Symmetrical Punch-Through TVS Device With Edge Implants
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Solution Overview
Problem
Conventional bidirectional transient voltage suppression (TVS) devices often exhibit asymmetrical breakdown voltages under positive and negative biases due to fabrication process limitations, leading to inadequate protection from over-voltage conditions of both polarities.
Innovation Solution
A symmetrical punch-through TVS device is developed with a mesa structure featuring beveled sidewalls and edge implants, which cause punch-through to occur in the bulk region rather than the lateral edges, ensuring symmetrical breakdown voltages by reducing the difference in breakdown voltages under positive and negative biases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bidirectional TVS diode is used, then the device can protect electrical nodes from over-voltage conditions, but the breakdown voltage is not symmetrical due to fabrication process limitations, resulting in inadequate protection from both positive and negative over-voltage conditions
Solution Approach 1:
The patent applies asymmetry principle by intentionally introducing edge implants at the lateral edges of the second semiconductor layer. These edge implants create an asymmetrical doping profile that compensates for the asymmetrical breakdown voltage caused by beveled sidewalls, thereby achieving symmetrical breakdown characteristics in the final device
Solution Approach 2:
The patent changes the doping concentration parameter by introducing edge implants with a third doping concentration at the lateral edges of the second semiconductor layer. This parameter modification alters the electric field distribution and punch-through characteristics, enabling symmetrical breakdown voltages despite the beveled sidewall geometry
2Device complexity
If punch-through occurs at lateral edges of the second semiconductor layer, then the device structure is simpler, but the breakdown voltage becomes asymmetrical, reducing protection effectiveness
Solution Approach 1:
The patent applies local quality principle by creating different doping concentrations at different locations within the second semiconductor layer. The bulk region maintains one doping concentration while the lateral edges receive edge implants with a different doping concentration, thereby locally modifying the punch-through characteristics to achieve symmetrical breakdown
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 solution achieves symmetrical breakdown voltages, enhancing protection from over-voltage conditions of both polarities and relaxing fabrication process restrictions, resulting in a more reliable and manufacturable TVS device with reduced leakage current.
Implementation Method 1
the edge implants are configured to cause punch-through to occur in the bulk region and not in the lateral edges of the second semiconductor layer
Data Source
AI summary
The present disclosure relates to a symmetrical, punch-through transient voltage suppression (TVS) device includes a mesa structure disposed on a semiconductor substrate. The mesa structure includes a first semiconductor layer of a first conductivity-type, a second semiconductor layer of a second conductivity-type disposed on the first semiconductor layer, and a third semiconductor layer of the first conductive-type disposed on the second semiconductor layer. The mesa structure also includes beveled sidewalls forming mesa angles with respect to the semiconductor substrate and edge implants disposed at lateral edges of the second semiconductor layer. The edge implants including dopants of the second conductive-type are configured to cause punch-through to occur in a bulk region and not in the lateral edges of the second semiconductor layer.