WO1998001297A1

WO1998001297A1 - Quartz construction

Info

Publication number: WO1998001297A1
Application number: PCT/US1997/011193
Authority: WO
Inventors: Leroy C. Delatorre
Original assignee: Panex Corporation
Priority date: 1996-07-09
Filing date: 1997-07-01
Publication date: 1998-01-15
Also published as: WO1998001732A1

Abstract

A construction consisting of separate quartz or glass members (40A, 40B) with a bonding system (59A, 59B) for attaching the members to one another. The bonding means includes metalized sealing surfaces (59A, 59B) on facing surfaces of adjacent members where the metalized sealing surfaces (59A, 59B) consist of layers of adhesive material (60), a barrier material (64) and a low temperature bonding metal (66) material where the layers define a thickness in Angstroms which is substantially less than the thickness of a glass frit used for similar bonding and which permits bonding of the bonding metal material at cold welding temperatures so that the surfaces of the bonding metal material can provide a bonded joint with a minimum of thickness thereby to relieve stress factors and preserve the original dimensional tolerances in a bonded joint.

Description

QUARTZ CONSTRUCTION

FIELD OF THE INVENTION

This invention relates to a quartz construction and more particularly to a system for bonding quartz members to one another.

BACKGROUND OF THE INVENTION

Quartz sensors are commonly used as pressure sensors in oil field applications of high temperature and pressure and require high accuracy. Quartz sensors are commonly used as pressure sensors in oil field applications at high temperature and pressure and require a high degree of accuracy.

Principally, a sensor requires a good quality-to-perfect crystal, selection of the type of cut, and extensive machining. Thickness shear mode quartz pressure sensors are highly temperature sensitive relative to their pressure response and a variety of systems have been tried to overcome the temperature dependent effect. For example, two crystals can be utilized where one of the crystals provides a reference. The use of two crystals obviously affect the temperature dynamic response because now there are two different temperature sensitive crystals. Various types of crystal cuts are also employed to minimize the temperature effects.

In a transducer construction, end cap members are typically attached to the ends of tubular crystal housing by a relatively thick glass or ceramic frit at a relatively high bonding temperature which can cause degradation of metal films. In a glass joint between the cap member and the sensor body there are two significant problems, i.e., a glass ceramic frit does not match the temperature coefficient of expansion for the quartz cap member and the sensor body and the glass frit joint can introduce measurement errors due to imperfect elasticity. In time and use, creep in the glass frit joint may occur which will affect loading of the resonator. To minimize these effects, the length of the housing wall between a centrally located resonator and the end caps are made as long as possible so that the glass frit joint is removed from the vicinity of the resonator. This, of course, increases the machining required of the housing to form the internal resonator section. Machining of quartz is not a simple proposition.

Another reason for a long housing length is an amplification factor of the radial force of pressure on the resonator due to the pressure applied. A long housing length will increase the pressure sensitivity of the sensor since the effect of radial force on resonator frequency is the underlying principle of operation of the sensor.

Heretofor, an analysis made of reducing the length of a housing wall to utilize a short resonator section and it was concluded that this was impractical because the pressure on the end caps would cause the end caps to bow inwardly under pressure to the point where the bowing effects counteract the applied radial pressure effect on the crystal. Also, in reducing the length of the housing wall, the effects of temperature and creep from the glass joint are introduced. Also, the stress factors could not be overcome. The present invention shows this analysis to be in error.

SUMMARY OF THE INVENTION

In the present invention, one application is for a quartz pressure transducer which is constructed with quartz members which are bonded to one another by a thin metal member. The quartz construction includes metalized bonding means on adjacent quartz members which cooperate to bond the quartz members to one another. The bonding means includes metalized sealing surfaces where the metalized sealing surfaces consist of layers of adhesive material, a barrier material and a low temperature bonding metal material where the layers define a thickness in Angstroms which is substantially less than the thickness of a glass or ceramic frit used for similar bonding and which permits bonding of the bonding metal material at cold welding temperature which are substantially below the bonding temperature of a glass frit.

The bonding means on a surface includes a base adhesive layer of metal film which will adhere to quartz (such as tantalum pentoxide), a metal film adhesive coating layer, which will adhere to the base adhere layer (such as copper), a barrier film layer (such as tantalum or nickel), and a exterior film layer of bonding metal (such as copper). The layer or coatings are between approximately 500 and 1000 Angstroms thick. If the exterior coating is copper on the adjoining surfaces, the copper is easily joined at 300°- 350°C into a solid bond which is considered cold welding. If the exterior coating on one surface is copper and the exterior coating on the other surface is nickel, the nickel and copper can be joined in an alloy form at temperatures of 1200° F.

DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a prior art transducer for comparison purposes;

Fig. 2 is a view in partial cross-section of a transducer embodying the present invention: Fig. 3 is a partial view of a metal film system for the present invention; and

Fig. 4 is a partial view of metal film system in a different form. DESCRIPTION OF THE INVENTION

Referring now to Fig. 1, a prior art device is illustrated as background for an understanding of the present invention. The transducer has a generally cylindrical housing 10 constructed from quartz and is provided with a cylindrical cavity 12 which is formed by machining. Disposed in the cavity 12 and integrally formed at its perimeter with sidewall 14 of the housing is a disc shaped resonator section 16. The sidewalls 14 of the housing 10 circumscribe the resonator section 16 and extend in opposite directions generally normal to the plane of the resonator section. The housing 10 and resonator section 16 are constructed from quartz and may be AT-cut quartz, BT-cut quartz, or rotated X-cut quartz. A peripheral web 18 joins the perimeter of the resonator section 16 to the sidewall 10 of the housing 10. Grooves 20, 21 can be provided for manufacturing purposes. Electrodes 22,24 are deposited on the spherical surfaces of the resonator section 16. The ends of the cylinder housing 10 are enclosed with end caps 26,28 of quartz. The end caps 26,28 are attached in a sealing relationship by a glass frit which is typically 500 to 5000 micro inches thick. The lengthwise spacing between the resonator section 16 and an end cap is made as large as possible to minimize the detrimental effect of the glass frit joint and to isolate the bowing effect of pressure on the end caps from the effect of radial pressure on the resonator section. When the wall spacing between the end cap and a resonator section is reduced, the bowing of the end caps can nullify the sensitivity of the resonator section.

The resonator section 16 is vibrated by coupling an oscillator 30 to the electrodes 22,24. The oscillator can be connected to a display device 32 for detecting and displaying frequency of vibration of the resonator section 16.

A disadvantage of applying the metal electrodes directly on the resonator surfaces is that temperature changes during use of the transducer can cause yielding in the metal films due to expansion mismatch. This produces unpredictable stresses in the resonator crystal and affects the accuracy and performance of the transducer. Also, metal ion migration can shift the mass of the electrodes and thus cause long term frequency shifts.

Referring now to Fig. 2, a quartz transducer is illustrated with cylindrical end cap members 40A, 40B and intermediate stress isolator members 42 A, 42B made of quartz and a central cylindrically shaped quartz resonator member 40 which has a relatively short height dimension "h" along its central axis as compared to the height dimensions Hj and H₂ of the end cap members and the stress isolator members. The resonator member 40 has opposing spherical surfaces 46,48 which define a resonator lens 50 and essentially small volumetric recesses 51 A and 5 IB with respect to the volume of the section 40. The resonator lens 50 has a central section 52 and a peripheral connective section 53. The relative thickness dimensions, for example can be h = 0.042"

Section 52 = 0.037" typ. Cavity = 0.001" to 0.005".

The members 40A, 40B, 42A, 42B have a dimension of H = 0.250" so that the assembly has an overall dimension of 1.042" and a diameter of 0.650". The diameter "d" of the resonator lens 50 is 0.400" and the radius of curvature of the convex sections is chosen to insure a mechanical Q that is greater than 10^s and decoupling from undesired modes of vibration. It will be noted that the cavity is essenti.ally small.

The end cap members 40A, 40B and the stress isolator members 42A, 42B are aligned to coincide with the crystallographic orientation of the resonator section 40 and are bonded to the resonator section 40 by metalized bonding seals or elements 56,58 which also function as electrodes for the transducer. The crystallographic alignment is required because the thermal expansion coefficient of crystalline quartz is a function of crystallographic direction and all of the elements are thus aligned with respect to thermal expansion. The area of the bonding seals 56,58 is chosen to be large enough so that the edge clamping force between adjacent elements or members due to external pressure exceeds the edge lifting effect due to the moment generated by the end bowing effect due to external pressure. The end cap members 40A, 42A are thick, so the bowing effect is small. The stress isolator members 40B and 42B serve as elastic elements to isolate the stress due to end bowing moments caused by pressure from the center resonator section 54 and thus prevent loss of sensitivity. As illustrated the end cap members 40B & 42B can have a recess 60,60A to accommodate any bowing effect and isolate the bowing effect from affecting the resonator section. The end caps are joined to stress isolator members by metalized seals 59A and 59B, however a glass frit can be used for these non-critical joints if application temperatures are not a problem. The magnitude of the end cap bowing under pressure is small and when coupled with the very small dimensions of the unsupported cylindrical section (.003") in the resonator member, very little shear force is developed in the bonding seal. This is important because shear force on bonding seals can result in bond creep and residual radial stress levels on the resonator section after the application of pressure. Any creep in the bond layer that occurs in the absence of shear forces can only serve to change the thickness of the bond layer since the remaining force is compressive. The resonator of the present invention will not react to this because it is sensitive primarily to radial forces and is not sensitive to the thickness of the bond seal element.

The resonator has the spherically opposed surfaces free of metalization and thus has a resonant frequency independent of the metalization. The spherical configuration develops a high Q with low losses through a well known energy trapping effect. The thickness of metal junctions of seal joints of the present invention is reduced relative to the thickness of a glass frit by a factor of 30 to 300. For example, a glass frit with ranges from 500 to 5000 micro inches while the metalized seal of the present invention can be 10 to 20 micro inches which is typically defined in Angstroms.

The disadvantage of using such a short unsupported cylindrical resonator section is that there is no radial pressure force amplification effect such as described in U.S. patent 3,561,832.

This does reduce the sensitivity of the sensor to pressure by a factor of 2 to 3 because only hydrostatic pressure stress is all that is sensed by the design of the present invention. The lower operating stress levels of the resonator section, however, allow operation of the quartz element at higher pressure and temperatures with less creep or possibility of recrystalization of the quartz crystals.

Referring now to Fig. 3, the metalizing process and system of the present invention is illustrated where an adhesive base 60 of tantalum pentoxide is applied with a thickness of about 500 Angstroms. Tantalum pentoxide is suitable as bonding to quartz is enhanced by providing an oxygen source. Next, another adhesive layer of copper 62 with a thickness of about 500 Angstroms is applied. Copper adheres well with tantalum pentoxide. Because the oxygen will inhibit cold welding the copper, a metal barrier film 64 of tantalum of about 1000 Angstroms is applied. For a metalizing seal, the last coat is a copper bond layer coating 66 of about 1000 Angstroms thickness. The facing surfaces of the copper bond layers of this thin layer composition can be cold welded at about 300°C. The resulting bond is only about 15 micro inches thick as compared to a conventional glass frit seal that has a finished thickness of 500-5000 micro inches. This has a substantial advantage in that stresses induced into the resonator by temperature expansion mismatch (coefficient of expansion) or creep of the bond are correspondingly reduced since the thinner bond offers proportionately less rigidity and is less affected by stress. The bond should be thin enough so that negligible stress error is introduced with the temperature expansion of the quartz. While copper is described, any electrically conductive metal suitable for solid state cold welding can be used, in combination with appropriate adhesive and barrier materials, and preferably should be resistive to corrosion. For example, gold can be used.

Tantalum pentoxide is utilized as a base layer because it adheres to quartz, a copper layer is used for attaching the tantalum pentoxide layer to the tantalum barrier layer. The tantalum barrier is coated with a copper bonding layer and prevents oxygen migration to the copper bonding layer and thus preserves the cold welding properties.

Referring now to Fig. 4 another system is illustrated where one surface 70 is provided with a metalized base film of tantalum oxide 71, a metal adhesive film of copper 72, a metal film of Nickel 73 as a barrier and an outer bonding metal film of copper 74. The other surface 77 is provided with a metalized base film of tantalum pentoxide 78, an adhesive layer of copper and an outer film of Nickel 80. The copper film 79 between the nickel films 73 .and 80 when heated to a cold welding temperature of 1200° F form a nickel copper alloy, high strength bond. By cold welding the very thin films to one another, the intrinsic tolerance properties of the members and the bond are maintained.

It will be apparent to those skilled in the art that various changes may be made in the invention without departing from the spirit and scope thereof and therefore the invention is not limited by that which is disclosed in the drawings and specifications but only as indicated in the appended claims.

Claims

CLAIMS 1. An integrated quartz or glass construction which includes at least two facing quartz elements which are bonded to one another by a metalized sealing element which has a thickness in Angstroms which is substantially less than the thickness of a glass frit used for similar bonding, said metalized sealing element being formed by joining thin metalization films on facing surfaces of said quartz elements to one another at cold welding temperatures.

2. The quartz construction as set forth in Claim 1 wherein the metalization films include an adhesive layer of oxygen containing metal for adhering to a quartz member.

3. The quartz construction as set forth in Claim 2 wherein the metalization films include a metal film layer for adhering to the oxygen containing metal.

4. The quartz construction as set forth in Claim 1 wherein the oxygen containing metal is tantulum pentoxide for adhering to a quartz member.

5. The quartz construction as set forth in Claim 2 wherein the metalization film for adhering to the tantulum pentoxide is copper.

6. The quartz construction as set forth in Claim 1 wherein the metalization films include an adhesive layer of oxygen containing metal for adhering to a quartz member, a metal film layer of copper for adhering to the oxygen containing metal and a film layer of nickel.

7. The quartz construction as set forth in Claim 6 wherein the oxygen containing metal is tantulum pentoxide for adhering to a quartz member.

8. The quartz construction as set forth in Claim 6 wherein the metalization films on at least one of said quartz members further includes a metal film of copper.

9. The quartz construction as set forth in Claims 1 to 5 wherein the metalization films are bondable at temperatures of about 300°C.

10. The quartz construction as set forth in Claims 6 to 8 wherein the metalization films are bondable at temperatures of about 1200°F.

11. The quartz construction as set forth in Claims 1 to 10 wherein the thickness of the metalization films is approximately 1000 Angstroms or less.

12. A method of making a composite quartz or glass construction including the steps of: applying adhesive layers of metal films on a first surface of a first quartz member with an inner layer which is compatible with adhering to quartz and with an outer layer which is compatible with welding to another metal film at cold welding temperatures; applying adhesive layers of metal films on a first surface of a second quartz member with an inner layer which is compatible with adhering to quartz and with an outer layer which is compatible with welding to another metal film at cold welding temperatures; contacting outer layers to one another and applying cold welding temperature to fuse the outer metal films to one another and form a metal seal bond between the quartz or glass members.

13. The method as set forth in Claim 12 and further including the steps of limiting the thickness of the film layer to 1000 Angstroms or less.

14. The method as set forth in Claim 13 and further including the steps of limiting the temperature to 1200°F or less.

15. The method as set forth in Claim 13 and further including the steps of limiting the temperature to 300 °C or less.

16. The method as set forth in Claim 12 and further including the steps of using tantulum pentoxide as a film layer to adhere to quartz.

17. The method as set forth in Claim 15 and further including the steps of using copper as a second adhesive layer.

18. The method as set forth in Claim 16 and further using a barrier layer over the copper layer to prevent oxygen migration and providing an outer layer of copper for bonding.

19. The method as set forth in Claim 17 wherein the barrier layer is nickel.