Variable Capacitor Circuit Using Shared Dielectric and FET Switch
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Solution Overview
Problem
Existing variable capacitance elements have a limited range of capacitance variation and cannot set capacitance to zero, which is insufficient for applications requiring significant frequency modulation, such as wideband communication systems and power supply circuits.
Innovation Solution
An electronic element comprising a switch configured as an electric field effect transistor with a capacitor that can vary capacitance from zero by using a dielectric layer sandwiched between terminal electrodes, allowing for wide-range capacitance variation including zero capacitance states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the distance between facing comb-tooth electrodes is changed to vary capacitance, then capacitance can be adjusted, but the range of variable capacitance is limited and cannot be set to zero
Solution Approach 1:
The capacitor is divided into two independent capacitors (first capacitor with gate insulating film and second capacitor with dielectric layer) that can be controlled separately. This segmentation allows one capacitor to be switched off while the other provides baseline capacitance, enabling capacitance to be varied including zero states without complex movable electrode structures.
Solution Approach 2:
The gate insulating film serves dual functions: as the dielectric layer for the first capacitor and as the insulating layer for the FET switch. This multi-functionality reduces the need for separate dielectric layers and simplifies the overall structure while achieving wide capacitance variation range.
2Strength
If the film thickness of gate insulating film is increased to increase withstand voltage, then voltage resistance improves, but capacitance value decreases in inverse proportion to film thickness
Solution Approach 1:
The total capacitance is segmented into two capacitors with different dielectric layers. The first capacitor (gate insulating film) provides high withstand voltage, while the second capacitor (dielectric layer) provides high capacitance. By controlling them independently, the system achieves both high voltage resistance and adequate capacitance value simultaneously.
Solution Approach 2:
Different dielectric materials are used for the two capacitors with different properties: gate insulating film with high breakdown voltage and dielectric layer with high permittivity. This parameter change in material selection allows optimization of both withstand voltage and capacitance value independently.
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
Enables capacitance variation over a wide range, including zero, enhancing the capability for frequency modulation in applications like wideband communication systems and power supply circuits.
Implementation Method 1
a gate insulating film that overlaps the channel forming film
Implementation Method 2
sandwiching a dielectric layer therebetween
Data Source
AI summary
An electronic element and a circuit device is provided that varies a physical quantity of a passive element in a wide range including when the physical quantity is zero. A variable capacitance element includes a switch and an element that configures a capacitor. The switch has a source electrode, a drain electrode, a channel forming film that overlaps at least a part of the source and drain electrodes, a gate insulating film that overlaps the channel forming film, and a gate electrode on the gate insulating film. The element has a terminal electrode electrically connected to the source electrode, and a terminal electrode that configures a capacitor between the terminal electrode and a part of the drain electrode by sandwiching a dielectric layer therebetween or being in contact with the dielectric layer. The dielectric layer and the gate insulating film are the same insulating film.