# Capacitance from data of a lock in amplifier [closed]

simulate this circuit – Schematic created using CircuitLab

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.

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. 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, Sparky256Jun 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.

• This is not remotely enough information. Expect it to be closed soon unless you provide much more. – WhatRoughBeast Jun 6 '18 at 14:05
• what kind of information? – leo electrics Jun 6 '18 at 14:10
• all that you can give about where that data comes from, how it was measured, what device under test is… – Marcus Müller Jun 6 '18 at 14:14
• 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. – Andy aka Jun 6 '18 at 14:24
• Also, you are not actually asking a question... – Daniel Jun 6 '18 at 14:46