Symmetrical Silicon Controlled Rectifier for Bi-Directional ESD Protection
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Solution Overview
Problem
Existing silicon controlled rectifier (SCR) devices for electrostatic discharge (ESD) protection are inadequate in providing protection against negative polarity electrostatic currents due to their asymmetric design, which limits their effectiveness in both positive and negative ESD scenarios.
Innovation Solution
A symmetrical SCR structure is designed with a P-type substrate, N-well, isolation structures, P-type and N-type doped regions, and P-type buried layers, allowing for bi-directional ESD current paths and reducing parasitic capacitance, enabling effective protection against both positive and negative ESD currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an asymmetric SCR structure with forward-bias diode is used, then the device can protect against positive polarity ESD currents, but it fails to provide adequate protection against negative polarity ESD currents
Solution Approach 1:
The patent applies asymmetry in reverse - it uses a symmetrical SCR structure where the doping concentrations and geometrical dimensions of the P-type and N-type regions are substantially equal, enabling bi-directional ESD protection. This symmetrical design allows the device to handle both positive and negative polarity ESD currents effectively, resolving the limitation of asymmetric single-polarity protection structures.
2Area of stationary object
If a compact SCR design is implemented, then the layout area is reduced, but the parasitic capacitance increases
Solution Approach 1:
The patent employs a shallow trench isolation (STI) structure that extends vertically into the substrate, effectively utilizing the third dimension to separate adjacent P-type and N-type regions. This vertical isolation approach reduces the horizontal layout area while simultaneously minimizing parasitic capacitance between opposite polarity regions, as the STI structure creates effective electrical separation without requiring large lateral spacing.
3Reliability
If the SCR structure is activated for ESD protection, then ESD current can bypass the circuit, but normal circuit operation may be compromised
Solution Approach 1:
The patent carefully controls the doping concentrations of the P-type and N-type regions to be substantially equal, and adjusts the breakdown voltage characteristics through precise doping profiles. By optimizing these parameters, the SCR structure maintains a high breakdown voltage under normal operating conditions, preventing unintended activation, while still providing robust ESD protection when high-voltage ESD events occur. The symmetrical design ensures consistent triggering characteristics for both positive and negative polarity ESD pulses.
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 symmetrical SCR structure provides robust ESD protection in both directions with smaller device sizes, effectively reducing parasitic capacitance and enhancing ESD discharge capacity, suitable for on-chip protection in general-purpose and high-speed applications.
Implementation Method 1
the detection of the static electricity can be classified into a positive polarity situation and a negative polarity situation. However, as the pn junction of the existent ESD protection structure is only capable of forming a forward-bias diode
Implementation Method 2
Due to its compact design, the SCR structure in the present invention affords high levels of ESD robustness... effectively reducing parasitic capacitance
Data Source
AI summary
A silicon controlled rectifier structure with the symmetrical layout is provided. The N-type doped regions and the P-type doped regions are disposed with the N-well and symmetrically arranged relative to the isolation structure in-between, while the P-type buried layer is located under the N-type doped regions and the P-type doped regions and fully isolates the N-type doped regions from the N-well.