US3056894A

US3056894A - Means for controlling the effective resistance of piezoelectric quartz crystals

Info

Publication number: US3056894A
Application number: US829323A
Authority: US
Inventors: William J Altier
Original assignee: Dynamics Corp of America
Current assignee: Dynamics Corp of America
Priority date: 1959-07-24
Filing date: 1959-07-24
Publication date: 1962-10-02
Anticipated expiration: 1979-10-02

Description

Oct. 2, 1962 J. ALTIER 3,056,894

W. MEANS FOR CONTROLLING THE EFFECTIVE RESISTANCE OF PIEZOELECTRIC QUARTZ CRYSTALS Filed July 24, 1959 3 Sheets-Sheet l INVENTOR WILLIAM J. ALTIER Oct. 2, 1962 w. J. ALTIER 3,056,894

MEANS FOR CONTROLLING THE EFFECTIVE RESISTANCE 0F PIEZOELECTRIC QUARTZ CRYSTALS Filed July 24, 1959 5 Sheets-Sheet 2 H630. F/G3b.

F7640. F/G.4b.

INVENTOR WILLIAM J. ALTiER Oct. 2, 1962 w. J. ALTIER 3,056,894

MEANS FOR CONTROLLING THE. EFFECTIVE RESISTANCE OF PIEZOELECTRIC QUARTZ CRYSTALS Filed July 24, 1959 3 Sheets-Sheet 3 INVENTOR WILLlAM J. ALTIER United States Patent William J. Altier, Carlisle, Pa., assignor to Dynamics Corporation of America, New York, N.Y., a corporation of New York Filed July 24, 1959, Ser. No. 829,323 Claims. (Cl. 310-83) This invention relates to piezoelectric quartz crystals and more specifically to a means for controlling the effective resistance of such quartz crystals.

The use of quartz crystals in high frequency devices is well known in the electronics art. One of the major problems in the use of quartz crystals is maintaining an operation which meets the requirements of the specified device in which the crystal is used. Unfavorable operation of the crystals has particularly been noted in devices which are subjected to a large degree of temperature variation during the operation of the device. In particular, unwanted variations and activity dips have been noted due to sudden or unwanted changes of the amplitude of vibration at the quartz crystal plate. The effective resistance of the crystal is the major determining factor of the amplitude of vibration at the quartz crystal plate and this invention has for one of its objects the controlling of this resistance in order to obtain a more stable operation of the quartz crystal device.

It is well known in the art that an inert gas such as nitrogen when placed within a crystal container transfers heat from the crystal to the radiating surface of the c0ntainer and permits the crystal to tolerate higher operating power. However, the gases that have been added in the past have had little or no effect on the effective resist ance of the crystal and therefore little or no effect on the amplitude of vibration at the quartz crystal plate.

Accordingly, it is an object of this invention to control and impose limitations upon the effective resistance of quartz crystal units.

Another object of this invention is to eliminate activity dips from the effective resistance curve of quartz crystal units over a variable temperature range.

A still further object of this invention is to provide means for controlling the effective resistance of crystals within specified effective resistance ranges.

Yet another object of this invention is to provide a means for controlling the effective resistance of quartz crystals which may be used in any existing hermetically sealed crystal containers.

Further objects and advantages of this invention will become apparent from the following description and claims and from the accompanying drawings wherein:

FIG. 1A, FIG. 2A, FIG. 3A and FIG. 4A are reproductions of frequency curves illustrating the effective resistance characteristics of crystals operating in an undampened manner.

FIG. 13, FIG. 23, FIG. 3B and FIG. 4B are reproductions of frequency curves representing the effective resistance of crystals when operating in the dampened manner of the present invention.

Briefly, this invention controls the effective resistance of quartz crystals by evacuating the quartz crystal chamber and filling the chamber with a gas having a high density and thereafter hermetically sealing the chamber.

The most satisfactory gases for use in this invention are halogenated chemically inert gases of heavy atomic mass. Examples of these gases are fluorinated gases such as tetrafiuoromethane (CR sulfur hexafluoride (SP and perfluoropropane (C F The higher density of these heavy gases, when placed Within the crystal chamber, has a dampening effect on the amplitude of ICC vibration at the quartz crystal plate and, thus, the activity of the crystal is diminished with a resulting increase of effective resistance. In many cases it is also desirable to use a mixture of nitrogen and one of the aforementioned gases in order to adjust for the required dampening according to the specifications of the crystal unit.

' The degree of the dampening increases in direct proportion to the increasing atomic weight of the gas. It is also noted that the greater the atomic weight of the gas, the greater the amount of heat that the gas will transfer from the crystal to the radiating surfaces of its container, thus permitting the crystal to tolerate higher operating power where necessary. Since quartz crystals are many times operated .at temperatures as low as -55 degrees centigrade, it is necessary that gases used to fill the crystal containers do not liquify above this temperature if the crystal containers are to have a diversified use.

The specific crystals and operating voltages are not dealt with since they do not form a part of the present invention. Although different crystals were used in FIGS. 1 through 4 in order to meet the specified requirements, the same crystal was used in obtaining the results illustrated by the A and B parts of each particular figure. Likewise, the base reference points on the chart have no significance other than for purposes of indicating the relative activity between the two figures. Since this invention may be used on all types of crystals for varying specifications, the invention is best illustrated by the relative activity of the crystals with and without the use of the above mentioned gases.

FIGURES 1A and 1B represent the operation of crystals under a condition wherein the specification called for the crystals to have a minimum effective resistance of 1500 ohms and a maximum effective resistance of 5500 ohms over the temperature range of 0 to 70 centigrade. On both graphs the zero degree centigrade reference point 1 .and the 70 centigrade reference point 2 represent the operating range of temperatures. Dashed line 3 is the minimum effective resistance line of 1500 ohms and dashed line 4 is the maximum effective resistance line of 5500 ohms. FIG. 1A shows the results of the crystal operating in an atmosphere of nitrogen with the resultant curve showing that the minimum effective resistance of 1500 ohms has been exceeded. FIG. 1B shows the results of the crystal operating under the same conditions with the exception that tetrafiuoromethane (CR has been substituted for the nitrogen used in FIG. 1A.

As can be seen from FIG. 1B the crystal operated within the specified resistance values with the use of the high density gas.

FIGS. 2A and 2B represent the operating characteristics of the crystals when the specification called for crystals having relatively consistent effective resistance values over the temperature range of a 4.0 centigrade to 70 centigrade rather than calling for crystals that had a maximum effective resistance value. In both figures point 6 on the graph represents the -40 starting point and point 7 represents the 70 operating point. For reference purposes, the dashed line 8 represents an effective resistance of 2000 ohms and dashed line 9 represents an effective resistance of 600 ohms. FIG. 2A represents the operation of the crystal when operating within an atmosphere of nitrogen. The crystals did not have a consistent effective resistance value but were quite erratic as is clearly evident by FIG. 2A. FIG. 2B represents the operation of the crystal when the container was filled with -a mixture of approximately 25% sulfur hexafluoride (SP and nitrogen. The results show that the resistance curve was smoothed out and erratic operation eliminated without seriously raising the maximum resistance.

FIGS. 3A and 3B show the operation of crystals wherein the specification calls for no activity dips or sharp changes in effective resistance. Points 11 and 12 represent the 40 centigradeand 70 centigrade points respectively. FIG. 3A represents the operation of the crystal under the normal influence of nitrogen and, as can be seen at 10, a severe activity dip occurred when approaching the 70 operating temperature. FIG. 3B

shows the operation of the crystal whensulfur hexafluoride (SP was placed in the crystal container. The dampening efiect of SP eliminated the activity dip which had occurred when nitrogen was used in the container.

FIGS. 4A and 4B represent the operation of the crystals when the specification required a frequency curve exhibiting a continuous negative drift over the temperature range of-" to 70 centigrade. Points 14 and 15 represent the 0 and 70 points respectively. Again, FIG. 4A represents the operation of the crystals when nitrogen was placed in the container. As can be seen at 20 a serious activity dip occurred in the continuous negative drift of crystal. The nitrogen was replaced With an atmosphere of sulfur hexafluoride and the results obtained are shown in FIG. 4B. .A smooth continuous negative drift frequency curve was obtained with the elimination of the activity dip which had occurred in the nitrogen atmosphere.

The foregoing illustrations are merely representative of the superior operating characteristics of crystals when the crystal containers are filled with a gas having a heavy density for increasing the effective resistance of the crystals. The use of these gases is in no Way limited to the particular specifications discussed hereinabove, since various applications of the principle of this invention will now 'be obvious to those skilled in the art. Likewise,

although some of the most satisfactory gases for this invention have been named, the invention is not limited to these gasessince any gas having a relatively high density could be used in achieving the superior results of this invention.

One specific crystal mounting is illustrated in 'FIG. 5

wherein a container 30 has a crystal 31 supported therein by means of wire clips 32 and 33. These wire clips are secured to the lead wires 39 and 40 which pass outwardly of base 34. The'wire clips

contact conductors

35 and 36 that extend along opposite sides of the crystal. The interior 37 of the container is filled with a gas as de scribed above and the container is hermetically sealed as shown. Further details of this particular crystal unit are described and illustrated in US. Patent No. 2,513 ,870

issued to PR. Hoffman and assigned to the assignee of the present invention.

However, the present invention is not limited tothe specific structure used as an illustrative example since any of the many well-known hermetically sealed containers could be satisfactorily used in carrying out the principles of the present invention.

1 claim:

1. A device for controlling the efiective resistance of piezoelectric crystals comprising a hermetically sealed container, a quartz crystal mounted within said container and a chemically inert gas of constant heavy atomic mass greater than that of air surrounding said crystal within said container.

2. 'A quartz crystal device comprising a hermetically sealed container, a quartz crystal unit mounted within said container and a chemically inert halogenated gas of substantially constant heavy atomic mass surrounding said unit for controlling the effective resistance of said crystal.

3. The device of claim 2 wherein said gas consists essentially of tetrafluoromethane.

4. The device of claim 2 wherein said gas consists essentially of sulfur hexafluoride.

5. The device of claim 2 wherein said gas consists essentially of perfluoropropane.

References Cited in the file of this patent UNITED STATES PATENTS 1,766,036 Crossley June 24,1930 1,789,369 Meissner Jan. 20, 1931 1,874,982 'Hansell Aug. 30, 1932 2,254,843 Grosdoff Sept. 2, 1941 2,358,087 Lane "Sept. 12, 1944

Claims

1. A DEVICE FOR CONTROLLING THE EFFECTIVE RESISTANCE OF PIEZOELECTRIC CRYSTALS COMPRISING A HERMETICALLY SEALED CONTAINER, A QUARTZ CRYSTAL MOUNTED WITHIN SAID CONTAINER AND A CHEMICALLY INERT GAS CONSTANT HEAVY ATOMIC MASS GREATER THAN THAT OF AIR SURROUNDING SAID CRYSTAL WITHIN SAID CONTAINER.