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Trench field effect transistor with reduced punch-through susceptibility and low R.sub.DSon

  • US 5,558,313 A
  • Filed: 02/10/1995
  • Issued: 09/24/1996
  • Est. Priority Date: 07/24/1992
  • Status: Expired due to Term
First Claim
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1. A field effect transistor comprising:

  • a substrate of a first conductivity type being a drain region;

    a lower layer of the first conductivity type formed on the substrate and having a doping level less than that of the substrate;

    an upper layer of the first conductivity type formed entirely overlying the lower layer and having a doping level less than that of the lower layer;

    a trench defined in the upper layer and lower layer and extending to within a predetermined distance of the drain region, the trench being at least partially filled with a conductive gate electrode;

    a source region of the first conductivity type formed in the upper layer and extending to a principal-surface of the upper layer and lying adjacent to sidewalls of the trench; and

    a body region of a second conductivity type extending from the principal surface of the upper layer down to and into at least an upper portion of the lower layer and being spaced apart from a lower portion of the trench, wherein two spaced apart portions of the body region lying respectively on two sides of the trench define a lateral extent of the upper layer, whereby an accumulation region extends from the body region to the lower layer when the transistor is on.

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