A MOSFET has a threshold voltage of 1 V and oxide thickness of 500 x 10-8 [εr = 3.9; ε0 = 8.85 x 10-14 F/cm, q = 1.6 x 10-19 c]. The region under the gate is ion implanted for threshold voltage tailoring. The base and type of impant required to shift threshold voltage to - 1 V are __________ .

• 8.6 x 1011/cm2, p-type
• 8.6 x 1011/cm2, n-type
• 0.86 x 109/cm2, p-type
• 1.02 x 1012/cm2, n-type

Correct Answer: 8.6 x 1011/cm2, p-type

Explanation:

V_T(new) = V_T(odd) +

= 6.903 x 10^-8

∴

∴

f_B = - 8.6 x 10¹¹

The threshold voltage is always negative for p-channel and hence implant is of p-type.