Angular velocity sensor and process for manufacturing the same

• US 6,532,817 B1
• Filed: 04/27/1999
• Issued: 03/18/2003
• Est. Priority Date: 05/06/1998
• Status: Expired due to Fees

• Current Assignee: Nihon Dempa Kogyo Company Limited, Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yukawa, Junichi, Ono, Kozo, Nakamaru, Kuniharu, Ishihara, Minoru, Terada, Jiro
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US09/300,009
• Time in Patent Office: 1,421 Days
• Field of Search: 735/041.6, 735/041.5, 735/041.4, 735/041.2, 735/040.4, 310/329, 310/370
• US Class Current: 73/504.16
• CPC Class Codes: G01C 19/5607 using vibrating tuning forks double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719

Abstract

An integral bimorph angular rate sensor is formed by directly bonding two tuning fork members in the thickness direction to enhance the detecting sensitivity of the angular velocity sensor. The individual tuning fork members are formed from a single crystalline piezoelectric material such as quartz and are bonded in the crystal axis direction as to establish a piezoelectric phenomenon wherein the piezoelectric materials of the bonded tuning fork members have inverse polarities in their width or thickness directions.

Claims

1. An angular velocity sensor comprising:

a tuning fork having;

(a) a first tuning fork member having at least two arms made of single crystalline piezoelectric material and at least one root member joining said arms; and

a second tuning fork member having a shape generally similar to that of the first tuning fork member, the second fork member made of single crystalline piezoelectric material,

said first tuning fork member and second tuning fork member being directly bonded to each other in the thickness direction of the first tuning fork member and second tuning fork member, said bond forming an interface therebetween extending in the width direction thereof without a central electrode and without adhesive disposed between said first and second tuning fork members, such that the polarity of the electric axis of the piezoelectric material for each of the first and second tuning fork members is inverted from each other in the width direction thereof, said tuning fork thereby comprising at least a first tuning fork arm and a second tuning fork arm, each of said first and second tuning fork arms having two opposed side surfaces extending across said interface and two opposed main surfaces orthogonal to said side surfaces, and a tuning fork root between said tuning fork arms;

(b) sense electrodes disposed across said interface on the two opposed side surfaces of each of said first and second tuning fork arms for detecting the electric charges generated as a result of the angular rotation of said sensor; and

(c) drive electrodes disposed on two opposed main surfaces of said first tuning fork arm for causing the tuning fork to vibrate in the width direction thereof.

2. The angular velocity sensor as claimed in claim 1 wherein the first tuning fork member and the second tuning fork member are directly bonded according to a method comprising the steps of:

smoothing the surfaces of the first tuning fork member and second tuning fork member;

performing a hydrophilic treatment on the surfaces thereof;

adsorbing hydroxide radicals onto the surfaces thereof; and

superposing and thermally treating the first tuning fork member and second tuning fork member.

3. An angular velocity sensor comprising:

a first tuning fork member including at least two arms made of single crystalline piezoelectric material and at least one root member joining said arms; and

a second tuning fork member having a shape generally similar to that of said first tuning fork member and made of single crystalline piezoelectric material directly bonded to the first tuning fork member in the thickness direction thereof, said bond forming an interface between said tuning fork members extending in the width direction thereof without the use of adhesive and without a central electrode disposed in said interface, with the polarity of the electric axes of the piezoelectric material of said first and second tuning fork members inverted from each other in the width direction;

wherein said bonded tuning fork members form a tuning fork with two tuning fork arms, each arm having four peripheral faces, two of said peripheral faces on opposed side surfaces of each of said tuning fork arms extending in the thickness direction across said interface; and

sense electrodes disposed on at least one of said opposed side surfaces extending across said interface for detecting electric charges generated as a result of the angular rotation of said sensor.

4. The angular velocity sensor as set forth in claim 3 further comprising at least one drive electrode disposed on one of said peripheral faces on at least one of said tuning fork arms extending in the width direction orthogonal to said side surfaces for causing the tuning fork arms of said sensor to vibrate in the width direction.

5. An angular velocity sensor comprising:

a tuning fork for the angular velocity sensor including;

a first tuning fork member having at least two arms made of single crystalline piezoelectric material and at least one root member joining said arms;

a second tuning fork member having a shape generally similar to that of the first tuning fork member, the second fork member made of single crystalline piezoelectric material, wherein said first tuning fork member and second tuning fork member are directly bonded to each other in the thickness direction and in the crystalline axis direction of the first tuning fork member and second tuning fork member, said bond forming an interface between said tuning fork members, and wherein said crystalline axis direction is defined so that the polarities of piezoelectric phenomenon of said first and second tuning fork members are opposite to each other in the width direction;

a drive electrode disposed on a first surface of a first arm of said tuning fork where said first and second tuning fork members are opposite to each other;

a first sense electrode disposed across said interface on a side surface of a first arm of said tuning fork where said first and second tuning fork members are opposite to each other; and

a second sense electrode disposed across said interface on a side surface of a second arm of said tuning fork where said first and second tuning fork members are opposite to each other;

wherein said first sense electrode and second sense electrode are formed so that each of said first sense electrode and seconds sense electrode extends over a boundary of bonding of said first and second tuning fork members;

wherein said drive electrode causes vibration of said tuning fork in the direction which is parallel to said first surface of said tuning fork; and

wherein said first and second sense electrodes detect electric charges generated by vibration of said tuning fork in the direction perpendicular to said first surface of said tuning fork.

6. The angular velocity sensor as claimed in claim 5, wherein the first tuning fork member and the second tuning fork member are directly bonded according to a method including the steps of:

smoothing the surfaces of the first tuning fork member and second tuning fork member;

performing a hydrophilic treatment on the surfaces thereof;

adsorbing hydroxide radicals onto the surfaces thereof; and

superposing and thermally treating the first tuning fork member and second tuning fork member.