VO2-based frequency-tunable MEMS planar resonator

Abstract

The present invention discloses a frequency-tunable MEMS planar resonator based on VO2, comprising: a SiO2 substrate; the SiO2 substrate being located at the bottom of the resonator; a bottom electrode being located above the SiO2 substrate; a Si3N4 double-ended fixed plate being located above the SiO2 substrate and the bottom electrode; a top electrode being located above the Si3N4 double-ended fixed plate and corresponding to the bottom electrode; a Si3N4 insulating layer being located above the Si3N4 double-ended fixed plate and the top electrode; a heating resistor being located above the Si3N4 insulating layer, with its maximum resistance region located in the middle region of the Si3N4 double-ended fixed plate; a VO2 layer being located above the Si3N4 double-ended fixed plate and the heating resistor; the heating resistor is made of Pt to increase its ability to withstand high temperatures, and the heating resistor is composed of Pt metal strips of different widths to ensure that the resistance value is maximized in the middle plate region of the Si3N4 double-ended fixed plate.

Description

Technical Field

[0001] This invention belongs to the field of electronic device technology, specifically relating to a frequency-tunable MEMS planar resonator based on VO2. Background Technology

[0002] Almost all electronic devices require frequency control, and resonators are specialized components that generate resonant frequencies. Since the mid-20th century, the main resonator market has been dominated by quartz crystal resonators and quartz oscillators. However, with continuous technological advancements, resonators are becoming increasingly smaller to meet the demands of the wearable market and mobile phone chips for highly integrated systems, while also meeting low power consumption requirements. At this point, traditional crystal resonators struggle to maintain their equivalent series resistance (ESR) characteristics, i.e., low power consumption, within such ultra-small sizes. Micro-electro-Mechanical Systems (MENS) technology, a novel multidisciplinary technology developed at the beginning of this century, involves mechanics, electronics, chemistry, physics, optics, biology, and materials science, and will have a revolutionary impact on human life and production in the near future.

[0003] Compared to traditional quartz crystal resonators, MEMS resonators fabricated using MEMS technology have high reliability, low power consumption, and low ESR characteristics. At the same time, their size is more than 50% smaller than that of traditional quartz crystal resonators, and due to their fabrication method, they are directly compatible with current integrated circuit chip processes.

[0004] Furthermore, to meet the requirements of different applications, MEMS resonators need to be able to operate at multiple resonant frequencies. While increasing the number of resonators is an option, this will inevitably increase the overall system size and power consumption, hindering high system integration.

[0005] Vanadium dioxide (VO2) is a phase change material, during which the internal stress of the structure undergoes significant changes. According to structural mechanics, when tensile or compressive loads are applied to a double-ended fixed beam, the resonant frequency of the beam will change. Summary of the Invention

[0006] The purpose of this invention is to provide a frequency-tunable MEMS planar resonator based on VO2, thereby solving the problem of achieving frequency tunability without changing the resonator's own structure.

[0007] The technical solution adopted in this invention is: a frequency-tunable MEMS planar resonator based on VO2, comprising, from bottom to top, a SiO2 substrate, a Si3N4 double-ended fixed plate, a Si3N4 insulating layer, a heating resistor, and a VO2 layer; a bottom electrode is disposed on the SiO2 substrate, and a top electrode is disposed on the Si3N4 double-ended fixed plate; the Si3N4 double-ended fixed plate is etched to create a micrometer-level gap between the Si3N4 double-ended fixed plate, the SiO2 substrate, and the bottom electrode; the top electrode corresponds to the bottom electrode; the heating resistor is located above the Si3N4 insulating layer, and its maximum resistance region is located in the middle plate region of the Si3N4 double-ended fixed plate.

[0008] The invention is further characterized in that,

[0009] The bottom electrode is configured on the SiO2 substrate by deposition and etching. The bottom electrode includes a bottom upper electrode and a bottom lower electrode, and the top electrode includes a top upper electrode and a top lower electrode. The top upper electrode and the top lower electrode and the bottom upper electrode and the bottom lower electrode are structurally positioned correspondingly and are respectively connected to the external circuit through metal microstrips.

[0010] The Si3N4 double-ended fixed plate includes a H-shaped plate frame, with an upper plate and a lower plate on each side of the middle beam. The positions of the upper plate and the lower plate correspond to the bottom upper electrode and the bottom lower electrode of the bottom electrode, so as to realize the coupling between the upper and lower electrodes during the operation of the resonator.

[0011] A Si3N4 insulating layer is deposited above the top electrode. The Si3N4 insulating layer has the same shape and size as the Si3N4 double-ended fixed plate, including an intermediate plate layer corresponding to the intermediate beam and upper and lower plate layers on both sides of the intermediate plate layer. The upper and lower plate layers correspond to the top upper electrode and the top lower electrode, respectively.

[0012] The heating resistor is deposited on a Si3N4 insulating layer. The heating resistor is composed of a pair of Pt metal microstrips with different widths. The middle part of each Pt metal microstrip is raised, and the Pt metal microstrip in the raised part is the narrowest to ensure the maximum resistance at this point.

[0013] The VO2 layer is deposited on top of the heating resistor using pulsed laser deposition. The VO2 layer is a cross structure composed of short and long VO2 plates, with the short VO2 plates located directly above the narrowest point of the Pt metal microstrip of the heating resistor.

[0014] The VO2 layer is a thin film made of VO2 phase change material.

[0015] The size and shape of the Si3N4 insulating layer are consistent with the Si3N4 double-ended fixed plate, achieving complete electrical insulation between the top electrode and the heating resistor.

[0016] The beneficial effect of this invention is that, without altering the structure of the MEMS resonator itself, it utilizes the stress change characteristics of VO2 material and metal microstrip during phase transition to modify the Young's modulus of the Si3N4 double-ended fixed composite planar resonator, thereby achieving frequency modification of the MEMS resonator. This provides conditions for the application of highly integrated systems under complex conditions. The frequency-tunable MEMS planar resonator based on VO2 proposed in this invention can be used in centimeter-wave band communication systems. Attached Figure Description

[0017] Figure 1 This is an exploded view of the structure of the frequency-tunable MEMS planar resonator based on VO2 according to the present invention;

[0018] Figure 2 for Figure 1 Schematic diagram of the resonator's substrate;

[0019] Figure 3 for Figure 1 Bottom electrode of the resonator;

[0020] Figure 4 for Figure 1 Resonator: Si3N4 double-ended fixed plate;

[0021] Figure 5 for Figure 1 Top electrode of the resonator;

[0022] Figure 6 for Figure 1 The Si3N4 insulating layer of the resonator;

[0023] Figure 7 for Figure 1 The heating resistor of the resonator;

[0024] Figure 8 for Figure 1 The VO2 layer of the resonator.

[0025] In the figure, 1. SiO2 substrate, 2. bottom electrode, 3. Si3N4 double-ended fixed plate, 4. top electrode, 5. Si3N4 insulating layer, 6. heating resistor, 7. VO2 layer, 8. bottom upper electrode, 9. bottom lower electrode, 10. intermediate beam, 11. upper plate, 12. lower plate, 13. metal microstrip, 14. top upper electrode, 15. top lower electrode, 16. intermediate plate layer, 17. upper plate layer, 18. lower plate layer, 19. Pt metal microstrip, 20. long VO2 plate, 21. short VO2 plate. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0027] This invention proposes a frequency-variable MEMS square resonator based on VO2, such as... Figure 1-2 As shown, it consists of a SiO2 substrate 1, a bottom electrode 2, a Si3N4 double-ended fixed plate 3, a top electrode 4, a Si3N4 insulating layer 5, a heating resistor 6, and a VO2 layer 7. It includes the SiO2 substrate 1, the Si3N4 double-ended fixed plate 3, the Si3N4 insulating layer 5, the heating resistor 6, and the VO2 layer 7 arranged sequentially from bottom to top. The bottom electrode 2 is disposed on the SiO2 substrate 1, and the top electrode 4 is disposed on the Si3N4 double-ended fixed plate 3. The Si3N4 double-ended fixed plate 3 is etched to create a micrometer-level gap between the Si3N4 double-ended fixed plate 3, the SiO2 substrate 1, and the bottom electrode 2. The top electrode 4 corresponds to the bottom electrode 2. The heating resistor 6 is located above the Si3N4 insulating layer 5, and its maximum resistance region is located in the middle plate region of the Si3N4 double-ended fixed plate 3.

[0028] like Figure 3 As shown, the bottom electrode 2 is configured on the SiO2 substrate 1 by deposition and etching. The bottom electrode 2 includes a bottom upper electrode 8 and a bottom lower electrode 9, as shown. Figure 5 As shown, the top electrode 4 includes a top upper electrode 14 and a top lower electrode 15; the top upper electrode 14 and the top lower electrode 15 and the bottom upper electrode 8 and the bottom lower electrode 9 are structurally positioned corresponding to each other and are respectively connected to the external circuit through the metal microstrip 13.

[0029] like Figure 4 As shown, the Si3N4 double-ended fixed plate 3 includes a H-shaped plate frame, with an upper plate 11 and a lower plate 12 on each side of the middle beam 10. The positions of the upper plate 11 and the lower plate 12 correspond to the bottom upper electrode 8 and the bottom lower electrode 9 of the bottom electrode 2, so as to realize the coupling between the upper and lower electrodes during the operation of the resonator.

[0030] like Figure 6 As shown, the Si3N4 insulating layer 5 is deposited above the top electrode 4. The Si3N4 insulating layer 5 has the same shape and size as the Si3N4 double-ended fixed plate 3, including the intermediate plate layer 16 corresponding to the intermediate beam 10, and the upper plate layer 17 and the lower plate layer 18 on both sides of the intermediate plate layer 16. The upper plate layer 17 and the lower plate layer 18 correspond to the top upper electrode 14 and the top lower electrode 15, respectively.

[0031] like Figure 7As shown, the heating resistor 6 is deposited on the Si3N4 insulating layer 5. The heating resistor 6 is composed of a pair of Pt metal microstrips 19 with different widths. The middle part of each Pt metal microstrip 19 is raised, and the Pt metal microstrip in the raised part is the narrowest to ensure the maximum resistance at this point.

[0032] like Figure 8 As shown, the VO2 layer 7 is deposited on the heating resistor 6 by pulsed laser deposition. The VO2 layer 7 is a cross structure composed of a short VO2 plate 21 and a long VO2 plate 20. The short VO2 plate 21 is located directly above the narrowest point of the Pt metal microstrip of the heating resistor 6.

[0033] VO2 layer 7 is a thin film made of VO2 phase change material.

[0034] The size and shape of the Si3N4 insulating layer 5 are consistent with the Si3N4 double-ended fixed plate 3, achieving complete electrical insulation between the top electrode 4 and the heating resistor 6.

[0035] The SiO2 substrate 1 is composed of a SiO2 wafer of a certain thickness.

[0036] It consists of an upper bottom electrode 8 and a lower bottom electrode 9, which can work independently.

[0037] The Si3N4 double-ended fixed plate 3 is configured on the SiO2 substrate 1 and the bottom electrode 2 by deposition and etching.

[0038] The top electrode 4 is located above the Si3N4 double-ended fixed plate 3. It consists of two independent top upper electrode 14 and top lower electrode 15, and their positions correspond to the bottom electrode 2. They can be driven by signals applied separately.

[0039] The shape and material of the Si3N4 insulating layer 5 are consistent with those of the Si3N4 double-ended fixed plate 3, thereby reducing the thermal stress problem caused by the mismatch of the thermal expansion coefficients of the materials.

[0040] The heating resistor 6 is composed of two parts, upper and lower, of Pt metal microstrip lines. Each part is composed of several segments of Pt metal microstrips with different widths. The Pt metal microstrips generate Joule heat during the application of current, thereby providing the temperature required for the phase transition of VO2 material.

[0041] The VO2 layer 7 undergoes a reversible phase transition under the Joule heating effect generated when current is applied to the heating resistor 6. The thermal stress generated during the phase transition can change the Young's modulus of the Si3N4 double-ended fixed plate 3, thereby changing the resonant frequency of the resonator with the Si3N4 double-ended fixed plate 3 as the main structure.

[0042] The resonant frequency of the MEMS resonator can be adjusted by controlling the magnitude of the current applied by the heating resistor 6 and the resulting Joule heat, thereby affecting the magnitude of the thermal stress, which in turn adjusts the Young's modulus of the Si3N4 double-ended fixed plate 3, and ultimately changes the resonant frequency of the MEMS resonator.

[0043] The working principle and process of the resonator of this invention are as follows:

[0044] When the heating resistor 6 is not loaded with current, and the frequency of the AC signal loaded between the top electrode 4 and the bottom electrode 2 is the same as the natural frequency of the double-ended fixed plate 3, the double-ended fixed plate 3 resonates. The coupling capacitance between the bottom electrode 2 and the top electrode 4 changes with the vibration of the square plate, thereby generating a current on the output electrode that is related to the capacitance change. This current is proportional to the vibration amplitude of the Si3N4 double-ended fixed plate 3. At this time, the resonant frequency is mainly determined by the Young's modulus of the double-ended fixed plate 3 as the main structure.

[0045] When current is applied to the heating resistor 6, Joule heating is generated. The Joule heating generated by the heating resistor 6 changes the temperature of the VO2 layer 7. During the temperature rise, the VO2 layer 7 undergoes a reversible phase transition. During the phase transition of the VO2 layer 7, thermal stress is generated, which changes the Young's modulus of the double-ended fixed plate 3, thereby changing the resonant frequency of the Si3N4 double-ended fixed plate 3. At this time, if the frequency of the AC signal applied between the top electrode 4 and the bottom electrode 2 is the same as the natural frequency of the Si3N4 double-ended fixed plate 3 after thermal change, the coupling capacitance between the bottom electrode 2 and the top electrode 4 changes with the vibration of the square plate, thereby generating a current related to the capacitance change on the output electrode. This current is proportional to the vibration amplitude of the Si3N4 double-ended fixed plate 3. At this time, the resonant frequency is mainly determined by the Young's modulus of the Si3N4 double-ended fixed plate 3 with deposited VO2 layer.

[0046] By adjusting the magnitude of the current applied to the heating resistor 6, the Joule heat generated by the heating resistor 6 is changed, thereby adjusting the temperature of the VO2 layer 7 and the resulting thermal stress, changing the Young's modulus of the Si3N4 double-ended fixed plate 3, and ultimately changing the resonant frequency of the resonator with the Si3N4 double-ended fixed plate 3 as the main structure.

[0047] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. All technical solutions falling within the scope of the present invention's concept are protected by the present invention. It should be noted that those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A frequency-tunable MEMS planar resonator based on VO2, characterized in that, The structure includes, from bottom to top, a SiO2 substrate (1), a Si3N4 double-ended fixed plate (3), a Si3N4 insulating layer (5), a heating resistor (6), and a VO2 layer (7); a bottom electrode (2) is disposed on the SiO2 substrate (1), and a top electrode (4) is disposed on the Si3N4 double-ended fixed plate (3); the Si3N4 double-ended fixed plate (3) is etched to create a micron-level gap between the Si3N4 double-ended fixed plate (3), the SiO2 substrate (1), and the bottom electrode (2); the top electrode (4) corresponds to the bottom electrode (2); the heating resistor (6) is located above the Si3N4 insulating layer (5), and its maximum resistance area is located in the middle plate area of ​​the Si3N4 double-ended fixed plate (3); The heating resistor (6) is deposited on the Si3N4 insulating layer (5). The heating resistor (6) is composed of a pair of Pt metal microstrips (19) with different widths. The middle part of each Pt metal microstrip (19) is raised, and the Pt metal microstrip in the raised part is the narrowest to ensure the maximum resistance at this point. The VO2 layer (7) is deposited on the heating resistor (6) by pulsed laser deposition. The VO2 layer (7) is a cross structure composed of a short VO2 plate (21) and a long VO2 plate (20). The short VO2 plate (21) is located directly above the narrowest point of the Pt metal microstrip of the heating resistor (6). The size and shape of the Si3N4 insulating layer (5) are consistent with the Si3N4 double-ended fixed plate (3), achieving complete electrical insulation between the top electrode (4) and the heating resistor (6).

2. The frequency-tunable MEMS planar resonator based on VO2 according to claim 1, characterized in that, The bottom electrode (2) is configured on the SiO2 substrate (1) by deposition and etching. The bottom electrode (2) includes a bottom upper electrode (8) and a bottom lower electrode (9). The top electrode (4) includes a top upper electrode (14) and a top lower electrode (15). The top upper electrode (14) and the top lower electrode (15) and the bottom upper electrode (8) and the bottom lower electrode (9) are structurally positioned correspondingly and are respectively connected to the external circuit through a metal microstrip (13).

3. The frequency-tunable MEMS planar resonator based on VO2 according to claim 1, characterized in that, The Si3N4 double-ended fixed plate (3) includes a H-shaped plate frame, in which an upper plate (11) and a lower plate (12) are provided on both sides of the middle beam (10), and the positions of the upper plate (11) and the lower plate (12) correspond to the bottom upper electrode (8) and the bottom lower electrode (9) of the bottom electrode (2), so as to realize the coupling between the upper and lower electrodes during the operation of the resonator.

4. The frequency-tunable MEMS planar resonator based on VO2 according to claim 3, characterized in that, The Si3N4 insulating layer (5) is deposited above the top electrode (4). The Si3N4 insulating layer (5) has the same shape and size as the Si3N4 double-ended fixed plate (3), including an intermediate plate layer (16) corresponding to the intermediate beam (10) and an upper plate layer (17) and a lower plate layer (18) on both sides of the intermediate plate layer (16). The upper plate layer (17) and the lower plate layer (18) correspond to the top upper electrode (14) and the top lower electrode (15), respectively.

5. The frequency-tunable MEMS planar resonator based on VO2 according to claim 1, characterized in that, The VO2 layer (7) is a thin film made of VO2 phase change material.

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