Threshold voltage roll-off compensation using back-gated mosfet devices for system high-performance and low standby power

摘要

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 L_nom. For the present invention, it is assumed that the channel length of these transistors at the completion of chip manufacturing is L_max. This enables one to set the off-current to the maximum value of I-off_max which is done by setting the threshold voltage value to Vt_min. The Vt_min 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 Vt_min, and the off-current is high, even higher than I-off_max. 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 Vt_min and hence an off-current that meets the predetermined specification, which is about equal to I-off_max.