The authors started studying and developing a new capacitor used for a 1.5 MHz highly-stable LC
tuning circuit in 1963. The high-stability of capacitor was severely required under the conditions that the signal voltage is from 1.4 to 9.2 V, the temperature is from -30 to 65°C and the period is for 20 years. The aging characteristics of the ceramic capacitors available 20 years ago were ΔC
=±0.1%/year or so, but the requirements was ΔC
=(-0.01±0.08)%/20 years. In addition, no design method to satisfy the requirements was established.
Therefore, the authors developed a ceramic capacitor housed in a low-humidity metallic case using a paraelectric (MgTiO3
) element, considering the stability of aging characteristics for 20 years.
It could be assumed during the study that the aging characteristics would change almost linearly with the logarithm of time under the influence of humidity. So, the authors proposed the characteristics change for 20 years could be expected based on the data for 10 days of the specimen. To confirm that the proposal was correct, they measured the aging characteristics for 20 years, and found that the measurement value was within the specified value of ΔC
which was (-0.01±0.08) %/20 years.