Keithley 2470

Model 2470
High Voltage SourceMeter Instrument User's Manual Section 6: Measure I-
V characteristics of FETs
2470-900-01 Rev. A / May 2019 6-17
-- Perform basic exponential fit
local diffHighV, diffLowV = 9.9e37, 9.9e37
local fitHighIndex = 0
local fitLowIndex = 0
local gateV = 0
local gateHighV = 0
local gateLowV = 0
-- Find actual gate voltage (and indexes) closest to fitHighV and fitLowV
for i = 1, gate.defbuffer1.n do
gateV = gate.defbuffer1.sourcevalues[i]
if math.abs(gateV - fitHighV) < diffHighV then
diffHighV = math.abs(gateV - fitHighV)
gateHighV = gateV
fitHighIndex = i
end
if math.abs(gateV - fitLowV) < diffLowV then
diffLowV = math.abs(gateV - fitLowV)
gateLowV = gateV
fitLowIndex = i
end
end
-- Find drain current and natural log of current at the two fit voltages
local drainHighI = drain.defbuffer1.readings[fitHighIndex]
local drainLowI = drain.defbuffer1.readings[fitLowIndex]
local ln_drainHighI = math.log(drainHighI)
local ln_drainLowI = math.log(drainLowI)
-- Find subthreshold swing, S, inverse of subthreshold slope, multiply by 1000 for mV/dec
local diffgateV = gateHighV - gateLowV
local diff_ln_drainI = ln_drainHighI - ln_drainLowI
local S = (diffgateV / diff_ln_drainI) * 1000
-- Print the results
print(string.format("Subthreshold Swing = %.4f mV/decade", S))
print(string.format("High current in fit = %.6E amps, low current in fit = %.6E amps",
drainHighI, drainLowI))
print("Index,".."\t".."gateV (V),".."\t".."drainI (A)")
for k = 1, stepPoints do
print(
string.format("%d,\t%.5f,\t%.6E",
k, gate.defbuffer1.sourcevalues[k], drain.defbuffer1.readings[k]
)
)
end