Piezoelectric element for an automatic frequency control circuit, oscillating mechanical system and device comprising the same, and method for manufacturing the piezoelectric element

Patent metadata

Field	Value
Publication number	US-10983479-B2
Application number	US-201816104212-A
Country	US
Kind code	B2
Filing date	Aug 17, 2018
Priority date	Sep 14, 2017
Publication date	Apr 20, 2021
Grant date	Apr 20, 2021

Abstract

A piezoelectric element for an automatic frequency control circuit, the element including: a balance spring formed of a strip of piezoelectric material; at least a first electrode, configured to be connected to the circuit and being disposed on all or part of one side of the strip; at least a second electrode configured to be connected to the circuit and being disposed on all or part of another one side of the strip distinct from the one side on which the first electrode is disposed, the piezoelectric material being a piezoelectric crystal or a piezoelectric ceramic; and at least two discontinuous layers of an insulating material, each discontinuous layer being disposed on at least one side of the strip and separating the first electrode from the second electrode, the layers of insulating material being distributed on predetermined portions of the balance spring substantially forming arcs in a predetermined angular periodicity.

First claim

What is claimed is:

1. A piezoelectric element for an automatic frequency control circuit, the piezoelectric element comprising:
a balance spring formed of a strip of piezoelectric material;
at least a first electrode, configured to be connected to the automatic frequency control circuit, and being disposed on all or part of one side of the strip of piezoelectric material;
at least a second electrode configured to be connected to the automatic frequency control circuit, and being disposed on all or part of another one side of the strip of piezoelectric material distinct from the one side on which the first electrode is disposed,
wherein the piezoelectric material is a piezoelectric crystal or a piezoelectric ceramic; and
at least two discontinuous layers of an insulating material, each discontinuous layer of insulating material being disposed on at least one side of the strip of piezoelectric material and separating the first electrode from the second electrode, the at least two discontinuous layers of insulating material being distributed on predetermined portions of the balance spring substantially forming arcs in a predetermined angular periodicity.

2. The piezoelectric element according to claim 1 ,
wherein the first electrode is disposed on all or part of a first side of the strip of piezoelectric material,
wherein the second electrode is disposed on all or part of a second side of the strip of piezoelectric material opposite to the first side,
wherein a first discontinuous layer of insulating material is disposed on a third side of the strip of piezoelectric material, and
wherein a second discontinuous layer of insulating material is disposed on a fourth side of the strip of piezoelectric material opposite to the third side.

3. The piezoelectric element according to claim 1 ,
wherein the piezoelectric element includes two first electrodes, two second electrodes, and four discontinuous layers of insulating material,
wherein the two first electrodes are connected in a first connection terminal configured to be connected to the automatic frequency control circuit, and are disposed on a first pair of opposite sides of the strip of piezoelectric material,
wherein the two second electrodes are connected in a second connection terminal configured to be connected to the automatic frequency control circuit, and are disposed on a second pair of opposite sides of the strip of piezoelectric material, and
wherein each discontinuous layer of insulating material is disposed astride on one of the sides of the first pair of sides and one of the sides of the second pair of sides of the strip of piezoelectric material.

4. The piezoelectric element according to claim 1 , wherein the piezoelectric crystal is a single crystal.

5. The piezoelectric element according to claim 1 , wherein the piezoelectric crystal is a single crystal chosen from the group consisting of topaz, berlinite, lithium niobate, lithium tantalate, gallium phosphate, gallium arsenate, aluminium silicate, germanium dioxide, a single crystal tourmaline, a single crystal from the group of zinc blende structure III-V semiconductors, or a single crystal from the group of wurtzite structure II-VI semiconductors.

6. The piezoelectric element according to claim 1 , wherein the piezoelectric crystal is single crystal quartz.

7. The piezoelectric element according to claim 6 , wherein the balance spring is machined in Z-cut single crystal quartz.

8. The piezoelectric element according to claim 6 , wherein the predetermined angular periodicity is substantially equal to 120°.

9. The piezoelectric element according to claim 6 , wherein the arcs each define an angular sector substantially equal to 60°.

10. The piezoelectric element according to claim 1 ,
wherein the piezoelectric element also includes a first groove made in a first upper side of the strip of piezoelectric material and a second groove made in a second lower side of the piezoelectric material strip, and
wherein the first electrode is disposed in the first groove, and the second electrode is disposed in the second groove.

11. The piezoelectric element according to claim 1 , wherein the insulating material is an oxide.

12. The piezoelectric element according to claim 1 , wherein the insulating material is chosen from the group comprising silica, alumina, hafnium oxide, and silicon nitride.

13. A method for manufacturing a piezoelectric element according to claim 1 , the method including the steps of:
machining a strip of piezoelectric material, the piezoelectric material being a piezoelectric crystal or a piezoelectric ceramic, from a crystal or a piezoelectric ceramic plate;
placing a first electrode on all or part of a first side of the strip of piezoelectric material;
placing a second electrode on all or part of a second side of the strip of piezoelectric material;
placing, on at least two faces of the strip of piezoelectric material, at least two discontinuous layers of an insulating material, each discontinuous layer of insulating material separating the first electrode from the second electrode, and the at least two discontinuous layers of insulating material being distributed over predetermined portions of the strip of piezoelectric material; and
winding the strip of piezoelectric material into a shape of a balance spring, the at least two discontinuous layers of insulating material being distributed over the predetermined portions of the strip of piezoelectric material, so as to substantially form arcs on the balance spring in a predetermined angular periodicity.

14. The manufacturing method according to claim 13 ,
wherein the balance spring of the wound strip of piezoelectric material is machined from a single crystal plate,
wherein the single crystal plate is coated with a first layer of Au/Cr and with a second layer of photosensitive resin, the first and the second layers then being exposed by photolithography,
wherein the single crystal plate is then machined by wet means using a hydrofluoric acid and using the Au/Cr layer as a mask,
wherein the photosensitive resin and the Au/Cr layer are removed,
wherein an insulating layer is deposited by cathodic sputtering or vacuum deposition, and is then structured by photolithography and wet etching, and
wherein the first and the second electrodes are deposited through a mask or structured by photolithography.

15. The manufacturing method according to claim 14 , wherein the single crystal plate is a quartz plate.

16. The manufacturing method according to claim 14 , wherein the insulating layer is an oxide, a nitride, a carbide, or a polymer.

17. An oscillating mechanical system for an automatic frequency control circuit, the oscillating mechanical system comprising:
a balance; and
a piezoelectric element provided with a balance spring, the balance spring being mounted on the balance and being formed of a strip of piezoelectric material, the piezoelectric element further comprising:
at least a first electrode, configured to be connected to the automatic frequency control circuit, and being disposed on all or part of one side of the strip of piezoelectric material;
at least a second electrode configured to be connected to the automatic frequency control circuit, and being disposed on all or part of another one side of the strip of piezoelectric material distinct from the one side on which the first electrode is disposed,
wherein the piezoelectric material is a piezoelectric crystal or a piezoelectric ceramic; and
at least two discontinuous layers of an insulating material, each discon

Assignees

• Swatch Group Res & Dev Ltd

Inventors

• Haemmerli Alexandre
• Gueissaz Francois
• Tombez Lionel
• Schnyder Bernhard
• Dalla Piazza Silvio

Classifications

• G04C3/047 Primary

  using other coupling means, e.g. electrostrictive, magnetostrictive · CPC title

• H03H9/19

  consisting of quartz · CPC title

• G04B17/063 Primary

  Balance construction (balances with frequency adjustment screw G04B18/006; balances with temperature compensation G04B17/222; balancing devices G04B17/28) · CPC title

• H03H9/02023

  consisting of quartz · CPC title

• G04B17/066

  Manufacture of the spiral spring (locking of the spiral spring by the regulating lever G04B18/026; spiral spring with temperature compensation G04B17/227; fixation of the spiral spring on the collet G04B17/32; mainspring G04B1/14) · CPC title