portion electrode5starts moving at a time0. The bias generating circuit20generates the 1 (one) pulse bias signal that rises to a predetermined level and falls down at the time0. The bias generating circuit20applies a bias voltage “j” shown inFIG. 8Ato between the first electrode2and the movable portion electrode5, resulting in oscillating the movable portion electrode5mandatorily. After the time0, because the bias signal is not applied, the movable portion electrode5that lost its forced power starts freely oscillating so as to restore its position by restoring force of movable springs54and55. Then, the movable portion electrode5finishes its free oscillation with its damped oscillation. The detecting part40detects a capacitance change “k” shown inFIG. 8Bfrom the time the bias is applied to the time the free oscillation is finished through the time0. Further, the detecting circuit40analyzes the freely-oscillating waveform from the time0, measures the capacitance change, and detects a resonance frequency, a damping property and Q-value. It is preferable to select a resonance frequency cycle to be a pulse width of the 1 pulse.

Here, as shown inFIG. 8AandFIG. 8B, the capacitance change “k” is picked up simultaneously with starting to apply the bias voltage “j”. In other words, the detecting circuit40starts detecting the resonance frequency, the damping property and the Q-value simultaneously with the bias generating circuit20starting to apply the bias voltage “j”. For this reason, a time lag to the start of the detection can be reduced in comparison with a method that the detecting circuit40starts detecting the resonance frequency, etc. after the bias generating circuit20has stopped applying the bias signal at the time0.

Incidentally, although the microstructure1shown inFIG. 2AandFIG. 2Bhas the first electrode2and the second electrode3separately as the fixed electrode4, it is possible to provide only one of the electrodes. In this case, it is only necessary to alternate the timing of applying the bias signal with the timing of taking out the detection signal.

Further, it is also possible to detect a noise arising from a resonance of the movable portion electrode5. This is achieved by detecting a capacitance between the second electrode3and the movable portion electrode5after applying a bias voltage to between the first electrode2and the movable portion electrode5, detecting a capacitance between the first electrode2and the movable portion electrode5after applying a bias voltage to between the second electrode3and the movable portion electrode5and then detecting a difference of these detected capacitances in the same phase.

FIG. 9is a plan view showing a microstructure1bof another embodiment of the present invention. The microstructure1shown inFIG. 2AandFIG. 2Bis an acceleration sensor. Meanwhile, the microstructure1bis an angular velocity sensor. An acceleration sensor is a sensor in which the movable portion electrode having a weight portion displaces for a direction of the acceleration when the acceleration is applied. Meanwhile, an angular velocity sensor is a sensor that constantly excites the movable portion electrode and displaces the movable portion for the direction perpendicular to the excitation direction by Coriolis force arising in the movable portion electrode when an angular velocity is applied. In an acceleration sensor, a direction for which the movable portion electrode displaces by the bias signal of the present invention and a direction for which the movable portion electrode displaces when an acceleration is applied are the same. Meanwhile, in an angular velocity sensor, it is necessary to measure characteristics in a state that the movable portion electrode is excited and by displacing the movable portion electrode by electrostatic attractive force for a direction for which the movable portion electrode displaces when an angular velocity is applied.

Referring toFIG. 9, more specific explanation will be given of the microstructure1bsuch as an angular velocity sensor. The microstructure1bsuch as an angular velocity sensor includes the first electrode2and the second electrode3of the fixed portion electrode4and the movable portion electrode5b. These elements are configured in the same way as the microstructure1shown inFIG. 1. The movable portion electrode5bis connected to connecting members63and64via exciting springs61and62. The connecting members63and64are supported by anchor portions71,72,73and74via detecting springs65,66,67and68. A third electrode81and a fourth electrode82are provided oppositely to the connecting members63and64.

Unlike the acceleration sensor shown inFIG. 2AandFIG. 2B, intervals in the up and down direction between a pectinate electrode of the movable portion electrode5band a pectinate portion of the first electrode2are arranged to be the same. This is because the movable portion is displaced for a direction of an arrow A by bias application, instead of the direction of an arrow “B” shown inFIG. 9of the paper. It is the same for intervals in the up and down direction between a pectinate electrode of the movable portion electrode5band a pectinate portion of the second electrode3. The movable portion electrode5bis excited for the direction of the arrow “A” shown inFIG. 9due to a bias applied to between the first electrode2and the movable portion electrode5b. In this state, when a rotative force is applied for a direction of an arrow C, the movable portion electrode5bis displaced for the direction of an arrow B by Coriolis force. A capacitance change detected between the second electrode3and the movable portion electrode5band between the fourth electrode82and the movable portion electrode5bincludes displacement elements caused by the rotation. The detecting circuit40detects an angular velocity based on these displacement contents.

Like the explanation forFIG. 1, when the bias signal is applied to between the first electrode2and the movable portion electrode5bfrom the bias generating circuit20, the movable portion electrode5bdisplaces for the direction of the arrow A shown inFIG. 9. If the bias signal is configured to have a frequency that resonates the movable portion for the direction of the arrow “A” by restoring force of the exciting springs61and62, the movable portion electrode5bdisplaces for the direction of the arrow B. A capacitance change of the movable portion electrode5band the fixed portion electrode4is detected between the second electrode3and the movable portion electrode5b.On the other hand, when the bias signal is applied to between the third electrode81and the movable portion electrode5b, the movable portion electrode5bdisplaces for the direction of the arrow B. A capacitance change between the movable portion electrode5bdisplacing for the direction of the arrow B and the second electrode3is detected from the fourth electrode82. This displacement of the movable portion electrode5bfor the direction of the arrow B is a pseudo displacement of a displacement due to Coriolis force arising at the movable portion electrode5bwhen an angular velocity is applied.

In this embodiment, it is preferable to synchronously detect the detection signal by a frequency of the bias signal applied to between the first electrode2and the movable portion electrode5band to take out a resonance signal following a frequency component of the bias signal.

Incidentally, the bias signal may be applied to between the third electrode81and the movable portion electrode5bas shown in above-describedFIG. 4AtoFIG. 8B.

Incidentally, when the microstructure1shown in theFIG. 1is tested in wafer state, a so-called stiction sometimes occurs. The stiction means that the pectinate portion21of the first electrode2and the pectinate electrode of movable portion52of the movable portion electrode5, for example, stick with each other, therefore their physical contact cannot unstick. When the stiction occurs, measurements can not be performed after that. Moreover, the device itself also becomes defective. Such a stiction sometimes has already occurred before measurement and sometimes occurs from displacement of the movable portion electrode5by applying the bias voltage to the movable portion electrode5during measurement.

To solve such a stiction, so-called air blow is performed. The air blow means blowing air at some timing of the measurement process of the microstructure1. The air blow may be performed by using an existing facility such as a prober that is provided for blowing away particles such as chipped lees on a wafer. And the air blow may also be performed by a new facility provided on a probe card. The air blow may be performed to all chips before measurement. The air blow may also be performed to all chips after measurement. Further, the air blow may also be performed to a chip during measurement when the chip is detected to have a possibility of a stiction by a measurement signal, and after that, measurement of the chip is performed again.

Embodiments of the present invention have been described above by referring to figures. However, the present invention is not limited to the embodiments shown in figures. It is possible to make various modifications or deformations to the embodiments shown in the figures within the same scope. of the present invention or within the scope of equivalency. For example, structures of above-mentioned microstructure, fixed electrode portion and movable portion electrode are examples. Therefore, it is possible to modify or deform the structures arbitrarily.