Multi-Gate FET Voltage Leveling for RF Switch Reliability

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Solution Overview

Problem

In RF switch circuits using multi-gate FETs, non-uniform AC voltage distribution across stacked transistors can lead to premature breakdown, reducing the power handling capability of the switch.

Innovation Solution

Implementing a voltage leveling circuit that ensures a more uniform distribution of AC voltages across multi-gate FETs in a stack by using capacitors and resistors to equalize voltage swings, preventing excessive stress on the first FETs in the stack.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a stack of multi-gate FETs is used to achieve higher power handling capability, then the power handling capability is improved, but non-uniform AC voltage distribution causes premature breakdown of the first FETs, worsening the reliability

Engineering Contradiction:

Improvepower handling capabilityVSAvoidpremature breakdown

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent applies the equipotentiality principle by introducing voltage leveling circuits that equalize the AC voltage distribution across stacked multi-gate FETs. These circuits include capacitors connected between the channel and gate, which create a capacitive voltage divider effect to distribute voltage more uniformly across all FETs in the stack, preventing the first FETs from experiencing excessive voltage stress and breakdown.

Inventive Principle:

Principle #12Equipotentiality

2Ease of operation

If multiple gates are positioned over the channel to enable better electrical control, then the control over channel conductivity is improved, but the device complexity increases

Engineering Contradiction:

Improveelectrical controlVSAvoiddevice complexity

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent merges multiple gate structures over a single channel to create a multi-gate FET configuration. This combining of multiple gates allows for enhanced electrical control of the channel conductivity while maintaining a compact integrated structure. The multiple gates can be controlled independently or together, providing versatile control capability without requiring separate discrete devices.

Inventive Principle:

Principle #5Merging (Combining)

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

This approach prevents premature breakdown of the first FETs in the stack, enhancing the power handling capability of the multi-gate FET switch by maintaining even voltage distribution across all FETs in the off-state.

Implementation Method 1

a first capacitor electrically connected between the channel and the first gate structure

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS10734516B2RF switches, integrated circuits, and devices with multi-gate field effect transistors and voltage leveling circuits, and methods of their fabrication

Publication Date: 2020.08.04 NXP USA INC

AI summary

Embodiments of field effect transistor (FET) circuits, RF switches, and devices include source and drain terminals coupled to an active surface of a semiconductor substrate, a channel in the substrate between the source and drain terminals, and a plurality of gate structures coupled to the active surface over the channel. A channel contact is coupled to the active surface over the channel between a first pair of the gate structures, and a first capacitor is electrically coupled between the channel contact and a gate structure of the plurality of gate structures.