A quartz crystal with low equivalent series resistance

Abstract

The application belongs to the technical field of piezoelectric frequency components, and discloses a quartz crystal with low equivalent series resistance, which comprises a quartz piezoelectric wafer base body; a front main electrode is arranged on the front surface of the quartz piezoelectric wafer base body; a back main electrode corresponding to the position of the front main electrode is arranged on the back surface; a plurality of acoustic barrier through grooves are arranged on the quartz piezoelectric wafer base body; the acoustic barrier through grooves are arranged along the periphery of the front main electrode and the back main electrode and do not contact the main electrodes. After the through acoustic barrier through grooves are arranged on the periphery of the electrode, an acoustic impedance mutation boundary is formed. When the outwardly leaking thickness shear vibration wave propagates to the inner side wall of the through hole, strong reflection occurs at the acoustic impedance mutation interface, most of the vibration energy is reflected back to the effective vibration area of the electrode center, cannot continue to diffuse outward, the equivalent series resistance of the quartz crystal is reduced, mechanical energy dissipation is reduced, and the quality factor is improved.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric frequency components technology, and relates to a quartz crystal with low equivalent series resistance. Background Technology

[0002] Quartz crystal resonators are core reference frequency components in electronic information systems. Due to the excellent piezoelectric properties and frequency-temperature stability of quartz crystals, they are known as the "heartbeat clock" of electronic devices and are widely used in consumer electronics, 5G communications, industrial control, automotive electronics, aerospace, and other fields. As electronic systems evolve towards miniaturization, low power consumption, and low phase noise, increasingly stringent requirements are being placed on the core performance indicators of quartz crystal resonators—equivalent series resistance (ESR) and quality factor (Q value): the lower the ESR, the easier it is for the device to start oscillate and the lower the power consumption; the higher the Q value, the better the frequency stability and the lower the phase noise.

[0003] The mainstream operating mode of quartz crystal resonators is the thickness shear vibration mode, typically represented by AT-cut quartz wafers. Its core working principle is based on the "energy trapping effect": by depositing metal excitation electrodes on the wafer surface, the mass loading effect of the electrodes causes the resonant frequency of the electrode region to be lower than that of the surrounding bare wafer region, thus forming an equivalent energy potential trap, confining the mechanical energy of the thickness shear vibration mainly to the region below the electrodes. Ideally, the vibration energy should be completely localized in the center region of the electrodes, without diffusing to the periphery of the wafer; however, in actual structures, traditional planar electrodes only create an acoustic impedance difference through the mass difference between the metal and the quartz, resulting in a gentle change in acoustic impedance at the electrode boundaries, failing to form a steep acoustic barrier.

[0004] The aforementioned structural defects lead to leakage problems: a portion of the thickness shear vibration energy diffuses along the wafer plane towards the edge region in the form of leakage waves. When this energy propagates to wafer support points, edge chamfers, or packaging bonding points, it is dissipated as heat through anchor point losses, edge scattering, and structural damping, ultimately resulting in increased ESR and decreased Q value. Especially with the trend of wafer miniaturization, electrode sizes continue to shrink, further weakening the energy trap's confinement capability and significantly increasing the leakage ratio. ESR deterioration has become a core bottleneck restricting the performance improvement of miniaturized quartz crystals.

[0005] To mitigate the energy limitation effect, the industry currently employs methods such as optimizing electrode size and thickness, fabricating Mesa protrusion structures, and beveling wafer edges. However, simply modifying the electrode provides limited energy improvement, while Mesa protrusions and beveled edges increase process difficulty and production costs, thus still having certain limitations. Summary of the Invention

[0006] The purpose of this invention is to provide a quartz crystal (structure) with low equivalent series resistance, which solves the technical problem in the prior art where traditional planar electrode quartz crystals rely solely on electrode mass loading to form an energy trap, resulting in a gradual change in acoustic impedance at the electrode boundary and easy leakage and diffusion of thickness shear vibration energy, leading to high equivalent series resistance and low quality factor, thus restricting the performance improvement of miniaturized quartz crystals.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A quartz crystal with low equivalent series resistance includes a quartz piezoelectric wafer substrate; a front main electrode is disposed on the front side of the quartz piezoelectric wafer substrate; and a back main electrode is disposed on the back side corresponding to the position of the front main electrode. The quartz piezoelectric wafer substrate is provided with a plurality of acoustic barrier channels; the acoustic barrier channels are arranged around the front main electrode and the back main electrode and do not contact the main electrodes; the acoustic barrier channels are channels that completely penetrate the quartz piezoelectric wafer substrate along the thickness direction; the acoustic barrier channels together form an acoustic impedance abrupt change boundary surrounding the main electrode region.

[0008] Furthermore, the front main electrode and the back main electrode are rectangular structures, and four acoustic barrier channels are provided, which are respectively arranged on the outside of the four sides of the rectangular main electrode and extend along the length direction of the corresponding side.

[0009] Furthermore, the acoustic barrier channels are not connected end to end, and the gaps between the channels are used to arrange electrode lead-out structures.

[0010] Furthermore, the front main electrode and the back main electrode are symmetrically arranged stacked metal structures, consisting of an adhesion layer and a main electrode layer; the adhesion layer is a Cr layer; and the main electrode layer is an Au layer.

[0011] Furthermore, the front side of the quartz piezoelectric wafer substrate is also provided with a front sub-electrode, an electrode lead-out guide strip, and an end welding pad; the front sub-electrode is diagonally distributed at the corner position of the quartz piezoelectric wafer substrate, and the end welding pad is provided at another set of diagonal positions of the quartz piezoelectric wafer substrate.

[0012] Furthermore, the electrode lead-out guide is connected between the front main electrode and the end welding pad, and is located at the gap of the adjacent acoustic barrier channel.

[0013] Furthermore, the reverse side of the quartz piezoelectric wafer substrate is provided with a reverse sub-electrode, a reverse lead-out guide strip, and a reverse welding pad that correspond one-to-one with the front sub-electrode, the electrode lead-out guide strip, and the end welding pad and are arranged symmetrically.

[0014] Furthermore, a preset distance is maintained between the inner wall of the acoustic barrier channel and the edge of the corresponding main electrode. The preset distance is 1 / 4 to 5 times the wavelength of the shear acoustic wave within the quartz wafer at the target resonant frequency, which is used to match the phase of the acoustic wave reflection.

[0015] Furthermore, the acoustic barrier channel is a hollow channel with a cross-sectional shape such as rectangular or wave-shaped, which can form a hollow cavity and achieve the contour of acoustic barrier.

[0016] Furthermore, the cross-section of the acoustic barrier channel is rectangular.

[0017] The beneficial effects of this invention are as follows: After setting a through-type acoustic barrier groove around the electrode, this invention forms an acoustic impedance abrupt change boundary. When the thickness shear vibration wave that leaks outward propagates to the inner wall of the through hole, it will be strongly reflected at the acoustic impedance abrupt change interface. Most of the vibration energy is reflected back to the effective vibration area at the center of the electrode and cannot continue to diffuse outward. This reduces the equivalent series resistance of the quartz crystal, reduces mechanical energy dissipation, and improves the quality factor. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the front planar structure of the quartz crystal of the present invention; Figure 2 This is a histogram of the equivalent series resistance distribution of a conventional planar electrode quartz wafer. Figure 3 This is a histogram showing the equivalent series resistance distribution of the improved quartz wafer according to the present invention.

[0019] In the figure: 100, quartz piezoelectric wafer substrate; 200, front main electrode; 300, end welding pad; 400, front secondary electrode; 500, electrode lead-out guide strip; 600, acoustic barrier channel. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1 As shown, a quartz crystal with low equivalent series resistance includes a quartz piezoelectric wafer substrate 100 and a front main electrode 200, a front secondary electrode 400, an electrode lead-out conductive strip 500, an end welding pad 300, and an acoustic barrier channel 600 disposed on the quartz piezoelectric wafer substrate 100.

[0022] In some embodiments, the quartz piezoelectric wafer substrate 100 is an AT-cut quartz wafer with a cut angle of 35°15′ and a cut angle deviation of ≤±10′; the wafer shape is rectangular with dimensions of 1.3mm×1.0mm and a nominal thickness of 33.4μm, corresponding to a resonant frequency of 50MHz for the fundamental frequency thickness shear vibration mode, except for other specifications and models of quartz wafers.

[0023] The front main electrode 200 is disposed in the central region of the front side of the quartz piezoelectric wafer substrate 100; two front secondary electrodes 400 are disposed, and are diagonally distributed at the corner positions of the quartz piezoelectric wafer substrate 100. It is worth noting that the reverse side of the quartz piezoelectric wafer substrate 100 is provided with a reverse main electrode and a reverse secondary electrode (not shown in the figure) that correspond one-to-one with the front main electrode 200 and the front secondary electrode 400.

[0024] In some embodiments, the front main electrode 200 and the back main electrode are identical except for their arrangement positions, and the front secondary electrode 400 and the back secondary electrode are identical except for their arrangement positions. The front main electrode 200 has a rectangular stacked structure with dimensions of 0.8 mm × 0.6 mm. From bottom to top, the electrode consists of a Cr adhesion layer and an Au main electrode layer. The Cr layer has a thickness of 5-15 nm and is used to enhance the bonding force between the metal and the quartz. The Au layer has a thickness of 100-500 nm and serves as the main conductive and mass loading layer. In some embodiments, the electrode may also be composed of a combination of materials such as Ag, Ti, and Al.

[0025] In some embodiments, two end welding pads 300 are provided, respectively located on another set of diagonal corners of the quartz piezoelectric wafer substrate 100, for subsequent conductive adhesive bonding or ultrasonic bonding during encapsulation, to achieve electrical connection between the wafer and external circuitry; the front main electrode 200 and the end welding pads 300 are connected by an electrode lead-out conductive strip 500. The electrode lead-out conductive strip 500 has a width of 50 μm and a thickness consistent with the front main electrode 200, and also employs a Cr / Au stacked structure.

[0026] In some embodiments, four acoustic barrier channels 600 are provided, which are located on the outside of the four sides of the rectangular front main electrode 200 and extend along the length of the sides; the acoustic barrier channels 600 do not contact the front main electrode 200 and penetrate both sides of the quartz piezoelectric wafer substrate 100.

[0027] In some embodiments, the acoustic barrier channel 600 is a through-hole hollow channel. The hollow cavity alters the propagation impedance of the thickness shear vibration wave, blocking its direct transmission path and thus achieving acoustic barrier. This invention exemplarily uses a rectangle as the cross-section of the channel; however, any cross-sectional profile capable of forming a hollow cavity is applicable, such as wave-shaped, circular, elliptical, trapezoidal, or polygonal shapes, and is not limited to the aforementioned forms; they will not be listed individually here.

[0028] In some embodiments, the acoustic barrier channel 600 is provided with eight channels, two of which are provided on the outer side of the side length of each rectangular front main electrode 200 and are not connected to each other.

[0029] In some embodiments, four acoustic barrier channels 600 together form an acoustic impedance abrupt boundary surrounding the front main electrode 200. This acoustic impedance abrupt boundary can effectively reflect thickness shear vibration waves attempting to leak outward, confining the vibration energy more tightly within the effective vibration region at the center of the electrode, significantly reducing energy diffusion to the wafer edge and the resulting losses. The four acoustic barrier channels 600 are not connected end-to-end, and the electrode lead-out guide strip 500 is disposed within the reserved space between the acoustic barrier channels 600, thereby connecting the front main electrode 200 and the end bonding pad 300.

[0030] In some embodiments, a preset distance is maintained between the inner wall of the acoustic barrier channel 600 and the corresponding electrode. This preset distance is set according to the wavelength of the sound wave at the target frequency, typically 1 / 4 to 5 times the wavelength, in order to achieve the optimal reflection phase.

[0031] The acoustic barrier channel 600 has a radial width of 10-50μm, a sidewall verticality of not less than 88°, a smooth inner wall, and minimal etching damage.

[0032] The present invention provides the following advantages by creating an acoustic barrier groove 600 on the quartz piezoelectric wafer substrate 100 to form an acoustic impedance abrupt change boundary: Enhanced energy trapping effect: The acoustic barrier channel 600 structure creates a physically strong acoustic discontinuity interface on the quartz piezoelectric wafer substrate 100, with an acoustic impedance difference much greater than that of the traditional electrode-bare wafer interface. This interface can more effectively reflect vibrational energy, significantly increasing the radial attenuation constant (α) of vibrational displacement / strain energy, thereby achieving a high degree of localization of vibrational energy in the electrode center region.

[0033] Reduced mechanical energy dissipation: Because the energy leakage path is effectively blocked, the energy leaking to the support structure and the edge of the wafer is greatly reduced, which significantly reduces the mechanical losses (support loss, edge scattering loss, etc.) inside the resonator.

[0034] Optimizing electrical parameters: The reduction in internal mechanical losses is directly reflected in the electrical parameters. Simultaneously, the quality factor (Q value) is correspondingly improved. Energy conversion efficiency is improved.

[0035] Good process compatibility: This structure can be integrated with the existing quartz crystal resonator manufacturing process through mature photolithography and etching processes (such as dry etching or wet etching), without the need to introduce complex epitaxial or bonding processes, and the cost is controllable.

[0036] Working principle: The core principle of this invention is to enhance the energy trapping effect under thickness shear vibration mode through an acoustically blocked 600-slot structure, thereby reducing energy leakage and lowering the equivalent series resistance. The specific principle is as follows: When a quartz crystal operates in the thickness shear vibration mode, the vibrational energy is primarily confined to the region below the electrodes due to the mass loading effect of the electrodes, i.e., the energy trapping effect. The vibrational displacement decays exponentially from the electrode edge towards the periphery of the crystal, satisfying the following displacement decay function:

[0037] In the formula, u(x) is the vibration displacement amplitude at a distance x from the electrode edge; u0 is the reference displacement amplitude at the electrode edge; the absolute value of |x| indicates that the vibration attenuation in the two directions from the electrode boundary to the inner side of the electrode and the outer side of the wafer is symmetrical; α is the attenuation constant.

[0038] The physical meaning of this formula is: vibrational energy decays rapidly in the bare crystal region, and the vibration amplitude is weaker the farther away from the electrode; the larger the decay constant α is, the faster the vibrational energy decays radially, the more concentrated the energy is below the electrode, and the smaller the corresponding equivalent series resistance ESR is.

[0039] The magnitude of the attenuation constant α is determined by the mass loading effect of the electrode, and its physical expression is:

[0040] In the formula, f e Δm is the resonant frequency of the electrode region, which decreases due to the mass loading effect of the electrode; M is the effective mass of the electrode; and Δm is the effective mass of the quartz crystal participating in the vibration. The physical meaning of α is: the larger α is, the faster the vibrational energy decays radially, the more concentrated the energy is below the electrode, and the smaller the corresponding equivalent series resistance (ESR).

[0041] In traditional planar electrode structures, the acoustic impedance difference is created solely by the mass difference between the electrode and the bare wafer. The impedance change at the electrode boundary is gradual, and the attenuation constant α is determined by the mass loading effect of the electrode itself, with a natural upper limit. Therefore, some vibrational energy will continuously diffuse towards the wafer edge in the form of leakage waves. After the energy leaks to the support point or wafer edge, non-ideal reflection, scattering, and support losses occur, ultimately being converted into heat energy dissipation, manifested as an increase in ESR and a decrease in Q value.

[0042] This invention, by setting a through-hole acoustic barrier groove 600 around the electrode, forms an acoustic impedance abrupt change boundary that is far stronger than that of a traditional electrode-bare wafer interface. When the thickness shear vibration wave leaking outward propagates to the inner wall of the via, it will be strongly reflected at the acoustic impedance abrupt change interface, and most of the vibration energy will be reflected back to the effective vibration area at the center of the electrode, unable to continue to diffuse outward. This effect is equivalent to significantly increasing the attenuation constant α, greatly accelerating the radial attenuation rate of the vibration energy, and achieving a high degree of localization of the vibration energy in the electrode region.

[0043] The degree of concentration of vibrational energy can be characterized by energy conversion efficiency:

[0044] In the formula, Ea is the mechanical vibration energy of the effective region below the electrode; Et is the total mechanical vibration energy contained in the entire crystal. The higher the value, the more concentrated the vibration energy is in the effective working area, the less useless energy leaks to the periphery, and the higher the energy utilization rate. The acoustic barrier channel 600 structure of this invention can significantly improve energy efficiency. Value, reducing energy loss at the source.

[0045] To verify the actual effect of the acoustic barrier slot 600 structure of this invention on reducing the equivalent series resistance, 1000 pieces each of conventional planar electrode structure samples and samples of the acoustic barrier slot 600 structure of this invention were prepared using quartz piezoelectric wafer substrates 100 from the same batch (i.e., Figure 2 and Figure 3 In the example where n=1000), the equivalent series resistance (ESR) was tested under the same process conditions and test environment (room temperature 25℃, standard excitation level). The test results are as follows: The comparative sample of conventional planar electrode quartz wafers adopts a traditional planar electrode structure with a 600mm acoustic barrier slot design. All other parameters, including wafer cut, thickness, electrode material, and electrode dimensions, are completely consistent with the example. Statistical analysis shows that the equivalent series resistance of 1000 conventional wafers follows a normal distribution, as shown in the histogram. Figure 2 As shown, the core statistical parameters are: Equivalent series resistance mean: 11.68Ω; standard deviation: 1.092Ω; parameter distribution range: approximately 9.7Ω~14.0Ω.

[0046] The improved quartz wafer sample of this invention uses a quartz crystal with an acoustically blocked 600-slot structure as described in this invention. The through-hole structure and electrode parameters are consistent with those of the aforementioned embodiments. Statistical analysis shows that the equivalent series resistance of 1000 improved wafers conforms to a normal distribution, as shown in the distribution histogram. Figure 3 As shown, the core statistical parameters are: Equivalent series resistance mean: 8.407Ω; standard deviation: 0.4175Ω; parameter distribution range: approximately 7.31Ω~9.44Ω.

[0047] A quantitative comparison of the two sets of test data reveals that: The average equivalent series resistance decreased from 11.68Ω to 8.467Ω, a reduction of approximately 27.5%, demonstrating that the acoustic barrier slot 600 structure of the present invention effectively blocks the leakage of vibration energy to the edge of the wafer by constructing a strong acoustic impedance abrupt boundary and enhancing the energy trapping effect, significantly reducing the equivalent series resistance of the quartz crystal and reducing mechanical energy dissipation; the parameter standard deviation decreased from 1.092Ω to 0.3548Ω, a reduction of approximately 67.5%, indicating that the solution of the present invention significantly improves the consistency of product parameters and significantly reduces parameter dispersion, which is beneficial to improving mass production yield and product performance stability.

[0048] The above experimental results are completely consistent with the working principle described above. The acoustic barrier constructed by the acoustic barrier channel 600 increases the radial attenuation constant α of the vibration displacement, improves the degree of energy localization and energy conversion efficiency η, reduces useless losses from the source, and is ultimately reflected in a significant reduction in equivalent series resistance and an improvement in performance consistency.

[0049] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A quartz crystal with low equivalent series resistance, comprising a quartz piezoelectric wafer substrate (100); a front main electrode (200) is disposed on the front side of the quartz piezoelectric wafer substrate (100); and a back main electrode is disposed on the back side corresponding to the position of the front main electrode (200); characterized in that: The quartz piezoelectric wafer substrate (100) is provided with a plurality of acoustic barrier channels (600); the acoustic barrier channels (600) are arranged along the periphery of the front main electrode (200) and the back main electrode, and do not contact the main electrodes; the acoustic barrier channels (600) are channels that completely penetrate the quartz piezoelectric wafer substrate (100) along the thickness direction; each of the acoustic barrier channels (600) together forms an acoustic impedance abrupt change boundary surrounding the main electrode region.

2. A quartz crystal with low equivalent series resistance according to claim 1, characterized in that: The front main electrode (200) and the back main electrode are rectangular structures. The acoustic barrier channel (600) is provided with four channels, which are respectively arranged on the outside of the four sides of the rectangular main electrode and extend along the length direction of the corresponding side.

3. A quartz crystal with low equivalent series resistance according to claim 2, characterized in that: Each acoustic barrier channel (600) is not connected end to end, and the gap between the channels is used to arrange the electrode lead-out structure.

4. A quartz crystal with low equivalent series resistance according to claim 1, characterized in that: The front main electrode (200) and the back main electrode are symmetrically arranged stacked metal structures, consisting of an adhesion layer and a main electrode layer.

5. A quartz crystal with low equivalent series resistance according to claim 2, characterized in that: The front side of the quartz piezoelectric wafer substrate (100) is also provided with a front sub-electrode (400), an electrode lead-out guide strip (500), and an end welding pad (300); the front sub-electrode (400) is diagonally distributed at the corner position of the quartz piezoelectric wafer substrate (100), and the end welding pad (300) is provided at another set of diagonal positions of the quartz piezoelectric wafer substrate (100).

6. A quartz crystal with low equivalent series resistance according to claim 5, characterized in that: The electrode lead-out guide strip (500) is connected between the front main electrode (200) and the end welding pad (300), and is located in the gap between the adjacent acoustic barrier channel (600).

7. A quartz crystal with low equivalent series resistance according to claim 6, characterized in that: The reverse side of the quartz piezoelectric wafer substrate (100) is provided with a reverse sub-electrode, a reverse lead-out guide strip and a reverse welding pad that correspond one-to-one with the front sub-electrode (400), the electrode lead-out guide strip (500) and the end welding pad (300) and are arranged symmetrically.

8. A quartz crystal with low equivalent series resistance according to claim 1, characterized in that: The inner wall of the acoustic barrier channel (600) maintains a preset distance from the edge of the corresponding main electrode. The preset distance is 1 / 4 to 5 times the wavelength of the shear sound wave within the quartz wafer at the target resonant frequency, and is used to match the phase of the sound wave reflection.

9. A quartz crystal with low equivalent series resistance according to claim 1, characterized in that: The acoustic barrier channel (600) is a hollow channel with a cross-sectional shape of rectangle or waveform, which can form a hollow cavity and realize the contour of acoustic barrier.

10. A quartz crystal with low equivalent series resistance according to claim 9, characterized in that: The acoustic barrier channel (600) has a rectangular cross-section.

Images