Open-Drain Signal Terminal ESD Protection via Parasitic Bipolar Transistor
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Solution Overview
Problem
Semiconductor devices with open-drain signal terminals face challenges in providing effective electrostatic discharge (ESD) protection due to the difficulty in implementing ESD protection elements between the signal terminal and the higher voltage VDD terminal, as conventional protection elements are not directly applicable, leading to inefficient discharge paths and potential drain diffusion layer breakdown.
Innovation Solution
The semiconductor device incorporates a parasitic bipolar transistor formed between a pair of second conduction-type regions and a second conduction-type guard ring region, which are coupled to the open-drain signal terminal, allowing direct discharge to the first power source terminal, and includes bypass regions to distribute current flow and prevent concentration on specific parasitic bipolar transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ESD protection elements are provided between the signal terminal and power source terminal VDD, then ESD protection is improved, but in open-drain signal terminals this is difficult to implement because voltage higher than VDD is applied in common use state
Solution Approach 1:
The patent introduces a parasitic bipolar transistor as an intermediary mechanism between the open-drain signal terminal and the power source terminal VDD. This parasitic bipolar transistor is formed by specific doping regions (first conduction-type well, second conduction-type regions, and guard ring regions) that enable ESD discharge without requiring a direct protection element connection. The intermediary structure allows ESD protection while maintaining compatibility with the open-drain terminal's voltage characteristics.
2Reliability
If ESD protection element is provided between signal terminal and power source terminal VDD, then discharge path is improved, but current concentrates on specific parasitic bipolar transistors causing drain diffusion layer breakdown
Solution Approach 1:
The patent segments the current discharge path by introducing multiple second conduction-type regions (first region, second region, third region) distributed across the structure. Each region forms its own parasitic bipolar transistor with the first conduction-type well and guard ring regions. This segmentation divides the concentrated current into multiple parallel discharge paths, preventing current overload on any single drain diffusion layer and avoiding breakdown.
Solution Approach 2:
The patent applies local quality by creating regions with different conduction types (first conduction-type well vs. second conduction-type regions) in specific locations. The guard ring regions are strategically positioned to control current distribution locally. This local differentiation of electrical properties ensures that current is distributed evenly across multiple parasitic bipolar transistors rather than concentrating on one location, protecting the drain diffusion layer from breakdown.
3Use of energy by moving object
If open-drain signal terminal structure is used, then power consumption is reduced by stopping power source supply, but signal terminal requires N-channel open-drain structure and cannot use conventional ESD protection elements
Solution Approach 1:
The patent enables the open-drain signal terminal structure to provide its own ESD protection through the parasitic bipolar transistor mechanism formed by the doped regions. The terminal structure itself, with the first conduction-type well, second conduction-type regions, and guard ring regions, generates the protective function without requiring external protection elements. This self-service approach maintains the power-saving benefits of the open-drain structure while providing inherent ESD protection capability.
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 configuration enables efficient ESD discharge from the open-drain signal terminal to the power source terminal, reducing the risk of drain diffusion layer breakdown and ensuring effective protection by dispersing current flow, thus enhancing the ESD protection mechanism.
Implementation Method 1
enables efficient ESD discharge from the open-drain signal terminal to the power source terminal
Implementation Method 2
The semiconductor device incorporates a parasitic bipolar transistor formed between a pair of second conduction-type regions and a second conduction-type guard ring region
Data Source
AI summary
A second conduction-type MIS transistor in which a source is coupled to a second power source over the surface of a first conduction-type well and a drain is coupled to the open-drain signal terminal is provided. A second conduction-type first region is provided at both sides of the MIS transistor in parallel with a direction where the electric current of the MIS transistor flows and coupled to the open-drain signal terminal. The whole these components are surrounded by a first conduction-type guard ring coupled to the second power source and the outside surrounded by the first conduction-type guard ring is further surrounded by a second conduction-type guard ring coupled to a first power source. Thereby, the semiconductor device is capable of achieving ESD protection of an open-drain signal terminal having a small area and not providing a protection element between power source terminals.