WO2020133004A1 - 一种薄膜体声波谐振器 - Google Patents

一种薄膜体声波谐振器 Download PDF

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Publication number
WO2020133004A1
WO2020133004A1 PCT/CN2018/124085 CN2018124085W WO2020133004A1 WO 2020133004 A1 WO2020133004 A1 WO 2020133004A1 CN 2018124085 W CN2018124085 W CN 2018124085W WO 2020133004 A1 WO2020133004 A1 WO 2020133004A1
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Prior art keywords
thin film
film bulk
bulk acoustic
temperature compensation
layer
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French (fr)
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张孟伦
庞慰
杨清瑞
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Tianjin University
ROFS Microsystem Tianjin Co Ltd
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Tianjin University
ROFS Microsystem Tianjin Co Ltd
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details

Definitions

  • the present invention relates to the field of communications, and in particular to a thin film bulk acoustic resonator.
  • Thin-film bulk acoustic resonators are the basic components of bulk acoustic wave devices. This type of resonator is a component based on piezoelectric technology.
  • CMOS Complementary Metal Oxide Semiconductor
  • Thin film bulk acoustic resonator is a resonator that uses acoustic resonance to achieve frequency selection of electrical signals of the same frequency.
  • the core part is composed of a top electrode-piezoelectric layer-bottom electrode sandwich structure, which generally works in the energy trap-thickness Vibration mode.
  • the thickness of the piezoelectric layer, metal or dielectric layer of the thin film bulk acoustic resonator and the speed of sound in it all change with temperature, so the resonance frequency of the piezoelectric acoustic resonator also changes with temperature.
  • the change of the sound wave propagation speed with temperature in each layer is the main reason for the change of the resonance frequency of piezoelectric acoustic wave resonator with temperature.
  • Most materials currently used in piezoelectric acoustic resonators exhibit a negative temperature coefficient, that is, the speed of sound becomes smaller as the temperature increases, because the material becomes "softened” at higher temperatures (for example, the cross-atomic force is weakened ).
  • a radio frequency (RF) filter composed of a piezoelectric acoustic wave resonator usually has a passband frequency response.
  • the frequency temperature coefficient (TCF) of the piezoelectric acoustic wave resonator will reduce the manufacturing yield of the radio frequency (RF) filter, because the pressure
  • the device or device composed of the electroacoustic resonator can only meet the requirements of the passband bandwidth within a certain temperature range.
  • a common method is to add a temperature compensation layer in the piezoelectric acoustic wave resonator stack structure, which may specifically be a layer of silicon dioxide (SiO 2 ) temperature compensation layer material.
  • a temperature compensation layer in the piezoelectric acoustic wave resonator stack structure, which may specifically be a layer of silicon dioxide (SiO 2 ) temperature compensation layer material.
  • the electromechanical coupling coefficient (Kt) value is an important parameter of the resonator. This parameter represents the ability of the resonator to convert mechanical energy and electrical energy.
  • a common method is to dope rare earth elements in the piezoelectric material.
  • the horizontal axis is the amount of Sc doping and the vertical axis is the temperature-frequency drift coefficient
  • the rare earth element in FIG. 1 is Scandium Sc
  • the resonator area is reduced, the leakage energy in the effective area of the resonator will increase, so that its Q The reduction will cause an increase in clutter in the resonator.
  • the present invention provides a thin film bulk acoustic wave resonator, which enables the thin film bulk acoustic wave resonator to have a high electromechanical coupling coefficient while keeping its temperature frequency drift coefficient constant, and can also make the thin film bulk acoustic wave resonator The area of the device increases.
  • embodiments of the present invention provide a thin film bulk acoustic resonator, including a top electrode, a piezoelectric layer, a bottom electrode, an acoustic reflection structure, a substrate, and a temperature with a thickness greater than a preset value A compensation layer; wherein the temperature compensation layer is also used to adjust the area of the thin film bulk acoustic resonator
  • the thickness of the temperature compensation layer is greater than the preset value, that is, the thickness of the temperature compensation layer is increased to compensate for the deterioration of the temperature frequency drift coefficient of the temperature compensation layer due to the increase in the content of the doped rare earth element in the piezoelectric layer, Eventually, the temperature-frequency drift coefficient of the thin film bulk acoustic resonator can be kept basically unchanged.
  • the thickness of the temperature compensation layer is increased, the electromechanical coupling coefficient of the thin film bulk acoustic resonator is reduced. According to the principle of the background technology, when the electromechanical coupling coefficient of the thin film bulk acoustic resonator is reduced, the bulk acoustic wave of the thin film will be reduced.
  • the area of the resonator becomes larger.
  • the energy leakage of the thin film bulk acoustic resonator due to its small area can be reduced, and the Q value of the thin film bulk acoustic resonator can be improved, while the generation of clutter can be reduced. That is, by increasing the thickness of the temperature compensation layer, the thin film bulk acoustic resonator can have a higher electromechanical coupling coefficient while maintaining its temperature frequency drift coefficient unchanged, and can also increase the area of the thin film bulk acoustic resonator.
  • the piezoelectric layer is doped with rare earth elements.
  • the rare earth element is any one or any combination of the following: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, yttrium, and scandium.
  • the temperature compensation layer is located in the piezoelectric layer.
  • the temperature compensation layer is two layers; one of the temperature compensation layers is located in the top electrode, and the other temperature compensation layer is located in the piezoelectric layer.
  • the temperature compensation layer is two layers; one temperature compensation layer is located in the bottom electrode, and the other temperature compensation layer is located in the piezoelectric layer.
  • a portion of the piezoelectric layer is doped with rare earth elements; the temperature compensation layer is located in a portion of the piezoelectric layer doped with rare earth elements.
  • the piezoelectric layer is doped with different proportions of rare earth elements in the thickness direction of the piezoelectric layer.
  • the ratio of rare earth elements doped in the direction from the bottom electrode to the top electrode is getting higher and higher.
  • the ratio of rare earth elements doped in the direction from the bottom electrode to the top electrode is getting lower and lower.
  • the top electrode has a bridge wing structure, an air gap is provided between the tail of the bridge wing structure and the piezoelectric layer, and the bridge wing structure is correspondingly located inside the acoustic reflection structure; and/or
  • the top electrode has a bridge structure, and there is an air gap between the center of the bridge structure and the piezoelectric layer.
  • the acoustic reflection structure is an acoustic mirror.
  • the acoustic mirror is located on the upper surface of the base or embedded in the base.
  • FIG. 1 is a graph of the amount of rare earth element doping and temperature compensation coefficient in the prior art
  • FIG. 2 is a schematic structural view of a thin film bulk acoustic resonator in the first embodiment
  • FIG. 3 is a schematic structural view of a thin film bulk acoustic resonator in the second embodiment
  • FIG. 4 is another schematic diagram of the structure of the thin film bulk acoustic resonator in the second embodiment
  • FIG. 5 is another schematic structural view of a thin film bulk acoustic resonator in the second embodiment
  • FIG. 6 is another schematic structural view of the thin film bulk acoustic resonator in the second embodiment
  • FIG. 7 is another schematic structural view of the thin film bulk acoustic resonator in the second embodiment
  • FIG. 8 is a schematic structural diagram of a thin film bulk acoustic resonator in a third embodiment
  • FIG. 9 is a schematic structural view of a thin film bulk acoustic resonator in a fourth embodiment
  • FIG. 10 is a schematic structural view of a thin film bulk acoustic resonator in a fifth embodiment
  • FIG. 11 is a schematic diagram of the structure of a thin film bulk acoustic resonator in a sixth embodiment.
  • the first embodiment of the present invention relates to a thin film bulk acoustic resonator.
  • the thin film bulk acoustic resonator includes a top electrode 201, a piezoelectric layer 202, a bottom electrode 203, an acoustic reflection structure 204, a substrate 205, and a temperature compensation layer 206 having a thickness greater than a preset value, which are sequentially connected in a positional relationship.
  • the temperature compensation layer 206 is used to adjust the area of the thin film bulk acoustic resonator.
  • the temperature compensation layer 206 is located in the piezoelectric layer 202.
  • the temperature compensation layer is two layers, and their materials may be the same or different.
  • the acoustic reflection structure 204 is an acoustic mirror.
  • the acoustic mirror is located on the upper surface of the base 205 or embedded inside the base 205.
  • the acoustic mirror is constituted by a cavity embedded in the substrate 205, but any other acoustic mirror structure such as a Bragg reflector is also applicable.
  • the materials of the top electrode 201 and the bottom electrode 203 can be gold (Au), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), titanium tungsten ( TiW), aluminum (Al), titanium (Ti) and similar metals are formed.
  • the material of the piezoelectric layer 202 may be aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO 3 ), quartz (Quartz), potassium niobate (KNbO 3 ), or Lithium tantalate (LiTaO 3 ), etc.
  • the above piezoelectric material is a piezoelectric thin film, and the thickness is less than 10 microns.
  • the aluminum nitride thin film is in a polycrystalline or single crystal form, and the growth method is thin film sputtering (sputtering) or organic metal chemical vapor deposition (MOCVD).
  • the material of the temperature compensation layer 206 may be polysilicon, borophosphate glass (BSG), silicon dioxide (SiO 2 ), chromium (Cr), or tellurium oxide (TeO (x) ).
  • the piezoelectric layer 202 is doped with rare earth elements.
  • the rare earth element may be any one or any combination of the following: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu) ), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), yttrium (Y) and scandium (Sc ).
  • the rare earth element is preferably scandium
  • the piezoelectric layer material is preferably aluminum nitride.
  • the vibration frequency f is fixed for specific technical index requirements.
  • the relationship between impedance Z and f is determined by the following expression:
  • ⁇ is the dielectric constant of the piezoelectric material
  • A is the effective area of the resonator
  • d is the thickness of the acoustic structure of the resonator.
  • the impedance of the film bulk acoustic resonator in the filter is a fixed value.
  • rare-earth element such as scandium
  • the speed of sound waves propagating therein will become slower. Since the required frequency f remains unchanged, if the velocity v becomes 1/k of the original through doping, the thickness of the corresponding piezoelectric layer 202 should also be strained to the original 1/k to ensure that the formula (3) is still true.
  • the molecule on the right side of equation (4) is d*d, so the molecule becomes the original 1/(k*k).
  • the area A also needs to be changed to 1/k to ensure that equation (4) is still true.
  • the thickness and area of the piezoelectric layer 202 can be reduced to 1/k.
  • the ratio of the circumference area of the thin film bulk acoustic resonator will increase, so that the transverse mode wave generated by the thin film bulk acoustic resonator is reflected back into the effective area at the edge of the resonator The energy decreases, which causes the Q value of the thin film bulk acoustic resonator to decrease.
  • the path of the reflection of the transverse mode wave at the edge of the thin film bulk acoustic resonator will be shortened, weakening their mutual cancellation effect, and thus making the thin film bulk acoustic resonator mixed Increased waves.
  • the temperature frequency drift coefficient of the temperature compensation layer of the thin film bulk acoustic resonator becomes worse and worse.
  • the electromechanical coupling coefficient of the thin film bulk acoustic resonator is reduced.
  • the area of the thin film bulk acoustic resonator becomes larger. Therefore, the energy leakage of the thin film bulk acoustic resonator due to the small area can be reduced, the Q value of the thin film bulk acoustic resonator can be improved, and the generation of clutter can be reduced.
  • the thin film bulk acoustic resonator can have a high electromechanical coupling coefficient while maintaining the temperature frequency drift coefficient unchanged, and can also increase the area of the thin film bulk acoustic resonator . It is worth mentioning that, after the thickness of the temperature compensation layer is adjusted, the temperature-frequency drift coefficient of the resonator is set to be better than -30ppm/°C. And the area of the resonator is not less than 1000 ⁇ m 2 .
  • the second embodiment of the present invention relates to a thin film bulk acoustic resonator.
  • the temperature compensation layer is two layers.
  • the temperature compensation layer 206 is two layers. One temperature compensation layer 206 is located in the top electrode 201, and the other temperature compensation layer 206 is located in the piezoelectric layer 202. Specifically, the temperature compensation layer 206 includes two layers including a first temperature compensation layer 2061 and a second temperature compensation layer 2062. The first temperature compensation layer 2061 is located in the top electrode 201. The second temperature compensation layer 2062 is located in the piezoelectric layer 202.
  • the temperature compensation layer 206 is usually composed of an insulating material, when the temperature compensation layer 206 is located between the two electrodes (the top electrode 201 and the bottom electrode 203) and the piezoelectric layer 202, it acts as a series capacitor, and the partial voltage between the two electrodes It will fall on the temperature compensation layer 206, so that the pressure drop in the piezoelectric layer 202 is reduced, and the electric field strength in the piezoelectric layer 202 is correspondingly reduced, thus affecting the electromechanical coupling coefficient of the resonator.
  • the top electrode 201 around the temperature compensation layer 206 has the same electric potential, so it is wrapped in
  • the electric field strength in the temperature compensation layer 206 in the top electrode 201 is close to zero.
  • the voltage drop between the top electrode 201 and the bottom electrode 203 of the resonator falling within the piezoelectric layer 202 increases, so that the electromechanical coupling coefficient of the resonator increases.
  • the temperature compensation layer 206 is two layers. One temperature compensation layer 206 is located in the bottom electrode 203, and the other temperature compensation layer 206 is located in the piezoelectric layer 202. Specifically, the temperature compensation layer 206 is two layers including a third temperature compensation layer 2063 and a fourth temperature compensation layer 2064. The third temperature compensation layer 2063 is located in the piezoelectric layer 202. The fourth temperature compensation layer 2064 is located in the bottom electrode 203.
  • the temperature compensation layer 206 is usually composed of an insulating material, when the temperature compensation layer 206 is located between the two electrodes (the top electrode 201 and the bottom electrode 203) and the piezoelectric layer 202, it acts as a series capacitor, and the partial voltage between the two electrodes It will fall on the temperature compensation layer 206, so that the pressure drop in the piezoelectric layer 202 is reduced, and the electric field strength in the piezoelectric layer 202 is correspondingly reduced, thus affecting the electromechanical coupling coefficient of the resonator.
  • the bottom electrode 203 around the temperature compensation layer 206 has the same electric potential, so it is wrapped in
  • the electric field strength in the temperature compensation layer 206 in the bottom electrode 203 is close to zero.
  • the voltage drop between the bottom electrode 203 of the resonator and the bottom electrode 203 within the piezoelectric layer 202 increases, so that the electromechanical coupling coefficient of the resonator increases.
  • the temperature compensation layer 206 is two layers. One temperature compensation layer 2065 is located in the top electrode 201, and the other temperature compensation layer 2066 is located in the bottom electrode 203. Alternatively, as shown in FIG. 6, both temperature compensation layers 206 are located in the top electrode 201. Or, as shown in FIG. 7, two of the temperature compensation layers are located in the bottom electrode 203.
  • the third embodiment of the present invention relates to a thin film bulk acoustic resonator.
  • the piezoelectric layer is asymmetrically doped with rare earth elements.
  • a part of the piezoelectric layer 202 is doped with rare earth elements.
  • the temperature compensation layer 206 is located in a part of the piezoelectric layer 202 doped with rare earth elements.
  • a part of the piezoelectric layer 202 is marked with doped rare earth element as 2021, and another part of the piezoelectric layer 202 is marked with no rare earth element as 2022.
  • the atomic radius of the rare earth element doped in part of the piezoelectric layer 202 is usually larger than the atomic radius of the piezoelectric layer 202 itself, so the stress of the piezoelectric layer 202 will change, and the piezoelectric layer 202 Only a part of them is doped with rare earth elements, so the portion of the piezoelectric layer 202 doped with rare earth elements has the highest stress, so adding a thin temperature compensation layer 206 to the doped portion of the piezoelectric layer 202 can play the most Good warming effect.
  • the stress change in the piezoelectric layer 202 can be changed by changing the doping method of the rare earth element in the piezoelectric layer 202, and then the position of the temperature compensation layer 206 can be flexibly changed, which can make the thin film bulk acoustic resonator design Without affecting other performance, it can have more flexibility. Furthermore, due to changes in the stress of the piezoelectric layer 202 after doping with rare earth elements, the electric dipole in the material of the piezoelectric layer 202 will change.
  • the material of the piezoelectric layer 202 When an electric field is applied to the piezoelectric layer 202, the material of the piezoelectric layer 202 There will be a greater mechanical response in the middle, so that the thin film bulk acoustic resonator can obtain a higher electromechanical coupling coefficient, which can compensate for the decrease in the mechanical and electrical coupling coefficient of the thin film bulk acoustic resonator caused by the addition of the temperature compensation layer 206 .
  • the piezoelectric layer 202 is doped with different proportions of rare earth elements in the thickness direction of the piezoelectric layer 202.
  • the proportion of rare earth elements doped in the direction from the bottom electrode 203 to the top electrode 201 is getting higher and higher.
  • the plane on which the top electrode 201 is located is the upper plane
  • the plane on which the substrate 205 is located is the lower plane.
  • the proportion of rare earth elements doped in the piezoelectric layer 202 is increasing from bottom to top. Therefore, the upper surface of the piezoelectric layer 202 has the maximum stress, so the temperature compensation layer 206 can be partially placed on the upper surface of the piezoelectric layer 202, which can achieve the best temperature compensation effect and can increase the bulk acoustic wave of the film.
  • the Q value of the resonator is the proportion of rare earth elements doped in the direction from the bottom electrode 203 to the top electrode 201 .
  • the electric dipole in the material of the piezoelectric layer 202 will change.
  • the material in the piezoelectric layer 202 will change.
  • a larger mechanical response will be generated, so that the resonator can obtain a higher electromechanical coupling coefficient, which can compensate for the decrease in the resonator electromechanical coupling coefficient caused by the addition of the temperature compensation layer.
  • the ratio of rare earth elements doped in the direction from the bottom electrode 203 to the top electrode 201 is getting lower and lower.
  • the plane on which the top electrode 201 is located is the upper plane
  • the plane on which the substrate 205 is located is the lower plane.
  • the ratio of rare earth elements doped in the piezoelectric layer 202 is getting lower from bottom to top. Therefore, the lower surface of the piezoelectric layer 202 has the greatest stress, so the temperature compensation layer 206 can be partially placed on the lower surface of the piezoelectric layer 202 to have the best temperature compensation effect, and at the same time can improve the film bulk acoustic resonance Q value of the device.
  • the fourth embodiment of the present invention relates to a thin film bulk acoustic resonator.
  • the top electrode has a bridge wing structure.
  • the top electrode 201 has a bridge wing structure 601.
  • the bridge wing structure 601 is correspondingly located inside the acoustic reflection structure 204.
  • the projection of the bridge wing structure 601 in the thickness direction is within the acoustic reflection structure 204 of the thin film bulk acoustic resonator.
  • the acoustic impedance in the air gap 602 does not match the acoustic impedance in the effective area of the thin film bulk acoustic resonator, which can further reduce the transverse mode of the thin film bulk acoustic resonator
  • the acoustic wave is reflected back into the thin film bulk acoustic resonator, and part of the acoustic wave energy is converted into a wave in a mode perpendicular to the resonator, so that the Q value of the thin film bulk acoustic resonator is further improved.
  • the thin film bulk acoustic resonator further includes a flat layer 603.
  • the material of the flat layer 603 may be silicon dioxide, silicon nitride, silicon carbide, or other suitable dielectric materials.
  • a flat layer 603 is located between the piezoelectric layer 202 and the substrate 205, and the flat layer 603 is located at one end of the bottom electrode 203 and is aligned with the end of the bottom electrode 203, thereby forming a flat and smooth surface It is helpful to deposit a good piezoelectric film at the connection between the bottom electrode 203 and the flat layer 603.
  • the fifth embodiment of the present invention relates to a thin film bulk acoustic resonator.
  • the top electrode has a bridge structure.
  • the top electrode 201 has a bridge structure 701. There is an air gap 602 between the center of the bridge structure 701 and the piezoelectric layer 202. Since the acoustic impedance in the air gap 602 under the bridge structure 701 does not match the acoustic impedance in the effective area of the thin film bulk acoustic resonator, it can further reflect the sound waves in the transverse mode of the thin film bulk acoustic resonator back into the resonator, and a part of it The energy of the acoustic wave is converted into a wave in a mode perpendicular to the resonator, so that the Q value of the thin film bulk acoustic resonator is further improved.
  • the thin film bulk acoustic resonator further includes a flat layer 603.
  • the material of the flat layer 603 may be silicon dioxide, silicon nitride, silicon carbide, or other suitable dielectric materials.
  • a flat layer 603 is located between the piezoelectric layer 202 and the substrate 205, and the flat layer 603 is located at one end of the bottom electrode 203 and is aligned with the end of the bottom electrode 203, thereby forming a flat and smooth surface It is helpful to deposit a good piezoelectric film at the connection between the bottom electrode 203 and the flat layer 603.
  • the sixth embodiment of the present invention relates to a thin film bulk acoustic resonator.
  • the top electrode has both a bridge wing structure and a bridge structure.
  • the top electrode 201 has a bridge wing structure 601 with an air gap 602 between the tail of the bridge wing structure 601 and the piezoelectric layer 202.
  • the bridge wing structure 601 is correspondingly located inside the acoustic reflection structure 204.
  • the projection of the bridge wing structure 601 in the thickness direction is within the acoustic reflection structure 204 of the thin film bulk acoustic resonator.
  • the acoustic impedance in the air gap 602 does not match the acoustic impedance in the effective area of the thin film bulk acoustic resonator, which can further reduce the transverse mode of the thin film bulk acoustic resonator
  • the sound is reflected back into the thin film bulk acoustic resonator, and part of the sound wave energy is converted into a wave in a mode perpendicular to the resonator, so that the Q value of the thin film bulk acoustic resonator is further improved.
  • the top electrode 201 has a bridge structure 701. There is an air gap 602 between the center of the bridge structure 701 and the piezoelectric layer 202. Since the acoustic impedance in the air gap 602 under the bridge structure 701 does not match the acoustic impedance in the effective area of the thin film bulk acoustic resonator, it can further reflect the sound of the transverse mode in the thin film bulk acoustic resonator back into the resonator, and a part of it The energy of the acoustic wave is converted into a wave in a mode perpendicular to the resonator, so that the Q value of the thin film bulk acoustic resonator is further improved.
  • the thin film bulk acoustic resonator further includes a flat layer 603.
  • the material of the flat layer 603 may be silicon dioxide, silicon nitride, silicon carbide, or other suitable dielectric materials.
  • a flat layer 603 is located between the piezoelectric layer 202 and the substrate 205, and the flat layer 603 is located at one end of the bottom electrode 203 and is aligned with the end of the bottom electrode 203, thereby forming a flat and smooth surface It is helpful to deposit a good piezoelectric film at the connection between the bottom electrode 203 and the flat layer 603.

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Abstract

一种薄膜体声波谐振器，包括位置关系依次相连的顶电极（201）、压电层（202）、底电极（203）、声反射结构（204）、基底（205）以及厚度大于预设值的温度补偿层（206）；其中，所述温度补偿层（206）还用于调节所述薄膜体声波谐振器的面积。使得薄膜体声波谐振器在具有较高机电耦合系数的同时，能够使其温度频率漂移系数保持不变，并且还可以使得薄膜体声波谐振器的面积增大。

Description

一种薄膜体声波谐振器 技术领域
本发明涉及通信领域，特别地涉及一种薄膜体声波谐振器。
背景技术
近年来随着无线通讯技术的不断发展，薄膜体声波谐振器在射频前端应用中的优势越来越明显，其中薄膜体声波谐振器是体声波器件的基本组成部分。该类型谐振器是一种基于压电技术的元器件，其尺寸极小，比单纯以电磁波为传播信号的元器件尺寸小4～5个数量级；插损小，Q值高(可达1000以上)(Q值即品质因数值)，工作频率高，可承受的功率容量比声表面波器件更大；并且可以与CMOS(CMOS为互补金属氧化物半导体的英文缩写)工艺兼容。鉴于以上优点薄膜体声波谐振器技术迅速占领了射频通信市场。同时，在传感器领域如生化检测等方面也有着广阔的应用前景。
薄膜体声波谐振器是一种利用声波谐振实现相同频率的电信号选频的谐振器，其核心部分是由顶电极-压电层-底电极三明治结构组成的，它一般工作在能陷-厚度振动模式。
薄膜体声波谐振器的压电层、金属或电介层的厚度以及其内的声速都随温度的变化而变化，因此压电声波谐振器的谐振频率也随温度的变化而变化。尽管各层随温度变化而产生的厚度膨胀或收缩会影响谐振频率，但各层内声波传播速度随温度的改变是影响压电声波谐振器谐振频率随温度改变的主要原因。目前应用在压电声波谐振器中的大部分材料都呈现出负的温度系数，即随温度的升高声速会变小，因为材料在较高温下会变“软化”(例如，跨原子力被减弱)。跨原子力的减小会导致材料弹性系数的减小，从而减小声速。由压电声波谐振器构成的射频(RF)滤波器通常有一个通带频率响应，压电声波谐振器的频率温度系数(TCF)会降低射频(RF)滤波器的制造良率， 因为由压电声波谐振器所构成的设备或器件只有在一定温度范围内才能满足通带带宽的要求。为了得到低的频率温度系数，一种常用的方法是在压电声波谐振器层叠结构中增加温度补偿层，具体可以是增加一层二氧化硅(SiO 2)温度补偿层材料。同时，在薄膜体声波谐振器的性能指标中，机电耦合系数(Kt)值是谐振器的一项重要参数，这项参数代表了谐振器转换机械能和电能的能力。为了提高谐振器的机电耦合系数，一种常用的方法为在压电材料中掺杂稀土元素。
但是，如图1所示(横轴为Sc的掺杂量，纵轴为温度频率漂移系数)，随着谐振器压电层中掺杂的稀土元素含量的增多(图1中的稀土元素为钪Sc)，会导致谐振器的温度频率漂移系数的恶化，同时也会伴随着谐振器面积的减小，而谐振器面积减小时会导致谐振器有效区域中泄露的能量增加，因而使其Q降低并且会导致谐振器中杂波的增多。
发明内容
有鉴于此，本发明提供一种薄膜体声波谐振器，使得薄膜体声波谐振器在具有较高机电耦合系数的同时，能够使其温度频率漂移系数保持不变，并且还可以使薄膜体声波谐振器的面积增大。
为解决上述技术问题，本发明的实施例提供了一种薄膜体声波谐振器，包括位置关系依次相连的顶电极、压电层、底电极、声反射结构、基底以及厚度大于预设值的温度补偿层；其中，所述温度补偿层还用于调节所述薄膜体声波谐振器的面积。
本发明中温度补偿层的厚度大于预设值，即通过增加温度补偿层的厚度，来弥补因压电层随掺杂稀土元素含量的增多而导致温度补偿层的温度频率漂移系数恶化的情形，最终能够使得薄膜体声波谐振器的温度频率漂移系数基本保持不变。由于在增加温度补偿层的厚度的同时，会导致薄膜体声波谐振器机电耦合系数的降低，结合背景技术的原理可知，当减小薄膜体声波谐振器的机电耦合系数时，会使得薄膜体声波谐振器的面积变大。从而可以减小薄膜体声波谐振器由于面积过小而导致的能量泄露，提高了薄膜体声波谐振器的Q值，同时能 够减小杂波的产生。即通过增加温度补偿层的厚度，能够使得薄膜体声波谐振器在具有较高机电耦合系数的同时，保持其温度频率漂移系数不变，并且还可以使得薄膜体声波谐振器的面积增大。
可选的，所述压电层掺杂有稀土元素。
可选的，所述稀土元素为以下任意一种或其任意组合：镧、铈、镨、钕、钷、钐、铕、钆、铽、镝、钬、铒、铥、镱、镥、钇以及钪。
可选的，所述温度补偿层位于所述压电层之中。
可选的，所述温度补偿层为两层；其中一层温度补偿层位于所述顶电极之中，另一层温度补偿层位于所述压电层之中。
可选的，所述温度补偿层为两层；其中一层温度补偿层位于所述底电极之中，另一层温度补偿层位于所述压电层之中。
可选的，所述压电层的其中一部分掺杂有稀土元素；所述温度补偿层位于掺杂有稀土元素的部分压电层中。
可选的，所述压电层在该压电层的厚度方向上掺杂不同比例的稀土元素。
可选的，由所述底电极至所述顶电极的方向上掺杂的稀土元素的比例越来越高。
可选的，由所述底电极至所述顶电极的方向上掺杂的稀土元素的比例越来越低。
可选的，所述顶电极具有桥翼结构，所述桥翼结构的尾部与所述压电层之间具有空气隙，并且所述桥翼结构对应位于所述声反射结构内部；和/或，所述顶电极具有桥部结构，且所述桥部结构的中心与所述压电层之间具有空气隙。
可选的，所述声反射结构为声学镜。
可选的，所述声学镜位于所述基底的上表面或嵌于所述基底的内部。
附图说明
附图用于更好地理解本发明，不构成对本发明的不当限定。其中：
图1是现有技术稀土元素的掺杂量与温度补偿系数的坐标图；
图2是第一实施方式中薄膜体声波谐振器的结构示意图；
图3是第二实施方式中薄膜体声波谐振器的结构示意图；
图4是第二实施方式中薄膜体声波谐振器的另一结构示意图；
图5是第二实施方式中薄膜体声波谐振器的另一结构示意图；
图6是第二实施方式中薄膜体声波谐振器的另一结构示意图；
图7是第二实施方式中薄膜体声波谐振器的另一结构示意图；
图8是第三实施方式中薄膜体声波谐振器的结构示意图；
图9是第四实施方式中薄膜体声波谐振器的结构示意图；
图10是第五实施方式中薄膜体声波谐振器的结构示意图；
图11是第六实施方式中薄膜体声波谐振器的结构示意图。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合附图对本发明的各实施例进行详细的阐述。然而，本领域的普通技术人员可以理解，在本发明各实施例中，为了使读者更好地理解本申请而提出了许多技术细节。但是，即使没有这些技术细节和基于以下各实施例的种种变化和修改，也可以实现本申请所要求保护的技术方案。
本发明的第一实施例涉及一种薄膜体声波谐振器。如图2所示，薄膜体声波谐振器包括位置关系依次相连的顶电极201、压电层202、底电极203、声反射结构204、基底205以及厚度大于预设值的温度补偿层206。其中，所述温度补偿层206用于调节所述薄膜体声波谐振器的面积。所述温度补偿层206位于所述压电层202之中。所述温度补偿层为两层，其材料可以相同也可以不同。其中，所述声反射结构204为声学镜。所述声学镜位于所述基底205的上表面或嵌于所述基底205的内部。在图2中声学镜为嵌入基底205中的空腔所构成，但是任何其它的声学镜结构如布拉格反射器也同样适用。
值得一提的是，顶电极201和底电极203的材料可以由金(Au)、钨(W)、钼(Mo)、铂(Pt)，钌(Ru)、铱(Ir)、钛钨(TiW)、铝(Al)、钛(Ti)等类似金属形成。
压电层202的材料可以为氮化铝(AlN)、氧化锌(ZnO)、锆钛酸铅(PZT)、铌酸锂(LiNbO 3)、石英(Quartz)、铌酸钾(KNbO 3)或钽酸锂(LiTaO 3)等。上述压电材料为压电薄膜，厚度小于10微米。氮化铝薄膜为多晶形态或者单晶形态，生长方式为薄膜溅射(sputtering)或者有机金属化学气相沉积法(MOCVD)。
温度补偿层206的材料可以为多晶硅、硼磷酸盐玻璃(BSG)、二氧化硅(SiO 2)、铬(Cr)或碲氧化物(TeO (x))。
优选的，所述压电层202掺杂有稀土元素。其中，所述稀土元素可以为以下任意一种或其任意组合：镧(La)、铈(Ce)、镨(Pr)、钕(Nd)、钷(Pm)、钐(Sm)、铕(Eu)、钆(Gd)、铽(Tb)、镝(Dy)、钬(Ho)、铒(Er)、铥(Tm)、镱(Yb)、镥(Lu)、钇(Y)以及钪(Sc)。所述稀土元素优选为钪，所述压电层材料优选为氮化铝。
本实施例中，对于特定的技术指标要求，振动频率f是固定的。而阻抗Z和f的关系由如下表达式确定：
Z＝d/(j2πfC)  (1)
其中，j是虚数单位。而C是谐振器的电容，可近似表示为：
C＝εA/d  (2)
其中，ε是压电材料的介电常数，A是谐振器的有效面积，d是谐振器声学结构的厚度。
而频率f和声波在压电材料中传播的速度v以及声学结构厚度之间又有如下关系：
f＝v/(2d)  (3)
将公式(2)和(3)式代入公式(1)中，可将Z表示成：
Z＝d*d/(jπvεA)  (4)
对于特定结构的滤波器而言，其滤波器中薄膜体声波谐振器的阻抗是固定值。实验表明当氮化铝结构的压电层202中掺入稀土元素(如钪)杂质时，声波在其中传播的速度将变慢。由于要求频率f保持不变，那么若通过掺杂使速度v变为原先的1/k时，相应的压电层202厚度也应变为原先的1/k才能保证(3)式仍然成立。同时，注意到(4)式右边的分子为d*d，因此分子变为原来的1/(k*k)。又由于要求Z也不 能发生变化，因此面积A也要相应的变为原来的1/k，才能保证(4)式仍然成立。那么结果是，通过对氮化铝结构的压电层202掺杂稀土元素，可使压电层202的厚度和面积均减小为原先的1/k。
但是当薄膜体声波谐振器的面积过小时，会导致薄膜体声波谐振器的周长面积比增大，从而薄膜体声波谐振器产生的横向模式的波在谐振器的边缘处反射回有效区域内的能量减少，导致薄膜体声波谐振器的Q值降低。同时当薄膜体声波谐振器的面积过小时，也会导致薄膜体声波谐振器边缘处横向模式的波被反射的路径变短，减弱了其相互间抵消作用，进而使得薄膜体声波谐振器中杂波增多。而且随着压电层202掺杂稀土元素的含量增加时，薄膜体声波谐振器温补层的温度频率漂移系数则会越来越差。
综上所述，由于在增加温度补偿层206厚度的同时，会导致薄膜体声波谐振器的机电耦合系数降低，结合背景技术的原理可知当减小薄膜体声波谐振器的机电耦合系数时，能够使得薄膜体声波谐振器的面积变大。从而可以减小薄膜体声波谐振器由于面积过小而导致的能量泄露，提高了薄膜体声波谐振器的Q值，同时能够减小杂波的产生。即通过增加温度补偿层206的厚度，能够使得薄膜体声波谐振器在具有较高的机电耦合系数的同时，能够保持温度频率漂移系数不变，并且还可以使得薄膜体声波谐振器的面积增大。值得一提的是，所述温度补偿层厚度调节之后，将所述谐振器的温度频率漂移系数设置为优于-30ppm/℃。并且所述谐振器的面积不小于1000μm 2。
本发明的第二实施例涉及一种薄膜体声波谐振器，本实施例中温度补偿层为两层。
如图3所示，所述温度补偿层206为两层。其中一层温度补偿层206位于所述顶电极201之中，另一层温度补偿层206位于所述压电层202之中。具体的，温度补偿层206为两层包括第一温补层2061，第二温补层2062。第一温补层2061位于所述顶电极201之中。第二温补层2062位于所述压电层202之中。由于温度补偿层206通常是由绝缘材料组成，所以当温度补偿层206位于两电极(顶电极201和底电极 203)与压电层202之间就作为一个串联电容，两电极之间的部分电压会落在温度补偿层206上，从而使得压电层202内的压降减小，压电层202内的电场强度也相应减小，因此对上述谐振器的机电耦合系数会产生影响。
当一部分温度补偿层206包裹在顶电极201之内后，由于在温度补偿层206的周围电极是相连接的，故在温度补偿层206周围的顶电极201中具有相同的电势，所以在包裹在顶电极201中的温度补偿层206中的电场强度接近为零。该谐振器顶电极201和底电极203之间落在压电层202之内的压降增大，使得该谐振器的机电耦合系数相比增大。
如图4所示，所述温度补偿层206为两层。其中一层温度补偿层206位于所述底电极203之中，另一层温度补偿层206位于所述压电层202之中。具体的，温度补偿层206为两层包括第三温补层2063，第四温补层2064。第三温补层2063位于所述压电层202之中。第四温补层2064位于所述底电极203之中。由于温度补偿层206通常是由绝缘材料组成，所以当温度补偿层206位于两电极(顶电极201和底电极203)与压电层202之间就作为一个串联电容，两电极之间的部分电压会落在温度补偿层206上，从而使得压电层202内的压降减小，压电层202内的电场强度也相应减小，因此对上述谐振器的机电耦合系数会产生影响。
当一部分温度补偿层206包裹在底电极203之内后，由于在温度补偿层206的周围电极是相连接的，故在温度补偿层206周围的底电极203中具有相同的电势，所以在包裹在底电极203中的温度补偿层206中的电场强度接近为零。该谐振器底电极203和底电极203之间落在压电层202之内的压降增大，使得该谐振器的机电耦合系数相比增大。
如图5所示，所述温度补偿层206为两层。其中一层温度补偿层2065位于所述顶电极201之中，另一层温度补偿层2066位于所述底电极203之中。或者，如图6所示，两层温度补偿层206都位于顶电极201之中。或者，如图7所示，其中两层温度补偿层都位于底电极203 之中。
本发明的第三实施例涉及一种薄膜体声波谐振器，本实施例中对压电层进行不对称掺杂稀土元素。
如图8所示，所述压电层202的其中一部分掺杂有稀土元素。所述温度补偿层206位于掺杂有稀土元素的部分压电层202中。图5中将压电层202的其中一部分如标注2021掺杂有稀土元素，压电层202的另一部分如标注2022不掺杂稀土元素。
通常情况下，在压电层202的其中一部分掺杂的稀土元素的原子半径通常比压电层202本身的原子半径大，故会引起压电层202的应力发生变化，而压电层202中只有其中一部分掺杂了稀土元素，所以掺杂了稀土元素的那部分压电层202的应力最大，从而在掺杂部分的压电层202中加入较薄的温度补偿层206就能起到最好的温补效果。而且可以通过改变压电层202中稀土元素的掺杂方式，来改变压电层202中的应力变化情况，进而可以灵活改变温度补偿层206所在的位置，可以使得薄膜体声波谐振器在设计时在不影响其它性能的同时，能够具有更强的灵活性。再者，由于掺入稀土元素后压电层202应力的变化，会导致压电层202材料中的电偶极子发生改变，当对压电层202施加一电场时，压电层202的材料中就会产生更大的机械响应，从而可以使得薄膜体声波谐振器获得更高的机电耦合系数，进而能够弥补由于加入温度补偿层206后所导致的薄膜体声波谐振器机电耦合系数降低的情况。
优选的，所述压电层202在该压电层202的厚度方向上掺杂不同比例的稀土元素。
比如，由所述底电极203至所述顶电极201的方向上掺杂的稀土元素的比例越来越高。具体地说，假设，以顶电极201所在平面为上平面，以基底205所在平面为下平面。压电层202中掺杂的稀土元素的比例从下至上越来越高。故，在压电层202的上表面具有最大的应力，因此可以将温度补偿层206部分放在压电层202的上表面，就能起到最好的温补效果，同时可以提高薄膜体声波谐振器的Q值。而且 由于掺入稀土元素后压电层202材料中应力的变化，会导致压电层202材料中的电偶极子发生改变，当对压电材料施加一电场时，压电层202材料中就会产生更大的机械响应，从而可以使得谐振器获得更高的机电耦合系数，进而能够弥补由于加入温补层后所导致的谐振器机电耦合系数的降低。
或者，由所述底电极203至所述顶电极201的方向上掺杂的稀土元素的比例越来越低。具体地说，假设，以顶电极201所在平面为上平面，以基底205所在平面为下平面。压电层202中掺杂的稀土元素的比例从下至上越来低。故，在压电层202的下表面具有最大的应力，因此可以将温度补偿层206部分放在压电层202的下表面就能起到最好的温补效果，同时可以提高薄膜体声波谐振器的Q值。
本发明的第四实施例涉及一种薄膜体声波谐振器，本实施例中顶电极具有桥翼结构。
如图9所示，所述顶电极201具有桥翼结构601。所述桥翼结构601的尾部与所述压电层202之间具有空气隙602，并且所述桥翼结构601对应位于所述声反射结构204内部。具体地说，结合图6所示的方向，所述桥翼结构601在厚度方向上的投影位于薄膜体声波谐振器的声反射结构204以内。由于桥翼结构601与压电层202之间具有空气隙602，空气隙602中的声阻抗与薄膜体声波谐振器有效区域中的声阻抗不匹配，能够进一步将薄膜体声波谐振器中横向模式的声波反射回薄膜体声波谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得薄膜体声波谐振器的Q值进一步提高。而通过增加温度补偿层206的厚度，使得在薄膜体声波谐振器压电层掺杂稀土元素含量增多时，具有较高机电耦合系数的同时，使其温度频率漂移系数不变，同时使得薄膜体声波谐振器的面积不至于过小。优选的，薄膜体声波谐振器还包括平坦层603。平坦层603的材料可以为二氧化硅、氮化硅、碳化硅等合适的介质材料。平坦层603位于所述压电层202和所述基底205之间，且所述平坦层603位于所述底电极203的其中一端且与所述底电极203的末端对齐，从而形成平整光滑的表面，有助 于在底电极203与平坦层603的连接处沉积良好的压电薄膜。
本发明的第五实施例涉及一种薄膜体声波谐振器，本实施例中顶电极具有桥部结构。
如图10所示，所述顶电极201具有桥部结构701。所述桥部结构701的中心与所述压电层202之间具有空气隙602。由于桥部结构701下空气隙602中的声阻抗与薄膜体声波谐振器有效区域中的声阻抗不匹配，能够进一步将薄膜体声波谐振器中横向模式的声波反射回谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得薄膜体声波谐振器的Q值进一步提高。而通过增加温度补偿层206的厚度，使得在薄膜体声波谐振器压电层掺杂稀土元素含量增多时，具有较高机电耦合系数的同时，使其温度频率漂移系数不变，同时使得薄膜体声波谐振器的面积不至于过小。优选的，薄膜体声波谐振器还包括平坦层603。平坦层603的材料可以为二氧化硅、氮化硅、碳化硅等合适的介质材料。平坦层603位于所述压电层202和所述基底205之间，且所述平坦层603位于所述底电极203的其中一端且与所述底电极203的末端对齐，从而形成平整光滑的表面，有助于在底电极203与平坦层603的连接处沉积良好的压电薄膜。
本发明的第六实施例涉及一种薄膜体声波谐振器，本实施例中所述顶电极既具有桥翼结构又具有桥部结构。
如图11所示，所述顶电极201具有桥翼结构601，所述桥翼结构601的尾部与所述压电层202之间具有空气隙602。并且所述桥翼结构601对应位于所述声反射结构204内部。具体地说，结合图6所示的方向，所述桥翼结构601在厚度方向上的投影位于薄膜体声波谐振器的声反射结构204以内。由于桥翼结构601与压电层202之间具有空气隙602，空气隙602中的声阻抗与薄膜体声波谐振器有效区域中的声阻抗不匹配，能够进一步将薄膜体声波谐振器中横向模式的声反射回薄膜体声波谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得薄膜体声波谐振器的Q值进一步提高。
所述顶电极201具有桥部结构701。所述桥部结构701的中心与所述压电层202之间具有空气隙602。由于桥部结构701下空气隙602中的声阻抗与薄膜体声波谐振器有效区域中的声阻抗不匹配，能够进一步将薄膜体声波谐振器中横向模式的声反射回谐振器内，并有一部分声波能量转成与谐振器垂直模式的波，从而使得薄膜体声波谐振器的Q值进一步提高。
优选的，薄膜体声波谐振器还包括平坦层603。平坦层603的材料可以为二氧化硅、氮化硅、碳化硅等合适的介质材料。平坦层603位于所述压电层202和所述基底205之间，且所述平坦层603位于所述底电极203的其中一端且与所述底电极203的末端对齐，从而形成平整光滑的表面，有助于在底电极203与平坦层603的连接处沉积良好的压电薄膜。
上述具体实施方式，并不构成对本发明保护范围的限制。本领域技术人员应该明白的是，取决于设计要求和其他因素，可以发生各种各样的修改、组合、子组合和替代。任何在本发明的精神和原则之内所作的修改、等同替换和改进等，均应包含在本发明保护范围之内。

Claims (19)

  1. 一种薄膜体声波谐振器，其特征在于，包括位置关系依次相连的顶电极、压电层、底电极、声反射结构、基底以及厚度大于预设值的温度补偿层；其中，所述温度补偿层还用于调节所述薄膜体声波谐振器的面积。
  2. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述压电层掺杂有稀土元素。
  3. 根据权利要求2所述的谐振器，其特征在于，所述压电层的材料成分为氮化铝，所述氮化铝中掺杂稀土元素。
  4. 根据权利要求2所述的薄膜体声波谐振器，其特征在于，所述稀土元素为以下任意一种或其任意组合：
    镧、铈、镨、钕、钷、钐、铕、钆、铽、镝、钬、铒、铥、镱、镥、钇以及钪。
  5. 根据权利要求1至4中任意一项所述的薄膜体声波谐振器，其特征在于，所述温度补偿层位于所述压电层之中。
    其中，所述温度补偿层为两层，两层所述温度补偿层的材料相同或不同。
  6. 根据权利要求1至4中任意一项所述的薄膜体声波谐振器，其特征在于，所述温度补偿层为两层；
    其中一层温度补偿层位于所述顶电极之中，另一层温度补偿层位于所述压电层之中。
  7. 根据权利要求1至4中任意一项所述的薄膜体声波谐振器，其特征在于，所述温度补偿层为两层；
    其中一层温度补偿层位于所述底电极之中，另一层温度补偿层位于所述压电层之中。
  8. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述压电层的其中一部分掺杂有稀土元素；
    所述温度补偿层位于掺杂有稀土元素的部分压电层中。
  9. 根据权利要求8所述的薄膜体声波谐振器，其特征在于，所述压电层在该压电层的厚度方向上掺杂不同比例的稀土元素。
  10. 根据权利要求9所述的薄膜体声波谐振器，其特征在于，由所述底电极至所述顶电极的方向上掺杂的稀土元素的比例越来越高。
  11. 根据权利要求9所述的薄膜体声波谐振器，其特征在于，由所述底电极至所述顶电极的方向上掺杂的稀土元素的比例越来越低。
  12. 根据权利要求1至4中任意一项所述的薄膜体声波谐振器，其特征在于，所述温度补偿层为两层；
    其中一层所述温度补偿层位于所述底电极之中，另一层所述温度补偿层位于所述顶电极之中。
  13. 根据权利要求1至4中任意一项所述的薄膜体声波谐振器，其特征在于，所述温度补偿层为两层；
    两层所述温度补偿层都位于所述顶电极之中或者所述底电极之中。
  14. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述温度补偿层厚度调节之后，将所述谐振器的温度频率漂移系数设置为优于-30ppm/℃。
  15. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述 谐振器的面积不小于1000μm 2。
  16. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述温度补偿层的材料为：多晶硅、硼磷酸盐玻璃(BSG)、二氧化硅(SiO 2)、铬(Cr)或碲氧化物(TeO (x))。
  17. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述顶电极具有桥翼结构，所述桥翼结构的尾部与所述压电层之间具有空气隙，并且所述桥翼结构对应位于所述声反射结构内部；
    和/或，所述顶电极具有桥部结构，所述桥部结构的中心与所述压电层之间具有空气隙。
  18. 根据权利要求1所述的薄膜体声波谐振器，其特征在于，所述声反射结构为声学镜。
  19. 根据权利要求18所述的薄膜体声波谐振器，其特征在于，所述声学镜位于所述基底的上表面或嵌于所述基底的内部。
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