Method of measuring the threshold voltage of metal-oxide semiconductor field-effect transistors

Claim 1

A method for measuring the threshold voltage of a MOSFET device having a source, a drain, and a gate, all formed on a substrate, the method comprising the steps of: (1) applying a variable DC voltage between the drain and the source, and grounding the source and the substrate; (2) varying the drain-to-source voltage among a first predetermined number of levels in a first range; (3) repeating the following steps for each level of the drain-to-source voltage: (i) applying a variable DC voltage between the gate and the source, and varying the gate-to-source voltage among a second predetermined number of levels in a second range, (ii) measuring the current flowing between the drain and the source for each level of the gate-to-source voltage, (iii) plotting a first curve which represents a drain-to-source current versus gate-to-source voltage characteristic, (iv) determining the position of a point on the plot for which a line tangential to the point has a slope that is maximum for the plot, and (v) linearly extrapolating the maximum slope line to obtain one K parameter value which is the intercept of the maximum slope line with the gate-to-source axis; (4) plotting a second curve which represents the K parameter versus drain-to-source voltage characteristic; and (5) extrapolating the second curve to obtain the intercept of the second curve with the K parameter axis, the intercept representing the threshold voltage of the MOSFET device.

Claim 2

A method for measuring the threshold voltage of a MOSFET device having a source, a drain, and a gate, all formed on a substrate, the method comprising the steps of: (1) applying a variable DC voltage between the drain and the source, and grounding the source and the substrate; (2) varying the drain-to-source voltage among a first predetermined number of levels in a first range; (3) repeating the following steps for each level of the drain-to-source voltage: (i) applying a variable DC voltage between the gate and the source, and varying the gate-to-source voltage among a second predetermined number of levels in a second range, (ii) measuring the current flowing between the drain and the source for each level of the gate-to-source voltage, (iii) plotting a first curve which represents a drain-to-source current versus gate-to-source voltage characteristic, (iv) determining the position of a point on the plot for which a line tangential to the point has a slope that is maximum for the plot, and (v) linearly extrapolating the maximum slope line to obtain one K parameter value which is the intercept of the maximum slope line with the gate-to-source axis; (4) plotting a second curve which represents the K parameter versus drain-to-source voltage characteristic; and (5) extrapolating the second curve to obtain the intercept of the second curve with the K parameter axis, the intercept representing the threshold voltage of the MOSFET device.