Hello everyone,
I would like to know what would be the effect on capacitance if we replace insulator with semiconductor. Just curious to know . What you guyz say?
semiconductor is partially conductive material, so the capacitor will have high leakage current between its two plates/leads, that is my very first thought of it.....
semiconductor is partially conductive material, so the capacitor will have high leakage current between its two plates/leads, that is my very first thought of it.....
Not quite. Saying a "semiconductor" is a "partially conductive material" is not exactly accurate. Its conductivity is determined by the dopants used.
Alec is right--if you have a P-N junction (P-doped semiconductor joined to an N-doped semiconductor", then you will get a varactor, which allows you to vary the capacitance based on a DC reverse bias voltage.
Actually I didnt think about it, but that is again interesting question. I would love to discuss both. As steven said, even I thought that capacitor will have leakage current and as a result the capacitance will decrease. But capacitance of capacitor is dependent on the relative permittivity of the material. If insulator SiO2 used whose relative permittivity is 3.9, and if replaced by Si whose relative permittivity is approx 11, then the numbers suggest that the capacitance will increase
Right, but someone mentioned earlier that semiconductors were partially conductive. I was just pointing out that that statement isn't entirely accurate
Right, but someone mentioned earlier that semiconductors were partially conductive. I was just pointing out that that statement isn't entirely accurate
For AC signals, you can represent the permittivity as a complex number, as follows, where σ is the conductivity and ω is the angular frequency, with j=sqrt(-1).
ε'=ε-jσ/ω
In general, the imaginary part of the permittivity represents losses of one type or another. Capacitors are rarely well described by a simple constant permittivity (except perhaps vacuum and air dielectric), and have frequency dependent real and imaginary parts to the permittivity. With enough effort you could analyze a particular semiconductor and develop a low frequency model that describes the behavior. My guess is you could find something already worked out in the literature too. Often you see such treatments when dealing with biological materials, which rarely are well approximated as pure insulators or pure conductors.
Leakage doesn't change the capacitance, it just makes a leaky capacitor (resistance in parallel with the capacitance) which won't hold the charge as long.
While I would not use the wording "leakage changes capacitance", I would also not say "leakage doesn't change capacitance". The situation is a bit complicated and it's not necessary to assign cause and effect. Real capacitors made with material dielectrics will have a very complicated frequency dependence to the capacitance. As I mentioned, the conductivity and other losses show up as the imaginary portion of the permittivity (if you do a sinusoidal analysis). The end result is a very complicated real and imaginary part, and these parts are related to each other through the Kramers-Kronig relations (a type of Fourier analysis). Hence, if you know the imaginary part of the permittivity (the losses), you can (in principle) know the real part. Also, the imaginary part of the capacitance changes the phase relation of the capacitor, and modifies the ideal 90 degree shift you expect between current and voltage.
Hello everyone,
I would like to know what would be the effect on capacitance if we replace insulator with semiconductor. Just curious to know . What you guyz say?
A semiconductor slab between the plates of a capacitor instead of a good dielectric insulator? You would have a leaky capacitor. The capacitance would depend on the permittivity and physical dimensions of the capacitor, like always. Leakage does not change the capacitance value, but it will affect the ability of the capacitor to store energy and also degrade most circuits. The conductivity of a semiconductor depends on the semiconductor material, temperature, and the doping concentration. A varactor is not relevant because we are not discussing junction diodes.
That's why I asked if the semiconductor was doped. If it was doped in such a way as to create a P-N junction, then a varactor would most definitely be relevant.
That's why I asked if the semiconductor was doped. If it was doped in such a way as to create a P-N junction, then a varactor would most definitely be relevant.
I believe the OP was referring to a semiconductor being doped for a homogeneous extrinsic result to be used as a dielectric slab, not a semiconductor being manufactured into a PN junction.
I believe the OP was referring to a semiconductor being doped for a homogeneous extrinsic result, not a semiconductors being manufactured into a PN junction.