Transistor providing different threshold voltages and method of fabrication thereof
A transistor includes a channel region with a first portion and a second portion. A length of the first portion is smaller than a length of the second portion. The first portion has a higher threshold voltage than the second portion. The lower threshold voltage of the second portion allows for an increased ON current. Despite the increase attained in the ON current, the higher threshold voltage of the first portion maintains or lowers a relatively low OFF current for the transistor.
1. A method for fabricating a transistor, comprising: a first portion of a channel region with a first depth;
second portion of the channel region with a second depth, wherein the second depth is lesser than the first depth;
implanting the first portion of the channel region with a dopant to provide a first threshold voltage for the transistor;
protecting the first portion of the channel region leaving the second portion of the channel region exposed;
identifying an amount of the dopant at the first depth that has a desired voltage characteristic; and
implanting the exposed second portion of the channel region with the identified amount of the dopant to provide a second threshold voltage for the transistor different than the first threshold voltage, wherein the implanting of the second portion is performed at an angle offset relative to a line perpendicular to the channel region.
2. The method of claim 1 , wherein the second threshold voltage is higher than the first threshold voltage.
3. The method of claim 2 , wherein the first threshold voltage causes an increase in an ON current for the transistor while the second threshold voltage causes a decrease in the OFF current for the device.
4. The method of claim 1 , further comprising:
forming the first portion with a first length;
forming the second portion with a second length, the second length being smaller than the first length.
5. The method of claim 4 , wherein the second length is determined by an equation α×L and the first length is determined by an equation L−(α×L), where L is a length of the channel region and α is a fraction less than one.
6. The method of claim 1 , further comprising:
forming the second portion in closer proximity to a source region of the transistor than the first portion.
7. The method of claim 1 , wherein the second portion is implanted to separate the first portion into two sub-portions.
8. The method of claim 1 , further comprising:
forming a third portion in the channel region, the third portion providing a different threshold voltage than the first portion.
9. The method of claim 8 , wherein the third portion is formed such that the first portion separates the third portion from the second portion.