Ballast resistors for transistor devices
View Patent ↗A transistor is formed with a source ballast resistor that regulates channel current. In an LDMOS transistor embodiment, the source ballast resistance may be formed using a high sheet resistance diffusion self aligned to the polysilicon gate, and/or by extending a depletion implant from under the polysilicon gate toward the source region. The teachings herein may be used to form effective ballast resistors for source and/or drain regions, and may be used in many types of transistors, including lateral and vertical transistors operating in a depletion or an enhancement mode, and BJT devices.
1. A transistor comprising:
a substrate having first, second, and third regions, wherein the second region includes a dopant of a first conductivity type, the first and third regions include a dopant of a second conductivity type, with at least a first subportion of the first region and a first subportion of the third region including a high concentration of the dopant, and the second region is disposed between the first and third regions and forms a body of the transistor;
a gate electrode overlying the second and third regions, without overlying at least said first subportion of the first region; and
an implant region of the second conductivity type and formed within and contiguously coupling the first, second, and third regions, and beneath the gate electrode,
wherein a portion of the implant region extends beyond an edge of the gate electrode toward said first subportion of the first region having the high dopant concentration,
wherein the first subportion of the first region is formed within a second subportion of the first region, the second subportion of the first region has a lower concentration of the dopant of the second conductivity type than the first subportion of the first region, the second subportion of the first region is between the first subportion thereof and the second region, the gate electrode overlies the second subportion of the first region, and a portion of the implant region is formed at least in the second subportion of the first region, and
wherein the implant region extends across the second subportion of the first region and into the first subportion of the first region.
2. A transistor comprising:
a substrate having first, second, and third regions, wherein the second region includes a dopant of a first conductivity type, the first and third regions include a dopant of a second conductivity type, with at least a first subportion of the first region and a first subportion of the third region including a high concentration of the dopant, and the second region is disposed between the first and third regions and forms a body of the transistor;
a gate electrode overlying the second and third regions, without overlying at least said first subportion of the first region; and
an implant region of the second conductivity type and formed within and contiguously coupling the first, second, and third regions, and beneath the gate electrode,
wherein a portion of the implant region extends beyond an edge of the gate electrode toward said subportion of the first region having the high dopant concentration,
wherein the first subportion of the first region is formed within a second subportion of the first region, the second subportion of the first region has a lower concentration of the dopant of the second conductivity type than the first subportion of the first region, the second subportion of the first region is between the first subportion thereof and the second region, the gate electrode overlies the second subportion of the first region, and a portion of the implant region is formed at least in the second subportion of the first region, and
wherein the implant region terminates within the second subportion of the first region and does not extend to the first subportion of the first region.
3. A transistor comprising:
a substrate having first, second, and third regions, wherein the second region includes a dopant of a first conductivity type, the first and third regions include a dopant of a second conductivity type, the first and third regions include a first subportion having a high concentration of the dopant of the second conductivity type and a second subportion having a lower concentration of the dopant of the second conductivity type, and the second region is disposed between the first and third regions and forms a body of the transistor, with the second subportions of the first and third regions being between the respective first subportion thereof and the second region;
a gate electrode overlying the second region, the second subportion of the first region, and the second subportion of the third region, without overlying the respective first subportion of the first and third regions, and
an implant region of the second conductivity type formed within and contiguously connecting the first, second, and third regions,
wherein the implant region is located beneath the gate electrode without extending beyond a perimeter of the gate electrode.
4. A transistor comprising:
a substrate having first, second, and third regions, wherein the second region includes a dopant of a first conductivity type, the first and third regions include a dopant of a second conductivity type, the first and third regions include a first subportion having a high concentration of the dopant of the second conductivity type and a second subportion having a lower concentration of the dopant of the second type, and the second region is disposed between the first and third regions and forms a body of the transistor, with the second subportions of the first and third regions being between the respective first subportion thereof and the second region;
a gate electrode overlying the second region, the second subportion of the first region, and the second subportion of the third region, without overlying the respective first subportion of the first and third regions, and
an implant region of the second conductivity type formed within and contiguously connecting the first, second, and third regions,
wherein the implant region extends beyond an edge of the gate electrode in the second subportion of the first region toward the first subportion of the first region, and wherein the implant region extends into the first subportion of the first region.
5. A transistor comprising:
a substrate having first, second, and third regions,
wherein the second region includes a dopant of a first conductivity type, the first and third regions include a dopant of a second conductivity type, the first and third regions include a first subportion having a high concentration of the dopant of the second conductivity type and a second subportion having a lower concentration of the dopant of the second conductivity type, and the second region is disposed between the first and third regions and forms a body of the transistor, with the second subportions of the first and third regions being between the first subportions thereof and the second region;
a gate electrode overlying the second region, the second subportion of the first region, and the second subportion of the third region, said gate electrode terminating outward of the respective first subportion of the first and third regions; and
an implant region having the second conductivity type formed within and contiguously coupling the respective second subportion of the first and third regions and the second region, beneath the gate electrode, wherein a portion of the implant region extends beyond an edge of the gate electrode toward the first subportion of the first region,
wherein the implant region extends into the first subportion of the first region.