WO2016192359A1 - 一种mems麦克风元件及其制造方法 - Google Patents

一种mems麦克风元件及其制造方法 Download PDF

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Publication number
WO2016192359A1
WO2016192359A1 PCT/CN2015/096915 CN2015096915W WO2016192359A1 WO 2016192359 A1 WO2016192359 A1 WO 2016192359A1 CN 2015096915 W CN2015096915 W CN 2015096915W WO 2016192359 A1 WO2016192359 A1 WO 2016192359A1
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Prior art keywords
capacitor
plate
back plate
diaphragm
mems microphone
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PCT/CN2015/096915
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English (en)
French (fr)
Inventor
郑国光
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Goertek Inc
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Goertek Inc
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Priority to US15/554,942 priority Critical patent/US20180041842A1/en
Publication of WO2016192359A1 publication Critical patent/WO2016192359A1/zh
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/04—Microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/005—Electrostatic transducers using semiconductor materials
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
    • H04R31/003—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor for diaphragms or their outer suspension
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
    • H04R7/04—Plane diaphragms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/16—Mounting or tensioning of diaphragms or cones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R2201/00—Details of transducers, loudspeakers or microphones covered by H04R1/00 but not provided for in any of its subgroups
    • H04R2201/003—Mems transducers or their use
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R2410/00—Microphones
    • H04R2410/01—Noise reduction using microphones having different directional characteristics
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers
    • H04R3/005—Circuits for transducers for combining the signals of two or more microphones

Definitions

  • the present invention relates to a microphone, and more particularly to a differential capacitive MEMS microphone component and a method of fabricating the same.
  • MEMS microphone is a kind of acoustic and electrical transducer made by micromachining technology, which has the characteristics of small volume, good frequency response and low noise. With the development of compact and thin electronic devices, MEMS microphones are increasingly being used on these devices.
  • the MEMS microphone product includes a MEMS chip based on capacitance detection and an ASIC chip.
  • the capacitance of the MEMS chip changes correspondingly with the input sound signal, and then the ASIC chip is used to process and output the changed capacitance signal.
  • a MEMS chip generally includes a substrate having a back cavity, a parallel plate capacitor composed of a back plate and a diaphragm disposed above the substrate, the diaphragm receiving an external sound signal and vibrating, thereby causing the parallel plate capacitor to generate a varying electrical signal. , to achieve the sound-electric conversion function.
  • the problem with the above technical solution is that the single capacitor detection cannot filter out the external interference signal, affect the noise level of the output signal, and reduce the signal to noise ratio.
  • the MEMS microphone is to be designed as a traditional differential capacitance detection, a three-layer film structure is adopted, the upper and lower layers are used as the back plate, the middle layer is used as the diaphragm, and the diaphragm forms capacitance with the back plate of the upper and lower layers, respectively.
  • Two capacitors form a differential capacitor.
  • a MEMS microphone element includes: a substrate having a first opening and a second opening penetrating up and down; and a first capacitor juxtaposed above the substrate And a second capacitor, the first capacitor is disposed above the first opening, the second capacitor is disposed above the second opening; the first capacitor includes a first back pole located below a first diaphragm corresponding to the first back plate, the second capacitor includes a second back plate located above and a second diaphragm opposite to the second back plate; The first capacitor and the second capacitor together form a differential capacitor.
  • the materials of the first diaphragm and the second back plate are the same, and the materials of the first back plate and the second diaphragm are the same.
  • the first diaphragm and the second diaphragm are electrically connected together as a common movable plate of the differential capacitor.
  • the sensing portions of the first back plate and the second back plate are respectively provided with a plurality of through holes, and the central positions of the first diaphragm and the second diaphragm are respectively provided with through holes.
  • the first backing plate, the first diaphragm, the second backing plate and the second diaphragm are formed by any one of the following materials: polysilicon, additional polysilicon layer on silicon nitride, additional metal on silicon nitride Floor.
  • the MEMS microphone element is adapted for use in two product configurations in which a sound signal enters above or below the MEMS microphone element.
  • a method of fabricating a MEMS microphone element comprising the steps of: S1, providing a substrate; S2, growing a first isolation layer on the substrate; S3, at the first isolation layer Growing a first plate material layer; patterning and etching the first plate material layer to form a first capacitor back plate, a second capacitor movable plate, and a first capacitor isolation back plate and a first isolation trench of the movable plate of the second capacitor; S4, depositing a second isolation layer on the first plate material layer; and opening a connection window on the second isolation layer above the movable plate of the second capacitor a movable plate that connects the movable plate of the first capacitor and the second capacitor; S5, a second plate material layer is grown on the second isolation layer; and the second plate material layer is patterned and etched to form the first a movable plate of the capacitor, a back plate of the second capacitor, and a movable plate and a second capacitor separating the first capacitor An isolation trench of the back
  • step S3 a plurality of through holes are formed in the back plate of the first capacitor and a through hole is formed in a central position of the movable plate of the second capacitor; in step S5, on the back of the second capacitor A plurality of through holes are formed in the electrode plate, and a through hole is formed at a center position of the movable plate of the first capacitor.
  • the thickness of the back plate of the first capacitor is greater than the thickness of the movable plate, and the thickness of the back plate of the second capacitor is greater than the thickness of the movable plate.
  • the MEMS microphone element is adapted for use in two product configurations in which a sound signal enters above or below the MEMS microphone element.
  • the differential capacitive MEMS microphone of the present invention designs a pair of differential capacitors side by side, and realizes differential detection through two layers of films.
  • the present invention has the following beneficial effects:
  • the manufacturing process is simple and easy to control. The process is fully compatible with current single-capacitance MEMS microphone processes and does not require process variations.
  • the inventors of the present invention have found that in the prior art, there is no single-chip differential capacitance MEMS microphone having a two-layer film structure, and therefore the present invention is a new technical solution.
  • 1-2 is a schematic structural view of an embodiment of a MEMS microphone of the present invention.
  • 3-4 are schematic diagrams showing the principle of differential detection of the MEMS microphone of the present invention.
  • 5-14 are schematic structural views of various stages of the manufacturing process of the MEMS microphone of the present invention.
  • this patent proposes a novel differential capacitive MEMS microphone.
  • a pair of differential capacitors are designed side by side, which is realized by two layers of film, which reduces the process difficulty.
  • the basic structure of the present invention includes a substrate 1 including a substrate 100 and a first isolation layer 200 over the substrate 100.
  • the base 1 is provided with a first opening 101 penetrating vertically and a second opening 102 penetrating vertically.
  • the first capacitor C1 and the second capacitor C2 are disposed in parallel above the substrate 1.
  • the first capacitor C1 is disposed above the first opening 101, and the second capacitor C2 is disposed above the second opening 102.
  • the first capacitor C1 includes a first back plate 12 located below, and a first diaphragm 11 located above the first back plate 12, and a second capacitor C2 including a second back plate 22 located above and located
  • the second diaphragm 21 opposite to the second back plate 22 is disposed below.
  • a second isolation layer 400 is disposed between the first back plate 12 and the first diaphragm 11 and between the second back plate 22 and the second diaphragm 21 to be in the first back plate 12 and the first vibration
  • a gap 109 is formed between the films 11 and between the second back plate 22 and the second diaphragm 21.
  • the first back plate 12 and the second back plate 22 are fixed plates, and the first diaphragm 11 and the second diaphragm 21 are movable plates.
  • the first capacitor C1 and the second capacitor C2 form a pair of differential capacitors, and the first diaphragm 11 and the second diaphragm 21 are electrically connected together as a common movable plate of the differential capacitor, the first back plate 12 and the second vibration
  • the membranes 21 are separated by an insulating layer 106, and the first diaphragm 11 and the second backing plate 22 are separated by an isolation groove 108.
  • the sensing portions of the first backing plate 12 and the second backing plate 22 are respectively provided with a plurality of through holes 104, and the central positions of the first diaphragm 11 and the second diaphragm 21 are respectively provided with through holes 103, through holes 103 and 104 together function to conduct sound and balance sound pressure.
  • the materials of the first diaphragm 11 and the second back plate 22 are the same, and the materials of the first back plate 12 and the second diaphragm 21 are the same.
  • the thickness of the back plate 12 of the first capacitor C1 may be equal to or greater than the thickness of the movable plate 11, and the thickness of the back plate 22 of the second capacitor C2 may be equal to or greater than the thickness of the movable plate 21.
  • the first back plate 12, the first diaphragm 11, the second back plate 22, and the second diaphragm 21 are formed of any one of the following materials: polysilicon, additional polysilicon layer on silicon nitride, and silicon nitride Metal layer.
  • the material of the first isolation layer 200 is, for example, silicon oxide.
  • the second isolation layer 400 may be, for example, an oxide layer, and the insulating layer 106 may be a part of the second isolation layer 400.
  • the MEMS microphone component is suitable for the TOP product structure in which the sound signal enters from above the MEMS microphone component, and also applies to the BOTTOM product structure entered below the sound signal.
  • the present invention provides two MEMS structures within a single chip.
  • the diaphragm 11 of the first capacitor C1 is on the top
  • the back plate 12 is on the bottom
  • the diaphragm 21 of the second capacitor C2 is on the bottom
  • the back plate 22 is on the top.
  • the back plate 12 of the first capacitor C1 and the diaphragm 21 of the second capacitor C2 are simultaneously fabricated, and are made of the same material, for example, polysilicon, or a material of an additional metal layer of silicon nitride; the vibration of the first capacitor C1
  • the back plates 22 of the film 11 and the second capacitor C2 are simultaneously formed, and are also made of the same material, for example, all of polysilicon.
  • the diaphragm 21 of the first capacitor C1 and the diaphragm 21 of the second capacitor C2 are formed by the first plate material layer 300, and the diaphragm 11 of the first capacitor C1 and the back plate 22 of the second capacitor C2 are Formed by the second plate material layer 500,
  • the invention electrically connects the diaphragm of the first capacitor C1 and the diaphragm of the second capacitor C2 by a special process design as a common movable plate of the differential capacitor.
  • the first diaphragm 11 moves downward, causing the spacing between the first diaphragm 11 and the first back plate 12 to decrease, and the first capacitance C1 to increase;
  • the second diaphragm 21 also moves downward, causing the spacing between the second diaphragm 21 and the second backing plate 22 to increase, and the second capacitance C2 to decrease.
  • the first diaphragm 11 moves upward, causing the spacing between the first diaphragm 11 and the first backing plate 12 to increase, and the first capacitor C1 is decreased;
  • the film 21 also moves upward, causing the spacing between the second diaphragm 21 and the second backing plate 22 to decrease, and the second capacitance C2 to increase.
  • the differential design of the present invention is advantageous for filtering electromagnetic noise and noise interference, and improving the signal-to-noise ratio and sound quality of the output signal.
  • a first isolation layer 200 is grown on the substrate 100, and the first isolation layer 200 is, for example, silicon oxide;
  • a first plate material layer 300 is grown on the first isolation layer 200, and the first plate material layer 300 is, for example, polysilicon;
  • the first plate material layer 300 is patterned and etched to form the back plate 12 of the first capacitor C1, the movable plate 21 of the second capacitor C2, and the first capacitor C1 is isolated.
  • a through hole 103 is defined in a central position of the movable plate 21 of the second capacitor C2;
  • a second isolation layer 400 is deposited on the first plate material layer 300, and the second isolation layer 400 is, for example, an oxide;
  • connection window 107 is formed on the second isolation layer 400 above the movable plate 21 of the second capacitor C2 for connecting the movable plate 11 and the second capacitor C2 of the first capacitor C1. Movable plate 21;
  • the second plate material layer 500 is directly grown on the second isolation layer 400,
  • the second plate material layer 500 is, for example, polysilicon;
  • the second plate material layer 500 is patterned and etched to form the movable plate 11 of the first capacitor C1, the back plate 22 of the second capacitor C2, and the isolated first capacitor C1.
  • the substrate 100 is etched from below by a DRIE process (Deep Reactive Ion Etching) to form a back cavity of the first MEMS structure and the second MME structure.
  • DRIE process Deep Reactive Ion Etching
  • the entire device is processed by a two-step release process release structure.
  • the first isolation layer 200 and the second isolation layer 400 of the first MEMS structure and the first isolation layer 200 of the second MEMS structure are first etched from the bottom.
  • the first capacitor C1 is A first opening 101 is formed below and a second opening 102 is formed below the second capacitor C2, and a gap 109 is formed between the back plate 12 of the first capacitor C1 and the diaphragm 11.
  • a second isolation layer 400 of the second MEMS structure is then etched from the top to form a gap 109 between the back plate 22 of the second capacitor C2 and the diaphragm 21.
  • the process flow is only an exemplary process. If necessary, the thickness of the back plate of the first capacitor C1 and the second capacitor C2 can be made larger than that of the first capacitor C1 and the second capacitor C2. The thickness is thicker.
  • the differential capacitive MEMS microphone of the present invention designs a pair of differential capacitors side by side, and realizes differential detection through two layers of films.
  • the present invention has the following beneficial effects:
  • the manufacturing process is simple and easy to control. The process is fully compatible with current single-capacitance MEMS microphone processes and does not require process variations.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Multimedia (AREA)
  • Manufacturing & Machinery (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
  • Pressure Sensors (AREA)

Abstract

本发明公开了一种MEMS麦克风元件，包括：基底，基底上设置有上下贯通的第一开孔和第二开孔；并列设置于基底上方的第一电容和第二电容，第一电容设置在第一开孔之上，第二电容设置在第二开孔之上；第一电容包括位于下方的第一背极板以及位于上方的与第一背极板相对的第一振膜，第二电容包括位于上方的第二背极板以及位于下方的与第二背极板相对的第二振膜；第一电容和第二电容构成一对差分电容。本发明实现了差分电容式MEMS麦克风，有利于滤除外界电磁和噪声干扰，提高输出信号的信噪比和收音质量。本发明还公开了一种制造MEMS麦克风元件的方法。

Description

一种MEMS麦克风元件及其制造方法 技术领域
本发明涉及一种麦克风，尤其涉及一种差分电容式MEMS麦克风元件及其制造方法。
背景技术
MEMS麦克风是一种用微机械加工技术制作出来的声电换能器，其具有体积小、频响特性好、噪声低等特点。随着电子设备的小巧化、薄型化发展，MEMS麦克风被越来越广泛地运用到这些设备上。
目前MEMS麦克风产品中包含一个基于电容检测的MEMS芯片和一个ASIC芯片，MEMS芯片的电容会随着输入声音信号的不同产生相应的变化，再利用ASIC芯片对变化的电容信号进行处理和输出从而实现对声音的拾取。MEMS芯片通常包括具有背腔的基底、在基底上方设置的由背极板和振膜构成的平行板电容器，振膜接收外界的声音信号并发生振动，从而使平行板电容器产生一个变化的电信号，实现声-电转换功能。
上述技术方案的问题在于，单个电容检测对外界的干扰信号无法滤除，影响输出信号的噪声水平，降低信噪比。
如果要将MEMS麦克风设计成传统的差分式电容检测，采用三层膜的结构，上下两层膜作为背极板，中间层作为振膜，振膜分别与上下层的背极板形成电容，这两个电容组成差分电容。在有声波作用在中间位置上的振膜时，振膜上下振动，进而差分电容中的一个增加，另一个减小，从而实现声波的差分检测。但这种方案的问题在于，工艺比较复杂，且很难控制上下背极板到振膜的间距相同，所以差分电容的静态电容和灵敏度都很难一致，削弱了差分的效果，与最初的目的相背离。
发明内容
本发明的目的是提供一种性能良好的差分电容式MEMS麦克风元件。
根据本发明的第一方面，提供了一种MEMS麦克风元件，包括：基底，所述基底上设置有上下贯通的第一开孔和第二开孔；并列设置于所述基底上方的第一电容和第二电容，所述第一电容设置在所述第一开孔之上，所述第二电容设置在所述第二开孔之上；所述第一电容包括位于下方的第一背极板以及位于上方的与第一背极板相对的第一振膜，所述第二电容包括位于上方的第二背极板以及位于下方的与第二背极板相对的第二振膜；所述第一电容和第二电容共同构成差分电容。
优选的，所述第一振膜和第二背极板的材质相同，所述第一背极板和第二振膜的材质相同。
优选的，所述第一振膜和第二振膜电连接在一起作为所述差分电容的公共可动极板。
优选的，所述第一背极板以及第二背极板的感应部分分别设置有多个通孔，所述第一振膜以及第二振膜的中心位置分别设置有通孔。
优选的，所述第一背极板、第一振膜、第二背极板以及第二振膜由下列材料任意之一形成：多晶硅、氮化硅上附加多晶硅层、氮化硅上附加金属层。
优选的，所述MEMS麦克风元件适用于声音信号从MEMS麦克风元件上方或者下方进入的两种产品结构。
根据本发明的第二方面，提供了一种制造MEMS麦克风元件的方法，包括如下步骤：S1、提供衬底；S2、在所述衬底上生长第一隔离层；S3、在第一隔离层生长第一极板材料层；对第一极板材料层进行构图和刻蚀以形成第一电容的背极板、第二电容的可动极板，以及隔离第一电容的背极板和第二电容的可动极板的第一隔离槽；S4、在第一极板材料层上沉积第二隔离层；在第二电容的可动极板上方的第二隔离层上开设连接窗口，用以连接第一电容的可动极板和第二电容的可动极板；S5、在第二隔离层生长第二极板材料层；对第二极板材料层进行构图和刻蚀以形成第一电容的可动极板、第二电容的背极板、以及隔离第一电容的可动极板和第二电容 的背极板的隔离槽；S6、刻蚀衬底和第一隔离层以在第一电容的下方形成贯通的第一开孔以及在第二电容下方形成贯通的第二开孔；以及刻蚀第二隔离层以在第一、第二电容、各自的背极板和可动极板之间形成间隙。
优选的，在步骤S3中，在第一电容的背极板上开设多个通孔以及在第二电容的可动极板的中心位置开设通孔；在步骤S5中，在第二电容的背极板上开设多个通孔以及第一电容的可动极板的中心位置开设通孔。
优选的，第一电容的背极板的厚度大于其可动极板的厚度，第二电容的背极板的厚度大于其可动极板的厚度。
优选的，所述MEMS麦克风元件适用于声音信号从MEMS麦克风元件上方或者下方进入的两种产品结构。
本发明的差分电容式MEMS麦克风，将一对差分电容并排设计，通过两层膜来实现差分检测，本发明具有以下有益效果：
1.实现差分电容式MEMS麦克风，有利于滤除外界电磁和噪声干扰，提高输出信号的信噪比和收音质量。
2.由于差分电容的背极板和可动极板之间的间隙是在同一步骤完成的，差分电容的间距可以做到完全一致，提高了差分的效果。
3.制造工艺流程简单并且容易控制。工艺流程与目前的单电容式MEMS麦克风的工艺完全兼容，不需要做出工艺的变动。
本发明的发明人发现，在现有技术中，还没有双层膜结构的单芯片差分电容式MEMS麦克风，因此本发明是一种新的技术方案。
通过以下参照附图对本发明的示例性实施例的详细描述，本发明的其它特征及其优点将会变得清楚。
附图说明
被结合在说明书中并构成说明书的一部分的附图示出了本发明的实施例，并且连同其说明一起用于解释本发明的原理。
图1-2是本发明MEMS麦克风实施例的结构示意图。
图3-4是本发明MEMS麦克风的差分检测的原理示意图。
图5-14是本发明MEMS麦克风的制造过程的各个阶段的结构示意图。
具体实施方式
现在将参照附图来详细描述本发明的各种示例性实施例。应注意到：除非另外具体说明，否则在这些实施例中阐述的部件和步骤的相对布置、数字表达式和数值不限制本发明的范围。
以下对至少一个示例性实施例的描述实际上仅仅是说明性的，决不作为对本发明及其应用或使用的任何限制。
对于相关领域普通技术人员已知的技术、方法和设备可能不作详细讨论，但在适当情况下，技术、方法和设备应当被视为说明书的一部分。
在这里示出和讨论的所有例子中，任何具体值应被解释为仅仅是示例性的，而不是作为限制。因此，示例性实施例的其它例子可以具有不同的值。
应注意到：相似的标号和字母在下面的附图中表示类似项，因此，一旦某一项在一个附图中被定义，则在随后的附图中不需要对其进行进一步讨论。
针对以上提出的问题，本专利提出一种新型的差分电容式MEMS麦克风。将一对差分电容并排设计，通过两层膜来实现，降低了工艺难度。
参考图1-2所示为本发明的基本结构，包括：基底1，基底1包括衬底100和位于衬底100上方的第一隔离层200。基底1上设置有上下贯通的第一开孔101和上下贯通的第二开孔102。并列设置于基底1上方的第一电容C1和第二电容C2，第一电容C1设置在第一开孔101之上，第二电容C2设置在第二开孔102之上。第一电容C1包括位于下方的第一背极板12、以及位于上方的与第一背极板12相对的第一振膜11，第二电容C2包括位于上方的第二背极板22以及位于下方的与第二背极板22相对的第二振膜21。第一背极板12和第一振膜11之间、第二背极板22和第二振膜21之间分别设置有第二隔离层400，以在第一背极板12和第一振膜11之间、第二背极板22和第二振膜21之间形成间隙109。
第一背极板12和第二背极板22为固定极板，第一振膜11和第二振膜21为可动极板。
第一电容C1和第二电容C2构成一对差分电容，第一振膜11和第二振膜21电连接在一起作为差分电容的公共可动极板，第一背极板12和第二振膜21之间通过绝缘层106隔离开，第一振膜11和第二背极板22之间通过隔离槽108隔离开。
其中，第一背极板12以及第二背极板22的感应部分分别设置有多个通孔104，第一振膜11以及第二振膜21的中心位置分别设置有通孔103，通孔103和104共同起到传导声音及平衡声压的作用。
其中，第一振膜11和第二背极板22的材质相同，第一背极板12和第二振膜21的材质相同。其中，第一电容C1的背极板12的厚度可以等于或者大于可动极板11的厚度，第二电容C2的背极板22的厚度可以等于或者大于可动极板21的厚度。
其中，第一背极板12、第一振膜11、第二背极板22以及第二振膜21由下列材料任意之一形成：多晶硅、氮化硅上附加多晶硅层、氮化硅上附加金属层。第一隔离层200的材质例如为氧化硅。第二隔离层400例如可以为氧化物层，绝缘层106可以是第2隔离层400的一部分。
从图1中可以看出，MEMS麦克风元件适用于声音信号从MEMS麦克风元件上方进入的TOP产品结构，也适用于声音信号下方进入的BOTTOM产品结构。
从图1-2中可以看出，本发明在单个芯片内设置有两个MEMS结构。第一电容C1的振膜11在上，背极板12在下；第二电容C2的振膜21在下，背极板22在上。第一电容C1的背极板12和第二电容C2的振膜21是同时制作的，为同样材质，例如都为多晶硅，或者都为氮化硅附加金属层的材质；第一电容C1的振膜11和第二电容C2的背极板22是同时制作的，也为同样材质，例如都为多晶硅。第一电容C1的背极板12和第二电容C2的振膜21是由第一极板材料层300形成的，第一电容C1的振膜11和第二电容C2的背极板22是由第二极板材料层500形成的，
本发明通过特殊的工艺设计，将第一电容C1的振膜和第二电容C2的振膜电连接在一起，作为差分电容的公共可动极板。在有声波作用时，第一电容C1增加则第二电容C2就会减小，第一电容C1减小则第二电容 C2增加。具体来说，在没有声波作用时，C1＝C2＝C0。当声波从声孔进入到麦克风内部时：
如果声压向下作用，参考图3所示，第一振膜11向下运动，导致第一振膜11和第一背极板12之间的间距减小，第一电容C1增大；第二振膜21也向下运动，导致第二振膜21和第二背极板22之间的间距增大，第二电容C2减小。从而第一电容C1>C0>第二电容C2。
如果声压向上作用，参考图4所示，第一振膜11向上运动，导致第一振膜11和第一背极板12之间的间距增大，第一电容C1减小；第二振膜21也向上运动，导致第二振膜21和第二背极板22之间的间距减小，第二电容C2增大。从而第一电容C1<C0<第二电容C2。
本发明这样的差分设计有利于滤除外界电磁和噪声干扰，提高输出信号的信噪比和收音质量。
下面参考图5-14介绍本发明MEMS麦克风的制造方法：
1)参考图5所示，提供衬底100；
2)参考图6所示，在衬底100上生长第一隔离层200，第一隔离层200例如选用氧化硅；
3)参考图7所示，在第一隔离层200生长第一极板材料层300，第一极板材料层300例如选用多晶硅；
4)参考图8所示，对第一极板材料层300进行构图和刻蚀以形成第一电容C1的背极板12、第二电容C2的可动极板21，以及隔离第一电容C1的背极板12和第二电容C2的可动极板21的第一隔离槽105；从图8中可以看出，在第一电容C1的背极板12上开设有多个通孔104以及在第二电容C2的可动极板21的中心位置开设有通孔103；
5)参考图9所示，在第一极板材料层300上沉积第二隔离层400，第二隔离层400例如选用氧化物；
6)参考图10所示，在第二电容C2的可动极板21上方的第二隔离层400上开设连接窗口107，用以连接第一电容C1的可动极板11和第二电容C2的可动极板21；
7)参考图11所示，在第二隔离层400直接生长第二极板材料层500， 第二极板材料层500例如选用多晶硅；
8)参考图12所示，对第二极板材料层500进行构图和刻蚀以形成第一电容C1的可动极板11、第二电容C2的背极板22、以及隔离第一电容C1的可动极板11和第二电容C2的背极板22的隔离槽108；从图12中可以看出，第一电容C1的可动极板11，也就是第一振膜11，与第二电容C2的可动极板21，也就是第二振膜21，在连接窗口107处连接到一起。
9)参考图13所示，通过DRIE工艺(Deep Reactive Ion Etching深反应离子刻蚀)从下方刻蚀衬底100，形成第一MEMS结构和第二MME结构的背腔。
10)通过两步释放工艺释放结构，完成整个器件加工。参考图14所示，先从底部刻蚀第一MEMS结构的第一隔离层200和第二隔离层400，以及第二MEMS结构的第一隔离层200，这一步完成后，第一电容C1的下方形成贯通的第一开孔101以及第二电容C2下方形成贯通的第二开孔102，并且在第一电容C1的背极板12和振膜11之间形成间隙109。然后从顶部刻蚀第二MEMS结构的第二隔离层400，在第二电容C2的背极板22和振膜21之间形成间隙109。
需要注意的是，本工艺流程仅仅是示例性流程，如有需要，可以将第一电容C1和第二电容C2的背极板的厚度制作得比第一电容C1和第二电容C2的振膜的厚度更厚。
本发明的差分电容式MEMS麦克风，将一对差分电容并排设计，通过两层膜来实现差分检测，本发明具有以下有益效果：
1.实现差分电容式MEMS麦克风，有利于滤除外界电磁和噪声干扰，提高输出信号的信噪比和收音质量。
2.由于差分电容的背极板和可动极板之间的间隙是在同一步骤完成的，差分电容的间距可以做到完全一致，提高了差分的效果。
3.制造工艺流程简单并且容易控制。工艺流程与目前的单电容式MEMS麦克风的工艺完全兼容，不需要做出工艺的变动。
虽然已经通过例子对本发明的一些特定实施例进行了详细说明，但是本领域的技术人员应该理解，以上例子仅是为了进行说明，而不是为了限 制本发明的范围。本领域的技术人员应该理解，可在不脱离本发明的范围和精神的情况下，对以上实施例进行修改。本发明的范围由所附权利要求来限定。

Claims (10)

  1. 一种MEMS麦克风元件，其特征在于，包括：
    基底(1)，所述基底(1)上设置有上下贯通的第一开孔(101)和第二开孔(102)；
    并列设置于所述基底(1)上方的第一电容(C1)和第二电容(C2)，所述第一电容(C1)设置在所述第一开孔(101)之上，所述第二电容(C2)设置在所述第二开孔(102)之上；
    所述第一电容(C1)包括位于下方的第一背极板(12)以及位于上方的与第一背极板(12)相对的第一振膜(11)，所述第二电容(C2)包括位于上方的第二背极板(22)以及位于下方的与第二背极板(22)相对的第二振膜(21)；
    所述第一电容(C1)和第二电容(C2)共同构成差分电容。
  2. 根据权利要求1的MEMS麦克风元件，其特征在于，所述第一振膜(11)和第二背极板(22)的材质相同，所述第一背极板(12)和第二振膜(21)的材质相同。
  3. 根据权利要求1的MEMS麦克风元件，其特征在于，所述第一振膜(11)和第二振膜(21)电连接在一起作为所述差分电容的公共可动极板。
  4. 根据权利要求1的MEMS麦克风元件，其特征在于，所述第一背极板(12)以及第二背极板(22)的感应部分分别设置有多个通孔(104)，所述第一振膜(11)以及第二振膜(21)的中心位置分别设置有通孔(103)。
  5. 根据权利要求1的MEMS麦克风元件，其特征在于，所述第一背极板(12)、第一振膜(11)、第二背极板(22)以及第二振膜(21)由下列材料任意之一形成：多晶硅、氮化硅上附加多晶硅层、氮化硅上附加金属层。
  6. 根据权利要求1-5任一项的MEMS麦克风元件，其特征在于，所述MEMS麦克风元件适用于声音信号从MEMS麦克风元件上方或者下方进入的两种产品结构。
  7. 一种制造MEMS麦克风元件的方法，其特征在于，包括如下步骤：
    S1、提供衬底(100)；
    S2、在所述衬底(100)上生长第一隔离层(200)；
    S3、在第一隔离层(200)生长第一极板材料层(300)；对第一极板材料层(300)进行构图和刻蚀以形成第一电容(C1)的背极板(12)、第二电容(C2)的可动极板(21)，以及隔离第一电容(C1)的背极板(12)和第二电容(C2)的可动极板(21)的第一隔离槽(105)；
    S4、在第一极板材料层(300)上沉积第二隔离层(400)；在第二电容(C2)的可动极板(21)上方的第二隔离层(400)上开设连接窗口(107)，用以连接第一电容(C1)的可动极板和第二电容(C2)的可动极板(21)；
    S5、在第二隔离层(400)生长第二极板材料层(500)；对第二极板材料层(500)进行构图和刻蚀以形成第一电容(C1)的可动极板(11)、第二电容(C2)的背极板(22)、以及隔离第一电容(C1)的可动极板(11)和第二电容(C2)的背极板(22)的隔离槽(108)；
    S6、刻蚀衬底(100)和第一隔离层(200)以在第一电容(C1)的下方形成贯通的第一开孔(101)以及在第二电容(C2)下方形成贯通的第二开孔(102)；以及刻蚀第二隔离层(400)以在第一、第二电容(C1、C2)各自的背极板和可动极板之间形成间隙(109)。
  8. 根据权利要求7的方法，其特征在于，在步骤S3中，在第一电容(C1)的背极板(12)上开设多个通孔(104)以及在第二电容(C2)的可动极板(21)的中心位置开设通孔(103)；在步骤S5中，在第二电容(C2)的背极板(22)上开设多个通孔(104)以及第一电容(C1)的可动极板(11)的中心位置开设通孔(103)。
  9. 根据权利要求7的方法，其特征在于，第一电容(C1)的背极板(12)的厚度大于其可动极板(11)的厚度，第二电容(C2)的背极板(22)的厚度大于其可动极板(21)的厚度。
  10. 根据权利要求7-9任一项的方法，其特征在于，所述MEMS麦克风元件适用于声音信号从MEMS麦克风元件上方或者下方进入的两种产品结构。
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