Patent Application
20080075308
The present invention will be described through detailed illustration of three embodiments referring to the drawings.
Referring to
The silicon substrate 1 includes an air chamber 5 defined therein.
The diaphragm 2 is mounted on the silicon substrate 1 so that the diaphragm 2 is aligned with the air chamber 5. The diaphragm 2 is suspended on the silicon substrate 1 by a suspension device 21. The suspension device 21 includes a plurality of corrugated cantilevers 21 a each including an end extended from the diaphragm 2 and an opposite end connected to the silicon substrate 1. Because of the suspension device 21, lateral movement of the diaphragm 2 is prevented while vertical movement of the diaphragm 2 is allowed. Hence, the stress in the diaphragm 2 is reduced while the sensitivity of the silicon condenser microphone is increased.
The back plate 4 is mounted on the silicon substrate 1 so that the diaphragm 2 is positioned between the silicon substrate 1 and the back plate 4. The back plate 4 includes a plurality of acoustic apertures 43 defined therein, a plurality of etching apertures 43a defined therein, an anti-sticking device 45 formed on a first side, a support device 31 formed on the first surface around the acoustic apertures 43 and a protective layer 42 formed on a second surface opposite to the first surface.
The acoustic apertures 43 are located within a region corresponding to the diaphragm 2. Sound can reach the diaphragm 2 through the acoustic apertures 43. The etching apertures 43a are used for the wet etching of internal layers.
The support device 31 is used to define an effective area of the diaphragm 2 that is vulnerable to variation in sound pressure. The support device 31 is made of a dielectric material. In the first embodiment, the support device 31 includes an annular ridge 31a.
The anti-sticking device 45 includes a plurality of bosses. The bosses of the anti-sticking device 45 may be made of a dielectric material to avoid the sticking of the diaphragm 2 to the back plate 4 during the manufacturing of the silicon condenser microphone.
The upper electrode 41 is attached to the first surface of the back plate 4 within the support device 31. The upper electrode 41 defines a plurality of apertures each for receiving a related one of the bosses of the anti-sticking device 45.
The diaphragm 2 is made of poly-crystalline silicon so that the upper electrode 41 and the diaphragm 2 together form a condenser wherein the diaphragm 2 is used as a lower electrode. When the sound reaches the diaphragm 2 through the acoustic apertures 43, the diaphragm 2 is deformed corresponding to the sound pressure. Accordingly, the capacitance of the condenser is changed.
According to the first embodiment of the present invention, the basic structure of the silicon microphone is made of poly-crystalline silicon by low pressure chemical vapor deposition (“LPCVD”). Diffusion and ion implantation are two means for doping silicon. Boron and phosphorous are commonly used dopant elements. The diaphragm 2 is made into a low-stress diaphragm by annealing.
The making of the anti-sticking device 45 is made by making the apertures in the upper electrode 41 by dry etching. Then, the protective layer 42 is deposited. Thus, the back plate 4 and its indentations are made. The indentations reduce the contact area between the back plate 4 and the diaphragm 2 during the making of an air gap 3 by wet etching so that the back plate 4 can easily be separated from the diaphragm 2 after the wet etching. Hence, the yield of the making of the silicon condenser microphone is increased. The air chamber 5 provides compressible air so that the diaphragm 2 can easily vibrate.
Referring to
Referring to
The present invention has been described via the detailed illustration of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.
