JP3216093B2 - Scanning probe microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope (Scanning Probe Microscope, abbreviated as SPM), and more particularly, to vibrating a mechanical resonance part such as a probe or a cantilever to which the probe is connected at its resonance frequency, The present invention relates to a dynamic observation method for detecting a change amount Δf of a resonance frequency when a probe and a sample come close to each other using a phase-locked loop (Phase Locked Loop, PLL).

[0002]

2. Description of the Related Art Conventionally, an atomic force microscope (Atomic For
The ce Microscope (abbreviation: AFM) is one of the scanning probe microscopes, and can observe the surface of a solid sample at a resolution of an atomic order. In the atomic force microscope, a dynamic observation method is adopted. The resonance frequency of the cantilever changes in response to a small force acting between the tip of the cantilever and the sample surface, and the cantilever and the sample are moved so that the amount of change Δf of the resonance frequency is kept constant. The surface of the sample is scanned by the cantilever while keeping the interval constant to form an image. This dynamic observation method has less damage to the sample by the cantilever when used in the atmosphere, and provides high resolution especially for observation of organic biomaterials. There is little influence of molecules and the like, and high resolution can be obtained in observation of a semiconductor surface and the like. When used in a vacuum, the Q value of the resonance of the cantilever is high, and even in air, when the Q value of the cantilever is high, it is advantageous to detect the variation Δf of the resonance frequency of the cantilever in frequency. That is, according to the prior art for detecting the change amount Δf of the resonance frequency in this manner, the frequency is detected as compared with the configuration for detecting the amplitude of the oscillation signal corresponding to the change amount Δf of the resonance frequency. Thus, the distance between the tip of the cantilever and the sample can be controlled with high sensitivity.

[0003] The phase locked loop circuit used for this frequency detection is simple to use, can be easily realized using an integrated circuit, and can detect the frequency over a wide resonance frequency range of the cantilever. There is an excellent advantage that it is possible, and furthermore, it is not necessary to accurately set the circuit constant of the circuit element every time the consumable cantilever is replaced, so that it is suitable for a commercially available atomic force microscope.

In the prior art using a phase locked loop circuit, a voltage controlled oscillator (hereinafter abbreviated as V) oscillating a reference frequency of the phase locked loop circuit.
Since CO) has a low Q value and a wide frequency variable range, the frequency detection sensitivity is low. Therefore, the minute change Δf in the resonance frequency cannot be accurately detected. Further, since the oscillation frequency is determined by the constant of the passive element, the temperature stability is low and the oscillation frequency is easily affected by a change in the environmental temperature.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-locked loop circuit having a voltage-controlled oscillation circuit having a high Q value and an oscillation frequency that is hardly affected by temperature, and has a high sensitivity regardless of a change in environmental temperature. An object of the present invention is to provide a scanning probe microscope capable of performing accurate observation.

[0006]

According to the present invention, there is provided (a) a probe or a mechanical resonance portion to which the probe is connected resonates, and the resonance frequency f1 changes according to the distance between the probe and the sample. (B) a frequency conversion circuit 13, which oscillates at a predetermined local oscillation frequency stabilized using a crystal oscillator or a high-stable piezoelectric oscillator. The local oscillation frequency is adjusted to a predetermined oscillation frequency so that the phase-locked loop circuit 14 performs phase synchronization regardless of a change in the resonance frequency f1 due to replacement of at least a part of the mechanical oscillation means. A frequency conversion circuit 13 which has an oscillator 39 and derives an intermediate frequency signal 44 by arithmetic processing from an oscillation signal 7 from a mechanical oscillation means and a local oscillation signal 40 from a local oscillator 39; (C) a phase-locked loop circuit 14, which is stabilized by using another crystal oscillator or a high-stability piezoelectric oscillator, from an intermediate frequency signal 44 and a voltage-controlled oscillation circuit 46; And a phase locked loop circuit 14 for detecting a change amount from the resonance frequency f1 by synchronizing the phase of the intermediate frequency signal with the reference frequency signal. (D) means for controlling displacement of the probe or the sample in response to the output of the phase locked loop circuit so that the amount of change from the resonance frequency f1 becomes a predetermined value. Is a scanning probe microscope. Further, according to the present invention, there is provided a machine which resonates a probe or a mechanical resonance unit connected to the probe, changes a resonance frequency f1 according to a distance between the probe and the sample, and outputs an oscillation signal 7 at the resonance frequency f1. And a frequency detecting device that receives an oscillation signal 7 from the mechanical oscillating device, detects a change amount from the resonance frequency f1, and responds to an output of the frequency detecting device to change from the resonance frequency f1. A frequency detecting device used in a scanning probe microscope including means 9 and 12 for controlling displacement of a probe or a sample so that the amount becomes a predetermined value. Oscillates at a predetermined local oscillation frequency stabilized by using a resonator or a high-stability piezoelectric oscillator, and changes in the resonance frequency f1 due to replacement of at least a part of the mechanical oscillation means. Instead, it has a local oscillator 39 whose change is adjusted to a predetermined oscillation frequency so that the phase lock of the phase locked loop circuit 14 is performed, and the oscillation signal 7 from the mechanical oscillator and the local oscillator 39 A frequency conversion circuit 13 that derives an intermediate frequency signal 44 by arithmetic processing based on the local oscillation signal 40; and (b) a phase locked loop circuit 14, which uses another crystal oscillator or a highly stable piezoelectric oscillator. It has a stabilized voltage controlled oscillation circuit 46, and a phase detector 45 to which an intermediate frequency signal 44 and a reference frequency signal 47 from the voltage controlled oscillation circuit 46 are provided. A frequency detector used in a scanning probe microscope, comprising: a phase locked loop circuit 14 that detects the amount of change from the resonance frequency f1 by synchronizing. Output device.

According to the present invention, a probe such as a cantilever provided to face a sample or a mechanical resonance portion to which the probe is coupled is connected to the resonance frequency f by a mechanical oscillation means.
Oscillate by oscillating at 1 and use a phase locked loop circuit to
The change amount Δf of the resonance frequency corresponding to the minute force interacting in a non-contact state between the probe and the sample is converted into a voltage and detected, and the change amount Δf is maintained at a predetermined value. As described above, the probe and the sample are displaced toward and away from each other, and an image of the sample surface by scanning can be obtained. In this way, in the mechanical oscillating means, the probe or the mechanical resonance section to which the probe is connected always oscillates by oscillating at the resonance frequency f1 which changes depending on the force acting between the probe and the sample. Is working. The frequency detection device includes a frequency conversion circuit 13
And a phase locked loop circuit 14. The frequency conversion circuit 13 converts a local oscillation signal from a local oscillator oscillated at a predetermined local oscillation frequency f2, stabilized using a crystal oscillator or a high-stable piezoelectric oscillator, and an oscillation signal from a mechanical oscillation unit. An intermediate frequency signal having the intermediate frequency f3 is derived by arithmetic processing, and given to a phase detector of the phase locked loop circuit. The displacement control means controls the displacement drive so that the resonance frequency f1 is maintained at a predetermined frequency f5, and thus the variation Δf, which is the difference between the resonance frequency f1 and the predetermined frequency f5, is a predetermined value. The means is driven and controlled to move the probe toward and away from the sample.

The phase detector of the phase locked loop circuit includes an oscillation signal from a mechanical oscillator and a reference frequency f oscillated by using another crystal oscillator or a highly stable piezoelectric oscillator.
4 is provided with a reference frequency signal 47 from a voltage controlled oscillation circuit stabilized without depending on the environmental temperature, and a signal having a voltage corresponding to the phase difference between the oscillation signal and the reference frequency signal is output from the phase detector. It is derived and provided to the displacement control means via a low-pass filter. Thus, the probe and the sample are displaced toward and away from each other by the displacement driving means as described above. Since the voltage-controlled oscillation circuit has the crystal oscillator or the high-stability piezoelectric oscillator as described above, the reference frequency f4 is stabilized, and the resonance frequency f1
Can be accurately detected, and thus the sensitivity can be increased.

[0009]

According to the present invention, the frequency range in which the phase locked loop circuit provided with the reference frequency oscillating circuit having the crystal oscillator or the high-stability piezoelectric oscillator is in a synchronized state is relatively narrow, and the probe or the probe is used. In order to be able to use a common phase-locked loop circuit even when the mechanical resonance unit connected to is a consumable and is frequently replaced and used and the resonance frequency is different each time it is replaced, A frequency conversion circuit is interposed between the mechanical oscillation means and the phase detector. The oscillation signal of the mechanical oscillation means is converted into an intermediate frequency signal f3 by this frequency conversion circuit. Accordingly, the phase locked loop circuit can be commonly used for various probes having different resonance frequencies f1 or a mechanical resonance unit to which the probes are connected without changing the configuration, constant, and the like of the phase locked loop circuit. become.

The local oscillator 3 provided in the frequency conversion circuit
Reference numeral 9 denotes a crystal oscillator or a high-stability piezoelectric oscillator, whereby a stable local oscillation frequency f2 is oscillated without depending on the environmental temperature, and a signal having an accurate intermediate frequency f3 can be obtained.

The oscillating frequency f1 of the mechanical oscillating means is determined mainly by a mechanical structure such as a probe. The reference frequency f4 is set so that the fluctuation voltage ΔV of the voltage V1 of the voltage control signal obtained from the low-pass filter becomes as large as possible in accordance with the variation Δf of the resonance frequency f1 of the mechanical oscillating means. It is determined to enable Therefore, the local oscillation frequency f2 of the frequency conversion circuit
Are the oscillation frequency f1 of the mechanical oscillation means and the reference frequency f4
And will be determined depending on

According to the present invention, in order to enable high-sensitivity frequency detection, the oscillation frequency f
Even if the change amount Δf of 1 is small, the fluctuation voltage ΔV of the voltage V1 obtained from the low-pass filter of the phase locked loop circuit can be obtained as large as possible.
In the present invention, the reference frequency f4 is stabilized without depending on the environmental temperature by using another crystal oscillator or a high-stability piezoelectric oscillator for the voltage-controlled oscillation circuit in the phase-locked loop circuit. The sensitivity can be improved.

In a configuration in which a frequency conversion circuit is interposed between the mechanical oscillating means and the phase detector of the phase locked loop circuit, another crystal oscillator or a high-stable piezoelectric oscillator is used for the local oscillator. The local oscillation frequency f2 can be stabilized without depending on the environmental temperature. This also makes it possible to accurately detect the slight variation Δf of the oscillation frequency f1 and improve the sensitivity.

According to the present invention, the local oscillator uses a crystal oscillator or a high-stability piezoelectric oscillator, and has a local oscillation frequency f2.
Is stabilized without depending on the environmental temperature, the fluctuation voltage ΔV corresponding to the minute variation Δf of the resonance frequency f1 can be accurately obtained, and the sensitivity can be further improved. it can.

According to the present invention, an atomic force microscope can be stably realized with high sensitivity. The present invention is applicable not only to an atomic force microscope but also to other scanning probe microscopes such as a scanning tunneling microscope.
ng Microscope (abbreviated as STM), scanning electrostatic force microscope, scanning magnetic force microscope, scanning Kelvin probe microscope, and other configurations.

[0017]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention. An atomic force microscope 1 which is one of the scanning probe microscopes has a surface 3 of a sample 2.
Next, the tip 5 of the cantilever 4 which is a probe vibrated at the resonance frequency f1 is relatively scanned, and the surface 3 is observed at a resolution of an atomic order by a dynamic observation method. The atomic force microscope 1 basically includes a mechanical oscillation unit 6 that oscillates the cantilever 4 at a resonance frequency f1 and oscillates, and a semiconductor integrated circuit that detects a frequency of a signal 7 representing the resonance frequency f1. Means 8, a displacement driving means 9 for driving the sample 2 relatively to the cantilever 4, and a displacement control means 12 for controlling the displacement driving means 9 in response to a voltage control signal 11 from the frequency detecting means 8. Including. The frequency detecting means 8 includes a frequency conversion circuit 13 and a phase locked loop circuit 14.

FIG. 2 is a simplified view of the cantilever 4 and its vicinity. The cantilever 4 is vibrated in a direction approaching / separating from the sample 2 by a piezoelectric element 15 as a driving means.

FIG. 3 is a diagram for explaining the interaction between the tip 5 of the cantilever 4 and the surface 3 of the sample 2. The resonance frequency f1 of the cantilever 4 changes due to the attraction or repulsion generated by the interaction between the cantilever 4 and the sample 2. In one embodiment of the present invention, the amount of change △ is the difference between the resonance frequency f1 and the predetermined frequency f5 so that the resonance frequency f1 due to this interaction is kept constant at the predetermined frequency f5.
The displacement control means 12 drives and controls the displacement drive means 9 so that f is kept constant at a predetermined value.
Is displaced in the z direction, which is the vertical direction, by the displacement driving means 9 so that the cantilever 4 and the sample 2 are displaced toward and away from each other. The displacement driving means 9 also scans the sample 2 while displacing the sample 2 in the x direction and the y direction orthogonal to each other in a plane perpendicular to the z direction. Thus, an image of the surface 3 of the sample 2 can be obtained.

FIG. 4 is a diagram for explaining the interaction 20 between the tip 5 of the cantilever 4 and the surface 3 of the sample 2. The cantilever 4 is attached to the weight 1 as shown in FIG.
7 can be approximated by a connected spring and the interaction 2
0 can be approximated by another spring. When the tip 5 of the cantilever 4 approaches the surface 3 of the sample 2, the spring constant of the cantilever 4 equivalently changes, thereby changing the resonance frequency f1.

FIG. 5 is a diagram showing a partial configuration of the mechanical oscillating means 6 related to the cantilever 4. Laser source 18
Is a semiconductor laser device, for example, and the laser beam 19 is applied to the cantilever 4. The laser light 19 is reflected by the cantilever 4, reflected and guided by the mirror 21, and received by the light receiving element 22. The light receiving element 22 has a pair of photodiodes 23 and 24. Each output of the photodiodes 23 and 24 is supplied to a differential amplifier 25, whereby a voltage signal 26 representing the amount of displacement of the cantilever 4 is obtained. Thus, the displacement of the cantilever 4 is enlarged and detected by the optical lever including the mirror 21 and the light receiving element 22, and the displacement of the cantilever 4 can be detected with high accuracy.

FIG. 6 is a view showing the oscillation operation characteristics of the cantilever 4 and the mechanical oscillation means 6. The cantilever 4 forms a harmonic vibration system, and the output signal 26 of the differential amplifier 25 has a phase delay of 90 degrees with respect to the signal 28 for driving and controlling the piezoelectric element 15 at the resonance frequency f1. In a frequency range lower than the resonance frequency f1, the phase delay is small, and at a frequency higher than the resonance frequency f1, the phase delay is large.

Referring again to FIG. 1, output signal 26 of differential amplifier 25 is provided to phase shifter 29, where the phase is delayed by 90 degrees. The output of the phase shifter 29 is applied to the amplitude controller 31 and inverted, whereby
This causes a phase lag, and the control signal 28 is positively fed back to the piezoelectric element 15. Therefore, the mechanical oscillation operation is continued at the resonance frequency f1 of the cantilever 4.

By the interaction 20 between the tip 5 of the cantilever 4 and the surface 3 of the sample 2, the resonance frequency f1 is
It changes from the predetermined frequency f5 by the amount of displacement Δf. Thus, the characteristics of the frequency and amplitude of the cantilever 4 are indicated by reference numerals 33 and 34. The frequencies at which the phase delay occurring in the cantilever 4 becomes 90 degrees are f5 and f1, and the characteristics of the frequency and the phase are indicated by reference numerals 35 and 36.

The output 7 of the differential amplifier 25 of the mechanical oscillating means 6 is given to the frequency conversion circuit 13 in the frequency detecting means 8. The output 7 of the differential amplifier 25 is the same signal as the output signal 26 described above, and is individually shown for the sake of illustration. The output 7 of the differential amplifier 25 is
It has a resonance frequency f1 and is provided to a frequency mixer. The frequency mixer 38 also has a local oscillator 39,
A signal 40 having a predetermined local oscillation frequency f2 is provided. The local oscillator 39 has a crystal oscillator 41, and the local oscillation frequency f2 is kept constant irrespective of a change in environmental temperature. The local oscillator 39 may be obtained by dividing a signal oscillated by the crystal oscillator 41. The frequency mixer 38 mixes the output 7 of the differential amplifier 25 and the output 40 of the local oscillator 39, and supplies the mixed signal 42 to the filter 43. Thus, a signal 44 having the intermediate frequency f3 is obtained. The intermediate frequency f3 is equal to the resonance frequency f
This is the sum or difference frequency between 1 and the local oscillation frequency f2.

The intermediate frequency f3 from the frequency conversion circuit 13
Is supplied to one input of a phase detector 45 of the phase locked loop circuit 14. The other input of the phase detector 45 is supplied with a signal 47 having a reference frequency f4 from the voltage controlled oscillation circuit 46. This voltage controlled oscillation circuit 46 has a crystal oscillator 48, and the reference frequency f4 is stabilized irrespective of a change in environmental temperature. The output signal 51 of the phase detector 45 corresponds to the phase difference between the intermediate frequency signal 44 corresponding to the resonance frequency signal 7 from the mechanical oscillating means 6 and the reference frequency signal 47 from the reference frequency oscillating circuit 46.

This signal 51 is filtered by a low-pass filter 53 and provided as an output 11 of the displacement control means 12 and, as indicated by reference numeral 54, is supplied to a reference frequency oscillating circuit 46 for changing the reference frequency f4. As a signal. Thus, the phase locked loop circuit 14 is in a state synchronized with the intermediate frequency signal 44 given to the phase detector 45.

The output 44 from the filter 43 of the frequency conversion circuit 13 has a frequency f3, and the frequency f3 changes by the same change Δf as the change Δf of the resonance frequency f1. The outputs 11 and 54 of the filter 53 are the same signal, and the voltage V1 is, as shown in FIG. 7, the voltage V1 corresponding to the variation Δf of the resonance frequency f1 and therefore the intermediate frequency f3. V changes.

In the displacement control means 12, the output 11 of the filter 53 is supplied to a control circuit 56. The control circuit 56 is also supplied with a signal having a predetermined voltage from a target value setting circuit 61. The control circuit 56 derives the control signal 62 so that the difference between the voltage of the output 11 and the target value output from the target value setting circuit 61 becomes zero and supplies the control signal 62 to the amplifier 63. The amplifier 63 includes a z-direction driving mechanism 6 of the displacement driving unit 9.
4 is operated. In this way, the distance between the tip 5 of the cantilever 4 and the surface 3 of the sample 2 is kept at a value corresponding to the voltage set by the target value setting circuit 61. The displacement driving means 9 also moves the sample 2 in the x direction and the y direction in a plane perpendicular to the z direction.
And a drive mechanism 65 for moving and scanning in the direction. Each of the driving mechanisms 64 and 65 can be realized by, for example, a piezoelectric element, a voice coil, or the like.

In another embodiment of the present invention, the sample 2 may be provided at a fixed position, the cantilever 4 may be displaced in the z direction, and the cantilever 4 may be scanned in the x and y directions. Is also good.

The interaction 20 between the tip 5 of the cantilever 4 and the surface 3 of the sample 2 is a force in the embodiment described above, but is a tunnel current in another embodiment of the present invention, or otherwise. May be a physical quantity.

In another embodiment of the present invention, it is also possible to provide the output 7 of the mechanical oscillating means 6 directly to the phase detector 45, in which case the frequency conversion circuit 13 is omitted. Can be done. Mechanical oscillation means 6
Is output from the differential amplifier 25 in the above embodiment, but is output from the phase shifter 29 or the amplitude control circuit 31 in another embodiment of the present invention. May be output.

[0033]

According to the present invention, in a phase locked loop circuit used to detect the resonance frequency f1 of a mechanical resonance unit to which a probe is connected, the voltage controlled oscillation circuit is a crystal oscillator or a highly stable crystal oscillator. Because of having the piezoelectric oscillator, its reference frequency f4 is stabilized irrespective of changes in the environmental temperature,
As a result, the minute variation Δf of the resonance frequency f1 can be accurately detected, and the surface of the sample can be observed with high sensitivity and accuracy.

According to the present invention, the resonance frequency f1 of the mechanical resonance section is frequency-converted by the frequency conversion circuit and is applied to the phase detector of the phase-locked loop circuit. Even if the changed mechanical resonance unit is replaced and its resonance frequency f1 changes, the configuration such as the subsequent phase locked loop circuit is commonly used by changing and adjusting the oscillation frequency of the local oscillator of the frequency conversion circuit. Will be able to do it. Further, by using this frequency conversion circuit, the optimum reference frequency f4 can be selected in the phase locked loop circuit, whereby the variation Δf can be detected with high sensitivity regardless of the environmental temperature. become.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a simplified view of a cantilever 4 and its vicinity.

FIG. 3 is a diagram for explaining an interaction between a tip 5 of a cantilever 4 and a surface 3 of a sample 2;

FIG. 4 is a diagram for explaining an interaction 20 between the tip 5 of the cantilever 4 and the surface 3 of the sample 2;

FIG. 5 is a diagram showing a configuration of a part of a mechanical oscillation unit 6 related to the cantilever 4;

FIG. 6 is a diagram showing oscillation characteristics of the cantilever 4 and the mechanical oscillation means 6;

FIG. 7 is a diagram for explaining an operation of the phase locked loop circuit 14.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Atomic force microscope 2 Sample 3 Surface 4 Cantilever 5 Tip 6 Mechanical oscillation means 8 Frequency detection means 9 Displacement drive means 12 Displacement control means 13 Frequency conversion circuit 14 Phase locked loop circuit 38 Frequency mixer 39 Local oscillator 41, 48 Crystal oscillator 43, 53 Filter 45 Phase detector 46 Reference frequency oscillation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 13/10-13/24 G12B 21/00-21/24 G01B 7/34 G01B 21/30 H01J 37 / 28 H03L 7/00-7/26 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. (a) Resonating a probe or a mechanical resonance part to which the probe is coupled, the resonance frequency f1 changes according to the distance between the probe and the sample, and the oscillation signal 7 of the resonance frequency f1 is changed. (B) a frequency conversion circuit 13, which oscillates at a predetermined local oscillation frequency stabilized by using a crystal oscillator or a high-stability piezoelectric oscillator; Regardless of the change of the resonance frequency f1 due to the exchange of a part, the phase locked loop circuit 14
And a local oscillator 39 whose change is adjusted to a predetermined oscillating frequency so that phase synchronization of the oscillating signal is performed. The oscillating signal 7 from the mechanical oscillating means and the local oscillating signal 40 from the A frequency conversion circuit 13 for deriving a frequency signal 44 by arithmetic processing; and (c) a phase-locked loop circuit 14, which is a voltage-controlled oscillation circuit stabilized using another crystal oscillator or a highly stable piezoelectric oscillator. 46, and a phase detector 45 to which an intermediate frequency signal 44 and a reference frequency signal 47 from a voltage controlled oscillation circuit 46 are provided. The resonance frequency is obtained by synchronizing the phase of the intermediate frequency signal and the reference frequency signal. (d) responding to the output of the phase-locked loop circuit 14, the amount of change from the resonance frequency f1 is predetermined. Scanning probe microscope characterized in that it comprises a means 9, 12 for performing displacement control of the probe or sample so that. 2. Resonating a probe or a mechanical resonance unit to which the probe is connected, and setting a resonance frequency f according to a distance between the probe and the sample.
1 changes, and a mechanical oscillating means for outputting an oscillation signal 7 of the resonance frequency f1; and a frequency detection device which receives the oscillation signal 7 from the mechanical oscillating means and detects an amount of change from the resonance frequency f1. Means for controlling the displacement of the probe or the sample so that the amount of change from the resonance frequency f1 becomes a predetermined value in response to the output of the frequency detection device. In the detection device, (a) the frequency conversion circuit 13 oscillates at a predetermined local oscillation frequency stabilized using a crystal oscillator or a highly stable piezoelectric oscillator, and at least a part of the mechanical oscillation means is replaced. Irrespective of the change of the resonance frequency f1 due to the
And a local oscillator 39 whose change is adjusted to a predetermined oscillating frequency so that phase synchronization of the oscillating signal is performed. The oscillating signal 7 from the mechanical oscillating means and the local oscillating signal 40 from the A frequency conversion circuit 13 for deriving a frequency signal 44 by arithmetic processing; and (b) a phase-locked loop circuit 14, which is a voltage-controlled oscillation circuit stabilized using another crystal oscillator or a highly stable piezoelectric oscillator. 46, and a phase detector 45 to which an intermediate frequency signal 44 and a reference frequency signal 47 from a voltage controlled oscillation circuit 46 are provided. The resonance frequency is obtained by synchronizing the phase of the intermediate frequency signal and the reference frequency signal. and a phase locked loop circuit (14) for detecting an amount of change from f1.