Abstract:
A sensor block that includes a plurality of sensor chips in combination. Each sensor chip includes a semiconductor substrate having a detection unit formed therein, and two glass substrates bonded to both sides of the semiconductor substrate. One of the glass substrates is shared among the sensor chips and serves as a base block to support the sensor chips.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is based on and claims the benefit of prior Japanese Patent Application No. 2005-322565, filed on Nov. 7, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a sensor block equipped with sensor chips (such as acceleration sensor chips, force sensor chips, temperature sensor chips, and biosensor chips)  
         [0004]     2. Description of the Related Art  
         [0005]     A conventional one-axis sensor chip of a triple-layered structure may include a semiconductor substrate having a detection unit formed therein, and glass substrates bonded to both sides thereof. Such one-axis sensor chips are attached to a base block, or a reference block, using an adhesive or the like to form a widely used sensor block.  
         [0006]     JP 2001-183389 discloses a sensor block, which includes a sensor chip bonded to a glass substrate, or a reference block, by anodic bonding with the use of no adhesive. This is effective to improve the accuracy that becomes worse due to a difference in thermal expansion coefficient between an adhesive and an element adhered thereto and to reduce thermal stresses exerted at the time of bonding and deformations of elements to be bonded.  
         [0007]     The sensor block thus configured, however, results in a larger size of the whole sensor and requires much expense in time and effort on works of adhering the sensor chip. A sensor block including a plurality of sensor chips suffers a reduction in reliability due to a difference in thermal expansion coefficient between elements or the like and a reduction in measurement accuracy due to accumulation of geometric errors.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is directed to a sensor block, which comprises a plurality of sensor chips in combination. Each sensor chip includes a semiconductor substrate having a detection unit formed therein, and two glass substrates bonded to both sides of the semiconductor substrate. One of the glass substrates is shared among the sensor chips and serves as a base block to support the sensor chips. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view showing a mounting structure of a sensor according to an embodiment of the present invention.  
         [0010]      FIG. 2  is an exploded perspective view of  FIG. 1 .  
         [0011]      FIG. 3  is a perspective view showing a mounting structure of a sensor according to another embodiment of the present invention.  
         [0012]      FIG. 4  is a perspective view showing a mounting structure of yet another sensor. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Embodiments of the present invention will now be described below with reference to the accompanying drawings.  
         [0014]      FIG. 1  is a perspective view of a sensor according to an embodiment of the present invention, and  FIG. 2  is an exploded perspective view thereof.  
         [0015]     A sensor block  10  comprises a base block  1 , which includes a glass substrate having electrodes la multi-face patterned thereon. Sensor chips  2 , or capacitive acceleration sensors operative to measure accelerations in this example, are mounted on X, Y and Z faces of the base block  1 , respectively. The sensor chip  2  includes a semiconductor substrate  3  having a weight  3   a  displaceable in response to the acceleration and an electrode  3   b ; and a glass substrate  4  having a surface opposite to the semiconductor substrate  3 , on which an electrode  4   a  is disposed to detect the relative displacement of the weight  3   a . The semiconductor substrate  3  is bonded to the glass substrate  4  by anodic bonding. The semiconductor substrate  3  is provided with a contact hole  3   d , which is surrounded by an insulator  3   c . The glass substrate  4  is provided with contact holes  4   b - d . The electrode la can be electrically bonded to an external component through the contact holes  3   d  and  4   b  filled with a electroconductive material such as a electroconductive resin. Similarly, the electrode  3   a  through the contact hole  4   c , and the electrode  4   a  through the contact hole  4   d . The electrodes  1   a  and  4   b  can be formed on the base block  1  and the glass substrate  4  using photolithography though a process of electroconductive ink printing or direct drawing may be employed to much easily implement the step of multi-face patterning.  
         [0016]     The following description is given to the effect of the sensor thus configured.  
         [0017]     Bonding surfaces on one side of the sensor chips  2  commonly to a single base block makes it possible to omit the glass substrate that has been interposed between the semiconductor substrate  3  and the base block  1  conventionally. This is effective to achieve a downsized sensor block and reduce the number of assembly steps. A reduction in elements of the glass substrate can relieve the measurement accuracy from becoming worse due to geometrical errors on combination of elements and can improve the measurement accuracy. An increase in the number of natural frequencies resulted from the downsized sensor can realize a faster response speed of the sensor block and achieve a reduced measurement time.  
         [0018]     This example uses anodic bonding as means to bond the base block  1  to the semiconductor substrate  3 . Alternatively, the base block  1  may be glass-glass bonded to the semiconductor substrate  3  through low melting glass such as flit glass interposed therebetween. Otherwise, Si—Si eutectic bonding through a thin film of Au—Ge or Au—Sn, or Si—Si bonding through a layer of SiO 2  may be used to carry out the present invention.  
         [0019]     In this embodiment, the sensor chips  2  are placed on X, Y and Z faces of a hexahedron to configure a multi-axis sensor. Alternatively, sensor chips  2 A may be arranged on opposite sides of a base block  1 A having electrodes  1 A a  formed on both sides to configure a double-sided sensor block  20  as shown in FIG.  3 . Otherwise, a plurality of sensor chips may be arranged on one side of a glass substrate  1 B to configure a compound sensor block  30  as shown in  FIG. 4 . These configurations also make it possible to carry out the present invention.  
         [0020]     In this embodiment, the sensor chips are exemplified as the capacitive acceleration sensor chips. Alternatively, a plurality of any sensor chips capable of detecting different physical quantities may be employed in combination so long as the substrate to be bonded to one side of the semiconductor substrate having the detection unit formed therein can be formed of the same material. For example, they may be acceleration sensor chips, force sensor chips, angular velocity sensor chips, motion sensor chips, temperature sensor chips, pressure sensor chips, optical sensor chips, and biosensor chips. In accordance with the use, the number and kind of sensor chips can be selected arbitrarily to carry out the present invention.