Bidirectional Silicon Controlled Rectifier for ESD Protection
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Solution Overview
Problem
Conventional no-snapback silicon controlled rectifiers are unidirectional, making them unsuitable for electro-static discharge protection circuit designs at both positive and negative high-voltage ports, as they exhibit a strong snapback effect that is not applicable to negative high-voltage ports.
Innovation Solution
A bidirectional silicon controlled rectifier structure is developed, featuring a P-type substrate with N-type and P-type wells, and shallow trench isolation, allowing for mirror symmetry and adjustable doping concentrations and trench widths to achieve a no-snapback effect, enabling operation at both positive and negative high-voltage ports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional unidirectional no-snapback silicon controlled rectifier is used, then the snapback effect is eliminated for positive high-voltage ports, but the device cannot be applied to negative high-voltage ports due to forward conduction of the internal parasitic diode
Solution Approach 1:
The patent applies asymmetry by introducing a third well (P-type well for N-type substrate or N-type well for P-type substrate) that breaks the symmetry of the conventional two-well structure. This asymmetric configuration creates different breakdown characteristics for positive and negative voltage conditions, enabling bidirectional protection while maintaining no-snapback effect. The third well is strategically positioned and doped to control the snapback behavior specifically for one polarity while allowing the other polarity to function differently.
Solution Approach 2:
The patent achieves universality by designing a silicon controlled rectifier structure that can handle both positive and negative high-voltage conditions. The device incorporates multiple wells (N-type and P-type) with specific doping concentrations and geometric configurations that enable it to function as an ESD protection device for both polarities. The structure universally protects against snapback effects while maintaining controlled forward conduction characteristics for bidirectional operation.
2Manufacturing precision
If the doping concentrations and trench widths are adjusted to achieve no-snapback effect, then the holding voltage approaches the trigger voltage, but the device structure becomes more complex
Solution Approach 1:
The patent applies local quality by implementing different doping concentrations in different regions of the device. Specifically, the first and second heavily doped regions have different doping concentrations from the third heavily doped region. This localized variation in doping quality allows precise control over the electrical characteristics at different locations, enabling the no-snapback effect to be achieved in specific regions while maintaining overall device functionality. The shallow trench isolation is also strategically placed to provide local electrical separation and control.
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 bidirectional silicon controlled rectifier effectively prevents snapback at negative high-voltage ports, ensuring compatibility with existing CMOS processes and reducing manufacturing complexity, thus enhancing electro-static discharge protection for both positive and negative high-voltage ports.
Implementation Method 1
shallow trench isolation is provided between the P-type heavily doped region and the N-type heavily doped region
Implementation Method 2
an internal parasitic diode formed by P+126 in P-type well 170->N+128 in N-type well 160 of the silicon controlled rectifier is in a forward conduction state
Implementation Method 3
dual positive feedbacks provided by those couplings between its internal parasitic PNP and NPN triodes
Data Source
AI summary
The present disclosure provides a silicon controlled rectifier and a manufacturing method thereof. The silicon controlled rectifier comprises: a P-type substrate; an N-type well 60, an upper portion of which is provided with a P-type heavily doped region 20 and an N-type heavily doped region 28; an N-type well 62, an upper portion of which is provided with a P-type heavily doped region 22 and an N-type heavily doped region 26; and a P-type well 70 connecting the N-type well 60 and the N-type well 62, an upper portion of which is provided with a P-type heavily doped region 24; wherein a first electrode is in mirror symmetry with a second electrode with respect to the P-type heavily doped region 24, and shallow trench isolations are respectively provided between the P-type heavily doped region 24 and each of the N-type heavily doped region 28 and the N-type heavily doped region 26.