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Charge Extraction

Models 2400, 2401, 2410, 2420, 2425, 2430, 2440, 6430
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ChrisDoohan
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Joined: August 12th, 2011, 12:28 pm
Country: United States

Charge Extraction

Post by ChrisDoohan » August 12th, 2011, 3:00 pm

Hi, I'm new to a lab that uses the Keithley 2400, and I'm trying to write a series of triggers to perform a charge extraction experiment, a little like the Haynes-Shockley experiment. I'd like to source a small voltage, around 1.5V, hold it steady for several seconds, and then drop the voltage to zero and watch how the current tails off versus time. I'd like to do so with something on the order of 1ms resolution. I'm not sure whether to use the sweep function or just set the voltage level, and whether to use the trigger or source delay. Tentatively, I thought the following code may be a good start:
*RST
:SOUR:VOLT:MODE FIX
:SOUR:VOLT:RANG 1
:SENS:CURR:RANG:AUTO ON
:SENS:CURR:PROT 20E-3
:SENS:CURR:NPLC .06
:SENS:FUNC "CURR"
:FORM:ELEM CURR
:SOUR:VOLT:LEV 1.5

then some delay would be added in here

:SOUR:VOLT:LEV 0
:OUTP ON
:READ?
:OUTP OFF

This I just cobbled together from example code in the user manual. I'd also like to know what the difference is between the triggers ":SOUR:VOLT 10" and ":SOUR:VOLT:LEV 10." Both are used in the example code, and I don't see any clear difference between them off hand.
I'd appreciate any help.
- Chris

Nathan S
Keithley Applications
Keithley Applications
Posts: 254
Joined: February 28th, 2011, 6:17 am
Country: United States
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Re: Charge Extraction

Post by Nathan S » August 15th, 2011, 6:07 am

Chris,

Starting at the end first, there is no difference between :SOUR:VOLT 10 and :SOUR:VOLT:LEV 10. If you have the 2400 User's Manual Rev. J from August 2007, page 18-18 or p. 334/518 of the PDF shows the :LEVel in brackets which means it is option to use that part of the command.

Back to your coding, I would use sweeps here as you can set up a custom delay with a source-memory sweep so you can play with those and your NPLC to get to around 1ms per point as the timing should be pretty repeatable. The explanation on Source memory sweeps begins on page 10-6 (p.190) of the aforementioned version of the PDF manual with Table 10-2 showing a list of the remote commands used and page 10-22 (p.206) having an example source memory sweep. So at that point, if you are using the 2400 to measure the current leakage of your device once you remove the voltage, you can just source 0V and measure current that way and just specify a number of 0V points until you believe your measurements would be done. Start with a delay of 0.00ms and make sure to set your NPLC to 0.01 for the lowest overhead time, then add delay accordingly to get to your desired 1ms per point as I'd guess the overhead and quickest points will be just shy of 1ms. You will also need to use a fixed measure range (autorange off) and disable auto-zero.

ChrisDoohan
Posts: 2
Joined: August 12th, 2011, 12:28 pm
Country: United States

Re: Charge Extraction

Post by ChrisDoohan » August 18th, 2011, 9:50 am

Thank you very much!

So let's say I have 4 different types of points:
1)Source 0 volts and measure current after a 1 second delay
2)Source -2 volts and measure current without delay
3)Source -2 volts and measure current with a 1 second delay
4)Source 0 volts again and measure with no delay

If I were to save the configurations for these points in the memory, is there some way I can tell the machine to perform a sweep where it take measurement 1) four times, measurement 2) one hundred times, measurement 3) 4 times, etc? I'm confused about how point count, trigger count, and arm count work.

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