Transistor Transient Characterization with Labview on Keithley 2612A

[provetta]

Hello everybody,

I just started working with LabView to characterize organic-based transistors with a keithley 2612A sourcemeter.

The connection to the instrument is already setup with two VIs to get IV curves and the time response of transistors by applying gate voltage square pulses. The transistor is hooked up in common source configuration i.e. Source and drain to the A channel and Source and Gate to the B channel.

I am now interested in applying constant Ig current and monitoring Isd current.

Since my VI for square wave voltage pulses is already setup (it already sources Vg and Vd to electrodes and measures Ig and Ids plotting also Vd), I naively tried to modify the string command to the Keithley by switching "smub.source.levelv=***" with "smub.source.leveli=***" in the subVI that imposes the square pulse with -1µA. To do this, I input -1E-6 value in the numeric control that used to feed into the Vg output. I made sure that the string command fed to the instrument was indeed "smub.source.leveli=-1E-6" by checking the string indicator while runnig the VI in debugging mode.

I don't get any error message and the main VI runs without errors but I don't see any change in applied Vg nor measured Ig.

Any idea why this shouldn't work?

Thank you very much in advance!

If anyone could and/or would help I can send screenshots of VI and its operation.

[cstorey]

Why not show us your code?  (VIs not screen shots) 

Are you using the Keithley 26xx driver there are good examples in there?  Find it here -  https://www.tek.com/source-measure-units/2635-software/keithley-series-2600-2600a-2600b-native-labvi...

As to your problem, its hard to say without seeing how you've configured everything prior to that one command.  But. before you specify a current level, you need to configure the SMU to source current and measure voltage.  Did you change all of that?  Did you reset compliance, measurement range, etc?  Surely the instrument throws errors even if your code doesn't.

[provetta]

Hello cstorey and thank you!

so here are the original VIs. main_t calls up the SMU VI which is the one I tried to modify.

Let me know what you think

thank you,

Tommaso

[cstorey]

Hi Tommaso,

I still don't fully understand what you are trying to do.  You want to apply a constant Igs and Vds then measure Vgs and Ids as a function of time?  (What kind of transistor?)  But this looks like there's a sweep/ramp being done??  

You also mention pulsing.  Please explain the measurement sequence a bit more.

Looking at your code it is a bit scrambled, and I don't have all the VIs.  From what I can see you never configure the SMU's  source or measure operations.  But your VI tries to set a voltage/current level (you had mentioned setting current??). You seem to be relying on a default state of the SMU, and thus can't make changes to Igs value because its expecting a voltage not a current.  You will need to explicitly setup the SMU to source I and measure V or vice-versa.  

I can help further if you give me more explanation.

Craig

[provetta]

Hello Craig,

so I am working with a kind of unusual type of transistor which are electrochemical transistors. the main difference with regular FET  is that instead of a dielectric there is an electrolytic solution. ions in the solution are pushed by the gate electrode into the active channel thereby having a non negligible gate current during device operation. I'd like to be able to pulse it at different Ig values while applying a constant Vds to get different rates of change of the Ids.

I'm sending you all the VIs but I'm not sure it will work... In any case from my understanding of the vi operation, the "SMU voltage source and measure plusdelay.vi" is the one controlling channel B (where my gate and source ground are connected). In the afore mentioned VI, I modified just the function value from Voltage to Current so that the command sent to the instrument in the OUTPUT SOURCE ENABLE is "source.leveli=1E-5"

The main VI (main Eleni.VI) allows also to define different values for the square wave function to scan through in the same measurement. Since I need to perform the Isd measurements at different Ig values this fuction is also of interest to me.

Hopefully I answered your questions and maybe you can give some more - very appreciated - advice.

Thank you and looking forward to hearing from you,

Tommaso

[cstorey]

Hi Tommaso,

I'll have a look at this tonight.  I think this can work with a little clean-up and some improved settings.

What are the bias and pulse conditions you wish to use, there are no default values saved in the VI.

Craig

[provetta]

Hi Craig,

that sounds great.

Vds needs to be kept constant at -0.8 V

More or less I need Ig pulses of 5 seconds on and 15-20 seconds off. 

Ig values between 1 - 20 µA should be ok. Vg would be vary to keep Ig constant and will take values between 0 and 1 V. (both Ig and Vg might be negative but depends on the seconducting material I'm using)

Thanks again, I really appreciate it

Tommaso

[cstorey]

Hi Tomasso,

I had a look at the code, but have problems following your logic.  There does not appear to be any synchronization between the gate pulse and the drain current measurement.  Normally you would need to setup the internal trigger model of the instrument to make sure that the measurements occur simultaneously.  How are you handling this?  I know your pulses are long so perhaps you got away with this before just by luck. There isn't even dataflow scheduling the measurements, so I'm not sure what the sequence would be.    There is an example in the driver, you might try that to see if it works for you.   When I have time I'll see if I can work out a pulse trigger model.  I've never tried current pulses, so it will be something new to learn.

Craig