Lateral Power MISFET Trench Dummy Gate Feedback Capacitance

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Solution Overview

Problem

In DC/DC converter circuits, power MISFETs face challenges with high switching losses and self-turn-on phenomena due to high feedback capacitance, which affects conversion efficiency, and existing structures struggle to reduce ON resistance while maintaining withstand voltage and breakdown resistance.

Innovation Solution

A power MISFET with a trench region formed shallower than the drift region, featuring a source and drain arrangement across a gate electrode with a dummy gate electrode between the gate and drain, reducing feedback capacitance without compromising withstand voltage or ON resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a trench power MOSFET is used to reduce cell size and ON resistance, then the ON resistance decreases, but the feedback capacitance becomes large causing increased switching loss and self-turn-on

Engineering Contradiction:

ImproveON resistanceVSAvoidswitching loss

Core Design Contradiction:

StrengthVSLoss of energy

Solution Approach 1:

The invention transitions from a conventional vertical trench structure to a lateral power MOSFET structure where the current flow and electric field distribution are reorganized in a lateral dimension. This dimensional change allows the drain and source to be arranged on the same surface plane, fundamentally altering the capacitance characteristics while maintaining low ON resistance through optimized lateral current paths.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The invention inverts the conventional power MOSFET architecture by placing the drain and source regions on the same surface rather than having the drain extend vertically. This inversion of the structural arrangement eliminates the overlap between gate and drain that causes feedback capacitance, while the lateral configuration maintains effective current conduction.

Inventive Principle:

Principle #13The other way round (Inversion)

2Loss of energy

If a lateral power MOSFET is used to reduce feedback capacitance, then the feedback capacitance decreases, but the cell size becomes large increasing ON resistance

Engineering Contradiction:

Improvefeedback capacitanceVSAvoidON resistance

Core Design Contradiction:

Loss of energyVSStrength

Solution Approach 1:

The invention applies local quality optimization by creating a concentrated high-field region at the drain edge through precise doping profiles and geometric design. This allows the electric field to be localized where needed for voltage blocking, while other regions maintain low resistance paths for current flow, achieving both low capacitance and low ON resistance simultaneously.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention utilizes parameter changes in the doping concentration profiles, junction depths, and geometric dimensions of the lateral structure to optimize the balance between breakdown voltage, ON resistance, and feedback capacitance. By adjusting these parameters, the device achieves superior performance across all three metrics compared to conventional structures.

Inventive Principle:

Principle #35Parameter changes

3Power

If the high-side switch is turned ON while the low-side switch is OFF, then voltage conversion occurs, but the drain voltage increase causes self-turn-on of the low-side switch

Engineering Contradiction:

Improvevoltage conversionVSAvoidself-turn-on

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The invention converts the harmful effect of drain voltage changes into a beneficial characteristic by using the lateral structure's inherent low feedback capacitance. The same voltage transitions that previously caused self-turn-on now produce minimal capacitive coupling, transforming the problem into an advantage for reliable high-frequency operation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8319289B2Power MISFET, semiconductor device and DC/DC converter

Publication Date: 2012.11.27 RENESAS ELECTRONICS CORP

AI summary

A technique for suppressing lowering of withstand voltage and lowering of breakdown resistance and reducing a feedback capacitance of a power MISFET is provided. A lateral power MISFET that comprises a trench region whose insulating layer is formed shallower than an HV-Nwell layer is provided in the HV-Nwell layer (drift region) formed on a main surface of a semiconductor substrate in a direction from the main surface to the inside. The lateral power MISFET has an arrangement on a plane of the main surface including a source layer (source region) and a drain layer (drain region) arranged at opposite sides to each other across a gate electrode (first conducting layer), and a dummy gate electrode (second conducting layer) that is different from the gate electrode is arranged between the gate electrode and the drain layer.