Abstract:
Disclosed is an angular velocity sensor superior in shock-proofness and in assembling properties. The angular velocity sensor  1  includes support members  10 A 1   , 10 A 2   , 10 B 1  and  10 B 2 , bonded to two nodal points of a pillar-shaped oscillator, generated on oscillations of the oscillator, in a manner of sandwiching the nodal points from upper and lower sides of the oscillator. The support members simultaneously serve for mechanically supporting and providing for electrical connection of the oscillator. Upper support members  10 A 1   , 10 A 2  and lower support members  10 B 1  and  10 B 2  for the nodal points include bent parts halfway, the bent parts being bent in the same direction with respect to the longitudinal direction of the oscillator. The upper support members and lower support members also include arms  12  extending at right angles to the up-and-down direction and to the longitudinal direction of the oscillator and junction parts  13  for the arms and the oscillator.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to an angular velocity sensor, including support members, which are bonded to nodal points of a pillar-shaped oscillator, generated on oscillations thereof, and which may be used simultaneously for mechanically supporting and electrically connecting said oscillator.  
         [0003]     This application claims priority of Japanese Patent Application No. 2003-351393, filed on Oct. 9, 2003, the entirety of which is incorporated by reference herein.  
         [0004]     2. Description of Related Art  
         [0005]     As angular velocity sensors for civil use, a so-called oscillation gyro type angular velocity sensor, in which bar-shaped oscillators are oscillated at a preset resonant frequency, and the Coriolis force, generated under the effect of the angular velocity, is detected by e.g. a piezoelectric device, to detect the angular angular velocity, is in wide-spread use.  
         [0006]     In these angular velocity sensors, the oscillator shape maybe exemplified by a square pillar shaped vibrating reed. For supporting the vibrating reed, two nodal points of the oscillations may be supported by electrically conductive members.  
         [0007]      FIG. 1  shows a method for supporting a conventional angular velocity sensor.  
         [0008]     In  FIG. 1 , a groove  95  is provided for extending longitudinally in a mid area along the width of a predetermined surface of an oscillator  96 , formed of a piezoelectric material, thereby splitting the predetermined surface of the oscillator  96  into a surface area  91   a  and a surface area  91   b . On the other hand, electrically conductive support members  40 ,  41  are mechanically and electrically connected to the oscillator  96  by connecting parts  40   a ,  41   a , respectively. The connecting methods may be exemplified by solder connection or by electrically conductive adhesives.  
         [0009]     With the above-described conventional angular velocity sensor, the oscillator  96  is oscillated by applying driving signals across the support members  40 ,  41 . If the oscillator  96  is rotated about the longitudinal direction as an axis, the Coriolis force is generated, so that electrical signals of opposite polarities, proportionate to the Corilois force, are generated on the surface areas  91   a ,  91   b  of the oscillator  96 . These electrical signals may be taken out from the support members  40  to detect angular angular velocity signals.  
         [0010]     The support members  40 ,  41  must have two contradictory functions, that is, a function of restraining the nodal points of oscillation and a function of affording certain degree of freedom to the nodal points, in order to permit oscillations of the oscillator  96 . If the restraint of the support members  40 ,  41  is strong, the amount of oscillations is decreased to lower the detection sensitivity for the angular velocity. If conversely the restraint is weak, the nodal points of oscillations are moved appreciably, thus presenting the problem of unstable characteristics.  
         [0011]     If, with the recent tendency towards device size reduction, the support members  40 ,  41  are linear in shape, as shown in  FIG. 1 , the distance is shorter, as a matter of course, thus raising the tenacity. Thus, such a technique is used which consists in bending the support members  50 ,  51  back and forth a plural number of times to lower the tenacity, as shown in  FIG. 2  (see, for example, the Patent Publication 1).  
         [0012]     On the other hand, an insert mold is used for securing a support member, in light of mass-producibility and cost reduction. With the insert mold, stationary positions of the upper and lower support members  50 ,  51  need to be shifted, because of the manufacture constraint, imposed on the insert mold. Thus, the upper and lower support members  50 ,  51  were necessarily arranged about the nodal points of the oscillation as axis.  
         [0000]     [Patent Publication 1] Japanese Patent Publication H-10-332379  
         [0013]     However, in case the upper and lower support members  50 ,  51  are arranged symmetrically, as shown in  FIG. 2 , the space free of the support members in the vicinity of the oscillator  96  is decreased, thus worsening the assembly property, such as handling. This problem is felt more acutely as the device size is reduced.  
         [0014]     On the other hand, if impact is applied from outside, the stress applied to the nodal points acts inversely at upper and lower points, because the upper and lower support members  50 ,  51  are arranged in the reverse directions, with the result that rotational moments are generated at the nodal points. Due to this rotational moment, there is raised a problem of destruction of the connection between the support members  50 ,  51  and the oscillator  96 .  
       SUMMARY OF THE INVENTION  
       [0015]     In view of the above-depicted problems of the prior art, it is an object of the present invention to provide an angular velocity sensor which is superior in impact-proofness and in assembling property.  
         [0016]     According to the present invention, the upper and lower support members, sandwiching an oscillator from upper and lower sides, in a support structure of the oscillator, used e.g. in an angular velocity sensor of the vibrating reed type, are bent in the same direction, thereby achieving an angular velocity sensor superior in impact-proofness and in assembling performance.  
         [0017]     An angular velocity sensor. of the present invention comprises support means bonded to two nodal points of a pillar-shaped oscillator, generated on oscillations of the oscillator, in a manner of sandwiching the nodal points from upper and lower sides of the oscillator. The support means also serves for mechanically supporting and providing for electrical connection of the oscillator. Upper support members and lower support members of the support means with respect to the nodal points include bent parts halfway. The bent parts are bent in the same direction with respect to the longitudinal direction of the oscillator. The Upper support members and lower support members of the support means also include arms extending at right angles to the up-and-down direction and to the longitudinal direction of the oscillator, and junction parts for connecting the arms to the oscillator.  
         [0018]     With the angular velocity sensor of the present invention, in which the upper and lower support members are arranged at substantially the same positions, the free space about the oscillator is appreciably increased as compared to that in the conventional system. This improves the handling properties and ease in operation during the assembling process to lower the production process. Moreover, further reduction in the device size may be possible.  
         [0019]     In addition, circuit components, such as chip components, may be provided in the increased space, thereby enabling device integration.  
         [0020]     Since the upper and lower support members are bent in the same direction and mounted facing each other, no rotational moment is applied to the nodal points of the oscillations, in case a force of impact is applied from outside, thus assuring impact proofness which is superior to that in case the upper and lower support members are arranged in the opposite directions to each other.  
         [0021]     The present invention is not limited to an angular velocity sensor of the vibrating reed type and may be applied to devices employing an oscillator which is in need of support members. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  shows an example of a conventional angular velocity sensor, in which  FIG. 1A ,  FIG. 1B  and  FIG. 1C  are a perspective view, a perspective view from above, and a perspective view from below, showing an oscillator part of a conventional angular velocity sensor, respectively.  
         [0023]      FIG. 2  shows an example of a conventional angular velocity sensor, in which  FIG. 2A ,  FIG. 2B  and  FIG. 2C  are a perspective view, a perspective view from above, and a perspective view from below, showing an oscillator part of another conventional angular velocity sensor, respectively.  
         [0024]      FIG. 3  is a perspective view showing an oscillator provided to an angular velocity sensor embodying the present invention.  
         [0025]      FIG. 4  is a block diagram showing an example of a circuit for employing the angular velocity sensor.  
         [0026]      FIG. 5  shows the results of comparison of physical properties of various materials.  
         [0027]      FIG. 6  is a perspective view showing the oscillator provided to an angular velocity sensor, looking from an upper side.  
         [0028]      FIG. 7  is a perspective view showing the state in which the angular velocity sensor has been directly mounted on a substrate without using components such as insert mold.  
         [0029]      FIG. 8  is a schematic plan view showing a typical shape of a connecting part of a support member for the oscillator in the angular velocity sensor.  
         [0030]      FIG. 9  shows an example of the method for manufacturing the angular velocity sensor.  
         [0031]      FIG. 10  is a graph showing measured results of sensitivity change characteristics against changes in the environmental temperature of the angular velocity sensor.  
         [0032]      FIG. 11  is a graph showing the temperature dependency of the resonation resistance/sensor sensitivity of the oscillator per se in the angular velocity sensor.  
         [0033]      FIG. 12  is a graph showing the relationship between the detuning degree and the aspect ratio of the cross-section of the oscillator in the angular velocity sensor.  
         [0034]      FIG. 13  is a cross-sectional view of the oscillator in the angular velocity sensor.  
         [0035]      FIG. 14  shows the relationship between the sensitivity and the electrode width ratio in the angular velocity sensor.  
         [0036]      FIG. 15  is a graph showing the relationship between the sensitivity and the detuning degree in the angular velocity sensor.  
         [0037]      FIG. 16  is a graph showing measured results of the oscillation frequency of the oscillator and the allowed adjustment quantity of a phase shifter of a driving circuit thereof, with the ratio of the thickness of the piezoelectric material in the angular velocity sensor to the thickness of the oscillator being changed. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]     Referring now to the drawings, certain preferred embodiments of the present invention are explained in detail. It is noted that the present invention is not limited to the embodiments as now explained, and may optionally be modified without departing from the scope of the invention.  
         [0039]      FIG. 3  is a perspective view of an angular velocity sensor  1 , embodying the present invention, and  FIG. 4  is a block diagram showing an embodiment of a driving detection circuit  30  for employing the angular velocity sensor  1 .  
         [0040]     Referring to  FIG. 3  and  FIG. 4 , the angular velocity sensor  1  of the present embodiment includes an oscillator la, operating as an oscillation gyroscope.  
         [0041]     Referring to  FIG. 3 , the oscillator la is composed of a substrate  2  and a piezoelectric member  3 , layered together, and is formed to a square pillar shape having a rectangular cross-section as taken along the plane perpendicular to the longitudinal direction, referred to below simply as the cross-section.  
         [0042]     This piezoelectric member  3  of the oscillator  1   a  is formed of piezoelectric ceramics, mainly composed of PZT (lead zirconate titanate), and is usually generated by polarization processing. A reference electrode  3   a  is formed on one  3 A of the major surfaces of the piezoelectric member  3  facing each other. This major surface  3 A, carrying the reference electrode, is the surface to be bonded to the substrate  2 . On the opposite side major surface  3 B of the piezoelectric member  3 , a driving electrode  3   b  and a pair of detection electrodes  3   c   1 ,  3   c   2  are arranged parallel to one another along the longitudinal direction of the oscillator  3 . The detection electrodes are separated from each other and extend with the driving electrode  3   b  in-between. The portion of the piezoelectric member carrying the driving electrode  3   b  operates as a piezoelectric device for driving  31 , while the portions of the piezoelectric member carrying the detection electrodes  3   c   1 ,  3   c   2  operate as piezoelectric devices for detection  32 ,  33 .  
         [0043]     The substrate  2  of the present oscillator la is formed of a material, which differs from PZT, and which, in the physical properties, is equivalent to or lower than the PZT, as the main component of the piezoelectric ceramics of the piezoelectric member  3 , such as ceramic materials, mainly composed of carbon, such as amorphous carbon or graphite.  
         [0044]     The results of comparison of the physical properties of the various materials are as shown in  FIG. 5 , from which it is seen that, while the PZT (BZ27M5 material), as the main component of the piezoelectric ceramics, has the Young&#39;s modulus of 103 GPa and a thermal expansion coefficient of 32×10 −7  to 35×10 −7 , the amorphous carbon has the Young&#39;s modulus of 30 to 33 GPa and a thermal expansion coefficient of 30×10 −7  to 35×10 −7 , and the graphite has the Young&#39;s modulus of 14 GPa and a thermal expansion coefficient of 32×10 −7 . Thus, the ceramics material, mainly composed of carbon, such as amorphous carbon or graphite, has physical properties, such as Young&#39;s modulus or thermal expansion coefficient, equal or inferior to those of PZT, as the main component of the piezoelectric ceramics.  
         [0045]     With this angular velocity sensor  1 , the piezoelectric member  3  is thinner in thickness than the substrate  2 . For example, the thickness of the piezoelectric member  3  and that of the substrate  2  are set to 0.2 mm and 0.8 mm, respectively.  
         [0046]     The oscillator la in the form of the square pillar is carried by support members  10 A 1 ,  10 A 2 ,  10 B 1  and  10 B 2 , which are bonded to two nodal points of the oscillator, generated on oscillations, for sandwiching these nodal points from the vertical direction. The node parts of the oscillator, generated at the time of oscillations, operate as mechanical support and the electrical connection portions.  
         [0047]     The support members  10 A 1 ,  10 A 2 ,  10 B 1  and  10 B 2  are formed e.g. of bronze or stainless steel. The support members  10 A 1 ,  10 A 2  overlying the nodal points and the support members  10 B 1 ,  10 B 2  underlying the nodal points, each include an arm  12 , including bent parts  11 ,  11  halfway, and a connecting portion  13  interconnecting the arm  12  and the oscillator  1   a . These parts are bent in the same direction relative to the longitudinal direction of the oscillator  1   a . Each arm  12  extends in a direction perpendicular to the up-and-down direction and the longitudinal direction of the oscillator la. The upper support member  10 A 1  has the connecting portion  13  bonded to the paired detection electrodes  3   c   1 ,  3   c   2  at the nodal point of the oscillations of the oscillator  1   a , while the support member  10 A 2  has the connecting portion  13  bonded to the driving electrode  3   b  at the nodal point of the oscillations of the oscillator  1   a . In an area of the piezoelectric member where the support member  10 A 2  bonded to the driving electrode  3   b  straddles the detection electrodes  3   c   1 ,  3   c   2 , the detection electrodes  3   c   1 ,  3   c   2  are partially removed to provide an insulator  18 , so that the arm  11  of the support member  10 A 2  is not contacted with the detection electrodes  3   c   1 ,  3   c   2 .  
         [0048]     As for the lower support members  10 B 1  and  10 B 2 , the connecting portion  13  is bonded to the substrate  2  of amorphous carbon, at the nodal point of oscillations of the oscillator  1   a , and is thereby electrically connected, via the substrate  2 , to the reference electrode  3   a.    
         [0049]     The piezoelectric member  3  of the angular velocity sensor  1  also has the function of producing oscillations and the function of detecting the oscillations. Thus, the angular velocity sensor  1  detects the Coriolis force, generated by rotation of the oscillator  1   a  during the oscillations by the function of producing the oscillations.  
         [0050]     That is, the angular velocity sensor  1  applies the voltage across the reference electrode  3   a  provided to the major surface  3 A of the piezoelectric member  3  of the oscillator  1   a , obtained on layering the substrate  2  and the piezoelectric member  3  together, and the driving electrode  3   b , provided to the other major surface  3 B, to cause oscillations of the oscillator  1   a  and detect the Coriolis force generated in the oscillator  1   a  to output an angular velocity detection signal as a signal corresponding to the Coriolis force from the detection electrodes  3   c   1 ,  3   c   2  provided to the opposite major surface  3 B.  
         [0051]     The oscillator  1   a  of the angular velocity sensor  1  is coupled to the driving detection circuit  30  via support members  10 A 1 ,  10 B 2  as shown in  FIG. 4 . The connecting portion  13  becomes the nodal point of oscillations of the oscillator  1   a , oscillated in resonation by this driving detection circuit  30 , such that the oscillator  1   a  is oscillated in resonation with the axial ends thereof as free ends.  
         [0052]     With the present angular velocity sensor  1 , in which the upper and lower support members  10 A 1 ,  10 A 2 ,  10 B 1  and  10 B 2  are arranged at substantially the same position, the free space about the oscillator  1   a  may be appreciably increased as compared to that of the conventional system. This improves the handling property and ease in operation during assembling, thereby reducing the manufacture cost. Moreover, circuit components, such as chip components, may be arranged in the increased space, thus assuring facilitated device integration. If a force of impact is applied from outside, the upper and lower support members  10 A 1 ,  10 A 2 ,  10 B 1  and  10 B 2  are arranged facing each other for flexing in the same direction, such that no rotational moment is applied to the nodal points of oscillations, thus assuring improved shock-proofness as compared to the case in which the upper and lower support members  10 A 1 ,  10 A 2 ,  10 B 1  and  10 B 2  are arranged facing each other for flexing in the opposite directions.  
         [0053]     Meanwhile, although the upper support members  10 A 1 ,  10 A 2 , and the lower support members  10 B 1  and  10 B 2  are arranged in vertically superposed relation to each other, as shown in  FIG. 6 , connection to the insert mold may be achieved unobjectionably by enlarging the shape of the stationary portions of the upper support members  10 A 1 ,  10 A 2 . In addition, the angular velocity sensor may directly be mounted on the substrate  60  without using components such as insert mold, by bending and elongating the upper support members  10 A 1 ,  10 A 2 , and by providing a connection part  15  for a substrate  60  on these support members  10 A 1 ,  10 A 2 , as shown in  FIG. 7 .  
         [0054]     The connecting portion  13  on the distal end of the arm  12  is bifurcated, so that the solder or an electrically conductive adhesive is intruded into the space defined between the bifurcated portions to achieve a high mechanical strength. If, with the size reduction of the oscillator  1   a , the connecting portion  13  is reduced in size, the mechanical connection strength may be increased in case the connecting portion  13  is semi-circular, as shown in  FIG. 8 (A), rather than circular in profile, for a limited space, since then the radius of the inner circle may be larger. In case the connecting portion  13  is furcated in three or more branches, similar effects may be achieved with a Y-shape shown in  FIG. 8 (B), a U-shape as shown in  FIG. 8 (C) or a tri-furcated shape, as shown in  FIG. 8 (D).  
         [0055]     Referring to  FIG. 4 , the driving detection circuit  30  includes an impedance converting circuit  4  and a differential amplifier  7 , connected to the detection electrodes  3   c   1 ,  3   c   2  of the oscillator  1   a  via support member  10 A 1 , an adder  5  connected to the impedance converting circuit  4 , an oscillation circuit  6 , connected to the adder  5 , a synchronization detection circuit  8 , connected to the oscillation circuit  6  and to the differential amplifier  7 , and a d.c. amplifier  9 , connected to the synchronization detection circuit  8 . An output of the oscillation circuit  6  is coupled to the driving electrode  3   b  via support member  10 A 2 . The reference electrode  3   a  of the oscillator la is electrically connected to the substrate  2 , formed of amorphous carbon, and is connected to a reference potential  37  via support members  10 B 1  and  10 B 2 .  
         [0056]     With the present driving detection circuit  30 , the oscillator  1   a  is oscillated by a free oscillation circuit, formed by the oscillator  1   a , impedance converting circuit  4 , adder  5  and the oscillation circuit  6 , and is warped and oscillated in a direction perpendicular to the forming surface of the piezoelectric device for driving  31 , used as a driving member.  
         [0057]     That is, the oscillator  1   a  is driven by an oscillation output Vgo of the oscillation circuit  6  being supplied to the piezoelectric device for driving  31 . An output Vg 1  of the piezoelectric device for detection  32  for the oscillator  1   a  and an output Vgr of the piezoelectric device for detection  33  are entered via impedance converting circuit  4  to the adder  5  as Vz 1 , Vzr. An addition output Vsa by this adder  5  is fed back to the oscillation circuit  6 .  
         [0058]     If, in this state, the oscillator  1   a  is rotated about its long axis, the direction of warping and oscillations is changed by the Coriolis force. Hence, an output differential Vg 1 -Vgr is generated between the piezoelectric devices for detection  32  and  33  to generate an output Vda from the differential amplifier  7 . The signal for driving the oscillator  1   a  at this time is the output of the piezoelectric devices for detection  32  and  33  for the standstill time and is a signal which is in phase and of the same magnitude for the piezoelectric devices for detection  32  and  33 . Hence, the signals for actuating the oscillator  1   a  are counterbalanced by the differential amplifier  7 . The signals by the Coriolis force are signals Vc 1 , Vcr, which are antiphase and of the same magnitude in the piezoelectric devices for detection  32  and  33 . Hence, the output Vda of the differential amplifier  7  is proportionate to Vc 1 -Vcr.  
         [0059]     The output Vda of this differential amplifier  7  is subjected to synchronous detection by the synchronization detection circuit  8  and thereby converted into a d.c. signal Vsd. This d.c. signal Vsd is obtained by full-wave rectifying the output Vda of the differential amplifier  7  at a timing of the clock signal Vck, output in synchronism with the driving signal by the oscillation circuit  6 , and by integrating the full-wave rectified signal. This signal Vsd may be d.c. amplified by the d.c. amplifier  9  to a predetermined magnitude to detect only an angular velocity signal produced by rotation.  
         [0060]     The impedance converting circuit  4  has a high impedance Z2 at an input and a low impedance Z3 at an output, and is used for separating an impedance Z1 across the piezoelectric devices  32 ,  33  and an impedance Z4 across the inputs of the adder  5 . Assuming that the impedance converting circuit  4  is not provided, the impedance Z1 across the piezoelectric devices  32 ,  33  and an impedance Z4 across the inputs of the adder  5  are not separated from each other, such that the output difference produced across the piezoelectric devices  32 ,  33  is the above output difference multiplied by Z4/(Z1+Z4), thus being smaller than the value when there is provided the impedance converting circuit.  
         [0061]     The impedance converting circuit  4  simply converts the impedance across the input and the output and does not affect the signal magnitude. Hence, the output Vg 1  of the piezoelectric device  32  is of the same magnitude as one output Vz 1  of the impedance converting circuit  4 , such that the output Vgr of the piezoelectric device  33  is of the same magnitude as the other output Vzr of the impedance converting circuit  4 . Thus, with the output Vsa of the adder  5 , the signal conforming to the Coriolis force is counterbalanced, such that the output is the sum of the outputs of the piezoelectric devices  32 ,  33  for standstill time. The positive feedback loop by the adder  5 , oscillator  1   a , impedance converting circuit  4  and the oscillation circuit  6  make up an oscillation circuit and is subjected to self-excited oscillations at the resonant frequency of the oscillator  1   a.    
         [0062]     If an output voltage of a switching regulator, produced with the oscillation frequency not less than hundreds of kHz, is supplied to the power supply of the driving detection circuit  30 , the power supply noise also appears across the two outputs of the impedance converting circuit  4 , thus proving a signal noise. If, in this case, the power supply noise appears in a differential fashion in the two outputs of the impedance converting circuit  4 , there is produced a potential difference, ascribable to the noise, across the two outputs Vz 1  and Vzr. The two outputs Vz 1  and Vzr of the impedance converting circuit  4 , corrupted by the signal noise, are summed by the adder  5  and supplied to the oscillator  1   a  through the oscillation circuit  6 .  
         [0063]     As a matter of course, the aforesaid signal noise is superposed on the output Vgo of the oscillation circuit  6 . However, since the oscillator  1   a  operates similarly to a bandpass filter, and hence the frequency components different than the resonant frequency of the oscillator  1   a  are removed. Thus, with the present driving detection circuit  30 , the output of the piezoelectric devices  32 ,  33  is freed of the aforementioned signal noise, so that the aforementioned signal noise is not contained in the output Vda, and hence is not affected by the power supply noise.  
         [0064]     Moreover, in the present embodiment, since the detection electrodes  3   c   1 ,  3   c   2  and the driving electrode  3   b  are arranged on the same surface of the angular velocity sensor  1 , the oscillator  1   a  may be produced, as shown in  FIG. 9 (C), by stacking a wafer  20 , as a substrate matrix, and a wafer  30 , as a matrix of the piezoelectric material, as shown in  FIG. 9 (A), bonding these wafers together, and slicing out square-shaped pillars from the so bonded wafers, as shown in  FIG. 9 (B). The wafer  30  is subjected to electrode plating on both sides thereof, before being bonded to the wafer  20 , to form respective electrodes thereon. The oscillator  1   a , produced by the above process, is extremely high in precision and may be produced to an extremely small size, while mass-producing effects may also be achieved. Additionally, the problem of non-alignment in the bonding position may be overcome. Moreover, the substrate exhibits machining performance comparable to that of the piezoelectric material, thus assuring facilitated slicing out of the oscillator from the substrate wafer and the piezoelectric wafer, as described above.  
         [0065]     There is also no necessity of providing the steps difficult to perform, such as bonding piezoelectric devices to the elastic metal oscillators or printing the electrodes on the curved surfaces.  
         [0066]     With the present angular velocity sensor  1 , the substrate  2 , bonded to the reference electrode  3   a , formed on one  3 A of the major surfaces of the piezoelectric member  3 , is formed of an electrically conductive material. It is also possible that the substrate  2 , formed of an insulating material, is plated with an electrically conductive material, and an electrode, electrically connected to the reference electrode  3   a , is formed on the two major surfaces  2 A,  2 B of the substrate  2  facing the major surface  3 A of the piezoelectric member  3 , and at least one lateral surface thereof contiguous to the two major surfaces  2 A,  2 B, thereby enabling a driving electrical field to be applied efficiently to the piezoelectric member  3  to improve the sensitivity.  
         [0067]     Although it may be contemplated that technical difficulties are enhanced with reduction in device size to render it difficult to achieve the precision, this problem may be addressed by applying the ultra-fine processing technique already established in the field of the LSI or head machining. Since the high dimensional accuracy may be achieved, it is possible to simplify the frequency adjustment of the oscillator.  
         [0068]     In addition, by applying the self-excited oscillation type driving circuit, the angular velocity sensor  1  of a high accuracy may be achieved by an extremely simplified circuit.  
         [0069]     Since the present angular velocity sensor  1  is of the self-excited oscillation type, there is no risk that the sensitivity of the sensor is lowered under the effect of temperature characteristics, as in the case of the separately excited angular velocity sensor.  
         [0070]      FIG. 10  shows measured results of sensitivity change characteristics against changes in the environmental temperature of the angular velocity sensor  1 . In  FIG. 10 , characteristics A 1  denote characteristics of the angular velocity sensor  1  in case the substrate  2  is formed of a material (amorphous carbon) having the Young&#39;s modulus and the thermal expansion coefficient equivalent or inferior to those of PZT, as a main component of the piezoelectric ceramics, making up the piezoelectric member  3 , whilst characteristics B 1  denote characteristics of the angular velocity sensor  1  in case the substrate  2  is formed of PZT.  
         [0071]     As may be seen from this  FIG. 10 , the oscillator  1   a  may be constructed which is less susceptible to changes in the environmental temperature by forming the substrate  2  of a material (amorphous carbon) having the Young&#39;s modulus and the thermal expansion coefficient equivalent or inferior to those of PZT, as a main component of the piezoelectric ceramics making up the piezoelectric member  3 .  
         [0072]     Moreover, with the present oscillator  1   a , changes with temperature of the resonant resistance of the oscillator per se may be lower, as shown by characteristics A 2 , shown in  FIG. 11 , than those in case the substrate is formed of PZT, as shown by characteristics B 2 , as a result of which the changes with temperature of the detection sensitivity of the angular velocity sensor are diminished. In addition, the correction may be facilitated, because the mode of the changes with temperature is linear.  
         [0073]      FIG. 12  shows the relationship between the detuning degree and the aspect ratio of the cross-section of the oscillator  1   a  in this angular velocity sensor  1 . Meanwhile, the detuning degree means the difference between the resonant frequency in the longitudinal direction and that in the transverse direction. The smaller the detuning degree, the higher becomes the sensitivity.  
         [0074]     In  FIG. 12 , characteristics A 3  denote those of the angular velocity sensor  1  in case the substrate  2  is formed of a material (amorphous carbon), having Young&#39;s modulus and the thermal expansion coefficient equivalent or inferior to those of PZT, as a main component of the piezoelectric ceramics making up the piezoelectric member  3 , and characteristics A 3  denote those in case the substrate  2  is formed of PZT.  
         [0075]     With the present angular velocity sensor  1 , the detuning degree may be in the vicinity of zero, by setting the ratio of the total width and the thickness, that is, the aspect ratio, of the cross-section of the oscillator  1   a , to 1.030 to 1.055, as indicated by a black frame which stands for the range of the aspect ratio of the oscillator  1   a  for the characteristics A 3  corresponding to the detuning degree of 0±200 Hz in  FIG. 12 . The detuning degree may readily positively adjusted by maintaining this range in the initial state.  
         [0076]     Meanwhile, in the present angular velocity sensor  1 , detection characteristics may be optimized by differentiating the widthwise electrode dimension W1 for the driving electrode  3   b  from the width-wise electrode dimension W2 for the detection electrodes  3   c   1 ,  3   c   2 , formed on the same plane as that for the driving electrode  3   b , as shown in  FIG. 13 . That is, the driving efficiency may be adjusted by adjusting the shape or the size of the driving electrode  3   b , while the detection efficiency may be adjusted by adjusting the shape or the size of the detection electrodes  3   c   1 ,  3   c   2 .  
         [0077]      FIG. 14  shows the measured results of the sensitivity of the angular velocity sensor  1 , when the ratio W1/W2, where W1 is the width of the driving electrode  3   b  and W2 is the width of the detection electrodes  3   c   1 ,  3   c   2 , is changed in a range of 1 to 2.8.  
         [0078]     It is seen from sensitivity characteristics, shown in  FIG. 14 , that the angular velocity sensor  1  exhibits sensitivity for the ratio W1/W2 such that 1&lt;W1/W2≦2.6, which is superior to that for the ratio W1/W2=1, and that, in particular, the angular velocity sensor  1  exhibits sensitivity for the ratio W1/W2 such that 1.8&lt;W1/W2 ≦2.0, which is twice or more as high as the sensitivity for W1/W2=1.  
         [0079]      FIG. 15  shows the relationship between the detuning degree and the sensitivity of the angular velocity sensor  1 .  
         [0080]     It is noted that the detuning degree means the difference between the resonant frequency along the longitudinal direction and that along the transverse direction and, the smaller the detuning degree, the higher becomes the sensitivity. TYPE 1 stands for a case where W1/W2 =1, whilst TYPE 2 stands for a case where W1/W2=1.9. As may be seen form  FIG. 15 , the sensitivity is preponderantly higher for W1/W2=1.9 than for W1/W2=1, without regard to the prevailing range of the detuning degree.  
         [0081]     In the present embodiment of the angular velocity sensor  1 , the thickness T1 of the piezoelectric member  3  is thinner than the thickness T1 of the substrate  2  and, as an example, the thickness T1 of the piezoelectric member  3  is set to 0.2 mm and that T2 of the substrate  2  is set to 0.8 mm. The oscillation frequency of the oscillator  1   a  and the allowed adjustment magnitude of the phase shifter of the driving circuit were measured, as the ratio of the thickness T1 of the piezoelectric member  3  to the thickness T0 of the oscillator la was changed, and the results shown in  FIG. 16  were obtained. With the above-described structure of the angular velocity sensor  1 , the resonant resistance and the oscillation frequency can be compressed to within a preset range, while the phase margin of the driving circuit for self-excited oscillations of the oscillator  1   a  can be assured, by setting the range of the ratio of the thickness T1 of the piezoelectric member  3  and the thickness T0 of the oscillator to 0.14 to 0.27, more specifically, by setting the thickness T1 of the piezoelectric member  3  to 0.15 mm to 0.25 mm against the thickness T0 of the oscillator  1   a  of 0.9 mm to 1.1 mm. In addition, adjustment to the preset detuning degree or the oscillation frequency may be facilitated because the degree of frequency changes against dimensional changes of the oscillator  1   a  may be decreased.