A temperature-compensated film bulk acoustic resonator with double conductive layers and a manufacturing method thereof

Abstract

The application discloses a temperature compensation type film bulk acoustic resonator with double conductive layers and a manufacturing method. The resonator comprises, from bottom to top, a substrate, a first cavity, a first bottom electrode, a second bottom electrode, a second cavity, a third bottom electrode, a piezoelectric layer and a top electrode. The first bottom electrode and the second bottom electrode are made of conductive materials with a large difference in thermal expansion coefficient. The first bottom electrode, the second bottom electrode and the second cavity are provided with a passivation layer on the side in the thickness direction. The first bottom electrode, the second bottom electrode, the second cavity and the third bottom electrode form a parallel plate capacitor. When the ambient temperature changes, the first bottom electrode and the second bottom electrode produce a concave or protruding due to the difference in thermal expansion coefficient, thereby changing the distance between the parallel plates, resulting in a change in the capacitance of the parallel plate capacitor, and realizing the frequency compensation of the FBAR. The method is simple in steps and convenient for large-scale manufacturing.

Description

TECHNICAL FIELD

[0001] The present application relates to a radio frequency communication device and a manufacturing method, in particular to a film bulk acoustic resonator and a manufacturing method. BACKGROUND

[0002] Film Bulk Acoustic Resonator (FBAR) has the advantages of high resonant frequency, high quality factor and small size, and the filter prepared therefrom has good performance, and gradually becomes a hotspot in the research of radio frequency filter. The key structural component of FBAR is a sandwich structure composed of an upper metal electrode-piezoelectric thin film-a lower metal electrode, and one of the mainstream working principles is that when a radio frequency alternating current signal is applied to the upper and lower electrodes of the FBAR, the piezoelectric thin film converts the electrical signal into a longitudinal wave propagating along the thickness direction of the thin film based on the inverse piezoelectric effect, and the longitudinal wave is reflected at the upper and lower interfaces of the sandwich structure. When the thickness of the piezoelectric oscillation stack is an odd multiple of the half wavelength of the acoustic wave, the longitudinal wave forms a standing wave oscillation, at which time the acoustic wave loss is the smallest. Then, the piezoelectric thin film converts the longitudinal wave into an electrical signal through the piezoelectric effect, realizing the frequency selection function of the electrical signal. The ideal electrical impedance characteristic of FBAR is shown in Figure 1 , wherein the frequency with the minimum impedance is the series resonance frequency f s , and the frequency with the maximum impedance is the parallel resonance frequency f p The relative frequency interval between the two is usually represented by the effective electromechanical coupling coefficient, and the larger the effective electromechanical coupling coefficient, the larger the relative interval between the two.

[0003] Since the elastic stiffness coefficients of the piezoelectric material and the electrode material decrease with the increase of temperature, the series and parallel resonance frequencies of the traditional FBAR decrease with the increase of temperature, thereby causing the passband of the filter composed of the FBAR to shift with the change of temperature. If the passband of the filter applied in the crowded communication frequency band shifts with the change of temperature, the filter will be difficult to effectively filter out the interference signals of the adjacent frequency band. Therefore, how to suppress the resonance frequency drift of FBAR caused by temperature is one of the key problems in the application of FBAR in filter.

[0004] One of the main ways to compensate for the temperature drift of the FBAR resonance frequency in the prior art is to connect a voltage-controlled capacitor in series or parallel with the FBAR, as shown in Figure 2The voltage-controlled capacitor can be a parallel-plate capacitor, a Schottky junction capacitor, or other capacitor whose capacitance changes with the voltage across it. When the ambient temperature changes, the resistance of the thermistor in the Wheatstone bridge changes, causing the voltage output by the bridge, i.e., the voltage across the voltage-controlled capacitor, to change, which in turn causes the capacitance of the voltage-controlled capacitor to change. When the capacitance of the FBAR in series or parallel changes, the resonant frequency of the FBAR also changes, and temperature compensation can be achieved through proper design. However, this method uses a Wheatstone bridge, so the overall device will have a large power consumption. In addition, the voltage-controlled capacitor changes the size of the capacitor by applying a DC bias voltage signal, which directly applies a DC bias signal to the original electrode, causing the excitation signal and the DC bias signal to interfere with each other. Therefore, it is necessary to propose a new temperature-compensated thin film bulk acoustic resonator to solve the above problems. SUMMARY

[0005] The present application aims to provide a temperature-compensated thin film bulk acoustic resonator with double conductive layers, which can compensate for the temperature of the FBAR in series or parallel, and a simple manufacturing method that can be mass-produced.

[0006] The technical scheme is a temperature-compensated thin film bulk acoustic resonator with double conductive layers, which comprises, from bottom to top, a substrate, a first cavity, a first bottom electrode, a second bottom electrode, a second cavity, a third bottom electrode, a piezoelectric layer, and a top electrode; wherein the first cavity is embedded on the upper surface of the substrate, and the edges of the first cavity and the second cavity are aligned in the thickness direction; the second bottom electrode, the second cavity, and the third bottom electrode form a parallel-plate capacitor; the overlapping area of the second cavity, the third bottom electrode, the piezoelectric layer, and the top electrode in the thickness direction of the resonator forms the effective resonant region of the thin film bulk acoustic resonator; the first bottom electrode, the second bottom electrode, and the second cavity are provided with a passivation layer on the side in the thickness direction; and the material thermal expansion coefficient difference between the first bottom electrode and the second bottom electrode is greater than 15 ppm / K.

[0007] Further, the material of the third bottom electrode is a metal material with an acoustic impedance greater than 50 mega acoustic ohms, the material of the passivation layer is a material with a thermal expansion coefficient less than 2 ppm / K and an acoustic impedance less than 20 mega acoustic ohms, and the thickness of the third bottom electrode and the passivation layer satisfies the Bragg reflection condition.

[0008] Further, the material combination of the first bottom electrode and the second bottom electrode is aluminum and molybdenum, aluminum and tungsten, aluminum and doped silicon, or aluminum and doped silicon nitride.

[0009] Further, the material of the third bottom electrode is tungsten or molybdenum, and the material of the passivation layer is silicon dioxide.

[0010] Further, the material of the substrate is single crystal silicon or sapphire, and the material of the piezoelectric layer is aluminum nitride or scandium-doped aluminum nitride.

[0011] The method for manufacturing the film bulk acoustic resonator comprises the following steps:

[0012] Step 1: sequentially performing a photoetching process, a chemical vapor deposition process and a chemical mechanical polishing process on the upper surface of the substrate to prepare a first cavity sacrificial layer in the substrate;

[0013] Step 2: sequentially performing a chemical vapor deposition process and a photoetching process to prepare a first insulating layer on the periphery of the first bottom electrode, then performing a magnetron sputtering process and a stripping process to prepare the first bottom electrode, and then repeating the steps to prepare a second bottom electrode;

[0014] Step 3: performing a chemical vapor deposition process and a photoetching process to prepare a third insulating layer on the periphery of the second cavity, and then performing a chemical vapor deposition process and a chemical mechanical polishing process to prepare a second cavity sacrificial layer;

[0015] Step 4: sequentially performing a magnetron sputtering process and a photoetching process to prepare a third bottom electrode, and then performing a magnetron sputtering process to prepare a piezoelectric layer;

[0016] Step 5: sequentially performing a magnetron sputtering process and a photoetching process to prepare a top electrode, and then etching a release hole to release the first cavity sacrificial layer and the second cavity sacrificial layer, so as to form a first cavity and a second cavity, and the preparation of the film bulk acoustic resonator is completed.

[0017] Beneficial effects: 1. In the application, the first bottom electrode, the second bottom electrode, the second cavity and the third bottom electrode form a parallel-plate capacitor. When the ambient temperature changes, the first bottom electrode and the second bottom electrode produce concave or convex due to the difference in the thermal expansion coefficient, so as to change the distance between the parallel plates and cause the capacitance of the parallel-plate capacitor to change, thereby realizing the frequency compensation of the FBAR. This method does not need an additional direct current bias signal, and does not cause the problem of mutual interference between the direct current signal and the radio frequency signal. In addition, the structure of the application can compensate the resonant frequency of the FBAR when the ambient temperature rises or falls, and is not limited to the case of temperature rise or temperature fall.

[0018] 2. In the application, the self-compensation of the series or parallel frequency of the FBAR can be realized by reasonably designing the structural parameters of the parallel-plate capacitor, and an external circuit such as a Wheatstone bridge is not needed to measure the change in temperature, so that large power consumption is not caused. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is an electrical impedance characteristic diagram of an ideal FBAR;

[0020] Figure 2This is a schematic diagram of the existing technology that uses a Wheatstone bridge and a voltage-controlled capacitor to compensate for the temperature of an FBAR.

[0021] Figure 3 This is a cross-sectional schematic diagram of the FBAR structure of the present invention;

[0022] Figure 4 This is a schematic diagram of the equivalent circuit model of FBAR near the resonant point;

[0023] Figures 5-9 This is a schematic diagram of the FBAR structure process flow of the present invention;

[0024] In the figure, the following labels are used: 101-DC voltage source; 102-first thermistor; 103-third thermistor; 104-second thermistor; 105-fourth thermistor; 106-first high-resistance resistor; 107-second high-resistance resistor; 108-variable capacitor; 109-thin film bulk acoustic resonator; 1-substrate; 2-first cavity; 201-first cavity sacrificial layer; 3-first bottom electrode; 4-second bottom electrode; 5-second cavity; 501-second cavity sacrificial layer; 6-third bottom electrode; 7-piezoelectric layer; 8-top electrode; 9-passivation layer; 901-first insulating layer; 902-second insulating layer; 903-third insulating layer. Detailed Implementation

[0025] The invention will now be further explained with reference to the accompanying drawings.

[0026] like Figure 3 As shown, the temperature-compensated FBAR of this invention includes, from bottom to top, a substrate 1, a first cavity 2, a first bottom electrode 3, a second bottom electrode 4, a second cavity 5, a third bottom electrode 6, a piezoelectric layer 7, and a top electrode 8. The first cavity 2 is embedded in the upper surface of the substrate 1, and the edges of the first cavity 2 and the second cavity 5 are aligned in the thickness direction. The second bottom electrode 4, the second cavity 5, and the third bottom electrode 6 constitute a parallel plate capacitor. The overlapping region of the second cavity 5, the third bottom electrode 6, the piezoelectric layer 7, and the top electrode 8 in the thickness direction of the resonator constitutes the effective resonant region of the resonator. A passivation layer 9 is provided on the periphery of the first bottom electrode 3, the second bottom electrode 4, and the second cavity 5 in the thickness direction.

[0027] The substrate 1 is made of a material with a low coefficient of thermal expansion, such as monocrystalline silicon or sapphire. Monocrystalline silicon is used in this embodiment. The first bottom electrode 3 and the second bottom electrode 4 are made of conductive materials with significantly different coefficients of thermal expansion, with a difference greater than 15 ppm / K, such as aluminum and molybdenum, aluminum and tungsten, aluminum and doped silicon, or aluminum and doped silicon nitride. In this embodiment, molybdenum is used for the first bottom electrode 3, and aluminum is used for the second bottom electrode 4. The third bottom electrode 6 is made of a metallic material with an acoustic impedance greater than 50 megohms, such as molybdenum or tungsten. Molybdenum is used in this embodiment. The piezoelectric layer 7 is made of a piezoelectric material, such as aluminum nitride or scandium-doped aluminum nitride. Aluminum nitride is used in this embodiment.

[0028] In this embodiment, a passivation layer 9 is disposed around the first bottom electrode 3, the second bottom electrode 4, and the second cavity 5. The material of the passivation layer 9 is a material with a thermal expansion coefficient of less than 2 ppm / K and an acoustic impedance of less than 20 megohms. In this embodiment, silicon dioxide is selected. Since the material of the third bottom electrode 6 is molybdenum, which has a large acoustic impedance, while the material of the passivation layer 9 is silicon dioxide, which has a small acoustic impedance, the thickness of the third bottom electrode 6 and the passivation layer 9 can be reasonably designed to form a Bragg reflector layer. That is, the thickness of the third bottom electrode 6 and the passivation layer 9 is set to an odd multiple of one-quarter of the leakage bulk acoustic wave wavelength to reduce the bulk acoustic wave energy leaked from the ineffective resonant region of the piezoelectric layer 7 to the substrate, thereby improving the quality factor of the resonator.

[0029] The principle of temperature compensation in this invention is explained in detail below. The circuit model of FBAR near the series-parallel resonant point can be derived from... Figure 4 The equivalent circuit shown is illustrated, where C0 is the static capacitance of the piezoelectric film, and C... m For dynamic capacitance related to mechanical vibration, L m For dynamic inductance related to mechanical vibration, R m This refers to the dynamic resistance related to mechanical vibration. When the frequency of the electrical signal is the series resonant frequency of the FBAR, L... m C m and R m The series branch formed by these components will produce series resonance, at which point the overall impedance of the circuit is at its minimum, characterizing the electrical properties of the FBAR near the series resonant frequency; when the frequency of the electrical signal is the parallel resonant frequency of the FBAR, C0 in the parallel branch and L in the series branch... m Parallel resonance occurs, at which point the overall impedance of the circuit is at its maximum, characterizing the electrical properties of the FBAR near the parallel resonant frequency. From this model, the formulas for calculating the series and parallel resonant frequencies of the FBAR can be obtained, namely:

[0030] (1)

[0031] (2)

[0032] When an FBAR generates parallel resonance, it can be equivalent to a pure resistor with impedance approaching infinity. The series capacitor C' has almost no effect on its parallel resonant frequency, but mainly affects its series resonant frequency. When the dynamic capacitor C... m When a series capacitor C' is connected, the external capacitance value will decrease. According to formula (1), the series resonant frequency of the FBAR will increase. When the FBAR generates series resonance, it can be equivalent to a pure resistor with impedance approaching 0. The parallel capacitor C'' has almost no effect on its series resonance, but mainly affects its parallel resonant frequency. When the static capacitor C0 is connected in parallel with the capacitor C'', the external capacitance value will increase. According to formula (2), the parallel resonant frequency will decrease. In this embodiment of the invention, a parallel plate capacitor composed of a first bottom electrode 3, a second bottom electrode 4, a second cavity 5 and a third bottom electrode 6, and a resonant structure composed of a third bottom electrode 6, a piezoelectric layer 7 and a top electrode 8 are connected in parallel as an example. When the ambient temperature rises, the first bottom electrode 3 and the second bottom electrode 4 will be concave due to the difference in their thermal expansion coefficients. At this time, the spacing between the parallel plate capacitors increases and the capacitance of the parallel plate capacitors decreases, that is, the capacitance of the capacitor connected in parallel with the FBAR decreases. The capacitance value presented by the static capacitance C0 of the parallel branch in the FBAR circuit model will decrease. As can be seen from formula (2), the parallel resonant frequency of the FBAR increases, which can cancel out the decrease in the parallel resonant frequency caused by the negative temperature frequency drift of the FBAR due to the temperature rise, that is, the temperature compensation of the FBAR is realized. Similarly, when the ambient temperature decreases, the first bottom electrode 3 and the second bottom electrode 4 will bulge upwards due to the difference in their thermal expansion coefficients. At this time, the spacing between the parallel plate capacitors decreases and the capacitance of the parallel plate capacitors increases. That is, the capacitance of the capacitor connected in parallel with the FBAR will increase, and the capacitance value of the static capacitor C0 of the parallel branch in the FBAR circuit model will increase. According to formula (2), the parallel resonant frequency of the FBAR decreases, which can offset the increase in the parallel resonant frequency caused by the negative temperature frequency drift of the FBAR due to the decrease in temperature. That is, the temperature compensation of the FBAR is realized.

[0033] The following example illustrates Figure 3 The manufacturing process of the resonator structure shown includes the following steps:

[0034] Step 1: As Figure 5 As shown, a photolithography process is performed on the upper surface of substrate 1 to etch the filling region of the first cavity sacrificial layer 201 on the upper surface of substrate 1. Then, a sacrificial layer material BPSG is deposited in the filling region of the first cavity sacrificial layer 201 by chemical vapor deposition. Finally, the BPSG on the surface of substrate 1 is removed by chemical mechanical polishing, thereby reducing the roughness of substrate 1 and the surface of the first cavity sacrificial layer 201.

[0035] Step 2: As Figure 6As shown in the figure, a chemical vapor deposition process is performed on the surface of the device to deposit a first insulating layer 901, and then a photoetching process is performed on the surface of the first insulating layer 901 to etch a first bottom electrode 3 deposition area. Then, a magnetron sputtering process is performed on the surface of the device to deposit metal molybdenum, and finally, a chemical mechanical polishing process is performed to remove the metal molybdenum on the surface of the first insulating layer 901 and reduce the roughness of the surface of the first bottom electrode 3 and the first insulating layer 901. The first bottom electrode 3 and the first insulating layer 901 are prepared. Repeat the above steps to prepare the second bottom electrode 4 and the second insulating layer 902.

[0036] Step 3: as shown in the figure, Figure 7 A chemical vapor deposition process is performed on the surface of the device to deposit a third insulating layer 903, and then a photoetching process is performed on the surface of the third insulating layer 903 to etch a second cavity sacrificial layer 501 filling area, and then a chemical vapor deposition process is performed to deposit a sacrificial layer material BPSG in the second cavity sacrificial layer 501 filling area. Finally, a chemical mechanical polishing process is performed to remove the BPSG on the surface of the third insulating layer 903 and reduce the roughness of the surface of the second cavity sacrificial layer 501 and the third insulating layer 903.

[0037] Step 4: as shown in the figure, Figure 8 A magnetron sputtering process is performed on the surface of the device to deposit metal molybdenum, and then a photoetching process is performed to pattern the metal molybdenum film to form a third bottom electrode 6. Finally, a magnetron sputtering process is performed to deposit a piezoelectric material on the entire surface of the device, and a chemical mechanical polishing process is performed to control the thickness of the piezoelectric film to form a piezoelectric layer 7.

[0038] Step 5: as shown in the figure, Figure 9 A magnetron sputtering process is performed on the surface of the device to deposit metal molybdenum, and then a photoetching process is performed to pattern the metal molybdenum film to form a top electrode 8. Finally, a sacrificial layer release hole is etched on the surface of the device, and the first cavity sacrificial layer 201 and the second cavity sacrificial layer 501 are released to form a first cavity 2 and a second cavity 5, completing the preparation of the film bulk acoustic resonator. The first insulating layer 901, the second insulating layer 902 and the third insulating layer 903 constitute a passivation layer 9.

[0039] The above only describes the preferred embodiments of the present application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of the present application.

Claims

1. A dual-conductive-layer temperature-compensated film bulk acoustic resonator, characterized by, The film bulk acoustic resonator comprises, from bottom to top, a substrate (1), a first cavity (2), a first bottom electrode (3), a second bottom electrode (4), a second cavity (5), a third bottom electrode (6), a piezoelectric layer (7) and a top electrode (8); wherein the first cavity (2) is embedded on the upper surface of the substrate (1), the edges of the first cavity (2) and the second cavity (5) are aligned in the thickness direction; the second bottom electrode (4), the second cavity (5) and the third bottom electrode (6) constitute a parallel-plate capacitor; the overlapping area of the second cavity (5), the third bottom electrode (6), the piezoelectric layer (7) and the top electrode (8) in the thickness direction of the resonator constitutes the effective resonant area of the film bulk acoustic resonator; the first bottom electrode (3), the second bottom electrode (4) and the second cavity (5) are provided with a passivation layer (9) on the side in the thickness direction; the material thermal expansion coefficient difference of the first bottom electrode (3) and the second bottom electrode (4) is greater than 15ppm / K; The material of the third bottom electrode (6) is a metal material with acoustic impedance greater than 50 mega acoustic ohm, the material of the passivation layer (9) is a material with thermal expansion coefficient less than 2ppm / K and acoustic impedance less than 20 mega acoustic ohm, and the thickness of the third bottom electrode (6) and the passivation layer (9) satisfies the Bragg reflection condition.

2. The dual-conductive-layer temperature-compensated film bulk acoustic resonator structure of claim 1, wherein, The material combination of the first bottom electrode (3) and the second bottom electrode (4) is aluminum and molybdenum, aluminum and tungsten, aluminum and doped silicon, and aluminum and doped silicon nitride.

3. The dual-conductive-layer temperature-compensated film bulk acoustic resonator of claim 1, wherein, The material of the third bottom electrode (6) is tungsten or molybdenum, and the material of the passivation layer (9) is silicon dioxide.

4. The dual-conductive-layer temperature-compensated film bulk acoustic resonator of claim 3, wherein, The material of the substrate (1) is single crystal silicon or sapphire, and the material of the piezoelectric layer (7) is aluminum nitride or scandium-doped aluminum nitride.

5. The method of manufacturing a film bulk acoustic resonator of any one of claims 1-4, wherein, The method comprises the following steps: Step 1: sequentially performing photolithography process, chemical vapor deposition process and chemical mechanical polishing process on the upper surface of the substrate (1) to prepare a first cavity sacrificial layer (201) in the substrate (1); Step 2: sequentially performing chemical vapor deposition process and photolithography process to prepare a first insulating layer (901) on the side of the first bottom electrode (3), then performing magnetron sputtering process and stripping process to prepare the first bottom electrode (3), and then repeating the steps to prepare the second bottom electrode (4); Step 3: preparing a third insulating layer (903) on the side of the second cavity (5) by chemical vapor deposition process and photolithography process, and then performing chemical vapor deposition process and chemical mechanical polishing process to prepare a second cavity sacrificial layer (501); Step 4: sequentially performing magnetron sputtering process and photolithography process to prepare the third bottom electrode (6), and then preparing the piezoelectric layer (7) by magnetron sputtering process; Step 5: sequentially performing magnetron sputtering process and photolithography process to prepare the top electrode (8), and then etching and releasing holes to release the first cavity sacrificial layer (201) and the second cavity sacrificial layer (501), form the first cavity (2) and the second cavity (5), and complete the preparation of the film bulk acoustic resonator.

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