Patent Publication Number: US-9420365-B2

Title: Silicon condenser microphone

Description:
FIELD OF THE INVENTION 
     The present invention relates to microphones, more particularly to a silicon condenser microphone. 
     DESCRIPTION OF RELATED ART 
     With the rapid development of wireless communication technologies, mobile phones are widely used in daily life. Users require mobile phones to not only have voice function, but also have high quality voice performance. In addition, with the development of mobile multi-media technologies, sounds, like music, voice, are of importance to a device for performing the multi-media functions. As a sound pick-up device, a microphone is a necessary and important component used in a mobile phone to convert sounds to electrical signals for transmitting the sounds to other devices. 
     Miniaturized silicon microphones have been extensively developed for over sixteen years, since the first silicon piezoelectric microphone reported by Royer in 1983. In 1984, Hohm reported the first silicon electret-type microphone, made with a metallized polymer diaphragm and silicon backplate. And two years later, he reported the first silicon condenser microphone made entirely by silicon micro-machining technology. Since then a number of researchers have developed and published reports on miniaturized silicon condenser microphones of various structures and performance. U.S. Pat. No. 5,870,482 to Loeppert et al reveals a silicon microphone. U.S. Pat. No. 5,490,220 to Loeppert shows a condenser and microphone device. U.S. Patent Application Publication 2002/0067663 to Loeppert et al shows a miniature acoustic transducer. U.S. Pat. No. 6,088,463 to Rombach et al teaches a silicon condenser microphone process. U.S. Pat. No. 5,677,965 to Moret et al shows a capacitive transducer. U.S. Pat. Nos. 5,146,435 and 5,452,268 to Bernstein disclose acoustic transducers. U.S. Pat. No. 4,993,072 to Murphy reveals a shielded electret transducer. 
     Various microphone designs have been invented and conceptualized by using silicon micro-machining technology. Despite various structural configurations and materials, the silicon condenser microphone consists of four basic elements: a movable compliant diaphragm, a rigid and fixed backplate (which together form a variable air gap capacitor), a voltage bias source, and a pre-amplifier. These four elements fundamentally determine the performance of the condenser microphone. In pursuit of high performance; i.e., high sensitivity, low bias, low noise, and wide frequency range, the key design considerations are to have a large size of diaphragm and a large air gap. The former will help increase sensitivity as well as lower electrical noise, and the later will help reduce acoustic noise of the microphone. The large air gap requires a thick sacrificial layer. For releasing the sacrificial layer, the backplate is provided with a plurality of through holes. 
     As known, a silicon condenser microphone is also named MEMS (Micro-Electro-Mechanical-System) microphone. A microphone related to the present application generally includes a substrate, a housing forming a volume cooperatively with the substrate, a MEMS die accommodated in the volume, and an ASIC (Application Specific Integrated Circuit) chip received in the volume and electrically connected with the MEMS die. 
     For a typical MEMS microphone, it receives high frequency signals or low frequency signals, or ultrasonic signals. When receiving ultrasonic signals, the MEMS microphone may be used as a component for performing Gesture Recognition. When receiving low frequency signals, the MEMS microphone has relatively high sensitivity. When receiving high frequency signals, (such as signals within 30 kHz˜60 kHz), however, the MEMS microphone has relatively lower sensitivity. The reason is that the sound pressure on the diaphragm caused by signals with low frequencies will keep constant, but the sound pressure on the diaphragm caused by signals with high frequencies will drop down. For example, the sound pressure on the diaphragm caused by signals of 60 kHz is 10 dB lower than the sound pressure on the diaphragm caused by signals of 1 kHz. Thus, the sensitivity of the MEMS microphone will rapidly drop down when receiving signals of high frequencies. 
     Accordingly, an improved silicon condenser microphone which can overcome the disadvantage described above is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an illustrative isometric view of a silicon condenser microphone in accordance with the present disclosure. 
         FIG. 2  is a cross-sectional view of the silicon condenser microphone in  FIG. 1 . 
         FIG. 3  is an isometric view of a first configuration of a partition of the silicon condenser microphone. 
         FIG. 4  is an isometric view of a second configuration of a partition of the silicon condenser microphone. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     The present invention will hereinafter be described in detail with reference to exemplary embodiments. 
     Referring to  FIG. 1 , an illustration of a silicon condenser microphone  10  of the present disclosure, the silicon condenser microphone  10  is a necessary component of a silicon condenser microphone package used for converting sounds into electrical signals. The silicon condenser microphone  10  includes a substrate  12  and a transducer unit  11  supported by the substrate  12 . 
     Referring to  FIG. 2  that is a cross-sectional view of the silicon condenser microphone  10  in  FIG. 1 , the transducer unit  11  further includes a backplate  113 , a diaphragm  112  arranged above the backplate  113 , and a top cover  111  for fixing the diaphragm  112  to the substrate  12 . An air gap is accordingly formed between the backplate  113  and the diaphragm  112 . Basically, the backplate  113  and the diaphragm  112  are both provided with voltage but are isolative from each other. Thus, a capacitor is thereby formed by the backplate  113  and the diaphragm  112 . The top cover  111  is an optional component for fixing the diaphragm  112 . The backplate  113  further includes a plurality of through holes  1130  for balancing the air pressure in the air gap during vibration of the diaphragm  112 . In this embodiment, the backplate  113  is directly arranged on the substrate  12 , and the diaphragm  112  is arranged above the backplate  113 . In other embodiment, the diaphragm  112  may be anchored to the substrate  12 , and the backplate  113  may be arranged above the diaphragm  112 . 
     The substrate  12  includes a side  121  defining a cavity  120 . In addition, the silicon condenser microphone  10  includes a partition  13  disposed in the cavity  120  for dividing the cavity  120  into an upper cavity  1201  and a lower cavity  1202 . For communicating the upper cavity  1201  with the lower cavity  1202 , the partition  13  includes at least one penetration. 
     Referring to  FIGS. 2-3 , a first configuration of the partition  13  is shown. The partition  13  includes a main body  131  and a plurality of perforations  130  penetrating the main body  131  for communicating the upper cavity  1201  with the lower cavity  1202 . In this embodiment, the partition  13  is parallel to the transducer unit  11 , more particularly parallel to the diaphragm  112  or to the backplate  113 . In fact, the partition  13  is used to dividing the cavity into two cavities, so, the position of the partition is not restricted to a position parallel to the transducer unit. However, the partition  13  should be connected to the side  121  with an edge of the partition  13  sealed with an inner surface of the side  121 . Optionally, the partition  13  is integrated with the side  121  by MEMS process. Position or amount of the perforations is adjustable according to actual requirements. The partition  13  with perforations  130  could adjust the sound pressure arriving at the diaphragm for improving the sensitivity of the silicon condenser microphone when the microphone receives signals with high frequencies. 
     Referring to  FIGS. 2 and 4 , a second configuration of the partition  13  is shown. The partition  13  includes a main body  131  and a protrusion  132  extending perpendicularly from the main body along a direction far away from the transducer unit  11 . A perforation  130  is formed penetrating the protrusion  132  and the main body  131 . A diameter of the protrusion is obviously smaller than that of the main body  131 . In this embodiment, the protrusion  132  forms only one perforation  130 , but in fact, the protrusion  132  may form a plurality of perforations according to actual requirements. And, the height or the diameter of the protrusion  132  may be adjusted according to actual applications. 
     The partition divides the cavity of the substrate into an upper cavity and a lower cavity, and airflow produced by the vibration of the sound waves enters the air gap from the lower cavity to the upper cavity via the perforation in the partition, which generates resonance in the cavity, and improves the sound pressure on the diaphragm. Therefore, the sensitivity of the silicon condenser microphone is accordingly improved. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.