WO2010032085A1

WO2010032085A1 - Method for growing synthetic crystals

Info

Publication number: WO2010032085A1
Application number: PCT/IB2008/053821
Authority: WO
Inventors: Remko Arentz
Original assignee: Remko Arentz
Priority date: 2008-09-19
Filing date: 2008-09-19
Publication date: 2010-03-25

Abstract

A crystal is grown from a crystal seed in a growing environment that is exposed to an electro-magnetic radiation field of a single specific frequency or of a plurality of specific frequencies. The electro-magnetic radiation field is generated by one frequency source or by a plurality of frequency sources (1, 2, 3) connected, to an antenna-array (6) consisting of one antenna or of a plurality of antennas inside the growing environment irradiating the crystal during the growth process. A crystal resonator manufactured from the grown crystal has ultra-high resonant frequency stability.

Description

METHOD FOR GROWING SYNTHETIC CRYSTALS Field of the invention

The present invention relates to a method of growing synthetic crystals and, more particularly, to growing synthetic crystals for the manufacture of crystal resonators with ultra high resonant frequency stability.

Background of the invention

Synthetic crystals, such as synthetic quartz crystals, are commonly grown using the hydrothermal growth method as described in U.S. Pat. No. 3,013,867 issued to CB. Sawyer on December 19, 1961. This involves growing synthetic homogeneous crystals from a hydrothermal growing solution under conditions of constantly controlled temperature and pressure. The process can take place in an apparatus consisting of a steel pressure vessel called an autoclave. A supply of nutrient material, such as quartz (Lasca), is placed in the bottom half of the autoclave. In the top half of the autoclave, seed crystals are hung. The baffle, a metal controlled opening, is placed between the upper and lower halves. An aqueous solution and additional chemicals are added to the autoclave. The temperature difference between the growing environment in the top half of the autoclave and the dissolving environment in the bottom half of the autoclave is the major control factor of the growth rate. In the warmer dissolving environment the crystal dissolves into the solution. The warm fluid which is less dense rises. In the growing environment the cooler temperature leads to supersaturation of the solution and causes precipitation on the seed crystals. The cooler fluid with greater density sinks into the dissolving environment and the cycle repeats. The temperature difference controls not only the supersaturation in the growth environment, but together with the baffle, controls the rate of fluid and heat transfer between the top and bottom environments. After sealing the vessel, the autoclave is heated to operating conditions with the use of external heaters. Typical operating conditions are between 350°C and 400°C although higher temperatures can be used. The internal pressure developed is controlled by the temperature and the amount of solution in the autoclave. A full production cycle can take from 2 weeks to over 4 months, depending on the requirements for the produced crystals.

The purity of the synthetically grown crystal is of importance for the frequency stability of the crystal resonator. One method of creating greater purity is the method of sweeping crystals. A crystal is subjected to an electric field at an elevated temperature. This method is described for quartz crystals in U.S. Pat. No. 3,932,777 issued to J. C. King on Jan. 13, 1976. and improvements on this method as described in U.S. Pat. No. 4,311 ,938 issued to Ballato , et al. on Jan 19, 1982. The presence of impurities such as sodium ions in a quartz crystal cause undesired effects in crystal resonators made from the quartz. The quartz material is "swept" free of these impurities to a large degree through this process. This method produces quartz crystal resonators for which the transient frequency change as a result of exposure to pulse irradiation is virtually eliminated. In contrast to the sweeping method the invention detailed in this disclosure improves the resonant frequency stability of a crystal resonator through the very specific frequency targeting of the crystal while it is in the growing environment during its growing stage.

The resonant frequency f_res of a crystal resonator is part of the design characteristics of the electronic circuit for which the crystal resonator is being manufactured. In current manufacture practice, the resonant frequency of a crystal resonator is to a large degree determined by the specific angles of cut used to cut the resonator crystal from the fully grown crystal and by the final size and shape of the crystal resonator. Many crystal resonators can be cut from one grown crystal and their individual resonant frequency can vary according to the difference in cut, shape and size. Methods are used such as described in U.S. Pat. 7,051 ,728 issued to Branham on May. 30, 2006.

Although current crystal growing methods and crystal resonator fabrication methods have created crystal resonators with acceptable resonant frequency stability, factors such as temperature change, time, drive energy, and other environmental conditions still impact the resonant frequency stability of crystal resonators substantially and cause undesired transient frequency drift.

Summary of the invention

The object of this invention is to provide a method for growing crystals for the manufacture of crystal resonators with ultra high resonant frequency stability. According to the invention this object is achieved by exposing the growing crystal to an electro-magnetic radiation field of a single specific target frequency fw as shown in Fig 1.a or to an electro-magnetic radiation field composed of a plurality of simultaneous specific target frequencies f_tar(i) to ft_ar(n) where f_tar(i) is the first specific target frequency and f_tar(Λi₎ is the last specific target frequency and the total number of unique frequencies in the electro-magnetic radiation field is n. This is shown in Fig 1.b. The electro-magnetic radiation field is maintained throughout the growth cycle of the crystal. After the growth cycle is complete, the crystal can be cut for the production of a crystal resonator using art established techniques.

The specific first target frequency f_tar(i₎ of the electro-magnetic radiation field equals the resonant frequency f_res of the crystal resonator which will be fabricated from the fully grown crystal when the growth cycle is complete. The resonant frequency fres of the crystal resonator is determined before the crystal growing process is started.

In Fig 1 .a the simplest form of the electro-magnetic radiation field is show with the great majority of the energy of the electro-magnetic radiation field vibrating at frequency W In Fig 1.b a more complex form of the electro-magnetic radiation field is shown with the great majority of the energy of the electromagnetic radiation field vibrating at n different target frequencies starting with target frequency f_tar(i₎ and ending with target frequency f_tar(/,₎. In Fig 1 .b the total number n of target frequencies used is 3. This more complex electro-magnetic radiation field allows the simultaneous targeting of several desired resonant frequencies during the growth process. One reason for the use of this more complex electro-magnetic radiation field is that one grown crystal can be used for the manufacture of many different crystal resonators with different resonant frequencies with the k different crystal resonators having k different resonant frequencies f_reS(i) to f_reS(/f) with f_reS(i) being equal to f_tar(i) and f_reS(/r) being equal to f_ta_r(/i₎- In this case it is important to minimize the interference effects each specific target frequency has on all other specific target frequencies. Another reason for the use of this more complex electro-magnetic radiation field is the further enhancement of the stability of the target frequency f _tar( i ₎ by use of a plurality of supporting frequencies such as the harmonic and sub harmonic frequencies of f_tar(i₎. In this case the frequencies f_tar(i₎ to f_tar(/i₎ are harmonically or sub harmonically related by f_tar(/i₎ being a whole number multiplication of f_tar(i₎ or a whole number division of ft_ar(i).

When the growing crystal is exposed to the electro-magnetic radiation field it is substantially altered by the electro-magnetic radiation field, rearranging the molecular and atomic structure. This rearranging process takes mainly place while the solution is in the supersaturated state and during precipitation on the seed crystal. It continues to a smaller degree in the solidified crystal structure that has formed on the crystal seed after precipitation has taken place and while the solidified crystal is still in the growing environment. The electro-magnetic radiation field creates a greater physical resonance in the crystalline structure to the frequency f_tar in the case of one used frequency or to f_tar(i) to f_tar(n) in the case of n used frequencies. Once the crystal growth cycle is complete the natural crystal resonance characteristics have been altered by the irradiation process and the grown crystal is physically different compared to a crystal grown in identical conditions without the irradiation field being present. In the simplest case, with the electro-magnetic radiation field having one frequency only, the grown uncut crystal which was exposed to the electro-magnetic radiation field during its growth cycle has a higher resonant frequency stability at this frequency ftar- This quality is revealed when a crystal resonator with resonant frequencyf_res being equal to f_tar is manufactured.

Brief description of the drawings

Fig 1.a shows a frequency versus amplitude graph of an example electromagnetic radiation field consisting of primarily one target frequency, W The frequency range displayed on the horizontal axis of the graph is from 10.0 MHz to 11.1 MHz. The amplitude of the signal is displayed in dB on the vertical axis of the graph. f_tar is being indicated on the graph by the number 1.The great majority of the energy of the electro-magnetic radiation field is vibrating at the target frequency f_tarwith f_tar being equal to 10.4 MHz.

Fig 1.b shows a frequency versus amplitude graph of an example electromagnetic radiation field consisting of primarily three target frequencies f_tar(i), ftar(2) and ftar(3)- In this example n equals 3. The frequency range displayed on the horizontal axis of the graph is from 16.1 MHz to 27.1 MHz. The amplitude of the signal is displayed in dB on the vertical axis of the graph. f_tar(i) is being indicated on the graph by the number 1 , f_tar(2) by the number 2 and f_tar(3) by the number 3. The great majority of the energy of the electro-magnetic radiation field is vibrating at the three target frequencies f_tar(i), ftar(2) and f_tar(3) with f_tar(i) being equal to 17.3 MHz, f_tar(2) being equal to 20.07 MHz and f_tar(3) being equal to 23.45 MHz. This electro-magnetic radiation field is created by merging the electro-magnetic output signal of three frequency sources (also known as mixing the signals of the three frequency sources, this is not adding the frequencies together) and irradiating this merged electro-magnetic output signal through the use of antennas.

Fig 2. a shows a simple representation of an autoclave. Number 1 indicates the growing environment, number 2 indicates the dissolving environment, number 3 indicates a seed crystal in the growing environment, number 4 indicates the baffle between the two environments, number 5 indicates the nutrient material (such as Lasca when Quartz crystals are grown), number 6 indicates the external heating units.

Fig 2.b shows an enlargement of part of the top section of Fig 2. a. Number 1 indicates the antenna feed cable which transfers the merged electro-magnetic output signal to the antenna. Number 2 indicates the antenna in the growing environment. The required specific size, shape and type of antenna is dependant upon several issues such as the type of autoclave, the number and size of crystals growing in the growing environment, the target frequency or frequencies used and the power level of the electro-magnetic output signal(s). The size of the autoclave and the number of crystals growing in the growing environment also effects the number of antennas required and the specific placement of these antennas.

Fig 2. c shows an enlargement of part of the top section of an autoclave similar to the autoclave in Fig 2. a with four individual antennas in the top section of the growing environment. Number 1 indicates the feed cables which transfer the merged electro-magnetic output signal to each of the four antennas. The signal to each antenna is identical in this example (parallel). Number 2, 3 ,4 and 5 indicate the four individual antennas which irradiate the electro-magnetic radiation field inside the growing environment. Number 6 indicates the feed cable connected to the source of the merged electro-magnetic output signal. Fig 3. a shows an autoclave connected to the merged electro-magnetic output signal of three frequency sources. Number 1 indicates the frequency source number one with an electro-magnetic output signal vibrating at f_tar(i). Number 2 indicates the frequency source number two with an electro-magnetic output signal vibrating at f_tar(2)- Number 3 indicates the frequency source number three with an electro-magnetic output signal vibrating at f_tar(3)- Number 4 indicates the signal mixer, where the three electro-magnetic output signals f_tar(i), ftar(2), and ftar(3) are merged into one electro-magnetic output signal (see also Fig 1.b for an example of such a signal). Number 5 indicates the cables connected to the merged electro-magnetic output signal of the signal mixer, feeding the antennas. The connection from the signal mixer to all 8 antennas is in parallel in this example. Number 7 (thin dotted lines inside the growing environment) indicates the anechoic shielding, reducing the interference patterns within the growing environment.

Description of the preferred embodiment

The electro-magnetic radiation field is created through the use of n frequency sources with each frequency source having a specific target frequency electromagnetic output signal with the first frequency source having an electro-magnetic output signal of target frequency f_tar(i) and the last frequency source having an electro-magnetic output signal of target frequency ftaψi). An example for a flexible frequency source is a frequency synthesizer. These n electro-magnetic output signals are mixed into one merged electro-magnetic output signal. This merged output signal has the great majority of its energy located at the n specific target frequencies. The merged electro-magnetic output signal is then irradiated into the top half of the autoclave through the use of one antenna where the solution is in supersaturation and where precipitation on the seed crystal(s) takes place. This is shown in Fig 2. a and Fig 2.b. This merged electro-magnetic output signal can also be irradiated into the growing environment through the use of several antennas connected in parallel to the merged electro-magnetic output signal. This is shown in Fig 2.c. As required, the electro-magnetic output signal of each individual frequency source can be connected to an individual radiating antenna. In case of multiple radiating antennas the undesired interference patterns in the electro-magnetic radiating field at the location of the growing crystal(s) are minimized according to art established RF interference procedures and can include specific location positioning of the antennas in relationship to the wavelength of the frequencies present in the electro-magnetic radiating field and the proper suppression of reflection signals from the growing environment by using anechoic shielding. Fig 3. a shows an example with an autoclave connected to the merged electro-magnetic output signal of three individual frequency sources. The 8 antennas in the growth environment are connected in parallel. The electro-magnetic radiation field is maintained throughout the entire growth cycle in the autoclave and the stability of the electro-magnetic radiation field generated by the frequency source(s) has a direct influence on the final resonant frequency stability quality of the grown crystal. It is therefore of great importance to use the highest quality frequency source(s) available, with the greatest frequency stability (lowest frequency drift through time, and highest frequency accuracy). Art established cutting techniques can now be use to produce the crystal resonator after the grow cycle is complete. The most widely used type of crystal for crystal resonators is currently quartz crystal. The above described method applies to all types of crystals that are grown using techniques such as the hydrothermal growing method. The above described method also applies to the synthetic fabrication of crystals used for semiconductor manufacture which require a specific highly stable resonant frequency which are grown through techniques such as the vapor disposition technique as described in U.S. Pat. No. 5,656,540. issued to Nomura, et al. August 12, 1997. In this case the growing environment would not be the top part of an autoclave but the vapor chambe. The vapor chamber would contain the electro-magnetic radiating field and would have a single radiating antenna or several radiating antennas creating the electro-magnetic radiation field while the vapor deposition process is taking place.

Claims

What is claimed is:

1. Method of growing a crystal with ultra high resonant frequency stability, said crystal being irradiated during its growth cycle with an electro-magnetic radiation field.

2. Method according to claim 1 wherein the irradiation period is equal to the entire growth cycle of said crystal.

3. Method according to claim 1 wherein the electro-magnetic radiation field is composed of a single specific target frequency f_tar.

4. Method according to claim 1 wherein the electro-magnetic radiation field is composed of a plurality of simultaneous specific target frequencies f_tar(i) toft_ar(n) where f_tar(i) is the first specific target frequency and f_tar(n) is the last specific target frequency and the total number of unique specific target frequencies present in the electro-magnetic radiation field is n with n > 1.

5. Method according to claim 3 wherein specific target frequency f_tar is equal to the resonant frequency f_res of the crystal resonators manufactured from the fully grown crystal when the growth cycle is complete.

6. Method according to claim 4 wherein specific target frequency f_tar(i) is equal to the resonant frequency f_reS(i) of crystal resonator₍i) manufactured from the fully grown crystal when the growth cycle is complete and specific target frequency ftar(n) is equal to the resonant frequency f_reS(/r) of crystal resonator^) manufactured from the fully grown crystal with the number of different crystal resonators with a different resonant frequency being manufactured being k with k >1.

7. Method according to claim 1 wherein the method of crystal growth is the hydrothermal growth method.

8. Method according to claim 1 wherein the method of crystal growth is the vapor disposition method.

9. Method according to claim 7 wherein the hydrothermal growth vessel is an autoclave.

10. Method according to claim 9 wherein the electro-magnetic radiation field is present in the top half of the autoclave where the solution in supersaturation precipitates on the seed crystal.

11. Method according to claim 1 wherein the crystal is quartz crystal

12. Method according to claim 1 wherein the electro-magnetic radiation field is created by the irradiation through z antennas directly connected to the electromagnetic output signal of z frequency sources with antanna^ connected to frequency source electro-magnetic output signal^ and antenna^ connected to frequency source electro-magnetic output signal^ with z > 1.

13. Method according to claim 1 wherein the electro-magnetic radiation field is created by the irradiation through w antennas directly connected in parallel to the electro-magnetic output signal of one frequency source with w ≥ 1.

14. Method according to claim 1 wherein the electro-magnetic radiation field is created by the irradiation through one antenna directly connected to the electromagnetic output signal of one frequency source.

15. Method according to claim 1 wherein the electro-magnetic radiation field is created by the irradiation through v antennas connected in parallel to one electro-magnetic output signal which is the merged electro-magnetic output signal of t frequency sources with t > 1 and v > 1.

16. Method according to claim 1 wherein the electro-magnetic radiation field is created by the irradiation through one antenna connected to one electromagnetic output signal which is the merged electro-magnetic output signal of x frequency sources with x > 1.

17. Method according to claim 4 wherein f_tar(Ai) is defined by: ftar(n) = ftar(i) - / with / = {2,3,4}

18. Method according to claim 4 wherein f_tar(n) is defined by: ftar(/i) = ftar(i) - y with J = [V₂, %, %}

19. Method according to claim 4 wherein the ultra high resonant frequency stability of said crystal exists at n frequencies f_tar(i) tof_tar(π).

20. Method according to claim 3 wherein the ultra high resonant frequency stability of said crystal exists at the frequency W