SiC Transient Voltage Suppressor Uniform Avalanche Design
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Solution Overview
Problem
Existing Transient Voltage Suppressor (TVS) devices face challenges in handling high current and temperature stresses, particularly in harsh environments like avionics and space applications, where they are prone to failure due to improper avalanche conditions and radiation exposure.
Innovation Solution
The design of SiC TVS devices is optimized to force avalanche to occur in the active area, with a graded epi structure creating a low electric field across the device, ensuring uniform current distribution and reduced series resistance, thereby enhancing thermal response and reliability under stringent conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low series resistance is used in the TVS device, then the clamp voltage remains constant during current decay, but the power and temperature stress on the TVS becomes very high
Solution Approach 1:
The TVS device is segmented into distinct regions: a lightly-doped drift region that extends across the active area and handles the bulk of the voltage blocking and avalanche dissipation, and a heavily-doped termination region at the periphery that provides low series resistance contact points. This segmentation allows the device to achieve both stable clamping and reduced thermal stress by distributing current paths across different doping regions.
Solution Approach 2:
Different regions of the TVS device are given different doping qualities optimized for their specific functions. The drift region has low doping concentration (10^15 to 10^17 atoms/cm³) to enable high breakdown voltage and uniform avalanche, while the termination region has high doping concentration (10^18 to 10^20 atoms/cm³) to provide low series resistance. This local quality differentiation resolves the contradiction between clamping stability and thermal management.
2Reliability
If the TVS device operates in harsh environments like space or high temperature, then it must withstand radiation and extreme conditions, but conventional TVS structures fail under these stringent stresses
Solution Approach 1:
The invention changes the fundamental doping parameters of the TVS structure, specifically using a lightly-doped drift region (10^15 to 10^17 atoms/cm³) extending to the substrate and a heavily-doped termination region (10^18 to 10^20 atoms/cm³). This parameter change creates a structure that maintains uniform electric field distribution during avalanche, preventing hot spots and improving reliability under radiation and high temperature conditions where conventional uniformly-doped structures fail.
3Device complexity
If avalanche occurs in the termination region, then the device structure is simple, but the current density becomes uncontrolled and the device fails under high current conditions
Solution Approach 1:
The termination region is given a distinct high-doping quality (10^18 to 10^20 atoms/cm³) compared to the drift region, creating a localized low-resistance contact area. This prevents avalanche from occurring in the termination by establishing a higher breakdown voltage threshold there, forcing avalanche to occur uniformly in the lightly-doped drift region instead, thereby maintaining device reliability under high current conditions.
Solution Approach 2:
The drift region is designed with sufficient extent and appropriate doping concentration to preemptively establish the primary avalanche path before termination breakdown can occur. By creating a low-doping region that spans the active area and interfaces with the substrate, the invention pre-determines the avalanche location in the drift region, preventing uncontrolled termination breakdown and ensuring reliable high-current 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
This approach allows SiC TVS devices to effectively handle high currents and temperatures, ensuring continuous operation and long-term reliability in extreme environments by preventing avalanche in the termination region and maintaining a low series resistance.
Implementation Method 1
The TVS function can be achieved with various devices, most common ones being Metal Oxide Varistors (MOVs), Zener or P-N Junctions operating in avalanche (Semiconductor Avalanche Diodes, or SADs)
Implementation Method 2
Material properties of SiC, like wide band-gap, high electric field, high saturated drift velocity and high thermal conductivity, strongly recommend SiC for power devices
Data Source
AI summary
A high power, high current Unidirectional Transient Voltage Suppressor, formed on SiC starting material is disclosed. The device is structured to avalanche uniformly across the entire central part (active area) such that very high currents can flow while the device is reversely biased. Forcing the device to avalanche uniformly across designated areas is achieved in different ways but consistently in concept, by creating high electric fields where the device is supposed to avalanche (namely the active area) and by relaxing the electric field across the edge of the structure (namely in the termination), which in all embodiments meets the conditions for an increased reliability under harsh environments.