Abstract:
An electric discharge device includes a bipolar transistor configuration comprising a base, an emitter, and a collector. At least one pinched resistor is formed in a region comprising both the base and emitter so as to produce a pinched resistive area that develops a voltage once the bipolar transistor experiences junction breakdown.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to the field of ESD cells, in particular to an ESD cell having a pinched resistive area. 
         [0002]      FIG. 1  is a cross-sectional view of a conventional bipolar transistor-based ESD protection structure  10 . Conventional bipolar transistor-based ESD protection structure  10  includes a P-type substrate  12 , an N-type collector region  14 , a P-type base region  16  (e.g., a P-type Si—Ge base region) and an N-type polysilicon emitter  18 . The conventional bipolar transistor-based ESD protection structure  10  also includes electrical isolation regions  20  and  22 . A metal base contact  24  makes contact with the P-type base region  16  via polysilicon line  26 . A metal emitter contact  28  is in contact with the N-type polysilicon emitter  18 , while a metal collector contact  30  is in contact with the N-type collector region  14 . The metal base contact  24 , the metal emitter contact  28  and the metal collector contact  30  each extends through dielectric layer  32 . 
         [0003]    Electrical schematics illustrating this conventional bipolar transistor-based ESD protection structure  10  arranged in a grounded base bipolar transistor-based ESD protection device and a Zener Triggered bipolar transistor-based ESD protection device are provided in  FIGS. 2A and 2B , respectively. 
       SUMMARY OF THE INVENTION 
       [0004]    According to one aspect of the invention, there is provided an electric discharge device (ESD). The ESD includes a bipolar transistor configuration comprising a base, an emitter, and a collector. At least one pinched resistor is formed in a region comprising both the base and emitter so as to produce a pinched resistive area that develops a voltage once the bipolar transistor experiences junction breakdown. 
         [0005]    According to another aspect of the invention, there is provided a method of forming an electric discharge device. The method includes providing a bipolar transistor configuration comprising a base, an emitter, and a collector. Also, the method includes forming at least one pinched resistor in a region comprising both the base and emitter so as to produce a pinched resistive area that develops a voltage once the bipolar transistor experiences junction breakdown. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic diagram of a conventional ESD device; 
           [0007]      FIGS. 2A-2B  are circuit diagrams representing conventional ESD devices; 
           [0008]      FIG. 3  is a schematic diagram illustrating a top view of the inventive ESD device; 
           [0009]      FIG. 4  is a schematic diagram illustrating a top view of another of the inventive ESD device; and 
           [0010]      FIG. 5  is a circuit diagram representing the inventive ESD device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    The invention involves the use of a pinched resistive area that develops a voltage once junction breakdown occurs. 
         [0012]      FIG. 3  shows the inventive ESD device  40  having a pinched resistive area  50 . The ESD  40  includes a N-type collector region  44 , a P-type base region  46 , and N+-type emitter regions  48 . Note the ESD device  40  resembles that of a bipolar transistor based ESD device. In other embodiments, the ESD device  40  can include a P-type material collector, a N-type base, and P+-type emitter. 
         [0013]    The invention includes a pinched resistive region  50  formed under the emitter regions  48  and the exposed P-type materials comprising the hole  42  and base region  46 . A hole  42  is formed in an area comprising the emitter regions  48  leaving an exposed region of the base region  46 . The materials inside the hole  42  is connected to the emitter region  48  using an interconnect, such as Al or the like. The collector  44  is connected to a respective node to be protected and the hole  42  and the emitter regions  48  can be connected to ground. Another way also is the hole  42  and the emitter regions  48  can be connected to a node to be protected and the collector  44  can be connected to a positive supply. 
         [0014]    In this embodiment, the hole  42  is circular shaped however in other embodiments the shape can vary depending on how much resistance is needed and materials used to form the hole  42 , thus one can control the resistive value of the ESD device  40 . 
         [0015]    The pinched resistive region  50  develops a voltage once junction breakdown occurs. If the voltage that is generated across the pinched resistive region  50  is of sufficient magnitude, it will forward bias the pn junction between the base region  46  and emitter regions  48 , which creates a normal bipolar transistor action so as to allow current to flow only thru the pinched resistive region. The excess current is pumped into the collector region  44 . Note the ESD device  40  resembles a bipolar transistor. The result of such a configuration is reduced surface power density and faster turn-on of the ESD device  40  which yields higher reliability and higher ESD rating. 
         [0016]      FIG. 4  shows the top view of the inventive ESD device  51 . The ESD device  51  includes a collector region  52  which is n-type. The collector region includes a base region  54  that includes emitter regions  58 . Each of the emitter regions  58  includes a hole  60  which produces pinched resistive regions similar to pinched resistive region  50 , as shown in  FIG. 3 . In other embodiments, the number of emitter regions  58  can vary depending on the size of base region  54 . As more pinched resistive regions are formed on a base-emitter region the more uniform the injection of the protection device become. In this embodiment, the hole  60  is circular shaped however in other embodiments the shape can vary depending on how much resistance is needed and materials used to form the base region  54 , thus one can control the resistive value of the ESD device  51 . 
         [0017]      FIG. 5  shows a circuit representation of the inventive ESD device  70 . The ESD device  70  includes a bipolar transistor  72  and a pinched resistor  74 . The bipolar transistor includes a collector  76 , an emitter  78 , and a base  80 . The base  80  of the transistor  72  is coupled to the pinched resistor  74 . The pinched resistor  74  is also coupled to the emitter  78  of the bipolar transistor  72 . Note the emitter  78  can be coupled to ground and the collector  76  can be coupled to a voltage source. 
         [0018]    The pinched resistor  74  develops a voltage once junction breakdown occurs. If the voltage that is generated across the pinched resistor  74  is of sufficient magnitude, it will forward bias the pn junction between the base  80  and emitter  78 , which creates a normal bipolar transistor action. The excess current is pumped into the collector  78 . 
         [0019]    Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.