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Instrumentation: Hewlett Packard 8116A Pulse/Function Generator stanfor reserch system lock in amplifier SR830 Transistor: Indium Gallium Zink Oxide 320/20

objective: Measure the capacitance of the gate dielectric as a function of VG

Firstly I USED a Source measuring Unit to perfor DC current characterization to verify that the transistor is working correctly.

I did 6 scans, changing Vgate of 1. then scanned through Vdrain and registered the data. Here i'm plotting ID/VD to show the output characteristics. enter image description here

We then performed a similar scan: with VD=0.1 and VD=5, scanning over VG, to get the transfer characteristics. this one didn't come out as we expected. enter image description here we expected a clear increase in ID at a certain value of VG, as it starts to conduct.

At this point I wanted to characterize the capacitance that forms between the gate electrode and the channel. We used AC voltage (from the function generator) and applied it to the gate. We had a Source and drain connection going out from which we measured current aplitude and phase (with a current amplifier and a lock in amplifier)

We did this at different DC VOltage offsets because Ctot=Cpar+C and Cpar is not affected by different DC voltages.

i'm not sure how to change the circuit or which symbol represents my transisoro/curicuit better. i hope this is enough detail

I have this set of data, and I need to find the capacitance.

-Amplitude input(V)= 3 -Frequency (kHz)=10 - Offset (V)= -6 +0.4 until 4.1

  • Amplitude lock =196.48, 197.7 201.1, 209.4, 222.6, 240.2, 268.3, 290.8, 313.7, 334.9, 352.3, 368.6, 366.8, 368.5, 369.5, 370.4, 371, 371.3, 371.7, 372, 372.2, 372.4, 372.5, 372.6, 372.7, 372.8, 372.9, 373, 373.1, 373.2, 373.3, 373.4, 373.5, 373.6, 373.7

  • Phase (degrees)= -99 basically always +-1

I've never drawn a circuit before, so didnt know how to insert a lock-in. Now, i basically think that the Capacitance can be calculated from Z=1/(CwJ) where i Know W for sure. however i'm not sure about the rest.


closed as unclear what you're asking by Andy aka, Marcus Müller, winny, Voltage Spike, Sparky256 Jun 8 '18 at 2:24

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ This is not remotely enough information. Expect it to be closed soon unless you provide much more. \$\endgroup\$ – WhatRoughBeast Jun 6 '18 at 14:05
  • \$\begingroup\$ what kind of information? \$\endgroup\$ – leo electrics Jun 6 '18 at 14:10
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    \$\begingroup\$ all that you can give about where that data comes from, how it was measured, what device under test is… \$\endgroup\$ – Marcus Müller Jun 6 '18 at 14:14
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    \$\begingroup\$ Why do you keeeeeeep repeating letters like "V V" and "kHz kHz"? Try formatting your question so that it doesn't look like a jumble of randomness. \$\endgroup\$ – Andy aka Jun 6 '18 at 14:24
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    \$\begingroup\$ Also, you are not actually asking a question... \$\endgroup\$ – Daniel Jun 6 '18 at 14:46

You are not asking a question per se, but are puzzled by the results. You should not be. Look at the distortion suddenly appear when Id is down to 1 nA or so, and then flat-lines below that.

All transistors have a minimum drain or collector current, regardless of drive voltage or current, where the basic atomic structure no longer allows electrons to flow. They are semi-conductors after all, which means they have a minimum current as well as the more obvious maximum current, even a pulsed current limit.

Look up these details on the datasheets for a given transistor, and it will list the minimum cut-off current where it will no longer conduct current. I am surprised to see it working down to tens of nano-amps.

  • \$\begingroup\$ ok, so is it possible to estimate the threshold from the graph? i was thinking that ID would drop to 0 so i could get the threshold value, but it doesn't seem like the case here \$\endgroup\$ – leo electrics Jun 9 '18 at 16:50

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