Transistor having peripheral channel
Transistors for use in semiconductor integrated circuit devices including a first source/drain region of the transistor is formed around a perimeter of a channel region, and a second source/drain region formed to extend below the channel region such that the channel region is formed around a perimeter of the source/drain region. Such transistors should facilitate a reduction in edge effect and leakage as the channel of the transistor is not bordering on an isolation region. Additionally, the use of a source/drain region extending through a channel region facilitates high-power, high-voltage operation.
1. A transistor, comprising:
a control gate;
a gate dielectric formed between the control gate and a semiconductor material;
a channel region formed in the semiconductor material below the gate dielectric;
a first source/drain region formed in the semiconductor material around a perimeter of the channel region;
a second source/drain region extending below the gate dielectric and through the channel region, such that the channel region is formed around a perimeter of the second source/drain region.
2. The transistor of claim 1 , wherein the semiconductor material has a first conductivity type, the channel region has the first conductivity type, the first source/drain region has a second conductivity type and the second source/drain region has the second conductivity type.
3. The transistor of claim 2 , wherein the first conductivity type is a p-type conductivity and the second conductivity type is an n-type conductivity.
4. The transistor of claim 2 , wherein the channel region is doped to increase its conductivity.
5. The transistor of claim 1 , wherein the semiconductor material is a silicon substrate.
6. The transistor of claim 1 , wherein a distance between the perimeter of the second source/drain region and the perimeter of the channel region is less than or equal to 0.5 μm.
7. The transistor of claim 1 , wherein a width of the second source/drain region is less than or equal to 1 μm.
8. The transistor of claim 1 , wherein a width of the first source/drain region is less than or equal to 2 μm.
9. The transistor of claim 1 , wherein features of the control gate, gate dielectric, channel region, first source/drain region and second source/drain region are square.
10. The transistor of claim 1 , further comprising:
one or more contacts coupled to the first source/drain region;
wherein the one or more contacts are further coupled to an access line of an array of memory cells.
11. The transistor of claim 10 , further comprising:
a well region formed at a level below the channel region and coupled to a bottom portion of the second source/drain region and having a same conductivity type as a conductivity type of the second source/drain region.
12. The transistor of claim 11 , wherein the semiconductor material has a first conductivity type, the second source/drain region has a second conductivity type and the well region has the second conductivity type.
13. The transistor of claim 11 , wherein the well region is coupled to receive a potential to be applied to the access line.
14. The transistor of claim 13 , wherein the control gate is coupled to receive a control signal to selectively couple the potential to the access line.
15. A memory device, comprising:
an array of memory cells logically arranged in rows and columns, with access lines coupled to control gates of the memory cells;
control logic for controlling access to the array of memory cells; and
a row decode circuitry for selectively driving access lines, wherein the row decode circuitry comprises at least one transistor having a first source/drain region coupled to an access line, a control gate coupled to receive a control signal, and a second source/drain region coupled to receive a potential to be applied to the access line, the transistor comprising:
a gate dielectric formed between the control gate and a semiconductor substrate; and
a channel region formed in the semiconductor material below the gate dielectric;
wherein the first source/drain region is formed in the semiconductor material around a perimeter of the channel region; and
wherein the second source/drain region extends below the gate dielectric and through the channel region, such that the channel region is formed around a perimeter of the second source/drain region.
16. The memory device of claim 15 , wherein the semiconductor material has a first conductivity type, the channel region has the first conductivity type, the first source/drain region has a conductivity type opposite the first conductivity type and the second source/drain region has the conductivity type opposite the first conductivity type.
17. The memory device of claim 15 , wherein the channel region is donut-shaped.
18. The memory device of claim 15 , further comprising:
a well region formed at a level below the channel region and coupled to a bottom portion of the second source/drain region and having a same conductivity type as a conductivity type of the second source/drain region; and
a contact laterally spaced apart from the second source/drain region and extending into the semiconductor material to at least a level of the well region;
wherein the contact is coupled to receive the potential to be applied to the access line.
19. The memory device of claim 15 , wherein features of the control gate, gate dielectric, channel region, first source/drain region and second source/drain region are circular.
20. The memory device of claim 15 , further comprising:
one or more contacts coupled to the first source/drain region;
wherein the one or more contacts are further coupled to an access line.
21. A memory device, comprising:
an array of memory cells logically arranged in rows and columns, with access lines coupled to control gates of the memory cells;
control logic for controlling access to the array of memory cells; and
a row decode circuitry for selectively driving access lines, wherein the row decode circuitry comprises at least one transistor having a first source/drain region coupled to an access line, a control gate coupled to receive a control signal, and a second source/drain region coupled to receive a potential to be applied to the access line, the transistor comprising:
a gate dielectric formed between the control gate and a semiconductor substrate;
a channel region formed in the semiconductor material below the gate dielectric;
a well region formed at a level below the channel region and coupled to a bottom portion of the second source/drain region and having a same conductivity type as a conductivity type of the second source/drain region; and
one or more contacts coupled to the first source/drain region;
wherein the one or more contacts are further coupled to an access line;
wherein the first source/drain region is formed in the semiconductor material around a perimeter of the channel region; and
wherein the second source/drain region extends below the gate dielectric and through the channel region, such that the channel region is formed around a perimeter of the second source/drain region.
22. The memory device of claim 21 , wherein the semiconductor material has a first conductivity type, the second source/drain region has a conductivity type opposite the first conductivity type and the well region has the conductivity type opposite the first conductivity type.
23. The memory device of claim 21 , wherein the well region is coupled to receive the potential to be applied to the access line.