Bi-directional BJT ESD Protection Structure
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Solution Overview
Problem
High voltage devices face challenges in electrostatic discharge (ESD) protection due to low on-state resistance, high breakdown voltage, and low holding voltage characteristics, which can lead to physical destruction and latch-up issues during ESD events, especially in motor driver circuits where negative feedback can cause parasitic diode turn-on and irregular operation.
Innovation Solution
A bi-directional bipolar junction transistor (BJT) structure is developed using a modified BCD process with an epitaxial process, featuring a p-type substrate, N+ doped buried layer, N-type well region, and P-type well regions with specific doped plates and gate structures, allowing for bi-directional ESD protection without increasing device size or introducing additional masks, and combining two low voltage NMOS transistors for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface or lateral rules are increased to improve ESD performance, then ESD protection capability is improved, but device size increases and on-state resistance cannot be kept low
Solution Approach 1:
The patent introduces a vertical dimension by forming a deep N-type well extending from the surface into the substrate, creating a three-dimensional ESD protection structure. This vertical N-type well works with the P-type well to form a bipolar transistor that provides ESD protection through the vertical current path, eliminating the need to increase lateral surface dimensions while maintaining effective ESD protection capability
Solution Approach 2:
The patent changes the doping parameters by creating a deep N-type well with specific doping concentration and depth, and forming a bipolar transistor structure with optimized P-type and N-type regions. This parameter optimization allows the device to achieve low on-state resistance while providing adequate ESD protection through the vertical structure, resolving the contradiction between ESD capability and device size
2Reliability
If the breakdown voltage is increased to exceed operating voltage for protection, then voltage protection range is improved, but trigger voltage becomes higher than breakdown voltage causing internal circuitry damage before protection activates
Solution Approach 1:
The patent forms a bipolar transistor structure with a deep N-type well and P-type well during the manufacturing process, pre-configuring the ESD protection path before the device operates. This preliminary structure ensures that when ESD events occur, the protection mechanism is already in place and can activate at the appropriate trigger voltage, preventing internal circuitry damage while providing broad voltage protection range
Solution Approach 2:
The patent introduces a bipolar transistor as an intermediary protection mechanism between the high voltage device and ESD events. The bipolar transistor structure, with its specific P-type and N-type well configuration, acts as a mediator that triggers at a controlled voltage level, diverting ESD current before it can damage internal circuitry while maintaining the high breakdown voltage characteristic needed for broad protection range
3Reliability
If low holding voltage is used to enable ESD current conduction, then ESD protection performance is improved, but latch-up occurs more frequently during normal operation
Solution Approach 1:
The patent applies local quality by creating a deep N-type well with specific doping characteristics in a localized region, and forming a bipolar transistor structure with optimized P-type and N-type regions. This localized structure provides low holding voltage for effective ESD protection while the deep well configuration and bipolar transistor design prevent unwanted latch-up during normal operation by controlling the electrical characteristics in the protection region independently from the main device operation
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 bi-directional BJT provides effective ESD protection with a breakdown voltage near the high voltage device operation voltage, lower trigger voltage, and higher holding voltage to prevent latch-up, ensuring reliable operation during both positive and negative ESD events without causing irregularities in motor driver circuits.
Implementation Method 1
a first bipolar transistor portion comprising a first N-type well, a first P-type well, a first N-type plate, and a first P-type plate; and a second bipolar transistor portion comprising a second N-type well, a second P-type well, a second N-type plate, and a second P-type plate
Data Source
AI summary
A bi-directional electrostatic discharge (ESD) protection device may include a substrate, an N+ doped buried layer, an N-type well region and two P-type well regions. The N+ doped buried layer may be disposed proximate to the substrate. The N-type well region may encompass the two P-type well regions such that a portion of the N-type well region is interposed between the two P-type well regions. The P-type well regions may be disposed proximate to the N+ doped buried layer and comprise one or more N+ doped plates and one or more P+ doped plates.