Polysilicon Diode Lateral Protection for Parasitic Currents
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Solution Overview
Problem
Conventional power ICs face issues with parasitic transistor effects and voltage variations due to the breakdown of diffusion diodes, leading to unintended currents and potential circuit malfunctions, especially at higher temperatures and when the gate insulating film is thicker.
Innovation Solution
A semiconductor device with a layered structure comprising diffusion diodes and polysilicon diodes, where the polysilicon diodes are reverse-connected upstream of the diffusion diodes, clamping the voltage to prevent high voltages from reaching the gate and reducing parasitic effects by blocking forward currents during abnormal operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diffusion diodes are used for protection, then voltage clamping is achieved, but parasitic transistor effects occur causing unintended currents
Solution Approach 1:
An n-type intermediate layer is introduced between the p-type base region and the n-type drift layer. This intermediate layer acts as a mediator that prevents the formation of parasitic transistors by blocking the current path that would otherwise flow through the base region, thereby eliminating the harmful parasitic effects while preserving the voltage clamping function of the diffusion diodes.
Solution Approach 2:
The harmful parasitic transistor effect is extracted and eliminated by removing the direct connection between the p-type base region and the n-type drift layer. The n-type intermediate layer effectively takes out the parasitic current path from the system, allowing the protection circuit to function without generating unintended currents.
2Strength
If thicker gate insulating film is used, then breakdown voltage increases, but voltage variations increase due to parasitic effects
Solution Approach 1:
The n-type intermediate layer serves as a stabilizing intermediary that prevents voltage variations caused by parasitic transistor effects. By blocking the formation of parasitic transistors, this intermediate layer ensures that the voltage across the gate insulating film remains stable and predictable, even when the film thickness is increased to achieve higher breakdown voltages.
3Strength
If multiple diffusion diodes are connected in series, then protection voltage increases, but device area increases
Solution Approach 1:
The protection circuit utilizes the vertical dimension by stacking the diffusion diodes in series along the depth direction of the semiconductor substrate. This vertical arrangement allows multiple diodes to be connected in series without proportionally increasing the horizontal device area, as the diodes share common regions (p-type base region and n-type drift layer) that are arranged vertically rather than laterally.
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 ensures reliable operation by preventing parasitic effects and reducing voltage variations, thereby minimizing unintended currents and enhancing the reliability and miniaturization of the semiconductor device.
Implementation Method 1
the diffusion diode undergoes breakdown, and the breakdown voltage of the diffusion diode is applied to the gate terminal
Data Source
AI summary
A diffusion diode including a p+ diffusion region, a p-type diffusion region, and an n+ diffusion region is formed in the front surface of a semiconductor substrate. A polysilicon diode including a p+ layer and an n+ layer is formed on top of a local insulating film formed on the front surface of the semiconductor substrate and faces the diffusion diode in the depth direction. The diffusion diode and the polysilicon diode are reverse-connected by electrically connecting the n+ diffusion region to the n+ layer, thereby forming a lateral protection device. The p+ layer and p+ diffusion region are respectively electrically connected to a high voltage first terminal and a low voltage second terminal of the lateral protection device. The polysilicon diode blocks a forward current generated in the diffusion diode when the electric potential of the first terminal becomes lower than the electric potential of the second terminal.