A method for compensating the
threshold voltage roll-off using transistors containing back-gates or body nodes is provided. The method includes designing a
semiconductor system or
chip having a plurality of transistors with a channel length of Lnom. For the present invention, it is assumed that the channel length of these transistors at the completion of
chip manufacturing is Lmax. This enables one to set the off-current to the maximum value of I-offmax which is done by setting the
threshold voltage value to Vtmin. The Vtmin for these transistors is obtained during
processing by using the proper
implant dose. After manufacturing, the transistors are then tested to determine the off-current thereof. Some transistors within the
system or
chip will have an off-current value that meets a current specification. For those
transistor devices, no further compensation is required. For other transistors within the
system or chip, the off-current is not within the predetermined specification. For those transistors,
threshold voltage roll-off has occurred since they are transistors that have a channel length that is less than nominal. For such short channel transistors, the threshold
voltage is low, even lower than Vtmin, and the off-current is high, even higher than I-offmax. Compensation of the short channel transistors is achieved in the present invention by biasing the back-gate or body node to give increased threshold
voltage about equal to Vtmin and hence an off-current that meets the predetermined specification, which is about equal to I-offmax.