JP3319015B2 - Semiconductor yaw rate sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor yaw rate sensor.

[0002]

2. Description of the Related Art Heretofore, a type using a piezoelectric ceramic as a yaw rate sensor has been used for controlling the attitude of an automobile and preventing camera shake of a consumer video camera. By the way, the application field of this sensor can be considered other than the above,
Accuracy and cost limit the development to others. Therefore, the applicant of the present application has proposed a novel semiconductor yaw rate sensor in Japanese Patent Application No. Hei 4-223072.

[0003]

However, in the semiconductor yaw rate sensor disclosed in Japanese Patent Application No. 4-223072, noise (thermal noise, 1 / f noise) is also amplified when the signal of the sensing section is amplified. S / N
There remains a problem that it is difficult to expect improvement.

An object of the present invention is to provide a semiconductor yaw rate sensor capable of improving S / N.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a semiconductor substrate.
Form a beam structure that is separated from the substrate on a part of the
On one surface of the weight formed at the tip and on the substrate wall surface facing the same weight surface
AC power is applied to excite the weight by static electricity,
One side of the weight and the same beam in the axial direction perpendicular to the excitation direction
The electrodes are arranged on the substrate wall surface facing the
Yaw that works in the same direction by electrically detecting the change in capacitance between the poles
Semiconductor yaw rate sensor that detects late
AndWhen a carrier is applied to one side between the opposed electrodes,
A yaw rate detection electrode which is the other between the opposed electrodes.
Modulating circuit for obtaining a detection signal superimposed on the carrier from the signal
And the center frequency matches the carrier, and the modulation circuit
And a band-pass filter for passing these signals.
The gist is a conductor yaw rate sensor.

[0006]

[Function] Excitation of the weight by static electricity by applying AC power,
A change in capacitance between opposing electrodes arranged in an axial direction perpendicular to the excitation direction is electrically detected. This signal is superimposed with a carrier in the modulator circuit modulates <br/>. Further, the signal from the modulation circuit passes through a band-pass filter whose center frequency matches the frequency of the carrier.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a plan view of the semiconductor yaw rate sensor, and FIG. 3 is a sectional view taken along line AA of FIG.
In the following description, when expressing the three-dimensional direction, FIG.
Is defined as an X-axis direction, an up-down direction is defined as a Y-axis direction, and a direction perpendicular to the paper is defined as a Z-axis direction.

The silicon substrate 51 is a flat plate, and the silicon substrate 51 has a rectangular recess 52 (depth: T). Inside the concave portion 52, two rod-shaped beams 53 extend from the left side surface of FIG.
A weight 55 is formed at the tip of. On the other hand, inside the concave portion 52, two rod-shaped beams 5 are seen from the right side surface of FIG.
4 is extended, and a weight 56 is formed at the tip of the beam 54. The weights 55 and 56 are wider than the beams 53 and 54 and are formed in a rectangular shape. Beam 53,
54 and the weights 55 and 56 have the same thickness.

Further, one side surface (upper surface in FIG. 2) of the weight 55 is slightly separated from the inner surface of the concave portion 52 (distance a). Similarly, the other side surface (the lower surface in FIG. 2) of the weight 55 and the inner surface of the concave portion 52 are slightly separated (distance a). Similarly, the bottom surface of the weight 55 (the lower surface in FIG. 3) and the inner surface of the concave portion 52 are slightly separated (distance d1).

On the other hand, one side surface (upper surface in FIG. 2) of the weight 56 and the inner surface of the concave portion 52 are slightly separated (distance a). Similarly, the other side surface (the lower surface in FIG. 2) of the weight 56 and the inner surface of the concave portion 52 are slightly separated (distance a). Similarly, weight 56
Is slightly separated from the inner surface of the concave portion 52 (distance d1).

As described above, the present sensor has a cantilever structure. In this structure, a distance d1 is formed by sacrifice layer etching or the like using surface micromachining technology. In FIG. 3, the weights 55, 5 on the bottom surface of the recess 52 are shown.
Electrodes 57, 58 are formed on the surface facing 6, and electrodes 59, 60 are formed on weights 55, 56 facing the electrodes 57, 58. Further, electrodes 59 and 60 are formed on the inner wall of the recess 52 facing the weights 55 and 56 (the upper surface of the recess 52 in FIG. 2), and the weights 55 and 60 facing the electrodes 59 and 60 are formed. Electrodes 61 and 62 are formed at the portion 56.

An electrode 6 is provided on the inner wall of the recess 52 facing the weights 55 and 56 (the lower surface of the recess 52 in FIG. 2).
3 and 64 are formed, and electrodes 65 and 66 are formed in portions of the weights 55 and 56 facing the electrodes 63 and 64.

In this structure, the electrodes 57, 58,
59, 60, 61, 62, 63, 64 are each insulated
Have been. And a capacitor at electrodes 59 and 57
C_{s +}And a capacitor C at electrodes 60 and 58_s-Is the electrode 59
And capacitor C at 61_{d +}, Electrodes 66 and 64
Sensor C _d-Is a capacitor C between electrodes 65 and 63_{e +},electrode
Capacitor C at 60 and 62_e-Are formed respectively
I have.

The beams 53 and 54 are respectively applied to the electrodes 5
9 (61, 65) and 60 (62, 66). Although 59, 61, and 65 have been described as separate electrodes for description, they are the same electrode (same potential). 60,6
2 and 66 are also described with different electrodes for the sake of description, but they are the same electrode (same potential).

FIG. 1 shows an electric circuit diagram of a semiconductor yaw rate sensor. The processing circuit of the sensor includes an oscillator 67, a sensing unit 68, a differential amplifier 69, and a bandpass filter 7.
0, a sample hold circuit 71, and a post-amplifier 72.

Although the capacitor Cr in FIG. 1 is not shown in FIGS. 2 and 3, it is connected in parallel with the resistor R,
r = C _{s +} = fixed capacitance designed as C _s− . Capacitor C _e +, C _e- drives the spindle 55 by the electrostatic force Fe. The capacitors C _{s +} and C _s− are capacitors for detecting the amount of displacement of the weights 55 and 56 in the Z-axis direction due to Coriolis force Fc.

The capacitors C _{d +} and C _d− shown in FIG. 2 are monitoring capacitors for detecting the amount of movement of the weights 55 and 56 in the Y-axis direction by the driving capacitors C _{e +} and C _e− . next,
In FIG. 1, the configuration other than the sensing unit 68 will be described.

The oscillator 67 has an oscillation frequency f of 10 KHz, and a voltage (AC power) for driving the weights 55 and 56.
And a signal (carrier) is applied to the capacitors C _{s +} and C _s− . The resistor R is connected to the capacitor C _{s +} or C _s− and C
A bias voltage is applied to the connection portion of r, and the value is set as R≫1 / ωCr. By applying a bias, subsequent signal processing is enabled.

The differential amplifier 69 amplifies the difference voltage between the inputs (capacitors C _{s +} , C _s− ). The center frequency of the band-pass filter 70 is 10 KHz, which matches the frequency of the carrier. Further, the band-pass filter 70 attenuates signals outside a predetermined frequency band (around the center frequency). In this embodiment, the band-pass filter 7
0 is a switched capacitor filter (abbreviation: SC).
F).

Sample hold circuit 71 (detection circuit)
Is for demodulating an AM-modulated signal described later. The operational amplifier 73 and the resistors 74 and 75 form a reference voltage in the processing circuit. The post-amplifier 72 amplifies the detected signal. Note that the post-stage amplifier 72 may not be provided.

In this embodiment, the electrodes 57, 58, 59, 6
A yaw rate detection electrode is constituted by 0, and an AM modulation circuit is constituted by the oscillator 67 and the differential amplifier 69.
Next, the operation of the semiconductor yaw rate sensor thus configured will be described.

The voltage V _IN (= V _CM · cos) from the oscillator 67
When the omega _c t) is applied to the capacitor C _e- and C _{e +,}
The electrostatic force Fe represented by the equation (1) is generated. _{Fe = (ε 0 S / 2a} 2) · V IN 2 ··· (1) However, epsilon _0; dielectric constant a; capacitor C _e- and C _{e +} spacing S; capacitor C _e- and C _{e +} of opposed electrodes Area The weights 55 and 56 are displaced in the Y-axis direction by the electrostatic force Fe. Assuming that the displacement amount is Dy, Dy = KFe (2) where K is a constant determined by the cantilever. However, at this time, the weights 55 and 56 move in different directions.

From the above equations (1) and (2), Y of the weights 55 and 56
The velocity in the axial direction is V_y55,V _y56Then V_y55= -V_y56 = K · ((ε₀S / 4a^Two) ・ V_cm ^Two・ 2ω_c・ Sin2ω_ct (3)

At this time, when the X axis is used as the rotation axis and rotated at an angular velocity ω, the Z axis is Coriolis force F _C55 = 2 mV _y55 ω, F
_C56 = 2 mV _y56 ω is generated. Thereby, the weight 5
5, 56 are respectively displaced in the Z-axis direction. This is D
If _{Z55, D Z56, D Z55 =} L 55 · F C55 D Z56 = L 56 · F C56 ··· (4) However, L _55, L _56; represented by the constant determined by the cantilever.

[0025] By designing the weight 55, 56 and a cantilever at the same size, it is _{L 55 = L 56 | D Z5} 5 | = | D Z56 | =
It can be expressed as Δd. That is, the capacities of C _{s +} and C _s− are as follows: C _{s +} = (ε ₀ · S) / (d + Δd), C _s− = (ε ₀ · S) / (d−Δd) (5) .

Therefore, the output V _pre of the differential amplifier 69 is V _pre = V _IN · {C _{s +} / (C _{s +} + Cr) -C _s- / (C _s- + Cr)}｝ AV 1 ≒ V _IN · (-Δd / 2d) · AV1 (6) where AV1 is represented by the amplification factor of the differential amplifier 69.

[0027] In addition, before the formula (3), (4) by Δd is _{Δd = L 55 · 2m · K} (ε 0 · S / 4a 2) · V CM 2 · 2ω c · ω · sin2ω c t ··· (7) is represented by

[0028] Further, (6), (7) a ^{_{V pre = AV1 · V CM 3}} · L 55 · 2m · K (ε 0 · S / 4a 2) · ω c · ω · (sinω c t + sin3ω c t ) (8)

Here, V _{CM on} the right side of the above equation (8)
^{The portion of 3} · L ₅₅ · 2m · K (ε ₀ · S / 4a ² ) · ω _c is a constant determined by the condition of the structure of the cantilever and the input voltage. From this equation (8), V _pre indicates that a voltage proportional to the angular velocity ω to be detected is expressed.
This is the input signal frequency f _IN = ω _C / 2π and its 3
It will be represented as a voltage output AM-modulated at twice the frequency.

Here, only the detection signal has been described so far. However, when the signal is processed by the differential amplifier 69, noise generated in its own circuit element and noise injected from the outside into the power supply system are also present. , Are also amplified by the differential amplifier 69. Thus (8) is ^{_{V pre = AV1 · V CM 3}} · L 55 · 2m · K (ε 0 · S / 4a 2) · ω c · ω · (sinω c t + sin3ω c t) + AV1 · V N. (9) Noise items AV ₁ and V _N that lower the S / N of the angular velocity ω to be detected are generated.

Therefore, the detected angular velocity is AM-modulated as shown in equation (9), and the center frequency fc of the band-pass filter 70 is passed through ω = ωC / 2π. Thereby, S / N is improved.

[0032] Then, when the output of the band pass filter 70 of f _c = ω _C / 2π and _{V BPF, V BPF = AV1 ·} V CM 3 · L 55 · 2m · K (ε 0 · S / 4a 2) · _{ω c · ω · sinω c t} + AV1 · V N (f c) becomes (10).

V _BPF is expressed by the following equation (10).
Term noise _{AV1 · V N (f c)} , that is, the frequency component is not left only the noise component of the same components as _{f c, AV1 · V N »AV1} · V N (f c) ··· (11) And an output proportional to the high S / N angular velocity ω is obtained. This is processed by a sample-and-hold circuit (detection circuit) 71 as necessary, so that an output V proportional to the angular velocity ω is obtained.
_{out V out ≒ AV1 · V CM} 3 · L 55 · 2m · K (ε 0 · S / 4a 2) · ω c · ω ··· (12) is obtained.

The signal is amplified by the post-amplifier 72 as required. As described above, in this embodiment, the oscillator 57 and the differential amplifier 69 (AM modulation circuit) apply the electrodes 57,
Signals from 59, 58, and 60 (electrodes for yaw rate detection) are superimposed, and a signal from a differential amplifier 69 is passed by a band-pass filter 70 whose center frequency matches the carrier. Therefore, when the signal is processed by the differential amplifier 69, there is noise generated in its own circuit element and noise injected from the outside into the power supply system, but these noises are removed. That is, noise (thermal noise, 1 / f noise) is amplified and S / N can be improved.

[0035]

As described in detail above, according to the present invention,
An excellent effect of improving S / N is exhibited.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a semiconductor yaw rate sensor.

FIG. 2 is a plan view of a semiconductor yaw rate sensor.

FIG. 3 is a cross-sectional view showing a cross section taken along line AA of FIG. 2;

[Explanation of symbols]

51 differential amplifier 70 band-pass filter as an oscillator 69 modulation circuit as an electrode 67 modulation circuit as a silicon substrate 55, 56 weight 57, 58, 59, 60 yaw rate detection electrode serving as a semiconductor substrate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-139719 (JP, A) JP-A-57-160067 (JP, A) JP-A-63-154915 (JP, A) JP-A-62 93668 (JP, A) JP-A-61-114123 (JP, A) JP-A-61-200428 (JP, A) JP-A-3-172711 (JP, A) JP-A-63-50716 (JP, A) WO 92/1941 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 19/56 G01P 9/04

Claims (1)

(57) [Claims] A beam structure separated from the substrate is formed on a part of the semiconductor substrate, and AC power is applied to one surface of the weight formed at the tip of the beam and the wall surface of the substrate facing the same weight surface, and the weight is generated by static electricity. Is excited, electrodes are arranged oppositely on a substrate wall surface facing one surface of the weight and the same beam surface in an axial direction orthogonal to the excitation direction of the weight, and a change in capacitance between the opposed electrodes is electrically detected. In a semiconductor yaw rate sensor configured to detect a yaw rate acting in the same direction, a carrier wave is applied to one of the opposed electrodes and
From the other yaw rate detection electrode between the counter electrodes.
A semiconductor yaw rate sensor, comprising: a modulation circuit that obtains a detection signal superimposed on a transmission wave; and a band-pass filter whose center frequency matches the carrier wave and that passes a signal from the modulation circuit.