Stress-isolated crystal resonator resonance element and crystal resonator

Abstract

The present invention provides a novel method for achieving high mechanical stress isolation and high-precision temperature sensing in a crystal oscillator.

Description

Technical Field

[0001] The present invention relates to quartz crystal frequency control devices used in various applications that require an accurate and stable frequency reference and / or timing signal. More specifically, the present invention relates to quartz crystal resonators having reduced sensitivity to mechanically and thermally induced stresses, and quartz crystal oscillators including such resonators.

Background Art

[0002] A crystal oscillator is an important component in a frequency control device that can generate an electronic signal characterized by high-frequency stability.

[0003] For example, a resonator such as the rectangular ("strip") crystal resonator shown in FIG. 1 includes a crystal oscillator piezoelectric resonance element (1) mounted on a substrate (2) and operating in a hermetically sealed environment. The area (3) of the piezoelectric material between and near the electrodes is called the active vibration area or active vibration region. This is because most of the vibration displacement occurs there during the normal operation of the resonance element.

[0004] A crystal resonator can be adversely affected by mechanical stress. The latter can be mechanically induced, as in the case of mechanical acceleration, shock, or vibration applied to the resonator, or thermally induced when the ambient temperature of the resonator changes. Mechanically or thermally induced stresses cause undesirable changes in the resonance frequency, resulting in degradation of the frequency stability of the frequency control device including the crystal resonator and affecting many performance parameters such as thermal hysteresis, sensitivity to acceleration, long-term frequency stability, reflow shift, frequency wander, mechanical shock response, etc.

[0005] Several approaches are known for reducing the sensitivity of resonators to mechanically and thermally induced stresses.

[0006] The use of a cantilever (single-ended beam) attachment of a resonant element is one such approach. A cantilever-attached resonant element is often mounted on a substrate using a softer and less rigid mounting material, which helps to further reduce the impact of mechanically or thermally induced stresses.

[0007] Also known are resonant elements having stress isolating structures as disclosed in Patent Document 1 and Patent Document 2, for example, in which two "tethers" are arranged to extend from near the active vibration region. The two "tethers" house two electrical signal lines of the resonant element and terminate in two separate areas of the piezoelectric material intended for mounting the resonant element. This type of resonant element is mounted using at least two mounting points arranged at two separate locations in the mounting area of the resonant element.

[0008] The present invention advances the current state of the art by providing a crystal oscillator resonant element and a resonator having a novel stress isolation structure that results in a reduced sensitivity to mechanically or thermally induced stresses and an improved resonator performance.

[0009] Another aspect of the present invention is that the stress isolation structure of the resonant element of the present invention also facilitates accurate sensing of the temperature of the resonant element, which is advantageous in improving the performance of frequency control devices that utilize temperature sensing of the resonator, such as, for example, temperature compensated crystal oscillators (TCXOs), oven-controlled crystal oscillators (OCXOs), and the like.

Summary of the Invention

[0010] As used in this specification and the claims, the term "comprising" means "including at least a part". When interpreting each statement containing the term "comprising" in this specification and the claims that include the term "comprising", there may also be components other than the term or the part preceding the term. Related terms such as "comprise" and "comprises" should be interpreted similarly.

[0011] One of the main aspects of the present invention is that an area of a resonant element (the "mounting area") intended for mounting the resonant element includes a single undivided or substantially undivided area such that the mounting point and all of the single undivided or substantially undivided area overlap, enabling the resonant element to be cantilever-mounted using either a single mounting point (the "single-point mounting") or more than one mounting point, and the active vibration area of the resonant element is semi-separated from the mounting area by one or more slots or voids arranged within the structure of the resonant element. In embodiments where the mounting points are located on the same side of the resonant element, this aspect of the present invention can be described by stating that the mounting area includes a single undivided or substantially undivided area that enables the resonant element to be cantilever-mounted by one or more mounting points with the single undivided or substantially undivided area located above, and the active vibration area of the resonator is semi-separated from the mounting area by one or more slots or voids arranged within the structure of the resonator.

[0012] It can be observed that since the single undivided or at least substantially undivided area and the mounting point overlap each other, the mounting point can be said to be completely connected by the body of the resonant element within the mounting region.

[0013] Another aspect of the present invention is that the above-described single, non-divided or substantially non-divided mounting area can be advantageously used as a location for placing the temperature sensing element. - This achieves proximity of the temperature sensing element to the resonance element, and as a result, achieves higher accuracy in temperature sensing of the resonance element while minimizing any adverse effects that the temperature sensing element may have on the active vibration area of the resonator.

[0014] The present invention will be further described with reference to the accompanying drawings.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2a

Figure 2b

Figure 2c

Figure 2d

Figure 2e

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Best Mode for Carrying Out the Invention

[0016] Without limiting the scope of the present invention, the present invention is illustrated herein by the following specific embodiments of resonating elements and resonators having stress isolation structures of the present invention.

[0017] In all of the embodiments described below, each of the resonating elements includes an active vibration area defined by the positions of two electrodes disposed on or in close proximity to opposing surfaces of the resonating element, and a mounting area that can be used for single-point or multi-point attachment of the resonating element and that is at least substantially undivided from the active vibration region by at least one void or slot disposed within the structure of the resonating element.

[0018] One embodiment of a resonating element having a stress isolation structure of the present invention is shown in FIG. 2a. The resonating element (1) includes two electrodes (2) disposed on opposing surfaces of the resonating element (1), thus defining the location of the active vibration region (located to the right of the dashed line in FIG. 2a), and a mounting area (located to the left of the dashed line) that includes an integrated single undivided area (3) that is semi-separated from the active vibration region by a void or slot (4). Both of the two signal lines (5) and (6) running from the two electrodes (2) terminate in the area (3).

[0019] Figure 2b shows yet another embodiment of the present invention. Two electrodes (2) arranged on two opposing surfaces of the resonance element (1) define the location of the active vibration region, which is stress-isolated from a single undivided mounting area (3) (located to the left of the dashed line in Figure 2b) by two gaps / slots (4). Two signal lines (5) and (6) running from the two electrodes (2) terminate at the area (3).

[0020] In yet another embodiment of the present invention shown in Figure 2c, the active vibration region of the resonance element (1) is defined by the positions of two electrodes (2) arranged on opposing surfaces of the resonance element (1) and stress-isolated from a mounting area (3) (located to the left of the dashed line in Figure 2c) by slots / gaps (4). Both of the two signal lines (5) and (6) running from the electrode (2) terminate at the area (3).

[0021] Figure 2d shows yet another embodiment of the present invention. Two electrodes (2) arranged on two opposing surfaces of the resonance element (1) define the location of the active vibration region, and the undivided mounting area (3) (located to the left of the dashed line in Figure 2d) is semi-isolated from the active region by three gaps / slots (4). Both of the two signal lines (5) and (6) running from the electrode (2) terminate at the area (3).

[0022] Figure 2e shows yet another embodiment of the present invention. Two electrodes (2) arranged on two opposing surfaces of the resonance element (1) define the location of the active vibration region, and the mounting area (3) (located to the left of the dashed line in Figure 2e) is semi-isolated from the active region by three gaps / slots (4). Both of the two signal lines (5) and (6) running from the electrode (2) terminate at the area (3).

[0023] Each of the resonance elements shown in Figures 2a to 2e can be attached to the substrate using one or more attachment points located within an undivided or substantially undivided area (3), in which case the one or more attachment points and the undivided or substantially undivided area (3) overlap each other.

[0024] An example of a single-point attachment is shown in FIG. 3. To constitute a single-point attachment of the resonance element (1) to the substrate using any of the currently known attachment materials, a single, undivided attachment area (3) that is semi-separated from the active vibration region of the resonance element by the slot (4) can be used. For example, a conductive adhesive (5) can be used to mechanically attach the resonance element (1) to the substrate (2), while at the same time ensuring the electrical connection of one of the electrodes (i.e., the electrode facing the substrate) to the conductive pad on the substrate (2). The second electrode can be electrically connected to the substrate using wire bonding to the conductive pad on the substrate. The resonance element (1) can be attached to the substrate (2) using more than one attachment point located under and overlapping the area (3).

[0025] FIG. 4 shows the structure of a resonator including the resonance element (1) of the present invention that is single-point attached to the surface of the substrate (2) of the resonator package, with the temperature sensing element (4) mounted within the attachment area (3) that is semi-separated and thus stress-isolated from the active vibration region (7). The active vibration region (7) is semi-separated from the attachment area (3) and thus stress-isolated by the slot / gap (6). The temperature sensing element (4) is connected to the conductive pads on the substrate (2) by two wire bonds (5). The temperature sensing element (4) is mounted on the surface of the resonance element, but its presence does not adversely affect the vibration in the active vibration region (7) due to the stress isolation of the active vibration region (7) from the attachment area (3) where the temperature sensing element is mounted. This enables a closer and thus more accurate sensing of the temperature of the resonance element without causing an undesirable degradation of the operation of the resonance element.

[0026] Returning to FIG. 3, when the resonant element of the present invention is used as part of a resonator having no temperature sensing element mounted in the mounting area, in order to improve the manufacturability of the resonator assembly by creating a support during the wire bonding process, it should be noted that the end point of the signal line of the upper electrode where one end of the wire bond is located can be moved to coincide with the mounting point 5.

[0027] (Structural advantages) The stress isolation structure of the present invention including a single substantially undivided mounting area suitable for single-point mounting of the resonant element to the substrate has many structural advantages compared to the prior art stress isolation structures. In particular, compared to a stress isolation structure including two separate "tethers", the structure of the present invention is (a) more mechanically rigid and (b) eliminates the need for any means of bringing one of the signal lines, such as for example a via plated through a resonant element or an edge-plated conductive connection, to the opposite side of the resonant element.

[0028] (Performance advantages) Compared to a prior art resonator having a resonant element including two "tethers", a resonator having a resonant element including the stress isolation structure of the present invention exhibits many performance advantages.

[0029] Modeling shows that a prior art cantilever-mounted stress isolation resonator exhibits a sensitivity to mechanical acceleration in the longitudinal direction of about 0.2863 ppb / g, whereas a resonator having the resonant element shown in FIG. 2a exhibits a sensitivity to acceleration in the longitudinal direction of about 0.2005 ppb / g, which is an improvement (reduction) of about 30% in acceleration sensitivity.

[0030] In the direction of the thickness of the resonant element, the magnitudes of the sensitivities to mechanical acceleration exhibited by the prior art resonator and the resonator of the present invention are correspondingly 0.0195 ppb / g and 0.0077 ppb / g, which is an improvement (reduction) of about 60%.

[0031] When exposed to an ambient temperature shift from 95°C to 130°C, the magnitudes of the strain-induced resonance frequency shifts in the prior art resonator and the resonator of the present invention are 558.36 ppb and 42.4040 ppb, respectively, which is an improvement (reduction) greater than one order of magnitude (i.e., greater than 10 times).

[0032] When exposed to a periodic ambient temperature change such that the ambient temperature changes from +25°C to +85°C, then decreases to -40°C, and then returns to +25°C, the maximum resonance frequency difference (the "frequency hysteresis") at the ambient temperature points when the temperature is moving in the opposite direction is on the order of 20 ppb in the prior art resonator, whereas the frequency hysteresis exhibited by the resonator of the present invention is approximately 10 ppb, which is a two-fold improvement (reduction).

[0033] Accurate sensing of the temperature of the resonance element is an important factor in achieving high frequency stability in frequency control devices such as temperature compensated crystal oscillators (TCXOs), oven controlled crystal oscillators (OCXOs), etc. Positioning the temperature sensing element directly on the surface of the resonance element, rather than positioning it in the vicinity of the resonance element, provides the highest temperature sensing accuracy, as shown in FIG. 5. Lines 1, 2, and 3 represent the modeled differences between the temperature of the active region of the rectangular "strip" resonance element and the temperature sensed by the temperature sensing element when the resonator undergoes a rapid temperature change from 0°C to +85°C, for each of the following three positions of the temperature sensing element: a position on the substrate and adjacent to the resonance element (line 1), a position on the substrate and under the active region of the resonance element (line 2), and a position directly on the surface of the resonance element (line 3).

[0034] As can be derived from FIG. 5, positioning the temperature sensing element directly on the surface of the resonant element provides the most accurate temperature sensing. However, as already described herein, positioning the temperature sensing element on the surface of the resonant element causes harmful effects in the extremely important active vibration region of the resonant element. Utilizing the resonant element of the present invention having a temperature sensing element installed in a stress-isolated mounting area makes it possible to accurately sense the temperature of the resonant element while presenting an advantageous new solution to avoid unwanted stress-related effects in the active vibration region. FIGS. 6 and 7 are useful for explaining the above solution.

[0035] FIG. 6 shows the stress distribution in a prior art resonant element (1) having a temperature sensing element (2) mounted directly on the surface of the prior art resonant element (1) when a resonator including the resonant element (1) undergoes a rapid temperature change from 0° C. to +85° C. As indicated by the position of the isostress lines in FIG. 6, there is significant (indicated by the isostress lines) stress propagation into the active vibration region (3). The calculated value of the von Mises stress in the active vibration region (3) is 314.37 kPa.

[0036] FIG. 7 shows the stress distribution in the resonant element of the present invention having a temperature sensing element (2) mounted directly on the surface of the resonant element (1) of the present invention when a resonator including the resonant element (1) undergoes a similar temperature change from 0° C. to +85° C. As shown in FIG. 7 by the position of the isostress lines, the active vibration region (3) is essentially isolated from thermally induced stresses. The calculated value of the von Mises stress in the active vibration region (3) in this case is 16.59 kPa, which is approximately 19 times less than in the prior art case shown in FIG. 6 and 6 times lower than in the prior art resonator even without the temperature sensing element (von Mises stress value: 100.02 kPa).

[0037] (Use) The stress isolation resonance elements and resonators implemented in accordance with the present invention can be advantageously used in various electronic devices and apparatuses. Such devices include, but are not limited to, crystal oscillators such as temperature compensated crystal oscillators (TCXOs) and oven controlled crystal oscillators (OCXOs). Various electronic devices will benefit from using the resonance elements and resonators of the present invention and devices incorporating the resonance elements and resonators of the present invention. Such devices include, but are not limited to, portable and fixed communication devices, high-speed networking devices, wireless communication devices, and navigation devices.

Prior Art Documents

Patent Documents

[0038]

Patent Document 1

Patent Document 2

Claims

1. A crystal oscillator element including a mounting area and an active vibration area, wherein the mounting area includes an area that is substantially undivided, and the substantially undivided area is suitable for cantilever mounting of the crystal oscillator element through the one or more mounting points in such a way that the one or more mounting points and the substantially undivided area overlap each other, and the active vibration area is semi-separated from the substantially undivided area suitable for cantilever mounting by at least one slot or void disposed within the crystal oscillator element. Crystal oscillator element.

2. An oscillator including the crystal oscillator element according to claim 1.

3. The oscillator according to claim 2, wherein the crystal oscillator element is cantilever-mounted at a single point on a substrate.

4. The oscillator according to claim 3, wherein the crystal oscillator element is electrically connected to a conductive pad on the surface of the substrate, and the crystal oscillator element is electrically connected to the conductive pad on the surface of the substrate by a wire bond connecting the crystal oscillator element and the conductive pad on the surface of the substrate.

5. The crystal oscillator element according to claim 1, wherein a temperature sensing element is attached to the substantially undivided area suitable for cantilever mounting.

6. An oscillator including the crystal oscillator element according to claim 5.

7. The oscillator according to claim 6, wherein the crystal oscillator element is attached to a substrate, and the temperature sensing element is connected to at least one conductive pad on the surface of the substrate by at least one wire bond connection.

8. The oscillator according to claim 7, wherein the crystal oscillator element is cantilever-mounted at a single point on the substrate.

9. An electronic device including the crystal oscillator element according to claim 1 or 5.

10. An electronic device including the oscillator according to claim 2, 3, 4, 6, 7 or 8.

11. The electronic device according to claim 9 or 10, wherein the electronic device is a crystal oscillator.

12. The electronic device according to claim 9 or 10, wherein the electronic device is a temperature-compensated crystal oscillator.

13. The electronic device according to claim 9 or 10, wherein the electronic device is an oven-controlled crystal oscillator.

14. An electronic device including the crystal oscillator element according to claim 1 or 5.

15. An electronic device including the oscillator according to claim 2, 3, 4, 6, 7 or 8.

16. An electronic device including the electronic device according to any one of claims 9 to 13.

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