I want to measure dielectric constant of my oxide thin film. I have deposited the thin film on Si substrate. For dielectric measurement MOS structure has been fabricated using Al as electrode on both top (Shadow mask 1mm dia) and bottom. I measured capacitance - frequency using Agilent E4980A precision LCR meter and calculated permittivity. I am getting fluctuation at low frequency (Please see the attachment). But high frequency data is okay. I have measured with a lot of samples but in all case i am getting this type of behavior.
What may the possible cause?
Is it instrumental Fault or some problem in connection?
Regards.
Most probably the fluctuations which you see in measured data are due to sensitivity of the measurement Instrument or parasitics. At low frequencies the impedance of the capacity is growing, which means you Need to measure very small currents, therefore the precision of the measurments drops down. Look more carefully at specifications of the Instrument and estimate measurement precision. If it is in the range of your fluctuations then you have to think about more accurate measurement scheema. When observed fluctuations are much higher then measurement precision specs then you have problems with parasitic distortion signals.
This is actually a well-known problem in very many material systems. Look up "1/f noise" or "flicker noise". It's even called "pink noise" sometimes. Basically, any thing that has charges hopping through a complicated system of defect sites can do this. It seems to be surface-related much of the time. If you barely touch two wires together, so that they are not connected so well, the current between them will have flicker noise and would produce a graph looking like yours with frequency. It is the same if you touch the wires through a thin, poor piece of insulation in a humid environment. .
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