Keithley S530 User Manual

Section 3: Test subroutine library reference S530 Parametric Test System Test Subroutine Library User's Manual
3-74 S530-907-01 Rev. A / September 2015
The steps used by this technique to find the maximum slope or maximum g
m
(where V
GS
step size is a
user-input variable):
1. From the last point below ithr (threshold I
DS
), measure four points (I
DS
, V
GS
). V
GS
is stepped,
and I
DS
is measured.
2. Calculate the first slope. This value is now the MAX SLOPE.
3. Step V
GS
, measure I
DS
.
4. Delete the first point in the five-point LLSQ array, and add the most recent point (shift left one
point).
5. Calculate the new slope.
6. Compare the new slope to MAX SLOPE.
7. Repeat steps 3 through 6 until the peak slope is crossed.
8. At peak slope, evaluate the V
GS
intercept (V
G
).
9. Calculate V
T
.
10. Return V
T
as vtext result and slope.
This subroutine is very sensitive to the V
GS
step size (vstep) and the start and stop points for the
binary search (vlow, vhigh), but is generally the most accurate way of evaluating the extrapolated
threshold voltage. The vtext2 subroutine is a further variation on this technique. The major
differences are that vtext2 uses the trigger and sweep calls to collect data, and it uses some
refinements in the data analysis. It also runs faster than the vtext subroutine.
If a zero or negative substrate pin is specified, the substrate is left floating. If the pin number is
greater than 0 and V
BS
is less than 0.9 mV, the substrate is grounded. In all other cases, it is
connected and forced.
The nmax parameter defaults to 21 steps if a smaller value is entered.
V/I polarities
The polarities of V
DS
and I
THR
are determined by the device type.
The vstep parameter is 10 mV to 100 mV. This depends on the vlow and vhigh parameters. For
an N-channel, if vlow = 0.0 and vhigh = 2.0, vstep should be positive.
Source-measure units (SMUs)
 SMU1: Forces vds, default current limit, measures I
DS
 SMU2: Searches V
GS
, default current limit
 SMU3: Forces vbs, default current limit

Keithley S530 Specifications

General

Brand	Keithley
Model	S530
Category	Test Equipment
Language	English