Issue with PXI 4132 SMU

[phx_tech]

I have observed PXI 4132 sometimes is load dependent. We were testing one particular device
which is a bi-directional part and when we forced a current across the device in the negative direction the whole
current is not available across a device (i.e) when I force -1mA across the device I should see a 1mA across the device.
However what we observe is that only 0.5mA is available across the device. This happens only in the negative direction.
2.)I have observed this behavior only in one particular device. We have tested the same device on keithley 2611 and they
are measuring good. I feel the problem has to be with the SMU.
how much output impedance is present in this SMU? How can this problem be solved?

[Brandon_G.]

Hi phx_tech,

What do you have your voltage limit set to?  If it's set really low, then perhaps you are hitting compliance in one direction but not another?  By a "bi-directional part" do you mean that the voltage magnitude is the same whether applying + 1 mA or - 1 mA?  Can you check if you're in compliance in the negative current direction?  What current range are you in when you perform this test?

Thanks!

Brandon G

[Brandon_G.]

P.S.  It maybe helpful if you can send us screenshot of Soft Front Panels if you're using this to test your DUT.

Thanks!

[phx_tech]

Hi Brandon,

   I am doing this measurement from ni dc source front panel. I have set the voltage limit to 10V . In the positive direction I am forcing a 1mA and i am reading 7.6V and in the negative direction when I force -1mA , I should read some thing around 6.9 V but I read 5.4 volts and the current across the device is not 1mA , I can see only 0.5mA across the device. The current range I used was 10mA. I also tried it with 1mA current range but there isnt much difference. When I use a resistor to perform the test or a simple diode it works perfectly fine.

[Brandon_G.]

Hi Phx_tech,

You're output could be oscillating, which can happen with very reactive loads ; do you have a scope you can place on the output to look at the voltage?  Also, since you're using the Soft Front Panel, can you tell me if the SMU is in compliance or not?  There should be an indicator right under the voltage and current measurements.

Thanks!

Brandon G

[Now_With_Underscores]

Tell us more about your DUT.  What is it?  I agree you should probe the output with a scope and see if the output is unstable... this could occur if, for example, your DUT has a high frequency load demand near the SMU's switching frequency.

For troubleshooting purposes, let's disconnect your DUT and connect a 9kΩ resistor across the output, then set the SMU to output 1mA and verify the SMU reads ~9V.  Next, take a 9V battery and place it in in series with the 9kΩ resistor, set the SMU to 0V, and verify that the SMU is sinking 1mA.  Let us know what you find.

[phx_tech]

Hi John / Brandon,

   I have performed the tests that you had mentioned in the previous post. Also I captured some screenshots when I put the original DUT. I have also attached some screeshots of the IV characterstics of the DUT in question. I am able to make accurate measurements with the keithley 2611, However there is some problem when I use SMU 4132. Appreciate your help. Please refer to the attached word document.

[Brandon_G.]

Hey phx_tech,

Thanks for sending us the detailed screenshots.  I'm assuming that you are using a 4 wire measurement topology since you are in Remote Sense?

Since the device is bi-directional, I'm curious what would happen if you forced a -1 mA current but then reversed the direction of the DUT so that you're essentially still performing case 1.  Can you try this? This may tell us if the problem follows the output current direction of the SMU or the direction of the DUT.

Also, I'm assuming the curve tracer is an independent test without the 4132 connected?  It would be useful to see what the DUT and 4132 are doing when connected together.  Would it be possible to send a scope capture with the DUT + 4132 connected together when the output is in compliance?

John, do you have any other suggestions?

Thanks!

Brandon G

[phx_tech]

Hi Brandon,

   Thank you for the reply. Please find attached the screen shot when I reverse the DUT orientation and force -1mA.  I will try and uplaod screen shots of the curve trace with DUT attached ASAP. 

[Brandon_G.]

Hey phx_tech,

Just to clarify, I am looking for a voltage vs time graph and not a voltage vs current graph (as shown on a curve tracer).  Do you have a oscilloscope available to get a voltage vs time graph?  If you don't have a scope available can you measure the AC voltage and DC voltage across the DUT when this behavior occurs?

It looks like from the most recent screenings, that the problem follows the polarity of the DUT and not the polarity of the SMU output.  You had said that the problem occurs "only in this particular DUT" and I was wondering if you can clarify this statement.  Do you mean, that the problem is occurring only with a single DUT, or is the problem occurring with all bi-directional diodes DUTs you tested but not occurring with other types of DUTs such as resistors, capacitors, etc?

Can you send us a wiring diagram of your DUT to the SMU?  From what I can tell, everything seems connected properly but perhaps there is some insight we can gather by looking at the schematic.  

Also, when this behavior occurs, can you use a DMM and measure the lead drop across the Hi lead and then again across the low lead.  The voltage drop should be < 1 V (and I expect it is with such a low current) but it would be a good idea to check.

Thanks phx_tech!

Brandon G