This has completely changed my perception of ceramic caps.
-80% at 12V bias?? Holy crap!
I'd have thought you saw this already; you've been around a while!
Well, welcome to the
daily 10,000, and, a good reminder that this will always be new to someone, and so always bears repeating (a thread subject that's otherwise been done to death)!
Folks, please do a little research before placing all ceramic caps in the same category.
It's well known that C0G/NP0 ceramic material is highly stable with temperature, voltage and age. In fact this ceramic is so good that it's utilized in the high end high resolution DMMs as the main integrating capacitor in the multi-slope intergrating ADCs
However, here's an example of the typical cheap ceramic thru-hole disc that's commonly utilized for power supply decoupling. This capacitor is obviously made with a high K dielectric and shows very poor stability with applied DC voltage and temperature.
BTW these plots were produced by some new Python routines for use with LCR meters for frequency, voltage and temperature sweeping and plotting, you can find details here:
https://www.eevblog.com/forum/testgear/lcr-meter-plot-software/
Best,
Indeed, type 2 (X7R etc.) are also highly microphonic (piezoelectric), so are contraindicated for sensitive and low frequency (e.g. audio processing) applications, perhaps controls as well (when precision and stable controls are demanded, or when the environment is high vibration).
C0G are nearly ideal; they often have Q factors in the thousands, making them excellent for snubber and resonant applications. They have low absorption and leakage too (which exact brands/families do, however, is a carefully guarded secret), although not quite as low absorption as polystyrene or glass did (I think?).
The main downside to C0G is cost: values under 1nF are competitive with X7R etc., but above, they diverge quickly*; and values above 100nF are hardly available at all, and quite pricey at that. Selection doesn't improve at low voltage ratings, because the ceramic layers are just too thin -- density isn't good. (The material has a lower K than titanates, but much higher breakdown field strength.) On the other hand, they excel at high voltages: you can hardly find a 100nF X7R that's any good (read: >= -30% of nominal value) at 250VDC, even in 2220 size; but C0G doesn't depend on voltage at all and a, 1210 I think?, will fit such a value and voltage rating. The energy density at higher voltages (200-600V say) in fact is competitive with electrolytics!
*If you're *really* sensitive on cost, or doing large quantities (100k+?), probably the divergence falls at an even lower point. In the thousands, for hand-wavy pricing, it's kind of just in the noise below 1nF.
Interesting quirk: the Q is so high, and the values small to modest, that it can be kind of awkward to wire C0Gs in parallel arrays. Even the minor stray inductance along a tightly packed array (say 6nH for a half dozen in a row over ground plane) is enough to resonate them, and you get bathtub-sloshing resonant modes, say in the 10s to 100s MHz -- which can therefore be relevant for EMI purposes, say in SMPS.
Tim