Multigate RF Switch with Grounded Schottky Gate for Isolation
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Solution Overview
Problem
Conventional radio frequency switch circuits using field-effect transistors (FETs) face issues with insufficient isolation and inability to convert load impedance, particularly in multiband, multimode applications, leading to degradation of isolation and efficiency characteristics.
Innovation Solution
A semiconductor device with a multigate FET configuration, where the Schottky electrode is grounded between two Schottky electrodes, forming a depletion layer capacitor that reduces input impedance and enhances isolation, and a radio frequency circuit that includes a capacitor connected to an amplifying circuit with semiconductor devices having their ohmic electrodes connected to the capacitor, allowing for impedance conversion and improved isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple FETs are connected in series to improve isolation characteristics, then isolation between off-channel ends is improved, but device complexity increases and load impedance conversion capability is lost
Solution Approach 1:
The patent divides the gate control into three separate gate electrodes (first gate, second gate, third gate) along the channel length. This segmentation allows independent control of depletion layers at different positions, achieving high isolation characteristics while maintaining a single transistor structure rather than requiring multiple series-connected devices.
Solution Approach 2:
The multigate FET structure performs multiple functions simultaneously: it provides high isolation characteristics through controlled depletion layers, maintains load impedance conversion capability through the continuous channel structure, and reduces device complexity by using a single transistor rather than multiple series-connected devices. The three gates can be controlled independently or together to achieve different operational modes.
2Device complexity
If a conventional switch circuit is used as a transmission line selection circuit, then circuit simplicity is maintained, but load impedance conversion capability is lost and power amplifier efficiency degrades
Solution Approach 1:
The multigate FET simultaneously provides switching functionality and load impedance conversion capability. The continuous channel structure with three gates allows the device to function both as a switch and as an impedance transformation element, eliminating the need for separate impedance matching circuits and improving power amplifier efficiency while maintaining circuit simplicity.
3Length of moving object
If depletion layer capacitors are connected in series in a multigate FET, then channel length is reduced, but off-channel impedance is not reduced and isolation remains insufficient
Solution Approach 1:
The patent segments the gate control into three independent gate electrodes along the channel. This allows the depletion layers formed by each gate to work cooperatively to reduce off-channel impedance, achieving both short channel length and high isolation characteristics simultaneously, unlike series-connected depletion layer capacitors which cannot reduce impedance effectively.
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 improves isolation and load impedance conversion, enhancing the performance of radio frequency switch circuits for multiband, multimode applications by reducing input impedance and optimizing power amplifier efficiency.
Implementation Method 1
forming a depletion layer capacitor that reduces input impedance and enhances isolation
Implementation Method 2
a first Schottky electrode and a second Schottky electrode which are provided between the first and the second ohmic electrodes and serve as gate electrodes of the field-effect transistor
Data Source
AI summary
A semiconductor device and a radio frequency circuit which are appropriate for multiband, multimode performance can be realized as a semiconductor device including a field-effect transistor formed on a semiconductor substrate, and include: ohmic electrodes serving as source and drain electrodes of the field-effect transistor, first and second Schottky electrodes provided between the ohmic electrodes and serving as gate electrodes of the field-effect transistor, and a third Schottky electrode provided and grounded between the first and second Schottky electrodes.