Temperature compensation type film bulk acoustic resonator with double conductive layers and manufacturing method

Abstract

The invention discloses a temperature compensation type film bulk acoustic resonator with double conducting layers and a manufacturing method. The resonator comprises 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 which are sequentially arranged from bottom to top. The first bottom electrode and the second bottom electrode are made of conductive materials with large thermal expansion coefficient difference. And passivation layers are arranged on the peripheral sides of the first bottom electrode, the second bottom electrode and the second cavity 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 environment temperature changes, the first bottom electrode and the second bottom electrode sink or protrude due to the difference of thermal expansion coefficients, then the distance between parallel plates is changed, the capacitance value of the parallel plate capacitor is changed, and frequency compensation of the FBAR is achieved. The method has simple steps and is convenient for large-scale manufacturing.

Description

Technical Field

[0001] The present invention relates to a radio frequency communication device and a manufacturing method, and in particular to a thin film bulk acoustic wave resonator and a manufacturing method. Background Art

[0002] Film Bulk Acoustic Resonator (FBAR) has the advantages of high resonant frequency, high quality factor, and small size. The filter prepared by it has good performance and has gradually become a hot spot in RF filter research. The key structural component of FBAR is a sandwich structure composed of an upper metal electrode-piezoelectric film-lower metal electrode. One of its mainstream working principles is that when the radio frequency AC signal is applied to the upper and lower electrodes of the FBAR, the piezoelectric film converts the electrical signal into a longitudinal wave propagating along the thickness direction of the film based on the inverse piezoelectric effect. 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 half the wavelength of the sound wave, the longitudinal wave forms a standing wave oscillation, and the sound wave loss is minimized at this time. Then, the piezoelectric film converts the longitudinal wave into an electrical signal through the piezoelectric effect, thereby realizing the frequency selection function of the electrical signal. The electrical impedance characteristics of an ideal FBAR are as follows: Figure 1 As shown, the frequency with the minimum impedance is the series resonant frequency f s The frequency with the maximum impedance is the parallel resonant frequency f p The relative frequency spacing between the two is usually represented by the effective electromechanical coupling coefficient. The larger the effective electromechanical coupling coefficient, the larger the relative spacing between the two.

[0003] Since the elastic stiffness coefficients of piezoelectric materials and electrode materials decrease with increasing temperature, the series and parallel resonant frequencies of traditional FBARs decrease with increasing temperature, which causes the passband of the filter composed of FBAR to shift with temperature changes. If the passband of the filter used in the crowded communication frequency band shifts with temperature changes, it will be difficult for the filter to effectively filter out interference signals in adjacent frequency bands. Therefore, how to suppress the resonant frequency drift of FBAR caused by temperature is one of the key issues in FBAR filter applications.

[0004] In the prior art, one of the main ways to compensate for the temperature drift of the FBAR resonant frequency is to connect a voltage-controlled capacitor in series or in parallel with the FBAR, such as Figure 2As shown. Among them, the voltage-controlled capacitor can be a parallel plate capacitor, a Schottky junction capacitor, or other capacitors whose capacitance changes with the voltage at both ends. When the ambient temperature changes, the resistance value of the thermistor in the Wheatstone bridge changes, causing the voltage output by the bridge, that is, the voltage at both ends of the voltage-controlled capacitor to change, which in turn causes the capacitance of the voltage-controlled capacitor to change. When the capacitance of the capacitor of the FBAR in series or parallel changes, its resonant frequency also changes, and temperature compensation can be achieved through reasonable design. However, since this method uses a Wheatstone bridge, the device as a whole will generate a large power consumption. In addition, the voltage-controlled capacitor changes the size of the capacitor by applying the size of the DC bias voltage signal. Since the DC bias signal is directly applied to the original electrode, this method has the problem of mutual interference between the excitation signal and the DC bias signal. Therefore, it is necessary to propose a new temperature-compensated thin film bulk acoustic resonator to solve the above problems. Summary of the invention

[0005] Purpose of the invention: In view of the above-mentioned prior art, a temperature-compensated thin film bulk acoustic wave resonator with double conductive layers is proposed, which can perform temperature compensation on the series or parallel resonant frequency of FBAR, and a method with simple manufacturing process and large-scale manufacturing is proposed.

[0006] Technical solution: A double-conductive-layer temperature-compensated thin-film bulk acoustic wave resonator, comprising 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 arranged in sequence from bottom to top; wherein the first cavity is embedded in 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 constitute 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 constitutes the effective resonance area of ​​the thin-film bulk acoustic wave resonator; the first bottom electrode, the second bottom electrode and the second cavity are provided with a passivation layer on the peripheral side in the thickness direction; the difference in the thermal expansion coefficient of the materials of the first bottom electrode and the second bottom electrode is greater than 15ppm / K.

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

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

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

[0010] Furthermore, 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 thin film bulk acoustic wave resonator comprises the following steps: Step 1: performing a photolithography process, a chemical vapor deposition process, and a chemical mechanical polishing process on the upper surface of the substrate in sequence to prepare a first cavity sacrificial layer in the substrate; Step 2: sequentially perform a chemical vapor deposition process and a photolithography process to prepare a first insulating layer around the first bottom electrode, and then perform a magnetron sputtering process and a stripping process to prepare the first bottom electrode; and then repeat the steps to prepare a second bottom electrode; Step 3: preparing a third insulating layer around the second cavity by chemical vapor deposition and photolithography, and then preparing a second cavity sacrificial layer by chemical vapor deposition and chemical mechanical polishing; Step 4: sequentially performing a magnetron sputtering process and a photolithography process to prepare a third bottom electrode, and then preparing a piezoelectric layer by a magnetron sputtering process; Step 5: sequentially perform magnetron sputtering process and photolithography process to prepare the top electrode, and then etch release holes to release the first cavity sacrificial layer and the second cavity sacrificial layer to form the first cavity and the second cavity, thereby completing the preparation of the thin film bulk acoustic wave resonator.

[0012] Beneficial effects: 1. In the present invention, 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 depressions or protrusions due to the difference in thermal expansion coefficients, thereby changing the spacing between the parallel plates, causing the capacitance of the parallel plate capacitor to change, thereby achieving frequency compensation of the FBAR. This method does not require an external DC bias signal, and does not cause the problem of mutual interference between the DC signal and the RF signal. In addition, the structure of the present invention can compensate for the resonant frequency of the FBAR when the ambient temperature increases or decreases, and is not limited to the case of temperature increase or temperature decrease.

[0013] 2. In the present invention, by reasonably designing the structural parameters of the parallel plate capacitor, self-compensation of the FBAR series or parallel frequency can be achieved, and no external circuit such as a Wheatstone bridge is required to measure the temperature change, so no large power consumption is generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The electrical impedance characteristic diagram of an ideal FBAR; Figure 2 It is a schematic diagram of the structure of using a Wheatstone bridge and a voltage-controlled capacitor to perform temperature compensation on FBAR in the prior art; Figure 3 is a cross-sectional schematic diagram of the FBAR structure of the present invention; Figure 4 Schematic diagram of the equivalent circuit model of FBAR near the resonance point; Figure 5-Figure 9 This is a schematic diagram of the FBAR structure process flow of the present invention; The reference numerals in the figure are: 101-DC voltage source; 102-first temperature-sensitive resistor; 103-third temperature-sensitive resistor; 104-second temperature-sensitive resistor; 105-fourth temperature-sensitive resistor; 106-first high-resistance resistor; 107-second high-resistance resistor; 108-variable capacitor; 109-thin film bulk acoustic wave 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 DESCRIPTION

[0015] The present invention will be further explained below in conjunction with the accompanying drawings.

[0016] like Figure 3 As shown, the temperature-compensated FBAR of the embodiment of the present invention includes: 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 arranged in sequence from bottom to top. Among them, 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 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 resonance area of ​​the 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 peripheral side in the thickness direction.

[0017] The material of the substrate 1 is a material with a low thermal expansion coefficient, such as single crystal silicon or sapphire. This embodiment uses single crystal silicon. The materials of the first bottom electrode 3 and the second bottom electrode 4 are respectively conductive materials with large differences in thermal expansion coefficients, and the difference is greater than 15ppm / K, such as aluminum and molybdenum, aluminum and tungsten, aluminum and doped silicon or aluminum and doped silicon nitride. In this embodiment, the first bottom electrode 3 is made of molybdenum, and the material of the second bottom electrode 4 is aluminum. The material of the third bottom electrode 6 is a metal material with an acoustic impedance greater than 50 megohms, such as molybdenum or tungsten. This embodiment uses molybdenum. The material of the piezoelectric layer 7 is a piezoelectric material, such as aluminum nitride or scandium-doped aluminum nitride. This embodiment uses aluminum nitride.

[0018] In this embodiment, a passivation layer 9 is arranged 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 2ppm / K and an acoustic impedance of less than 20 megaohms. In this embodiment, silicon dioxide is selected. Since the material of the third bottom electrode 6 is molybdenum, which has a large acoustic impedance, and 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 reflection 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 wavelength of the leaked bulk acoustic wave, so as to reduce the bulk acoustic wave energy leaked from the non-effective resonance area in the piezoelectric layer 7 to the substrate, thereby improving the quality factor of the resonator.

[0019] The principle of temperature compensation of the present invention is described in detail below. The circuit model of FBAR near the series-parallel resonance point can be expressed as Figure 4 The equivalent circuit shown is where C 0 is the static capacitance of the piezoelectric film, C m is the dynamic capacitance associated with mechanical vibration, L m is the dynamic inductance associated with mechanical vibration, R m is the dynamic resistance related to mechanical vibration. When the frequency of the electrical signal is the series resonance frequency of the FBAR, L m , C m and R m The series branch formed by the circuit will produce series resonance. At this time, the overall impedance of the circuit is the smallest, which represents the electrical characteristics of FBAR near the series resonance frequency. When the frequency of the electrical signal is the parallel resonance frequency of FBAR, C in the parallel branch 0 L in the series branch m Parallel resonance is generated, and the overall impedance of the circuit is the largest at this time, which characterizes the electrical characteristics of FBAR near the parallel resonance frequency. From this model, the calculation formula for the series and parallel resonance frequencies of FBAR can be obtained, namely: (1) (2) When FBAR produces parallel resonance, it can be equivalent to a pure resistor with an impedance approaching infinity. The series capacitance C' has almost no effect on its parallel resonance frequency, but mainly affects its series resonance frequency. m When the series capacitor C' is connected, the capacitance value presented to the outside will become smaller. From formula (1), it can be seen that the series resonant frequency of the FBAR will increase. When the FBAR produces 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 C 0When the capacitor C'' is connected in parallel, the capacitance value presented to the outside will become larger. It can be seen from formula (2) that the parallel resonant frequency will decrease. In the embodiment of the present invention, a parallel plate capacitor composed of the first bottom electrode 3, the second bottom electrode 4, the second cavity 5 and the third bottom electrode 6 and a resonant structure composed of the third bottom electrode 6, the piezoelectric layer 7 and the 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 sag downward due to the difference in thermal expansion coefficients. At this time, the spacing between the parallel plate capacitors increases, and the capacitance of the parallel plate capacitor decreases, that is, the capacitance of the capacitor connected in parallel with the FBAR decreases. The static capacitance C of the parallel branch in the FBAR circuit model 0 The capacitance value presented to the outside will decrease. From formula (2), it can be seen that the parallel resonant frequency of FBAR increases, which can offset the decrease in parallel resonant frequency caused by the negative temperature frequency drift of FBAR caused by the temperature increase, that is, the temperature compensation of FBAR is achieved. Similarly, when the ambient temperature decreases, due to the difference in thermal expansion coefficients between the first bottom electrode 3 and the second bottom electrode 4, the first bottom electrode 3 and the second bottom electrode 4 will bulge upward. 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 in parallel with FBAR will increase, and the static capacitance C of the parallel branch in the FBAR circuit model 0 The capacitance value presented to the outside will increase. From formula (2), it can be seen that the parallel resonant frequency of FBAR decreases, which can offset the increase in parallel resonant frequency caused by the negative temperature frequency drift of FBAR caused by temperature reduction, thus achieving temperature compensation of FBAR.

[0020] The following is an example Figure 3 The manufacturing process of the resonator structure shown includes the following steps: Step 1: If Figure 5 As shown, a photolithography process is performed on the upper surface of the substrate 1 to etch out a filling area of ​​the first cavity sacrificial layer 201 on the upper surface of the substrate 1, and then a sacrificial layer material BPSG is deposited in the filling area of ​​the first cavity sacrificial layer 201 by a chemical vapor deposition process. Finally, a chemical mechanical polishing process is performed to remove the BPSG on the surface of the substrate 1 and reduce the roughness of the surfaces of the substrate 1 and the first cavity sacrificial layer 201.

[0021] Step 2: If Figure 6 As shown, a chemical vapor deposition process is performed on the surface of the device to deposit the first insulating layer 901, and then a photolithography process is performed on the surface of the first insulating layer 901 to etch out the 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 the roughness of the first bottom electrode 3 and the first insulating layer 901 is reduced, and 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.

[0022] Step 3: If Figure 7 As shown, a chemical vapor deposition process is performed on the surface of the device to deposit the third insulating layer 903, and then a photolithography process is performed on the surface of the third insulating layer 903 to etch out the second cavity sacrificial layer 501 filling area, and then a sacrificial layer material BPSG is deposited in the second cavity sacrificial layer 501 filling area by a chemical vapor deposition process. 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 second cavity sacrificial layer 501 and the third insulating layer 903 surfaces.

[0023] Step 4: Figure 8 As shown, metal molybdenum is deposited on the surface of the device by magnetron sputtering, and then the metal molybdenum film is patterned by photolithography to form a third bottom electrode 6. Finally, piezoelectric material is deposited on the entire surface of the device by magnetron sputtering, and the thickness of the piezoelectric film is controlled by chemical mechanical polishing to form a piezoelectric layer 7.

[0024] Step 5: Fig. 9 As shown, metal molybdenum is deposited on the device surface by magnetron sputtering process, and then the metal molybdenum film is patterned by photolithography process to form the top electrode 8. Finally, the sacrificial layer release hole is etched on the device surface, and the first cavity sacrificial layer 201 and the second cavity sacrificial layer 501 are released to form the first cavity 2 and the second cavity 5, and the preparation of the thin film bulk acoustic wave resonator is completed. The first insulating layer 901, the second insulating layer 902 and the third insulating layer 903 constitute the passivation layer 9.

[0025] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A temperature-compensated thin film bulk acoustic resonator with double conductive layers, characterized in that: The invention comprises 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) which are arranged in sequence from bottom to top; wherein 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 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 resonance area of ​​the thin film bulk acoustic wave 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 peripheral side in the thickness direction; and the difference in thermal expansion coefficient between the materials of the first bottom electrode (3) and the second bottom electrode (4) is greater than 15 ppm / K.

2. The temperature-compensated thin film bulk acoustic resonator with double conductive layers according to claim 1, characterized in that: The material of the third bottom electrode (6) is a metal material with an acoustic impedance greater than 50 mega-ohms, the material of the passivation layer (9) is a material with a thermal expansion coefficient less than 2 ppm / K and an acoustic impedance less than 20 mega-ohms, and the thicknesses of the third bottom electrode (6) and the passivation layer (9) meet Bragg reflection conditions.

3. The temperature-compensated thin film bulk acoustic resonator structure with double conductive layers according to claim 1 or 2, characterized in that: The material combinations of the first bottom electrode (3) and the second bottom electrode (4) are aluminum and molybdenum, aluminum and tungsten, aluminum and doped silicon, and aluminum and doped silicon nitride.

4. The temperature-compensated thin film bulk acoustic resonator with double conductive layers according to claim 2, characterized in that: The material of the third bottom electrode (6) is tungsten or molybdenum, and the material of the passivation layer (9) is silicon dioxide.

5. The temperature-compensated thin film bulk acoustic resonator with double conductive layers according to claim 4, characterized in that: 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.

6. The method for manufacturing a thin film bulk acoustic wave resonator according to any one of claims 1 to 5, characterized in that: The steps include: Step 1: performing a photolithography process, a chemical vapor deposition process, and a chemical mechanical polishing process on the upper surface of the substrate (1) in sequence to prepare a first cavity sacrificial layer (201) in the substrate (1); Step 2: sequentially performing a chemical vapor deposition process and a photolithography process to prepare a first insulating layer (901) around the first bottom electrode (3), and then performing a magnetron sputtering process and a stripping process to prepare the first bottom electrode (3); and then repeating the steps to prepare a second bottom electrode (4); Step 3: preparing a third insulating layer (903) around the second cavity (5) by chemical vapor deposition and photolithography, and then preparing a second cavity sacrificial layer (501) by chemical vapor deposition and chemical mechanical polishing; Step 4: sequentially performing a magnetron sputtering process and a photolithography process to prepare a third bottom electrode (6), and then preparing a piezoelectric layer (7) by a magnetron sputtering process; Step 5: sequentially performing a magnetron sputtering process and a photolithography process to prepare a top electrode (8), and then etching a release hole to release the first cavity sacrificial layer (201) and the second cavity sacrificial layer (501), thereby forming a first cavity (2) and a second cavity (5), and completing the preparation of the thin film bulk acoustic wave resonator.

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