Integrated MOSFET-JFET Die for Low Forward Voltage Reverse Blocking

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Solution Overview

Problem

Conventional battery charging circuits with Schottky diodes have issues with package size and cost due to the need for a separate diode and MOSFET package, and they lack effective reverse blocking during accidental short circuits.

Innovation Solution

Integration of a diode-connected enhancement mode junction field effect transistor (JFET) with a MOSFET on a single semiconductor die, which functions as a reverse blocking diode with a low forward voltage drop and low reverse leakage current, replacing the conventional Schottky diode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a Schottky diode and MOSFET are packaged separately in a co-package, then reverse blocking function is provided, but package size and manufacturing cost increase

Engineering Contradiction:

Improvereverse blocking functionVSAvoidpackage size

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent integrates the Schottky diode and MOSFET onto a single semiconductor die by forming the diode using the MOSFET's drain region and substrate, eliminating the need for a separate diode die and reducing package size while maintaining reverse blocking functionality

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The MOSFET structure is designed to serve dual functions: the main MOSFET for power switching and the integrated diode structure (using drain-substrate junction) for reverse blocking, allowing one device to perform multiple functions that previously required separate components

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If a Schottky diode and MOSFET are packaged separately in a co-package, then reverse blocking function is provided, but manufacturing cost increases

Engineering Contradiction:

Improvereverse blocking functionVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If a MOSFET with built-in body diode is used, then device simplicity is maintained, but reverse blocking during short circuit fails

Engineering Contradiction:

Improvedevice structure simplicityVSAvoidreverse blocking during short circuit

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent modifies the local structure by creating a specially doped drain region with specific conductivity type opposite to the substrate, forming a diode structure with appropriate forward voltage drop characteristics that enables reverse blocking while maintaining the overall MOSFET structure

Inventive Principle:

Principle #3Local quality

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 integration reduces package size and manufacturing costs while providing effective reverse blocking and low forward voltage drop, comparable to a PN junction diode, and low reverse leakage current, enhancing the safety and efficiency of battery charging circuits.

Implementation Method 1

a diode-connected enhancement mode junction field effect transistor (JFET) with its source, body and gate connected together and biased at a positive voltage with respect to its drain... functions like a diode but has a lower turn-on voltage than a conventional PN diode

Methodology Applied

Scientific EffectDepletion region:

Implementation Method 2

The JFET channel element zones act primarily as resistive current paths shunting the equivalent P-N junction diode elements. The conductivity of the JFET channel element zones depends upon the coverage of their neighboring depletion zones

Methodology Applied

Scientific EffectDepletion zone:

Implementation Method 3

A battery charging source having a first charging terminal and a second charging terminal with the first charging terminal connected to the first battery terminal. A serial connection of a MOSFET and an enhancement mode JFET for bridging the second charging terminal to the second battery terminal

Methodology Applied

Scientific EffectField effect transistor conduction:

Data Source

PatentUS8669613B2Semiconductor device die with integrated MOSFET and low forward voltage diode-connected enhancement mode JFET and method

Publication Date: 2014.03.11 ALPHA & OMEGA SEMICONDUCTOR INC

AI summary

A semiconductor die with integrated MOSFET and diode-connected enhancement mode JFET is disclosed. The MOSFET-JFET die includes common semiconductor substrate region (CSSR) of type-1 conductivity. A MOSFET device and a diode-connected enhancement mode JFET (DCE-JFET) device are located upon CSSR. The DCE-JFET device has the CSSR as its DCE-JFET drain. At least two DCE-JFET gate regions of type-2 conductivity located upon the DCE-JFET drain and laterally separated from each other with a DCE-JFET gate spacing. At least a DCE-JFET source of type-1 conductivity located upon the CSSR and between the DCE-JFET gates. A top DCE-JFET electrode, located atop and in contact with the DCE-JFET gate regions and DCE-JFET source regions. When properly configured, the DCE-JFET simultaneously exhibits a forward voltage Vf substantially lower than that of a PN junction diode while the reverse leakage current can be made comparable to that of a PN junction diode.