DMOS transistor with a poly-filled deep trench for improved performance
First Claim
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1. A transistor structure comprising:
- a lateral DMOS transistor comprising a source, a drain, a body region, a gate, and a drift region between the drain and the body region, the drift region having a conductivity type, the DMOS transistor being built on a substrate having a conductivity type opposite to that of the drift region; and
at least one pair of parallel opposing floating trenches, wherein a controllable current path exists in-between opposing floating trenches in the drift region, each floating trench comprising a conductive or semiconductor material that has no external electrical contact, the conductive or semiconductor material extending into the substrate and being insulated from any surrounding material by a dielectric,the trenches having a length dimension running along the drift region between the source and drain, the gate having a width dimension running along the body region, the gate width dimension being substantially perpendicular to the length of the opposing floating trenches,wherein an operating bias voltage applied to the drain capacitively couples a potential to the opposing floating trenches through the drift region and the substrate,the opposing floating trenches being arranged so that the potential coupled to the opposing floating trenches causes a first lateral depletion region to extend from a first one of the opposing floating trenches toward an opposing second one of the opposing floating trenches, and causes a second lateral depletion region to extend from the second one of the opposing floating trenches toward the first one of the opposing floating trenches, such that the first lateral depletion region and the second lateral depletion region merge in the drift region at a certain drain bias.
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Abstract
Floating trenches are arranged in the layout of a single DMOS transistor or an array of DMOS transistors, the array forming a single power transistor. The trenches run perpendicular to the gate width direction either outside the transistor(s) or between rows of the transistors. The floating trenches are at a potential between the drain voltage and the substrate voltage (usually ground). The potentials of the opposing trenches cause merging depletion regions in the drift region. This merging shapes the field lines so as to increase the breakdown voltage of the transistor and provide other advantages. The technique is applicable to both lateral and vertical DMOS transistors.
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Citations
20 Claims
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1. A transistor structure comprising:
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a lateral DMOS transistor comprising a source, a drain, a body region, a gate, and a drift region between the drain and the body region, the drift region having a conductivity type, the DMOS transistor being built on a substrate having a conductivity type opposite to that of the drift region; and at least one pair of parallel opposing floating trenches, wherein a controllable current path exists in-between opposing floating trenches in the drift region, each floating trench comprising a conductive or semiconductor material that has no external electrical contact, the conductive or semiconductor material extending into the substrate and being insulated from any surrounding material by a dielectric, the trenches having a length dimension running along the drift region between the source and drain, the gate having a width dimension running along the body region, the gate width dimension being substantially perpendicular to the length of the opposing floating trenches, wherein an operating bias voltage applied to the drain capacitively couples a potential to the opposing floating trenches through the drift region and the substrate, the opposing floating trenches being arranged so that the potential coupled to the opposing floating trenches causes a first lateral depletion region to extend from a first one of the opposing floating trenches toward an opposing second one of the opposing floating trenches, and causes a second lateral depletion region to extend from the second one of the opposing floating trenches toward the first one of the opposing floating trenches, such that the first lateral depletion region and the second lateral depletion region merge in the drift region at a certain drain bias. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A lateral DMOS transistor structure comprising a source, a drain, a body region, a gate, and a drift region between the drain and the body region, wherein the source, drift region, and drain are of a first conductivity type, and the body region is of a second conductivity type, the structure further comprising an epitaxial layer of a first conductivity type in which is formed the source, drain, drift region, and body region, and further comprising a substrate of the second conductivity type and a highly doped buried layer of the first conductivity type between the substrate and the epitaxial layer;
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at least one pair of parallel opposing floating trenches, wherein a controllable current path exists in-between opposing floating trenches in the drift region, each floating trench comprising a conductive or semiconductor material that has no external electrical contact, the conductive or semiconductor material being insulated from any surrounding material by a dielectric, the trenches having a length dimension running along the drift region between the source and drain, the gate having a width dimension running along the body region, the gate width dimension being substantially perpendicular to the length of the opposing floating trenches, wherein the opposing floating trenches are arranged such that an operating bias voltage applied to the drain capacitively couples a potential to the opposing floating trenches through the drift region and the substrate, the opposing floating trenches being arranged so that the potential coupled to the opposing floating trenches causes a first lateral depletion region to extend from a first one of the opposing floating trenches toward an opposing second one of the opposing floating trenches, and causes a second lateral depletion region to extend from the second one of the opposing floating trenches toward the first one of the opposing floating trenches, such that the first lateral depletion region and the second lateral depletion region merge in the drift region at a certain drain bias. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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Specification