Abstract:
The present invention proposes a voltage-clipping device utilizing a pinch-off mechanism formed by two depletion boundaries. A clipping voltage of the voltage-clipping device can be adjusted in response to a gate voltage; a gap of a quasi-linked well; and a doping concentration and a depth of the quasi-linked well and a well with complementary doping polarity to the quasi-linked well. The voltage-clipping device can be integrated within a semiconductor device as a voltage stepping down device in a tiny size, compared to traditional transformers.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor manufacturing process, more particularly, the present invention relates to a voltage stepping down device manufacturing process. 
   2. Description of Related Art 
   In traditional arts, stepping down a higher voltage potential to a lower voltage potential is well known to the industrial fields. Voltage stepping down devices, such as voltage dividers and transformers, are widely used to supply a predetermined voltage potential to electronic systems. A transformer includes plural coupled coils having proportional turn numbers to each other for achieving voltage stepping down. However, transformers are generally huge in size and cannot be easily integrated within semiconductor devices. Therefore, higher manufacturing cost and huge space occupation are their inevitable disadvantages. 
   Voltage dividers formed with resistors generally suffer from resistance variation problems. Temperature dependence of resistors lowers the precision of the voltage potential supplied by voltage dividers. Moreover, the power consumption caused by resistors is another issue to be concerned. In general-purpose applications, when a constant voltage source is needed in an electronic circuit, a device capable of supplying stable voltage potential with lesser die space occupation and lower power consumption is especially desired by the industrial filed. 
   SUMMARY OF THE INVENTION 
   The present invention proposes a voltage-clipping device utilizing a pinch-off mechanism formed by two depletion boundaries. A clipping voltage of the voltage-clipping device can be adjusted in response to a gate voltage; a gap of a quasi-linked well; and a doping concentration and a depth of the quasi-linked well and a well/body with complementary doping polarity to the quasi-linked well. The voltage-clipping device has a tiny size and can be integrated within a semiconductor device as a voltage stepping down device. 
   The quasi-linked well is formed by controlling a distance between two adjacent wells. A middle-doped region with different doping concentration from the two adjacent wells is formed between the two adjacent wells. 
   The middle-doped region associates with complementary doped regions complementary to the quasi-linked well for forming two depletion boundaries. The two depletion boundaries are varied in response to the gate voltage and voltage potentials applied to the quasi-linked well. Variations of resistance, voltage and current of the quasi-linked well are controlled by the two depletion boundaries and voltage potentials applied to the quasi-linked well. 
   It is to be understood that both the foregoing general descriptions and the following detailed descriptions are exemplary, and are intended to provide further explanation of the invention as claimed. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  shows a cross-sectional view of a voltage-clipping device according to a preferred embodiment of the present invention. 
       FIG. 2  shows two depletion boundaries of voltage-clipping device under different gate-voltage potentials according to an embodiment of the present invention. 
       FIG. 3  shows a characteristic property of an input voltage and an output voltage under different gate-voltage potential applied to the voltage-clipping device according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a cross-sectional view of a voltage-clipping device  100  according to an embodiment of the present invention. The voltage-clipping device  100  comprises a P-type substrate  90  with resistivity ranging from 10 ohm-cm to 100 ohm-cm. As shown in  FIG. 1 , a quasi-linked N-type well  210  is formed by two adjacent N-type wells  212  and  214  in the P-type substrate  90  featuring a gap with a width G there-between. With the gap, a discontinuous ion-doping region is formed in a middle-doped region II. The discontinuous ion-doping region is parallel to a surface of the P-type substrate  90 . The equivalent doping concentration of the middle-doped region II is slighter than regions I and III. 
   The doping concentration of the quasi-linked N-type well  210  ranges from 1.7E17/cm 3  to 8.3E18/cm 3 . The depth of the quasi-linked N-type well  210  ranges from 2 μm to 10 μm. The width G of the gap required for the quasi-linked N-type well  210 , for example, ranges between 0 μm and 20 μm. 
   A P-type well (or a P-type body)  30  with P-type conductive ions is formed in the quasi-linked N-type well  210 . The doping concentration of the P-type well  30  ranges from 3.3E17/cm 3  to 1E19/cm 3 . The depth of the P-type well  30  ranges from 1 μm to 5 μm. 
   A gate region  55  with P+-type conductive ions forms a gate terminal VG of the voltage-clipping device  100 . The gate region  55  is disposed in the P-type well  30 . An input region  56  with N+-type conductive ions forms an input terminal VDI of the voltage-clipping device  100 . An output region  53  with N+-type conductive ions forms an output terminal VDO of the voltage-clipping device  100 . The input region  56 , the output region  53  and the gate region  55  of the voltage-clipping device  100  are doped with a higher ion concentration than the quasi-linked N-type well  210 , for example, ranging from 1E22/cm 3  to 5E23/cm 3 . The input region  56  and the output region  53  are disposed in the quasi-linked N-type well  210 . A field oxide layer  330  is formed for serving as isolation structures. 
   Referring to  FIG. 2 , when an input voltage V D-IN  with a positive-voltage potential is applied at the input terminal VDI of the voltage-clipping device  100 , an output voltage V D-OUT  will be generated at the output terminal VDO of the voltage-clipping device  100  via the conduction of the quasi-linked N-type well  210 . The output voltage V D-OUT  is then varied in linear proportion to the input voltage V D-IN . The input voltage V D-IN  and the output voltage V D-OUT  result in a first depletion boundary  61  following a geometric shape of the quasi-linked N-type well  210 . 
   When a gate-voltage potential V G  is applied at the gate terminal VG of the voltage-clipping device  100 , a second depletion boundary is generated accordingly. Referring to  FIG. 2 , when the gate terminal VG is applied with a zero-voltage potential, the second depletion boundary is shown along a dotted line  60   b . When the gate terminal VG is floated or applied with a positive-voltage potential, the second depletion boundary is shown along a dotted line  60   a . When the gate terminal VG is applied with a negative-voltage potential, the second depletion boundary is shown along a dotted line  60   c.    
   Referring to  FIG. 2  and  FIG. 3 , when the gate terminal VG is applied with a negative-voltage potential, as the input voltage V D-IN  increases, the first depletion boundary  61  will continuously approach to the second depletion boundary. When the first depletion boundary  61  and the second depletion boundary, as shown in dotted line  60   c , pinch off, the conduction path between the input terminal VDI and the output terminal VDO is cut off. Therefore, the output voltage V D-OUT  is clipped at the same voltage potential as the input voltage V D-IN  when the first depletion boundary  61  and the second depletion boundary pinch off. 
     FIG. 3  shows the characteristic property of the input voltage V D-IN  and the output voltage V D-OUT  according to an embodiment of the present invention. When a negative-voltage potential is applied to the gate terminal VG, the output voltage V D-OUT  will be clipped at an output voltage potential V DO1 , which is equal to an input voltage potential V DI1  when the two depletion boundaries pinch off (as shown in point A). When the gate terminal VG is applied with a zero-voltage potential, the output voltage V D-OUT  will be clipped at an output voltage potential V DO2 , which is equal to an input voltage potential V DI2  when the two depletion boundaries pinch off (as shown in point B). When the gate terminal VG is floated or applied with a positive voltage, the output voltage V D-OUT  will be clipped at an output voltage potential V DO3 , which is equal to an input voltage potential V DI3  when the two depletion boundaries pinch off (as shown in point C). Voltage potentials V DI1 , V DI2 , V DI3 , V DO1 , V DO2 , and V DO3  can be expressed by following inequalities:
 V DI1 &lt;V DI2 &lt;V DI3   (1) V DO1 &lt;V DO2 &lt;V DO3   (2) 
   In addition, the gap having the width G for the quasi-linked N-type well  210  facilitates to pinch off the connection path between the input terminal VDI and the output terminal VDO of the voltage-clipping device  100 . 
   Referring to  FIG. 2 , the voltage-clipping device  100  further comprises a fringe P-type well  15 . The fringe P-type well  15  is disposed adjacent to the quasi-linked N-type well in a distance w. The distance w is adjusted to increase a breakdown voltage of the voltage-clipping device  100 . 
   According to the present invention, the output voltage V D-OUT  of the voltage-clipping device  100  is controlled to be clipped at a predetermined voltage potential, which can be applied as a tiny voltage stepping down device in the semiconductor device. In general-purpose application, the present invention supplies a cost-effective and an accurate voltage stepping down device. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.