Stress-isolated quartz crystal resonant element and quartz crystal resonator

Abstract

The present invention provides a novel way to achieve high mechanical stress isolation and high precision temperature sensing in quartz crystal resonators.

Description

Technical Field

[0001] The present invention relates to quartz crystal frequency control devices for use in various applications requiring accurate and stable frequency references and / or timing signals. More particularly, the present invention relates to quartz crystal resonators having reduced sensitivity to mechanical and thermally induced stresses, and quartz crystal oscillators including such resonators. Background Art

[0002] Quartz crystal resonators are key components in frequency control devices, capable of generating electronic signals with high frequency stability.

[0003] Resonator (e.g. Figure 1 The rectangular ("strip") quartz crystal resonator shown comprises a quartz crystal piezoelectric resonant element (1) mounted on a substrate (2) and operated in a hermetically sealed environment. The region of piezoelectric material (3) between and adjacent to the electrodes is referred to as the active vibration region or active vibration zone, as this is where most of the vibration displacement occurs during normal operation of the resonant element.

[0004] Quartz crystal resonators can be adversely affected by mechanical stress. The latter can be induced mechanically, for example in cases where mechanical acceleration, shock or vibration is applied to the resonator, or thermally, when the ambient temperature of the resonator changes. Mechanically or thermally induced stresses cause undesired changes in the resonant frequency, resulting in impaired frequency stability of frequency control devices including quartz crystal resonators and adversely affecting many performance parameters, such as thermal hysteresis, sensitivity to acceleration, long-term frequency stability, reflow shift, frequency drift, mechanical shock response, etc.

[0005] Several methods are known to reduce the sensitivity of a resonator to mechanically and thermally induced stresses.

[0006] One such approach is to use cantilever mounting of the resonant element. Cantilever mounted resonant elements are typically mounted to the substrate using a softer, less rigid mounting material, which helps further reduce the effects of mechanical or thermally induced stresses.

[0007] Resonant elements with stress isolation structures are also known, such as those disclosed in US 8,912,711 and US 9,991,863, in which two "tethers" are arranged to extend from near the active vibration area. The two "tethers" accommodate two electrical signal lines of the resonant element and terminate in two separate piezoelectric material areas for mounting the resonant element. This type of resonant element is mounted using at least two mounting points located in two separate locations of the mounting area of ​​the resonant element.

[0008] The present invention advances the prior art by providing quartz crystal resonant elements and resonators having novel stress isolation structures that result in reduced sensitivity to mechanically or thermally induced stresses and 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 helps to accurately sense the temperature of the resonant element, which is beneficial to improving the performance of frequency control devices that utilize resonator temperature sensing (e.g., temperature compensated crystal oscillators (TCXOs), oven-controlled crystal oscillators (OCXOs), etc.). Summary of the invention

[0010] The term "comprising" as used in this specification and claims means "consisting at least in part of..." When interpreting each statement in this specification and claims containing the term "comprising", features other than the feature or features preceding the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0011] One of the main aspects of the present invention is that the area of ​​the resonant element for mounting the resonant element ("mounting area") comprises a single undivided or substantially undivided area that enables cantilever mounting of the resonant element using a single mounting point ("single point mounting"), or more than one mounting point such that all mounting points overlap with said single undivided area, and the active vibration area of ​​the resonator is semi-separated from the mounting area by one or more slots or voids arranged in 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 may be described in the following manner: the mounting area comprises a single undivided or substantially undivided area that enables cantilever mounting of the resonant element. The active vibration area of ​​the resonator is covered by said single undivided or substantially undivided area via one or more mounting points, and the active vibration area of ​​the resonator is semi-separated from the mounting area by one or more slots or voids arranged in 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 area.

[0013] Another aspect of the invention is that the aforementioned single undivided or substantially undivided mounting area can advantageously be used as a location for placing a temperature sensing element - this allows for close proximity of the temperature sensing element to the resonant element and, therefore, greater accuracy in temperature sensing of the resonant element while minimizing any adverse effects that the temperature sensing element may have on the active vibrating region of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention is further described with reference to the accompanying drawings, in which:

[0015] Figure 1 A prior art "strip" resonator is shown having a resonant element two-point mounted to a substrate of the resonator package.

[0016] Figure 2a to Figure 2e Several embodiments of resonant components incorporating the stress isolation structure of the present invention are shown.

[0017] Figure 3 The resonant element of the present invention is shown mounted in a single-point cantilever style and electrically connected to the substrate of the resonator package.

[0018] Figure 4 A resonant element of the present invention is shown having a temperature sensing element mounted in a stress-isolating mounting region, the resonant element being single-point cantilever mounted and connected to a substrate of a resonator package.

[0019] Figure 5 A comparison of temperature sensing of the resonant element for three different positions of the temperature sensing element is shown.

[0020] Figure 6 The distribution of thermally induced stresses in a prior art resonant element is shown.

[0021] Figure 7 The distribution of thermally induced stresses in the resonant element of the invention is shown. DETAILED DESCRIPTION

[0022] Without limiting the scope of the present invention, the latter is described herein by way of the following specific embodiments of the resonant element and resonator having a stress isolation structure of the present invention.

[0023] In all embodiments described below, each resonant element comprises: an active vibration region defined by the positions of two electrodes disposed on opposite surfaces of the resonant element or arranged in close proximity to opposite surfaces of the resonant element; a mounting region comprising an undivided or at least substantially undivided region that can be used for single-point or multi-point mounting of the resonant element and is semi-separated from the active vibration region by at least one gap or groove disposed in the structure of the resonant element.

[0024] Figure 2aOne embodiment of the resonant element with stress isolation structure of the present invention is shown. The resonant element (1) includes two electrodes (2) and a mounting area (located on the left side of the dotted line). The two electrodes (2) are arranged on opposite surfaces of the resonant element (1) to define the position of the active vibration area (located on the left side of the dotted line). Figure 2a The mounting area includes an integrated single undivided area (3) which is semi-separated from the active vibration area by a gap or groove (4). The two signal lines (5) and (6) extending from the two electrodes (2) both terminate in the area (3).

[0025] Figure 2b Two electrodes (2) disposed on opposite sides of the resonant element (1) define the location of the active vibration region, and the active vibration region is connected to a single undivided mounting area (3) (located at Figure 2b The two signal lines (5) and (6) extending from the two electrodes (2) are both terminated in the region (3).

[0026] In another embodiment of the present invention, Figure 2c As shown, the active vibration area of ​​the resonant element (1) is defined by the positions of two electrodes (2) arranged on opposite surfaces of the resonant element (1), and the stress is generated by the gap / groove (4) and the mounting area (3) (located at Figure 2c The two signal lines (5) and (6) extending from the electrode (2) are both terminated in the region (3).

[0027] Figure 2d Another embodiment of the present invention is shown. Two electrodes (2) arranged on opposite sides of the resonant element (1) define the position of the active vibration area, and the undivided mounting area (3) (located at Figure 2d The left side of the dashed line in the middle is half-separated from the active region by three gaps / grooves (4). The two signal lines (5) and (6) extending from the electrode (2) both terminate in the region (3).

[0028] Figure 2e Another embodiment of the present invention is shown. Two electrodes (2) arranged on opposite sides of the resonant element (1) define the position of the active vibration area, and the mounting area (3) (located at Figure 2e The left side of the dashed line in the middle is half-separated from the active region by three gaps / grooves (4). The two signal lines (5) and (6) extending from the electrode (2) both terminate in the region (3).

[0029] Figure 2a to Figure 2eEach resonant element shown in can be mounted to the substrate using one or more mounting points located in the undivided or substantially undivided area (3), in which case the one or more mounting points and the undivided or substantially undivided area (3) will overlap each other.

[0030] An example of a single point installation is Figure 3 As shown. A single undivided mounting region (3) is semi-separated from the active vibration region of the resonant element (1) by a groove (4), and can be used to cantilever-mount the resonant element (1) to a substrate at a single point using any currently known mounting material: for example, a conductive glue (5) can be used to mechanically mount the resonant element (1) to the substrate (2) while ensuring that one of the electrodes (i.e., the electrode facing the substrate) is electrically connected to a conductive pad on the substrate (2). A second electrode can be electrically connected to the substrate using a wire bond (6) to a conductive pad on the substrate. More than one mounting point located below the region (3) and overlapping the region (3) can be used to mount the resonant element (1) to the substrate (2).

[0031] Figure 4 The structure of a resonator is shown, which includes a resonant element (1) of the present invention, which is single-point mounted to the surface of a substrate (2) of the resonator package, and a temperature sensing element (4) is mounted in a mounting area (3), which is semi-separated and therefore stress-isolated from an active vibration area (7). The active vibration area (7) is semi-separated from the mounting area (3) and is therefore stress-isolated by a groove / gap (6). The temperature sensing element (4) is connected to a conductive pad on the substrate (2) by two bonding wires (5). Although the temperature sensing element (4) is mounted on the surface of the resonant element, its presence does not adversely affect the vibration in the active area (7) due to the stress isolation of the active area (7) from the mounting area (3) (where the temperature sensing element is mounted). This allows the temperature of the resonant element to be sensed more closely and therefore more accurately without causing undesirable degradation in the operation of the resonant element.

[0032] Return to reference Figure 3 It should be noted that when the resonant element of the present invention is used as part of a resonator and the temperature sensing element is not mounted in the mounting area, the endpoint of the signal line of the upper electrode (where one end of the bonding wire (6) is located) can be moved to overlap with the mounting point (5) so as to improve the manufacturability of the resonator assembly by creating support during the wire bonding process.

[0033] Structural advantages

[0034] The stress isolation structure of the present invention includes a single substantially undivided mounting area suitable for single-point mounting of a resonant element to a substrate, and has a number of structural advantages over the prior art. Specifically, compared to stress isolation structures including two separate "tethers", the structure of the present invention (a) is more mechanically rigid, and (b) eliminates the need for any means of bringing one of the signal lines to the opposite side of the resonant element, such as a plated through hole or edge plated conductive connection through the resonant element.

[0035] Performance advantages

[0036] Resonators having a resonant element of the present invention including a stress isolation structure exhibit a number of performance advantages compared to prior art resonators having a resonant element including two "tethers."

[0037] Modeling shows that the prior art cantilever mounted stress-isolated resonator exhibits a sensitivity to mechanical acceleration in the longitudinal direction of about 0.2863 ppb / g, while Figure 2a The resonator of the resonant element shown exhibits a sensitivity to acceleration in the longitudinal direction of about 0.2005 ppb / g, an improvement (reduction) in acceleration sensitivity of about 30%.

[0038] In the thickness direction of the resonant element, the prior art resonator and the resonator of the present invention exhibit sensitivities to mechanical acceleration of 0.0195 ppb / g and 0.0077 ppb / g, respectively, which is an improvement (reduction) of about 60%.

[0039] When the ambient temperature changes from 95°C to 130°C, the magnitudes of the resonant frequency shifts induced by strain in the prior art resonator and the resonator of the present invention are 558.36 ppb and 42.4040 ppb, respectively, an improvement (reduction) of more than an order of magnitude (i.e., more than 10 times).

[0040] When the ambient temperature changes periodically, from +25°C to +85°C, then drops to -40°C, and then returns to +25°C, the maximum resonant frequency difference ("frequency hysteresis") of the ambient temperature points when the temperature moves in the opposite direction can be as high as 20 ppb in the prior art resonators, while the resonators of the present invention exhibit a frequency hysteresis of approximately 10 ppb, an improvement (reduction) of 2 times.

[0041] Accurately sensing the temperature of the resonant element is a key factor in achieving high-frequency stability in frequency control devices such as temperature compensated crystal oscillators (TCXOs) and oven controlled crystal oscillators (OCXOs). Placing the temperature sensing element directly on the surface of the resonant element (rather than close to the resonant element) achieves the highest temperature sensing accuracy, such as Figure 5Lines 1, 2, and 3 represent the modeled difference between the temperature of the active region of the rectangular "strip" resonant element and the temperature sensed by the temperature sensing element when the resonator is subjected to a rapid temperature change from 0°C to +85°C, for three locations of each temperature sensing element: on the substrate and close to the resonant element (line 1), on the substrate and below the active region of the resonant element (line 2), and directly on the surface of the resonant element (line 3).

[0042] from Figure 5 It can be seen that placing the temperature sensing element directly on the surface of the resonant element allows for the most accurate temperature sensing. However, as already mentioned herein, the positioning of the temperature sensing element on the surface of the resonant element causes detrimental effects in the extremely important active vibration region of the resonant element. Utilizing the resonant element of the present invention, wherein the temperature sensing element is mounted in a stress-isolated mounting region, an advantageous novel solution is provided, whereby the temperature of the resonant element can be accurately sensed while avoiding undesirable stress-related effects in the active vibration region. Figure 6 and Figure 7 Used to illustrate the above technical solution.

[0043] Figure 6 The stress distribution in a prior art resonant element (1) is shown when the resonator including the resonant element (1) is subjected to a rapid temperature change from 0°C to +85°C, wherein a temperature sensing element (2) is directly mounted on the surface of the prior art resonant element (1). Figure 6 As shown by the location of the medium stress line, a considerable amount of stress (represented by the isostrain lines) propagates into the active vibration region (3). The calculated von Mises stress value in the active vibration region (3) is 314.37 kPa.

[0044] Figure 7 The stress distribution in the resonant element (1) of the present invention is shown when the resonator including the resonant element (1) is subjected to a similar temperature change from 0°C to +85°C, wherein the temperature sensing element (2) is directly mounted on the surface of the resonant element (1) of the present invention. Figure 7 As shown by the location of the medium stress line, the active vibration zone (3) is essentially isolated from the thermally induced stress. The von Mises stress value in the active vibration zone (3) calculated in this case is 16.59 kPa, which is as low as Figure 6 This is about one nineteenth of the prior art case shown, and as low as about one sixth of the prior art (von Mises stress value: 100.02 kPa) which does not even have a temperature sensing element.

[0045] application

[0046] Stress-isolated resonant elements and resonators implemented in accordance with the present invention may be advantageously used in a variety of electronic devices and equipment. Such devices include, but are not limited to, quartz crystal oscillators (XOs), including temperature compensated crystal oscillators (TCXOs) and oven controlled crystal oscillators (OCXOs). A wide variety of electronic devices will benefit from using the resonant elements and resonators of the present invention, and devices containing the resonant elements and resonators of the present invention; such devices include, but are not limited to, portable and fixed telecommunications equipment, high-speed network equipment, radio communication equipment, and navigation equipment.

Claims

1. A quartz crystal resonator element, comprising a mounting area and an active vibration area, wherein the mounting area comprises a substantially undivided area, the undivided area being suitable for cantilever mounting the resonator element via one or more mounting points in the following manner, wherein the one or more mounting points and the undivided area overlap each other, and wherein the active vibration area is semi-separated from the undivided area suitable for cantilever mounting by at least one groove or gap arranged in the resonator element.

2. A resonator comprising the quartz crystal resonator element according to claim 1.

3. The resonator of claim 2, wherein the quartz crystal resonant element is single-point cantilever mounted to a substrate. 4 . The resonator according to claim 3 , wherein the quartz crystal resonant element is electrically connected to a conductive pad on the surface of the substrate through a bonding wire connecting the quartz crystal resonant element and the substrate pad.

5. The quartz crystal resonator element of claim 1 wherein a temperature sensing element is attached to the substantially undivided region suitable for cantilever mounting.

6. A resonator comprising the quartz crystal resonator element according to claim 5.

7. The resonator of claim 6, wherein the quartz crystal resonant element is mounted to a substrate and the temperature sensing element is electrically connected to at least one conductive pad on the surface of the substrate by at least one wire bond connection.

8. The resonator of claim 7, wherein the quartz crystal resonant element is single-point cantilever mounted to the substrate.

9. An electronic device comprising the quartz crystal resonator element according to any one of claims 1 and 5.

10. An electronic device comprising the resonator according to any one of claims 2, 3, 4, 6, 7 and 8.

11. The electronic device according to any one of claims 9 and 10, wherein the electronic device is a quartz crystal oscillator.

12. The electronic device according to any one of claims 9 and 10, wherein the electronic device is a temperature compensated crystal oscillator.

13. The electronic device according to any one of claims 9 and 10, wherein the electronic device is an oven-controlled crystal oscillator.

14. An electronic device comprising the quartz crystal resonator element according to any one of claims 1 and 5.

15. An electronic device comprising the resonator according to any one of claims 2, 3, 4, 6, 7 and 8.

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

Images