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Connecting SMU2400 and 8009 Fixture

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nico_C
Posts: 6
Joined: January 31st, 2011, 7:33 am
Country: France

Connecting SMU2400 and 8009 Fixture

Post by nico_C » September 19th, 2018, 8:36 am

Hi,

We would like to use 8009 Fixture to perform resistivity measurements. Unfortunately, we do not own a 6517B electrometer.

While we are aware it is not the proper way, we would like to use a Keithley 2400 SMU to source Voltage and measure Current. But we have trouble connecting the 8009 to the 2400.

We have a modified 237-ALG-2 cable, with triax on one side, and 3 banana plugs (Red, Black and Green) on the other side.

Our current setup is (see image):

SMU 2400 ------------------------------------------------------8009
Force Hi --------------------------------------------------------- Source Hi
Force Lo --------------------------------------------------------- Source Lo
Sense Hi ------------------- (Triax red) ------------------- Triax connector
Sense Lo ------------------- (Triax black) ------------------- Triax connector

<floating> ------------------- (Triax green) ------------------- Triax connector


Are we right ? Or should we use the back connectors of the 2400, to use guard (if so, how should we connect ?)
Thanks a lot for your help.

Nico_C
Attachments
8009_plus_SMU2400.jpg
8009_plus_SMU2400.jpg (118.38 KiB) Viewed 1882 times

nico_C
Posts: 6
Joined: January 31st, 2011, 7:33 am
Country: France

Re: Connecting SMU2400 and 8009 Fixture

Post by nico_C » September 26th, 2018, 7:41 am

[ Replying to myself ]

After further examination of the inner wirings of the 8009 Fixture, we try a new way to connect our SMU 2400.
Drawing and - are self-explanatory.

Theses wirings seem more correct to us, and any comments are welcomed.

Thanks to Tektronix Support service, we get a Keithley 6517 electrometer to perform comparative measurements with our samples.
Attachments
IMG_20180921_171807.jpg
IMG_20180921_171807.jpg (225.87 KiB) Viewed 1790 times
IMG_20180921_171758.jpg
IMG_20180921_171758.jpg (202.29 KiB) Viewed 1790 times
8009_wirings_volume_surligné.jpg
8009_wirings_volume_surligné.jpg (291.29 KiB) Viewed 1790 times

Andrea C
Keithley Applications
Keithley Applications
Posts: 1244
Joined: October 15th, 2010, 10:35 am
Country: United States
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Re: Connecting SMU2400 and 8009 Fixture

Post by Andrea C » October 4th, 2018, 5:49 am

The electrometer is giving you a voltage source and a separate amp meter. The SMU has voltage source and amp meter too, but the amp meter will be on the "hi side". You are constrained to make the current measurement on the same terminal that is also forcing the voltage. If you simply cannot get an electrometer, you'd be better served to get a power supply to act as the voltage source and use the SMU as an amp meter (force 0V and measure I).

The volume resistivity in particular could be problematic.

Keep in mind that the term "guard" with a SMU vs an electrometer has significant different implementations. In very general and high level, guarding means to place a voltage potential on a node to create an error reducing effect.

With a SMU, the guard is a driven guard. This means there is a voltage follower circuit and whatever voltage potential is on the force HI will also be on the guard. If an unwanted current leakage path exists from force HI to some node, then connection of the guard to that node will bring the delta V to zero and leakage currents are greatly reduced.

In contrast, the electrometer in current measure mode has no driven guard. In the diagrams of the 6517B with 8009, the guarding is achieved by connecting to the amp meter LO.
6517B_Volume_Resistivity.PNG
6517B_Volume_Resistivity.PNG (23.62 KiB) Viewed 1641 times
For volume resistivity, any current that might flow on surface of the sample from top electrode (that is at some positive voltage potential) and over the edge of sample will encounter the outer ring electrode which is at LO. The charge will be swept away rather than be able to enter the center electrode and be measured by the amp meter.
Your SMU based drawing will instead have a positive voltage on the guard ring and current will be flowing on the bottom surface of the sample between guard and the LO.

nico_C
Posts: 6
Joined: January 31st, 2011, 7:33 am
Country: France

Re: Connecting SMU2400 and 8009 Fixture

Post by nico_C » October 5th, 2018, 3:10 am

Hi Andrea,
Thank you for you reply.
Your explanation on guarding is by far the best I have ever read. Especially the difference between SMU driven guard and Electrometer guard.

Following the scheme Fig. 47, here is the new connections I would apply:
new_SMU_connections.jpg
new_SMU_connections.jpg (284.37 KiB) Viewed 1623 times
Please correct me if needed. I guess a simple (and independant) benchtop power supply will source a known voltage Vs (say Vs = +100V), and the SMU, in amp meter mode as you described, would measure current I. Then, I could calculate resistance by R = Vs / I

That way, I need to know more accurately Vs. What if I use a second SMU to replace the power supply ? (or the 2-channels SMU that is sitting on my desk, to be correct ?)

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