LDMOS Drift-Region Field Control Using Biased Shallow-Trench Field Plates
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Solution Overview
Problem
High-voltage power MOSFETs face challenges in managing high electric fields, which can lead to avalanche breakdown due to excessive voltage exposure at the drain/body interface, particularly in devices with deep trenches and closely spaced field plates.
Innovation Solution
The implementation of Laterally-Diffused Metal-Oxide-Semiconductor (LDMOS) transistors with longitudinally extending trenches and conductive field plates, electrically isolated by dielectric material, allows for the depletion of majority carriers in the drift region, thereby controlling the electric field and preventing breakdown by distributing the voltage drop across the depletion regime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep trenches with closely spaced field plates are used in high-voltage power MOSFETs, then the device can tolerate high voltages across terminals, but the semiconductor material between trenches becomes substantially depleted of majority carriers causing excessive voltage exposure at the drain/body interface that can cause avalanche breakdown
Solution Approach 1:
The drift region is divided into multiple laterally-separated regions by introducing纵向 trenches between closely spaced横向 trenches. This segmentation creates isolated depletion zones that prevent excessive voltage concentration at any single interface, thereby reducing avalanche breakdown risk while maintaining overall voltage tolerance
Solution Approach 2:
A lightly-doped drift region is introduced as an intermediary layer between the body and drain contact region. This drift region acts as a voltage-distributing medium that spreads the electric field across its volume, preventing excessive voltage exposure at the drain/body interface and eliminating avalanche breakdown conditions
2Reliability
If the semiconductor material is substantially depleted of majority carriers between closely spaced deep trenches, then high-voltage drain bias can be distributed across the depletion regime, but the drain/body interface is exposed to excessive voltage causing avalanche breakdown
Solution Approach 1:
The patent transitions from a two-dimensional depletion structure (between closely spaced trenches) to a three-dimensional depletion architecture by adding纵向 trenches that extend through the drift region. This creates a volumetric depletion regime that distributes voltage across multiple spatial dimensions, preventing excessive voltage concentration at the drain/body interface
3Reliability
If deep trenches with dielectric sidewalls and bottom isolating field plates are used, then majority carriers can be depleted from surrounding semiconductor material, but closely spaced trenches cause substantial depletion between trenches leading to avalanche breakdown
Solution Approach 1:
The drift region is segmented into laterally-separated depleted regions by纵向 trenches, creating isolated depletion zones. This segmentation allows each trench to deplete carriers in its local region without causing substantial depletion across the entire drift region, thereby maintaining carrier control while preventing avalanche breakdown
Solution Approach 2:
Carrier depletion is made local rather than global by using纵向 trenches to confine depletion to specific lateral regions. Each trench creates a localized depletion zone with dielectric isolation, allowing precise control of carrier distribution while preventing excessive overall depletion that would lead to avalanche breakdown
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 effectively increases breakdown voltages and maintains the electric field below critical thresholds, preventing avalanche breakdown while allowing for lower resistance profiles in the drift region, thus enhancing the operational reliability of high-voltage devices.
Implementation Method 1
The field plate can be biased to deplete majority carriers from the surrounding semiconductor material
Implementation Method 2
substantially depleting majority carriers throughout a longitudinal extent of the drift region
Implementation Method 3
The conductive field plates are separated from the drift region by a dielectric material
Implementation Method 4
a high-voltage drain bias can be distributed across the depletion regime so that the drain/body interface is not exposed to an excessive voltage
Data Source
AI summary
Apparatus and associated methods relate to controlling an electric field profile within a drift region of an LDMOS device using biased field plates to deplete majority carriers from a drift region between a body/drift-region metallurgical junction and a drain contact. Such field plates are located in trenches that longitudinally extend within the drift region. Field plates are laterally spaced apart from each other at a distance that permits substantial depletion of majority carriers between adjacent field plates. Trenches have trench bottoms located within a drift-region/substrate metallurgical junction so as to permit substantial depletion of majority carriers between trench bottoms and the drift-region/substrate metallurgical junction. Between adjacent trenches, dopant concentrations can be increased up to a threshold that can be substantially depleted under specified bias conditions. Such control of the electric field profile within the drift region may advantageously optimize a breakdown-voltage/on-resistance characteristic of the LDMOS device.