Variable Capacitance Element Using Sr-Based Insulator
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Solution Overview
Problem
Variable capacitance elements with comb-shaped electrodes suffer from increased stray capacitance and inadequate heat cycle resistance due to differences in thermal expansion coefficients between the dielectric and insulating materials.
Innovation Solution
Incorporating an insulating material containing at least Sr, and optionally Ti and/or Zr, for the insulating elements to reduce stray capacitance and enhance heat cycle resistance by matching the thermal expansion coefficients with the dielectric material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If comb-shaped electrodes are used to increase capacitance, then the capacitance variable rate increases, but stray capacitance increases due to the electrode structure
Solution Approach 1:
The electrode is divided into multiple finger-like segments arranged in a comb pattern, with each segment contributing to the overall capacitance while maintaining electrical connection through the substrate. This segmentation increases the effective capacitance area without requiring a single large electrode that would generate excessive stray capacitance.
Solution Approach 2:
The electrode structure transitions from a planar configuration to a three-dimensional comb-like arrangement extending in multiple directions. This dimensional change increases the effective capacitance surface area while distributing the electrode mass to reduce parasitic effects.
2Reliability
If different materials are used for the variable capacitance layer and insulating element, then the permittivity can be optimized, but heat cycle resistance becomes insufficient due to different coefficients of thermal expansion
Solution Approach 1:
The material composition parameters of the insulating element are adjusted by incorporating specific ratios of Sr, Ti, and Zr to modify its coefficient of thermal expansion. This parameter change allows the insulating element's thermal expansion characteristics to better match those of the BST variable capacitance layer, reducing thermal stress during temperature cycling.
Solution Approach 2:
The insulating element is constructed as a composite material combining SrTiO3 and SrZrO3 in specific proportions. This composite structure enables independent optimization of both permittivity and thermal expansion coefficient, achieving a balance between electrical performance and thermal stability that cannot be obtained with single-phase materials.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively decreases stray capacitance and improves heat cycle resistance, ensuring reliable performance across varying temperatures.
Implementation Method 1
an insulating material which contains at least Sr and which may preferably further contain Ti and/or Zr
Implementation Method 2
a capacitance that is varied by changing a permittivity of a dielectric layer by an applied voltage
Implementation Method 3
changing a permittivity of a dielectric layer
Implementation Method 4
matching the thermal expansion coefficients with the dielectric material
Data Source
AI summary
A variable capacitance element includes a variable capacitance layer made of a dielectric material, an electrode to obtain electrostatic capacitance in the variable capacitance layer, insulating elements that face each other via the variable capacitance layer, and a lead element extending from the electrode, wherein the insulating elements are made of an insulating material which contains Sr and at least one of Ti and Zr.