Temperature-Controlled Frequency-Tunable MEMS Bandstop Filter Based on VO2 Phase-Change Material

Abstract

The temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material disclosed by the present invention sequentially includes, from bottom to top: a SiO2 substrate, a bottom electrode including four independent electrode modules, a Si3N4 doubly-clamped plate including four plates, a top electrode including four independent electrode modules, a Si3N4 insulating layer, a heating resistor, and a VO2 layer; the top electrode corresponds to the bottom electrode; the heating resistor is located above the Si3N4 insulating layer and the region with the maximum resistance thereof is located at both ends of the Si3N4 doubly-clamped plate; the heating resistor is made of Pt to increase its high-temperature resistance, and at the same time, the heating resistor is composed of Pt metal strips with different widths to ensure the maximum resistance values in the upper and lower plate regions of the Si3N4 doubly-clamped plate.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic devices, and particularly relates to a temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material. Background Art

[0002] Almost all electronic devices require frequency control, and resonators are dedicated components for generating resonant frequencies. Since the mid-20th century, the main resonators in the main resonator market have been quartz crystal resonators and quartz oscillators. However, with the continuous development of technology, the size of resonators has become smaller and smaller to meet the needs of the wearable market and the highly integrated system requirements of mobile phone chips, while also meeting the low-power consumption requirements. At this time, it is very difficult for traditional crystal resonators to maintain the equivalent series resistance (ESR) characteristics, that is, the low-power consumption characteristics, in the "ultra-small size". Micro Electro-Mechanical Systems (MEMS) technology is a new type of interdisciplinary technology developed at the beginning of this century, involving multiple disciplines such as mechanics, electronics, chemistry, physics, optics, biology, and materials, and will have a revolutionary impact on human life and production in the near future.

[0003] Compared with traditional quartz crystal resonators, MEMS resonators fabricated by MEMS technology have characteristics such as 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 processing method, they can be directly compatible with the current integrated circuit chip process.

[0004] In addition, in order to meet the application requirements under different conditions, it is required that MEMS resonators can operate at multiple resonant frequencies. Although increasing the number of resonators is an optional solution, this will inevitably increase the volume of the entire system, increase the power consumption of the system, and is not conducive to the high integration of the system.

[0005] Vanadium dioxide (VO2) is a phase change material, and during its phase change process, the internal stress of the structure will change greatly. According to the relevant knowledge of structural mechanics, when a tensile or compressive load is applied to a doubly-clamped beam, the resonant frequency of the doubly-clamped beam will change. Summary of the Invention

[0006] The purpose of the present invention is to provide a temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material to solve the problem of achieving frequency tunability without changing the structure of the resonator itself.

[0007] The technical solution adopted by the present invention is: a temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material, and the filter is composed of two MEMS plate resonators with independently tunable frequencies; it includes a SiO2 substrate, and the SiO2 substrate is located at the bottom of the filter; a bottom electrode is arranged above the SiO2 substrate, and a Si3N4 double-clamped plate including four plates is located above the bottom electrode. A number of micron-level gaps are formed between the Si3N4 double-clamped plate and the bottom electrode and the SiO2 substrate through etching; a top electrode is arranged above the Si3N4 double-clamped plate, and the top electrode is located at the four plates of the Si3N4 double-clamped plate, and the position corresponds to that of the bottom electrode one by one; a Si3N4 insulating layer is arranged above the top electrode, and the Si3N4 insulating layer is used to isolate the electrical connection between the top electrode and the heating resistor; the heating resistor is located above the Si3N4 insulating layer; a VO2 layer is arranged above the heating resistor.

[0008] The characteristics of the present invention also lie in that

[0009] The bottom electrode is configured on the SiO2 substrate by deposition and etching methods. The bottom electrode includes bottom electrode a, bottom electrode b, bottom electrode c, and bottom electrode d; bottom electrode c and bottom electrode d are arranged opposite to each other, and bottom electrode a and bottom electrode b are arranged opposite to each other between bottom electrode c and bottom electrode d; bottom electrode a, bottom electrode b, bottom electrode c, and bottom electrode d are respectively connected to the external circuit through microstrip line a, microstrip line b, microstrip line c, and microstrip line d.

[0010] A Si3N4 double-clamped plate is configured on the bottom electrode by deposition and etching methods; the Si3N4 double-clamped plate is a closed plate frame, and symmetrically arranged plates a and b, plates c and d are respectively arranged on both sides of the middle beam of the Si3N4 double-clamped plate, and the positions of plates a, b, c, and d correspond to those of bottom electrode a, bottom electrode b, bottom electrode c, and bottom electrode d respectively.

[0011] Four independent electrodes a, b, c, and d are configured on the Si3N4 double-clamped plate by deposition and etching methods, and the positions correspond to plates a, b, c, and d of the middle beam of the Si3N4 double-clamped plate respectively. Electrodes a, b, c, and d are respectively connected to the peripheral circuit through microstrip lines.

[0012] The Si3N4 insulating layer is deposited above the top electrode, and the Si3N4 insulating layer has the same shape and size as the Si3N4 double-clamped plate, and the positions correspond to each other up and down; complete electrical insulation between the top electrode and the heating resistor is achieved.

[0013] The heating resistor is deposited on the Si3N4 insulating layer. Each heating resistor is composed of a pair of Pt metal microstrips with different widths in each section, which are distributed oppositely. There are two rectangular protrusions in the middle part of each Pt metal microstrip. The Pt metal microstrip in the protrusion part is the narrowest to ensure the largest resistance here.

[0014] The VO2 layer is deposited above the heating resistor by pulsed laser deposition. The VO2 layer and the heating resistor structure composed of Pt metal microstrips are complementary, and the shape is a double-cross structure surrounded by two Pt metal microstrips; the short cross of the VO2 layer is directly above the narrowest part of the Pt metal microstrip of the heating resistor.

[0015] The VO2 layer is a thin film made of VO2 phase change material.

[0016] The beneficial effect of the present invention is that, without changing the structure of the MEMS resonator itself, by utilizing the characteristics of the stress change of the VO2 material and the metal microstrip during the phase change process, the change of the frequency of the MEMS resonator is realized, thereby providing conditions for the application of high-integration systems under complex conditions. The frequency-tunable MEMS plate resonator based on VO2 proposed by the present invention can be used in centimeter-wave band communication systems BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is an exploded view of the structure of the temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material of the present invention;

[0018] Figure 2 is Figure 1 Schematic diagram of the substrate of the filter;

[0019] Figure 3 is Figure 1 Bottom drive electrode of the filter;

[0020] Figure 4 is Figure 1 Si3N4 doubly-clamped beam of the filter;

[0021] Figure 5 is Figure 1 Top drive electrode of the filter;

[0022] Figure 6 is Figure 1 Si3N4 insulating layer of the filter;

[0023] Figure 7 is Figure 1 Heating resistor of the filter;

[0024] Figure 8 is Figure 1 VO2 layer of the filter;

[0025] Figure 9It is the equivalent mechanical model diagram of the present invention;

[0026] Figure 10(a) is the state diagram of the symmetric mode of the filter of the present invention;

[0027] Figure 10(b) is the state diagram of the asymmetric mode of the filter of the present invention;

[0028] Figure 11 It is the equivalent circuit model of the filter of the present invention.

[0029] In the figure, 1. SiO2 substrate, 2. bottom electrode, 3. Si3N4 doubly-clamped plate, 4. top electrode, 5. Si3N4 insulating layer, 6. heating resistor, 7. VO2 layer, 8. bottom electrode a, 9. bottom electrode b, 10. bottom electrode c, 11. bottom electrode d, 12. microstrip line a, 13. microstrip line b, 14. microstrip line c, 15. microstrip line d, 16. middle beam, 17. plate a, 18. plate b, 19. plate c, 20. plate d, 21. electrode a, 22. electrode b, 23. electrode c, 24. electrode d, 25. Pt metal microstrip. Detailed implementation manners

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following will further describe in detail the implementation manners of the present invention with reference to the accompanying drawings of the specification and embodiments.

[0031] The temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material proposed by the present invention, as Figure 1-2 shown, the filter is composed of two MEMS plate resonators with individually tunable frequencies; it includes a SiO2 substrate 1, and the SiO2 substrate 1 is located at the bottom of the filter; a bottom electrode 2 is disposed above the SiO2 substrate 1, and a Si3N4 doubly-clamped plate 3 including four plates is located above the bottom electrode 2. A number of micron-level gaps are formed between the Si3N4 doubly-clamped plate 3 and the bottom electrode 2 and the SiO2 substrate 1 through etching; a top electrode 4 is disposed above the Si3N4 doubly-clamped plate 3, and the top electrode 4 is located at the four plates of the Si3N4 doubly-clamped plate 3, and the position corresponds to that of the bottom electrode 2 one by one; a Si3N4 insulating layer 5 is disposed above the top electrode 4, and the Si3N4 insulating layer 5 is used to isolate the electrical connection between the top electrode 4 and the heating resistor 6; the heating resistor 6 is located above the Si3N4 insulating layer 5; a VO2 layer 7 is disposed above the heating resistor 6.

[0032] The SiO2 substrate 1 is composed of a polished SiO2 wafer with a certain thickness.

[0033] The bottom electrode 2 is configured on the SiO2 substrate 1 by deposition and etching methods. The bottom electrode 2 includes bottom electrode a 8, bottom electrode b 9, bottom electrode c 10, and bottom electrode d 11. The bottom electrode c 10 and the bottom electrode d 11 are arranged opposite to each other, and the bottom electrode a 8 and the bottom electrode b 9 are arranged opposite to each other between the bottom electrode c 10 and the bottom electrode d 11. The bottom electrode a 8, the bottom electrode b 9, the bottom electrode c 10, and the bottom electrode d 11 are respectively connected to an external circuit through microstrip line a 12, microstrip line b 13, microstrip line c 14, and microstrip line d 15.

[0034] On the bottom electrode 2, a Si3N4 double - ended clamped flat plate 3 is configured by deposition and etching methods. The Si3N4 double - ended clamped flat plate 3 is a closed flat plate frame. On both sides of the middle beam 16 of the Si3N4 double - ended clamped flat plate 3, there are respectively a structurally symmetric flat plate a 17 and flat plate b 18, flat plate c 19 and flat plate d 20. The positions of the flat plate a 17, flat plate b 18, flat plate c 19, and flat plate d 20 respectively correspond to the bottom electrode a 8, bottom electrode b 9, bottom electrode c 10, and bottom electrode d 11.

[0035] On the Si3N4 double - ended clamped flat plate 3, four independent electrodes a 21, electrode b 22, electrode c 23, and electrode d 24 are configured by deposition and etching methods, and their positions respectively correspond to the flat plate a 17, flat plate b 18, flat plate c 19, and flat plate d 20 of the middle beam 16 of the Si3N4 double - ended clamped flat plate 3. The electrodes a 21, electrode b 22, electrode c 23, and electrode d 24 are respectively connected to a peripheral circuit through microstrip lines.

[0036] The Si3N4 insulating layer 5 is deposited above the top electrode 4. The Si3N4 insulating layer 5 has the same shape, size, and material as the Si3N4 double - ended clamped flat plate 3, and their positions correspond to each other up and down. Thus, the stress problem caused by the mismatch of the thermal expansion coefficients of materials is reduced, and complete electrical insulation between the top electrode 4 and the heating resistor 6 is achieved.

[0037] The heating resistor 6 is deposited on the Si3N4 insulating layer 5. Each heating resistor 6 is composed of a pair of Pt metal microstrips with different widths in each section distributed oppositely. In the middle part of each Pt metal microstrip 25, there are two rectangular protrusions, and the Pt metal microstrip in the protrusion part is the narrowest to ensure the largest resistance here. By adjusting the magnitude of the current of the heating resistor 6, the thermal stress borne by the composite beam with the Si3N4 double - ended clamped flat plate 3 as the main body is changed, and the resonant frequency of the composite beam with the Si3N4 double - ended clamped flat plate 3 as the main body is changed to adjust the operating frequency of the filter.

[0038] When no current is applied to the heating resistor, and the signal frequency applied between the top electrode and the bottom electrode is the same as the resonance frequency of the Si3N4 clamped-clamped beam, the Si3N4 clamped-clamped beam resonates, the flat plate in the area where the top electrode is located bends, and at this time, the coupling capacitance between the top electrode and the bottom electrode reaches the maximum value, and the signal is isolated.

[0039] When current is applied to the heating resistor, the VO2 layer 7 will undergo a phase change under the action of Joule heat, thereby generating thermal stress on the Si3N4 clamped-clamped beam and changing the resonance frequency of the composite beam with the Si3N4 clamped-clamped beam as the main body. At this time, if the signal frequency applied between the top electrode and the bottom electrode is the same as the resonance frequency of the Si3N4 clamped-clamped beam, the Si3N4 clamped-clamped beam resonates, the flat plate in the area where the top electrode is located bends, and at this time, the coupling capacitance between the top electrode and the bottom electrode reaches the maximum value, and the radio frequency signal is isolated.

[0040] The working frequency range of the MEMS filter can be adjusted by adjusting the magnitude of the current applied to the heating resistor 6 to generate different magnitudes of thermal stress, thereby changing the working frequency range of the MEMS filter.

[0041] The VO2 layer 7 is deposited above the heating resistor 6 by pulsed laser deposition. The structure of the VO2 layer 7 and the heating resistor 6 composed of Pt metal microstrip is complementary, and the shape is a double-cross structure surrounded by two Pt metal microstrips; the short crossbar of the VO2 layer 7 is directly above the narrowest part of the Pt metal microstrip of the heating resistor 6.

[0042] The VO2 layer 7 is a thin film made of VO2 phase change material.

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

[0044] Figure 9 is the equivalent mechanical model of the present invention. This filter is essentially composed of two superimposed flat plate resonators. In the figure, M i and M j represent the equivalent mass of each flat plate resonator, k i and k j represent the equivalent stiffness coefficient of each resonator, and k ij represents the elastic coupling coefficient of the masses of the two resonators.

[0045] Figure 10(a)-Figure 10(b)For the vibration modes of the two resonators in the present invention, one is the symmetric mode, that is, the flat plates a17 and b18 (or flat plates c19 and d20) simultaneously contact the bottom electrodes a8 and b9 (or bottom electrodes c10 and d11); while the flat plates c19 and d20 (or flat plates a17 and b18) do not contact the bottom electrodes c10 and d11 (or bottom electrodes a8 and b9); the other is the asymmetric mode, that is, the flat plates a17 and c19 (or flat plates b18 and d20) contact the bottom electrodes a8 and c10 (or bottom electrodes b9 and d11) while the flat plates b18 and d20 (or flat plates a17 and c19) do not contact the bottom electrodes b9 and d11 (or bottom electrodes a8 and c10); the two vibration modes are coupled through the intermediate beam.

[0046] Figure 11 The equivalent circuit model of the present invention, each resonator is composed of an RLC resonant circuit, the input voltage V in is capacitively loaded to the resonator i via the input impedance R in and the metal electrode C0, and then the vibration frequency of the resonator i is coupled to the resonator j via the coupling beam. The resonator i and the resonator j form a filter structure, and the final signal is output to the terminal part R out .

[0047] When a driving signal is applied between the bottom electrode 2 and the top electrode 4, and no current is applied to the heating resistor 6, when the frequency of the applied driving signal is consistent with the resonance frequency of the Si3N4 clamped-clamped flat plate 3, the coupling capacitance between the bottom electrode 2 and the top electrode 4 of the Si3N4 clamped-clamped flat plate 3 is the largest, and at this time the RF signal is isolated.

[0048] When a driving signal is applied between the bottom electrode 2 and the top electrode 4, and a current is applied to the heating resistor 6, the VO2 thin film undergoes a phase change under the action of Joule heat, thereby generating a thermal stress on the Si3N4 clamped-clamped flat plate 3. The existence of the thermal stress changes the resonance frequency of the Si3N4 clamped-clamped flat plate 3. When the frequency of the applied driving signal is consistent with the resonance frequency of the Si3N4 clamped-clamped flat plate 3, the coupling capacitance between the bottom electrode 2 and the top electrode 4 of the Si3N4 clamped-clamped flat plate 3 is the largest, and the MEMS filter composed of two MEMS resonant beams realizes the isolation of the signal.

[0049] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations of the present invention. All technical solutions within the scope of the present invention's concept belong to the protection scope of the present invention. It should be noted that those of ordinary skill in the art can make changes, modifications, substitutions, and deformations to the above embodiments within the scope of the present invention.

Claims

1. A temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material, characterized in that, The filter is composed of two MEMS plate resonators with separately adjustable frequencies; it includes a SiO2 substrate (1), and the SiO2 substrate (1) is located at the bottom of the filter; a bottom electrode (2) is arranged above the SiO2 substrate (1), and a Si3N4 doubly clamped plate (3) including four plates is located above the bottom electrode (2). A number of micron-level gaps are formed between the Si3N4 doubly clamped plate (3) and the bottom electrode (2) and the SiO2 substrate (1) through etching; a top electrode (4) is arranged above the Si3N4 doubly clamped plate (3), and the top electrode (4) is located at the four plates of the Si3N4 doubly clamped plate (3), and the position corresponds to that of the bottom electrode (2) one by one; a Si3N4 insulating layer (5) is arranged above the top electrode (4), and the Si3N4 insulating layer (5) is used to isolate the electrical connection between the top electrode (4) and the heating resistor (6); the heating resistor (6) is located above the Si3N4 insulating layer (5); a VO2 layer (7) is arranged above the heating resistor (6). The bottom electrode (2) is configured on the SiO2 substrate (1) through deposition and etching methods. The bottom electrode (2) includes a bottom electrode a (8), a bottom electrode b (9), a bottom electrode c (10), and a bottom electrode d (11); the bottom electrode c (10) and the bottom electrode d (11) are arranged oppositely, and the bottom electrode a (8) and the bottom electrode b (9) are arranged oppositely between the bottom electrode c (10) and the bottom electrode d (11); the bottom electrode a (8), the bottom electrode b (9), the bottom electrode c (10), and the bottom electrode d (11) are respectively connected to an external circuit through a microstrip line a (12), a microstrip line b (13), a microstrip line c (14), and a microstrip line d (15). The heating resistor (6) is deposited on the Si3N4 insulating layer (5). Each heating resistor (6) is composed of a pair of Pt metal microstrips with different widths in each section distributed oppositely. There are two rectangular protrusions in the middle part of each Pt metal microstrip (25), and the Pt metal microstrip in the protrusion part is the narrowest to ensure the largest resistance here. The VO2 layer (7) is deposited above the heating resistor (6) through pulsed laser deposition. The VO2 layer (7) and the heating resistor (6) composed of Pt metal microstrips are complementary in structure, and the shape is a double-cross structure surrounded by two Pt metal microstrips; the short cross of the VO2 layer (7) is directly above the narrowest part of the Pt metal microstrip of the heating resistor (6).

2. The temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material according to claim 1, wherein On the bottom electrode (2), a Si3N4 doubly-clamped plate (3) is configured by deposition and etching methods; the Si3N4 doubly-clamped plate (3) is a closed plate frame. On both sides of the middle beam (16) of the Si3N4 doubly-clamped plate (3), there are symmetrically-structured plate a (17) and plate b (18), plate c (19) and plate d (20). The positions of plate a (17), plate b (18), plate c (19) and plate d (20) respectively correspond to bottom electrode a (8), bottom electrode b (9), bottom electrode c (10), and bottom electrode d (11).

3. The temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material according to claim 2, wherein On the Si3N4 doubly-clamped plate (3), four independent electrodes a (21), electrode b (22), electrode c (23) and electrode d (24) are configured by deposition and etching methods, and their positions respectively correspond to plate a (17), plate b (18), plate c (19) and plate d (20) of the middle beam (16) of the Si3N4 doubly-clamped plate (3). The electrodes a (21), b (22), c (23) and d (24) are respectively connected to the peripheral circuit through microstrip lines.

4. The temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material 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 doubly-clamped plate (3) and is vertically corresponding in position; it realizes complete electrical insulation between the top electrode (4) and the heating resistor (6).

5. The temperature-controlled frequency-tunable MEMS band-stop filter based on VO2 phase change material 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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