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Connecting Ground Problem

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__vhb__
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Joined: June 2nd, 2015, 5:05 am
Country: Germany

Connecting Ground Problem

Post by __vhb__ » June 2nd, 2015, 5:25 am

Hi,
I use 2 Keithleys 2612 and 2612a for my project. One for applying voltage and one for measuring the voltage of some other parts. When I start measuring transfer curve with only one Keithley (2612a), there is no problem in measurements. Of course transfer curve with the other one (2612) shows higher current and the calibration which is done before measurement gives high capacitance. I changed the wires but this problem still remained and the biggest problem is that when I connect the ground of 4 channels together (Grounds of channels A & B of 2612 with channels A & B of 2612a), transfer curves shows higher amount of current. I have to set the grounds the same because for next measurement I have to use both Keithleys.
Does one of the Keithleys (maybe 2612) have been damaged? I also checked the samples without Labview program and when there is no connection between grounds of 2 Keithleys, Drain current is low and acceptable but when I add the grounds of the other Keithley, current goes one order in magnitude higher.
Would some one please hlep me?

Andrea C
Keithley Applications
Keithley Applications
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Re: Connecting Ground Problem

Post by Andrea C » June 3rd, 2015, 3:16 am

Can you elaborate about the transfer curve with the 2612 shows higher capacitance?

Can you do a simple IV sweep on a resistor with each SMU channel of your 2612 and validate that each channel is functional?

For connection of the LO of the four SMU channels together, you are doing something like the figure below illustrates? But you connect the LO of all four SMU channels together.
multi2612_connect_LOs.PNG
multi2612_connect_LOs.PNG (37.59 KiB) Viewed 18460 times

__vhb__
Posts: 3
Joined: June 2nd, 2015, 5:05 am
Country: Germany

Re: Connecting Ground Problem

Post by __vhb__ » June 4th, 2015, 1:19 pm

Andrea C wrote:Can you elaborate about the transfer curve with the 2612 shows higher capacitance?

Can you do a simple IV sweep on a resistor with each SMU channel of your 2612 and validate that each channel is functional?

For connection of the LO of the four SMU channels together, you are doing something like the figure below illustrates? But you connect the LO of all four SMU channels together.
multi2612_connect_LOs.PNG
Hi Andrea C,
Thanks for your support.
Can you elaborate about the transfer curve with the 2612 shows higher capacitance?
In the case of using only 2612, the transfer curve looks the same as 2612a and both machines show almost the same current range and higher capacitance (2612) just affects the gate source capacity measurement but in the case of connected grounds of both 2612 and 2612a (as you showed) unfortunately there is a huge difference in current in both off current and on current. I do not have a schematic now. I also connected a sample to 2612a and applied the voltage manually. when there was no ground sharing, everything was ok but when I connected the ground of the 2612 manually, the current went high hugely (from 10-20 uA to 250-300 uA). Of course 2612 was on but both channels were off.

Can you do a simple IV sweep on a resistor with each SMU channel of your 2612 and validate that each channel is functional?
Yes, I did it for each device on the transfer curve and no difference in current in the separated ground state. So I think each device separately acts well except for 2612 for capacitance measurement.

For connection of the LO of the four SMU channels together, you are doing something like the figure below illustrates? But you connect the LO of all four SMU channels together.
Yes, exactly. the ground connected as you showed.

__vhb__
Posts: 3
Joined: June 2nd, 2015, 5:05 am
Country: Germany

Re: Connecting Ground Problem

Post by __vhb__ » June 4th, 2015, 1:57 pm

Maybe following schematic can help you.

Image

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