Integrated circuit with depletion mode JFET
An integrated circuit having an n-channel MOSFET device and a JFET device. The integrated circuit includes a semiconductor layer having an upper surface, an MOS transistor device formed in a doped well of a first conductivity type extending from the semiconductor upper surface and a JFET device. The JFET device includes a channel region in the semiconductor layer spaced from, and having a peak concentration positioned a predetermined distance below, the upper surface. An associated method of manufacturing includes introducing p-type dopant into the semiconductor surface to form a p-well in which the NMOS device is formed and a source and a drain of the JFET device. N-type dopant is introduced into the semiconductor surface to form an n-type region of the NMOS device below the p-well and a gate region of the JFET device. P-type dopant is introduced into the semiconductor layer to simultaneously form a higher concentration p-type region in the p-well of the NMOS device and a channel region extending between the source and drain of the JFET.
1. An integrated circuit, comprising:
a semiconductor layer of a first conductivity type having an upper surface;
a depletion-mode transistor that comprises:
a source region and a drain region, each extending from the upper surface into the semiconductor layer; and
a channel region of the first conductivity type located at a first distance from the upper surface and laterally extending between the source region and the drain region;
a first gate of a second conductivity type comprising:
a first gate region located at a second distance from the upper surface greater than the first distance, said first gate region being adjacent to the channel region; and
a first well that laterally surrounds the semiconductor channel and extends from the upper surface to the first gate region; and
a second gate of the second conductivity type positioned adjacent to the upper surface between the source region and the drain region; and
a MOS transistor that comprises:
a second well for operatively forming therein a second-conductivity-type channel for conducting charges between a source and a drain of the MOS transistor, said second well being a well of the first conductivity type and extending from the upper surface into the semiconductor layer; and
an isolation structure of the second conductivity type comprising:
a third well that extends from the upper surface into the semiconductor layer and laterally surrounds the second well; and
an isolation region located at the second distance from the upper surface and laterally extending between sides of the third well to enable the isolation structure to isolate the second well from at least a portion of the semiconductor layer.
2. The integrated circuit of claim 1 , wherein:
the first conductivity type is a p type; and
the second conductivity type is an n type.
3. The integrated circuit of claim 1 , wherein the first gate separates the semiconductor channel from the portion of the semiconductor layer.
4. The integrated circuit of claim 1 , wherein the channel region has a peak dopant concentration at a distance of at least 0.5 micron from the upper surface.
5. The integrated circuit of claim 1 , wherein a semiconductor region located between the upper surface and the channel region has a net concentration of a dopant corresponding to the first conductivity type of less than about 10 16 cm −3 .
6. The integrated circuit of claim 5 , wherein the semiconductor region located between the upper surface and the channel region is positioned at a distance of about 0.3 micron from the upper surface.
7. The integrated circuit of claim 1 , wherein the MOS transistor further comprises a region of the first conductivity type located at the first distance from the upper surface and laterally extending between the sides of the third well.
8. The integrated circuit of claim 7 , wherein said region of the first conductivity type located at the first distance is positioned along a lower portion of the second well.
9. The integrated circuit of claim 7 , wherein the isolation structure isolates said region of the first conductivity type located at the first distance from the portion of the semiconductor layer.
10. The integrated circuit of claim 7 , wherein said region of the first conductivity type located at the first distance has a dopant concentration that is at least as high as a net dopant concentration in the channel region.